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jeffjohnvol
04-12-2007, 08:55 AM
Hello,· my degree is EE and I experimented with 68HC11's in college, but 16 years of the soft life working in database programming, I don't have the tools or the skills to do what I need to do from scratch.· I'm hoping someone here might be willing to do a project for me provided I can afford it, lol.

My dad and I built an inclinator at our family lake house.· This is a cart that runs on pipes that lowers people, supplies, etc 150 feet down the hill at 30 degrees slope.· It works great, using a motor controller driving a 3 phase VFD 3 HP motor.

My issue with this inclinator is that I would like to have some kind of safety such that if the drive shaft snaps, and the spools "free-spool", there is a way to detect it and trigger a brake of some kind.

For some background, here are some clips of it in action:

http://www.youtube.com/watch?v=AbFDJBHZUqE
http://www.youtube.com/watch?v=-jNwK68F8ps
http://www.youtube.com/watch?v=CLjmnQte-JM

Here is another discussion I had with some others in terms of finding a mechanical·solution:
http://groups.google.com/group/comp.home.automation/browse_thread/thread/bd20a006271a3480/5d6f16c3a416828c?lnk=st&q=freespool+motor+controller&rnum=1#5d6f16c3a416828c

I'm trying to find an easy way to measure RPM and if a certain RPM is exceeded, give an output that I can drive a relay.· From that point, I can come up with a way to activate a brake or whatever.

The spools rotate at about 30 rpm at current max speed.· At 35 rpm, I'd like to activate something.· I've looked for easy ways of measuring this, but I think using a stamp may be the best way.· But, I have never worked with them and don't even know which controller to start with.

I would rather just pay someone for a solution, hopefully a solution that I can modify and recode as necessary.· I have a basic understanding of electronics and am a decent programmer.

Any suggestions?

Thanks.
Jeff

QuattroRS4
04-12-2007, 05:55 PM
If you were to have 2 mechanical brakes on the cart·held open by the tension on the main cables (one for each cable) - if one of the cables were to snap this leads to the corresponding brake being applied - The motor drive unit should have an overload - if the brake was applied due to a cable snap - the motor contactor overload would trip as it would be in overcurrent trying to pull the load against the brake. A further safety is a 'light curtain' at the winch stage (number of sensors looking at the cables) if there was a snap the cable would drop out of the 'light curtain' triggering 1)A motor shut off. 2) The tension is lost on the cable - so at the cart the mechanical brake is applied. In·the·Up cycle·case the motor would be shut off either by overload (due to brake applied on cart)·or by no cable in the 'light curtain' - which ever happens first.On a down cycle .. the motor overload will probably not trip .. but·loss of a cable in the ·'light curtain' will shut off the motor.The important thing is that the brake is always applied on a cable snap.I noticed a hand held also - an EMO button to kill the winch motor on that control .. also on the cart you could employ a 'dead man pedal' this has to be engaged·to release the brakes·even if the rig is optimal..... I think that no matter what is done here a mechanical brake is a MUST ....

Regards,
Quattro

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'Necessity is the mother of invention'

Post Edited (QuattroRS4) : 4/12/2007 11:08:10 AM GMT

stamptrol
04-12-2007, 07:09 PM
Jeff,

Nice cottage/house/villa, by the way!

From a liability point of view, you might not get too many takers for this job!

However, these are the points you might want to look at yourself:

1. The car has to be able to grab the rails and hold itself with full load and at full speed. Say both cables broke on the way down with all hands onboard. Alternatively, a third cable whose only purpose is to catch a runaway condition. It would normally run under very light load and be locked if the cable speed went too high. (mechanical overspeed trip device). It can be rigged on pulleys top and bottom and run up the track bed "clothes-line" style. From experience, its not likely the gearbox is going to fail and let both spools run away.

2. You can detect a break in one of the cables at the winch end by having a lever-type limit switch held in the "on" position when the cable is OK. If one or the other breaks, the lever moves and opens the winch-motor circuit. Also, are there mechanical limit switches at top and bottom just in case the remote stops working ?

3. I realize this is probably going to be used only by your family, but there are a couple other safety issues. One is, as demonstrated in the video, the possibility of someone extending their legs thru the rail at the front and being jammed against the concrete at the bottom. Same setup as the car approaches the main cottage.....several pinch points between railings of the car and cottage.

4. Once you get the car to be able to hold itself on the rails, having an emergency stop or even a dead-man control on the car would be wise. Or, at least some way of detecting that the remote has stopped communicating.

Detecting rpm is easy with the stamp and some sort of switch, photocell or Hall effect sensor watching the spools go around. But, the last thing you want on an outdoor, seasonal use device is a safety system dependent on electronics. Even after 40 years in the electrical industry, I must admit there are some things best done mechanically!

Cheers,

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Tom Sisk

http://www.siskconsult.com
·

jeffjohnvol
04-12-2007, 07:56 PM
Quattro, very valid points. The cables are seperately connected to the cart. Each cable supports 17K lbs so I have 2 in case one breaks. We considered a deadman switch also, but since the cart is sometimes empty (as in that 3rd video) that would require someone to lock the deadman in place, which could defeat the purpose of it. There are buttons on each end of the run to recall the cart as well as a hand held remote.

We've really been looking at the tension holding the brake solution too, but when empty the tension isn't very high, and also, due to the length of the cable run, a free-spool condtion could still have tension in the cables due to drag.

The motor does perform a shutdown if there is a surge. Before I got better wheels, the cart got hung up for a bit, and when it released with a hard jerk, the motor got an overvoltage condition and shut down.

This is why I would like to have some way of measuring the RPM of the spool and can execute a spool brake if it exceeds a certain amount. The shaft the spools are on is 1.75" and I can install a shaft brake, but I need a way of determining when I need to do it, thus my original post.

Thanks!
Jeff

jeffjohnvol
04-12-2007, 08:19 PM
Tom, thanks for the compliments, quite nice of you to say that.

To your points:
1) yes, this is something I have strongly considered, but my concern is how to determine an overspeed condition. The likelihood of both cables snapping is pretty remote, IMO. I have a max load of (500lbs+200lbs)*sin(29)=340 lbs on the cables (static, anyway) and each is rated for 17,000 lbs. It's nice to hear that your gearbox experience says its unlikely to snap, but that’s the condition I'm worried about, the achille's heel of this device, imo.

2) I considered this also, but the wire rope is pretty stiff, and even layed out (when near the bottom) it would be difficult to detect slack in the device. There are actually 3 switches at each level. The first one 10 feet from the end activates a slow stop. The other two near the very end are e-stops. One is a system shutdown switch and another activates a full brake mode. You can see a demo of it in action here: http://www.youtube.com/watch?v=kjAROvNST0I

3) I get a lot of comments about this. The clip with my daughters was before I had pickets on the cart. When Julia had her legs hanging down in the front, she was still a good 4 feet above the rail. Near the top, there is a good 12 inches between the cart and the deck. The only time it was a risk was when I had my head hanging over to check out the wheel action and the deck almost hit my head. I don't do that any more :). Valid points though!

4) As I was telling Quattro, this is like an elevator in that you can recall the cart from the top or the bottom (empty), so a deadman switch would be hard to manage.

I agree, if I had a perfect mechanical solution that would be preferred. Or, if there was some kind of simple electronic method, such as a device that produced a voltage proportional to RPM would be good too. I am able to provide a protected area for the device.

Thanks again for your well thought out proposals!

QuattroRS4
04-12-2007, 10:53 PM
So the mechanical aspects have been well thought out by you already... So you want to engage a mechanical brake at the winch stage incase of a free spool event (gearbox failure) So you are looking at a basic stamp 2 ?? Using a command like 'pulsein' reading the frequency of a pulse derived from a sensor looking at the winch pulley (sensor - reed or optical - the choice is yours) .. would this be a fair assumption ?


Regards,
Quattro

▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
'Necessity is the mother of invention'

DiablodeMorte
04-13-2007, 06:48 AM
I don't know exactly how the wheels look but if you could drill holes in one of them at regurarly space intervals you could creat some type of encoder. If the wheels are large enough you could use magnets like Bike speedometers do!

-My 2 cents

jeffjohnvol
04-13-2007, 08:31 AM
QuattroRS4 said...
So the mechanical aspects have been well thought out by you already... So you want to engage a mechanical brake at the winch stage incase of a free spool event (gearbox failure) So you are looking at a basic stamp 2 ?? Using a command like 'pulsein' reading the frequency of a pulse derived from a sensor looking at the winch pulley (sensor - reed or optical - the choice is yours) .. would this be a fair assumption ?


Regards,
Quattro


Yes, that is what I'm thinking.· Preferably some kind of sensor that is pretty reliable.· I had to do a project in college using photosensors to guage what kind of coin was dropped in a slot.· It worked, but wasn't always perfect.
If there was a way to do it with just electronics, I wouldn't mind that either.· Hard to find off the shelf items for something like that.
Once I'm able to determine the condition is met, there are many ways I could stop the thing, such as a brake caliper and a hydraulic pump or the like.
Thanks.
Jeff

jeffjohnvol
04-13-2007, 08:33 AM
DiablodeMorte said...
I don't know exactly how the wheels look but if you could drill holes in one of them at regurarly space intervals you could creat some type of encoder. If the wheels are large enough you could use magnets like Bike speedometers do!

-My 2 cents
I was kind of thinking of putting a tab on one of the spools that hits·a switch everytime it goes around, and running that switch through a debounce circuit of some kind.

T Chap
04-15-2007, 01:36 AM
Pretty neat gadget. For sensors that could be durable in the elements, maybe try some magnets glued to the spools, with a hall sensor located nearby to detect the magnets. You could use more magnets in the path to get a better resolution if needed. The code would be always timing the positive etdges and determining if the speed was too high. The hall sensors could be potted in electronic potting epoxy, with lead wires coming out of it, so that the electronics stayed water tight.

Robert Kubichek
04-15-2007, 01:58 AM
Why don't you use a counterweight clutch-brake mounted on the cart axle(s)
It/they would only start braking if a certain rpm is met, and apply the brakes harder if the set rpm is exceeded..
It is simple and has no electronics, and much safer..

Bob

jeffjohnvol
04-15-2007, 09:52 PM
TChapman said...
Pretty neat gadget. For sensors that could be durable in the elements, maybe try some magnets glued to the spools, with a hall sensor located nearby to detect the magnets. You could use more magnets in the path to get a better resolution if needed. The code would be always timing the positive etdges and determining if the speed was too high. The hall sensors could be potted in electronic potting epoxy, with lead wires coming out of it, so that the electronics stayed water tight.
Thanks.· That may be a good way to go if its plug and play.· I don't have the testing apparatus to experiment with it unfortunately.· Switches I know how to test with a continuity tester.· I've never used the hall effect sensor.· The spools are heavy iron, I don't know if they could generate a magnetic field or not from movement or the magnet itself.

jeffjohnvol
04-15-2007, 10:08 PM
Robert Kubichek said...
Why don't you use a counterweight clutch-brake mounted on the cart axle(s)
It/they would only start braking if a certain rpm is met, and apply the brakes harder if the set rpm is exceeded..
It is simple and has no electronics, and much safer..

Bob
Bob, I did look at a clutch brake setup at the top (on the spools) but even with another parallel shaft below geared to spin more (2:1 ratio or more) we wouldn't be able to get a centrifugal clutch (like go-cart) to activate.· They need a minium of 1200 rpm, and the current base speed is 30 rpm, so the gearing may prove to be too much.

The problem with doing the mechanism on the cart is that the wheels are basically casters for smooth operation.· Getting traction with a wheel/axle would be pretty difficult the way it works now, and a wet steel rail could mess that up.

ANOTHER PROBLEM DISCOVERED
==========================
The CW would be another good solution if implemented, because this weekend we discovered another issue.· When there is too much load on the cart, the motor controller is stopping with an OBF fault which is an over-braking fault.· Basically, the cart when it goes down is in regenerative mode and the back current exceeds a limit and causes a shutdown.· The fixes are to lower the HSP (high speed value) or reduce the number of people on the cart.· The motor controller is a 220 volt 3 phase VFD and is pretty cool.· Fairly programmable in terms of basic settings, max speed, ramp up, ramp down, etc, but not as programmable as a stamp.

My dad who helped me build this thing and did all the motor controller work said we need a brake resistor to fix this problem.· It is a 5 ohm resistor that handles 500 watts.· It's about a foot long wire wound ceramic.· We'll have to build a cage around it to prevent anyone touching it.· It only activates when there is back current.

The CW would reduce the back current as would any other method of resistance, but the work involved is fairly daunting, even if I only do a 1/3 or 1/2 track and gear it with pulleys.· The long term maintenance would be an issue too, more cables to replace etc.

PAR
04-16-2007, 03:45 AM
jeffjohnvol said...
...

My dad and I built an inclinator at our family lake house.· This is a cart that runs on pipes that lowers people, supplies, etc 150 feet down the hill at 30 degrees slope.· It works great, using a motor controller driving a 3 phase VFD 3 HP motor.

My issue with this inclinator is that I would like to have some kind of safety such that if the drive shaft snaps, and the spools "free-spool", there is a way to detect it and trigger a brake of some kind.
...
Lots of proposed solutions to your safety need for a snapped drive shaft / free-spooling problem.
But, what are the various failure points in your system, and what are the various likelihoods (hard to determine, no doubt) of each failing and creating a dangerous situation for the passengers?· --broken drive shaft? broken cable? failed clevis? derailed cart? no electricity for main or backup safety circuits? failed end-of-trip off-switch? cracked rail pipe? etc, etc....? Is the drive shaft failure by snapping your single largest risk?
(I noticed that you installed railing balusters on the cart, after the first video --the one where your daughter(?) hung her legs over the front edge of the cart's floor towards the bottom of the ride: good way to have your legs involved in a crushing accident!. That was a good safety feature.)
PAR

Post Edited (PAR) : 4/16/2007 6:51:19 AM GMT

bennettdan
04-16-2007, 07:35 AM
jeffjohnvol,
··· What you need to do is have a mechanical brake setup on the cart itself and you can use a braking system like on a old elevator its the same principle as a steam engine govenor. The balls on the end of the vertical rod spin because its linked to the shaft that has the wheels on it if it spins to fast·the balls will pull outward and push down on the rod inside of the shaft and apply the brakes. I hope you can understand how it works with such a plain drawing.

jeffjohnvol
04-16-2007, 08:00 PM
PAR said...

·
Lots of proposed solutions to your safety need for a snapped drive shaft / free-spooling problem.
But, what are the various failure points in your system, and what are the various likelihoods (hard to determine, no doubt) of each failing and creating a dangerous situation for the passengers?· --broken drive shaft? broken cable? failed clevis? derailed cart? no electricity for main or backup safety circuits? failed end-of-trip off-switch? cracked rail pipe? etc, etc....? Is the drive shaft failure by snapping your single largest risk?
(I noticed that you installed railing balusters on the cart, after the first video --the one where your daughter(?) hung her legs over the front edge of the cart's floor towards the bottom of the ride: good way to have your legs involved in a crushing accident!. That was a good safety feature.)
PAR

PAR, Yes, I believe the broken shaft to be the most likely point of failure at this point.· There could be at least three things to cause this:· A broken shaft from motor to gearbox, a broken shaft or stripped gear inside the gearbox, or the mating flange that joins the spool to the gearbox.· The other items you mention have been accounted for, 2 cables (each capable of 17K lbs) attached when only 1 necessary, the rail is 1/4" thick pipe wall (2.5" pipe) and is welded all together as a single unit.· If it derails, its a 4 foot fall to soft earth.· In a power loss situation the system freezes solid.· For the failed "ramp to stop" trip switch (my biggest concern at one point) was a push plate at the top that hits the E-Stop that does a very fast shutdown.· In one of the Utube posts above I show a demonstration of the switch minus the push plate.

Yes, the balusters were always part of the plan.· The vid with my girls was the first weekend we got the prototype working.· Her legs were actually about 4 feet above the rail at that point, but on the sides there was a potential for personal injury.

Its funny, most of the possible points of failure go through your mind when you are riding it.·

jeffjohnvol
04-16-2007, 08:15 PM
bennettdan said...
jeffjohnvol,
··· What you need to do is have a mechanical brake setup on the cart itself and you can use a braking system like on a old elevator its the same principle as a steam engine govenor. The balls on the end of the vertical rod spin because its linked to the shaft that has the wheels on it if it spins to fast·the balls will pull outward and push down on the rod inside of the shaft and apply the brakes. I hope you can understand how it works with such a plain drawing.

bennettdan, yes, I have seen one of these work before and I understand the drawing. Part of the problem though is the rail is 2.5" schedule 40 pipe. Getting traction to spin the wheel on that pipe for a regulator like that may be difficult to manage. The current wheels are just casters, so there is no drive shaft to attach to. The attachment is a picture of the wheels I put on this weekend, and got rid of those other single wheels.

Given the fact that the pipe could be wet, rusty, dusty or some other situation that could prevent traction in an outdoor environment, I would be worried about tuning such a mechanical control system. Plus, given the fact that I can adjust the speed through the controller, I might have to fine tune when changing speeds. In theory that regulator would work, as an incremental brake or pulling a pin, but I would prefer a more exact solution, hence RPM measurement at the top.

Thanks!

bennettdan
04-16-2007, 08:52 PM
Yes i understand what you are saying but you can setup a brake setup to clamp to the pipe kind of like disc brakes on a car and they are not affected by weather to bad Oil might be the only thing you woul have to worry about. Its just most of us agree it needs to be on the cart itself and mechanical due to power loss or even just the most minor power short will kill it. One more thing you might think about is some kind of anchor like on and arm to dig into the ground to stop you. It is a very cool project by the way.

jeffjohnvol
04-16-2007, 09:51 PM
bennettdan said...
Yes i understand what you are saying but you can setup a brake setup to clamp to the pipe kind of like disc brakes on a car and they are not affected by weather to bad Oil might be the only thing you woul have to worry about. Its just most of us agree it needs to be on the cart itself and mechanical due to power loss or even just the most minor power short will kill it. One more thing you might think about is some kind of anchor like on and arm to dig into the ground to stop you. It is a very cool project by the way.


I hear you about the brakes. I know the brake would hold strong. Some segments of 3 inch pipe would hold tremendously, especially if there was some abrasive matter added to the mating surface. My concern is how to determine when that condition applies. We considered having the tension of the cart hold the brakes off, but the weight of an empty cart would need to be sufficient to provide tension, and the cables are so stiff and so long, I'm worried that a falling cart (rollercoaster) would have tension on the cable as it drug it against the supports. Currently, when the cart is at the bottom, the cables (even when pulling) sag onto the supports some. The anchor solution is a good one also, one that we have considered by using hooks to grap the supports and to activate a brake or a some garage door springs, but there again, when to activate would hard to resolve.

I understand everyone's concern about the brakes on the cart. If I had a single cable, I would whole heartedly agree. We went through the added expense of building 2 drums and adding an extra cable to account for a possible cable break. A fully loaded cart has about 350 lbs of tension on the cables which is 2% of the max load of a single cable. We initially looked at running 300 feet of chain in a continuous loop, but we were concerned about a break, so we went with the double cable. If I had a chain down the middle, I could accurately guage the speed, but then again it would be mechanical control, or a battery powered activation. Currently, the cart is "dumb" and has no wires to it. At the head unit (spools) we have a fixed place where I can have power supplied sensors and direct access to the controller as well as other methods of braking the spools.

The one thing I have learned about doing this project is that many of the things that I consider doing, are in reality extremely difficult to apply to the actual real world device. Being outdoors, and slight variations in the distances on the pipes and variations in the cart make things difficult to make work.

A short out of an electric device is definitely a concern as well, although I can have the sensors exposed to the weather, and the device in a protected, heated environment.

bennettdan
04-16-2007, 11:18 PM
Yes, The brakes are a hard one to figure out. Where was you planning to install the brakes on the shaft where the spools are at? IF so you could install a halleffect sensor and detect the speed of the shaft and then apply brakes if you are sure that your double cable system will hold up.

jeffjohnvol
04-16-2007, 11:27 PM
bennettdan said...
Yes, The brakes are a hard one to figure out. Where was you planning to install the brakes on the shaft where the spools are at? IF so you could install a halleffect sensor and detect the speed of the shaft and then apply brakes if you are sure that your double cable system will hold up.
We were thinking of either buying a shaft brake such as: http://www.idicb.com/dynacorp/shaft-mounted-brakes.htm

or run a gear to a another parallel shaft below where we would install a disc brake or two from a junk yard (rebuilt of course).· We could use an electric hydraulic pump to activate it.

Although you can't see it, the shaft extends about 6 inches on the far side of the head unit.· Its a 1.75" shaft with a keyway.· I can get gears for it for another lower shaft, or put a shaft brake directly onto the shaft.

BTW, most of our stuff we got from mcmaster.com· They are great for mechanical gear.

Another idea I had was to use the parallel shaft below, with a large drum filled half way with sand/water.· Just the resistance of turning it may make the whole thing somewhat neutral in terms of drag.

Paul Baker
04-17-2007, 01:02 AM
What about the idea of mounting a third shaft which is not a support shaft (likely between the two support shafts), drill periodic holes in it, then have a solenoid mounted on the cart which enagages and catches the next hole in a run away condition? As an extra safety measure, the solenoid should be engaged when unpowered.

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Paul Baker (mailto:pbaker@parallax.com)
Propeller Applications Engineer
[/url][url=http://www.parallax.com] (http://www.parallax.com)
Parallax, Inc. (http://www.parallax.com)

jeffjohnvol
04-17-2007, 01:07 AM
Okay, if I were to use the BASIC Stamp 2pe Motherboard with a basic stamp, I have a few Q's for you experts:

1. Would this be a good platform (motherboard that is) to use for my purpose?

2. Could I use a hall sensor input from say 20-30 feet of wire? My control box (see attached) is about 20 feet away.

3.· I read that this MB has for digital I/O's, which I may use to drive the motor controller later.· Do I need a daughterboard for those outputs?· I didn't see any connection points.

4.· Is there a way to get more digital inputs?· I have 2 switched stops as well as 4 inputs from the remote to play with.

Thanks in advance.

Jeff



BTW, I'm thinking that using a microcontroller to drive the motor controller may provide more opportunities for safety, in terms of control.· One catestrophic failure I'm concerned about is if the cart is at the top, and the UP button is hit, or if the Ramp To Stop (RTS) switch is missed.· I have a pushplate that forces a shutdown, but I haven't attempted a full speed test.· A microcontroller may give me more control in terms of determining the relative location of the cart to "disable" badly timed·commands such as UP when its at the top.

jeffjohnvol
04-17-2007, 01:19 AM
Paul Baker (Parallax) said...
What about the idea of mounting a third shaft which is not a support shaft (likely between the two support shafts), drill periodic holes in it, then have a solenoid mounted on the cart which enagages and catches the next hole in a run away condition? As an extra safety measure, the solenoid should be engaged when unpowered.


Thanks Paul.· Determining the runaway condition is my concern at this point.· The cart at a normal speed, fully loaded would probably rip the solenoid off.· The cart empty weighs so much I can barely lift one corner of it when I'm working on it.· We would need something heavy duty, and something that if executed wouldn't send the passengers over the front.· And if I can help it, I want to avoid having anything powered on the cart, to avoid recharging etc.· Good thoughts though.· Jeff

bennettdan
04-17-2007, 01:19 AM
I work in industrial environment I use Grainger and McMaster Carr very well. The Shaft brakes and twin cable should be safe enough just keep a good check on your cables a routine PM should be started on your rig. If you adapted the disc brakes off say a truck then apply pressure to it that should work fine you might could use Air pressure from a small compressor to apply the pressure. We used a simular setup on printing presses at my last plant it used compressed air through a regulator then the regulator was hooked to a small servo motor this allowed the PC to apply a variable pressure supply to the brakes to pull tension.

jeffjohnvol
04-17-2007, 01:25 AM
Yeah, I love that mcaster site, Grainger too (got the motor controller from there). One of my neighbors is a retired jet mechanic for American Airlines. He suggested I spray the cables with LPS-3, a parafin based protectant to prevent rust and to provide overall protection to the cables and other metal parts that I don't want to rust. Good thoughts on the air compressor, probably less expensive than hydraulic.

jeffjohnvol
04-17-2007, 02:51 AM
I have been looking at the 24 volt version which would work well for me because I already have a 24 volt bus in the main controller (see attached drawing in earlier post)

http://www.parallax.com/detail.asp?product_id=30064

It also has 10 digital inputs and 8 digital outputs which would be plenty for me.

I guess right now though is that my problem would be the hall sensor. First off, it will be about 20 feet away from the controller (is this a problem?) and as the spools start moving, the accelleration time of 6 seconds may cause a pulse to be missed if its too slow. As I read it, the BS2 can only measure a max pulse width of 0.13107 seconds, so I may miss one or two. Not a big deal for RPM measurement, but if I wanted to determine where the cart is, it could throw things off.

Also, is it possible to determine if a remote switch was hit twice within a 2 second interval? The FAQ says there aren't any timers, so is this even possible?

Thanks.
Jeff

kelvin james
04-17-2007, 01:16 PM
I still think your best bet is the centrifugal clutch brake. You can use a speed increase gear head to bring the rpm activation down to a slow speed, approx. 50 to 60 rpm.

Loopy Byteloose
04-17-2007, 01:46 PM
In principle, you have the same problems as an elevator.
Having the Counter Weight to compensated for at least dead load [and maybe a minimal live load of one human] reduces other design parameters.

A purely mecahnical brake system for a runaway seems to be also a must as that mode of failure is sometimes precipitated by a power failure.

If there isn't enough friction in the rails to stop the carriage; the cables have to provide the braking. In that case, larger or redundant braking cables are indicated.

Having a 'crash absorber' at the bottom is a good idea too. Either large springs or other shock absorbing devices.

Regarding safety issues, the electronics engineering is secondary to the mechanical.

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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········


···················· Tropical regards,····· G. Herzog [·黃鶴 ]·in Taiwan

jdolecki
04-17-2007, 03:49 PM
Safety brakes are mechanical for a reason. The mechanical clamping part is spring loaded in refrence to the load supporting the cart. There will always be a load aginst the cable attachment point if seperation or freewheeling should occure then the springs will apply the brakes.

If you must have electric how·about a speed sensing circuit on the cart? If a max speed occures then the brakes woud be applied.

Also the brakes shoud be held off under power. This way if power failure occures the brakes will automatically apply.

I hoe i didnt repeat any body.

John

jeffjohnvol
04-17-2007, 08:03 PM
Kramer and John, Thanks for your input. I'm not debating between a mechanical or electrical brake, but rather a mechanical or electrical method of determining an overspeed condition. I know there are very expensive centrifugal braking systems that exist in the elevator world, but I'm somewhat limited to what I can build, and I think electrical measurement is more dependable than mechanical given my current conditions of what I can reasonably construct.

I can monitor periodically the operating state of a stamp, and could even test it by putting a magnet on a disk and running it past the sensor to see if the brake is applied properly.

I also think, imho, that it would be just as secure to apply the brake to the spool rather than the cart. At the spool, I have a fixed position and plenty of power there. Any powered solution on the cart would require much maintenance (recharging, etc). I understand what you say about a power off condition would trigger it, but that would require I turn it off sometimes to save battery, and I think it would take to much juice on even a car battery to release the brake each time.

A loss-weight activated spring brake was strongly considered as well, but things can rust and/or get stuck over the years. There would be increased maintenance and imo, more potential points of failure.

The cables are way overkill. A single cable can handle things easily (2% at max load), and we have an extra cable as a backup. I have a friend who is a mechanical engineer that has reviewed my setup. He agrees with me that the brake should be at the head unit.

We are considering a backup of an emergency pin to pull to drop a spring loaded anchor that stretches a few garage door springs (with a cable limiter inside them) as a manual emergency stop.

A crash absorber at the bottom is in the plans, that’s a very good point.

Thanks.
Jeff

jeffjohnvol
04-17-2007, 08:05 PM
kelvin james said...
I still think your best bet is the centrifugal clutch brake. You can use a speed increase gear head to bring the rpm activation down to a slow speed, approx. 50 to 60 rpm.
Kelvin, that was my first choice, but I couldn't find a clutch brake with a low enough RPM, even with gearing.· 1200 rpm was the smallest I found, which would require a 20:1 gear ratio.

One guy here at the office suggested a gear 3:1 that drove a big fan.· The faster it went the more aire resistance there would be.

Loopy Byteloose
04-17-2007, 11:01 PM
Please, no matter what you do...
Post a sign that clearly indicated the maximum number of passengers at any one time. At the top landing and at the bottom. My guess is that one or two adults until you have things really sorted out. If you are moving heavy stuff, do so without people on board.

It is all too easy after a party to have six people crowd into what you have for a quick ride down. I have doubts that the gear boxes and braking have that all worked out. Cables are quite strong and most likely the least of your worries.

Again, counter weight tremendously improves your safety and control. Steel/cast iron is double the mass of concrete; so it is the most compact cheap counter weight. Concrete and aluminum are nearly the same mass. Ideally, you may be able to have an emergency brake that grabs the counter weight's cable.

Having the twin cables is fairly good. But if the winches are not rated to pull the whole load individually; a failure of one may cascade into a failure of the second. Significant redundancy is the usually primary path to safety. I do realize it is costly, but go the extra distance and have a system that you can fully trust; even when you are not there.

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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········


···················· Tropical regards,····· G. Herzog [·黃鶴 ]·in Taiwan

Dave Hein
04-17-2007, 11:07 PM
Jeff,

After looking at your videos I would be concerned about the possiblity of the cart tipping or derailing. Do you have a way to keep the wheels from coming off the track? You would need something that cups the bottom of the track. I assume the supports for the tracks are directly below the center, so your anti-derailment device would have to hang below either side of track with a gap in the middle. This could be part of the braking system as well -- sort of like caliper brakes on a bicyicle.

In the case of both cables failing, the braking action will tend to cause the cart to tip over on the downhill side. It is important that the anti-derailing device prevents this from happening. You could sense the tension of the cables by how much they can be deflected, similar to the way someone tests the tension on a fanbelt by pushing on it. You could build a tension detector that pushes on a normally-open switch. As long as the switch is closed it will energize a solenoid that keeps the brakes open. The brakes will engage if one of the two switches opens, or the circuit loses power, or a wire breaks. I would hang the tension sensors on the cables near the attachment point to the cart. I wouldn't put tension sensors inline with the cable. This would just introduce another possible failure mode.

To me, the possbility of tipping is a bigger issue. If there are four adults on the cart, and everyone leans over the railing at the same time this could produce enough leverage to tip the cart sideways. If everyone leans over the downhill railing the uphill wheels could raise up from the track. The tension on the cables should keep the cart from tipping backwards, but the uphill wheels could derail. You could reduce this possbility by raising the height of your safety rail, but I still think there should be a device to keep the wheels on the track.

Dave Hein

jeffjohnvol
04-17-2007, 11:21 PM
Dave, its actually pretty stable, and the cables run through the top part of the cart down to the lower side. Also, I have replaced the wheels from the video with wheels that I posted on one of the earlier replies. This lowered the cart about 6 inches, which increased the stability even more.

Is it possible to turn it over? Yes, but they would really need to try to do so. It weighs about 200-300 lbs without anyone in it. It is 32 inches wide, and the rails are 30 inches apart on center. When I work on it and try to lift one side to get access to work on a wheel or whatever, I nearly strain my back to lift it. Plus, the uphill portion is angled, to get closer to the cart.

if it does tip over, it would be a somewhat soft landing. Its a forest floor and 2/3 of the way the cart is only 6 inches to 2 feet above the ground.

I can see your point of view tho. The videos look worse then it actually is. Plus, we now have benches on the thing, so stting increases the lower center of gravity.

Thanks.
Jeff

Dave Hein
04-18-2007, 12:16 AM
Jeff,

I'm just thinking of some worse case scenarios. I agree, the cart "probably" won't derail. However, if someone wanted to try to tip the cart for fun they could stand outside the railing and lean out. The moment arm of the cart is only 15 inches. Two 175-pound guys could tip the cart if their center of mass was about 13 inches outside of the cart. Of course, a 4-foot fall to soft ground probably won't hurt them, but a 300 pound cart falling on them might sting a bit.

Also, attaching the cable to the back of the cart actually makes it more likely that it will tip backwards when the cart first starts moving. If four 175-pound guys were at the back of the cart its center of mass would be a foot or so in front of the back wheels, and about 5 or 6 feet above the wheels. A quick tug would send it tumbling backwards. The only thing keeping it from tumbling would be the cable pushing against the front of the cart. It would be like pulling the rug out from under someone. If you pull slowly they won't fall, but a quick tug will send them tumbling.

If it were me I would put some sort of postive retention on the wheels to ensure that the cart could never tip or derail.

Dave

jeffjohnvol
04-18-2007, 12:33 AM
Dave, the cables go through the topside of the cart (just below the floor) , and then back to the lower side wheels, bolted to steel. So the front is actuall held down by the tension of the cable. So, in a sense, it is doing what you mentioned. Its impossible to tip the cart back without breaking the front of the cart from the cables.

Also, I know this will stir debate, but to keep the cables equallay taut, each cable is attached to its side of the cart, and another segment of cable about 6 feet long is attached to each of these cables, and then through two pulleys near the back of the cart. Therefore, the tension is maintained, so if one spool wraps over but the other one doesnt, the 6 foot cable distributes the tension evenly. Some people look at the pulleys and say "ah, if one cable breaks, it will roll through the pulleys and let loose" but thats not the case because each spool dead ends onto the cart, and its only the segment that is on pulleys. I hope I didn't confuse.

DiablodeMorte
04-18-2007, 05:57 AM
I realize this is a little off topic so I'll try to add something worthwhile at the bottom of my post:

Where did you get those buttons? I want some! By "Those Buttons" I mean the buttons on your control box, very professional looking!


worthwhile Part:
Thinking... Thinking... Ok, Here's a plan, Let's assume your place a new rail on the elevator, I'm sure you could rig a device that when the towing lines went lax(Ie, use some type of counter springs to rule our just general taughtness by the shear weight of the lines) a spring loaded brake engaged, but would not engage at the top or bottom because some type of physical barrier would stop that process. I think that might work.

jeffjohnvol
04-18-2007, 10:04 AM
DiablodeMorte said...
I realize this is a little off topic so I'll try to add something worthwhile at the bottom of my post:

Where did you get those buttons? I want some! By "Those Buttons" I mean the buttons on your control box, very professional looking!


worthwhile Part:
Thinking... Thinking... Ok, Here's a plan, Let's assume your place a new rail on the elevator, I'm sure you could rig a device that when the towing lines went lax(Ie, use some type of counter springs to rule our just general taughtness by the shear weight of the lines) a spring loaded brake engaged, but would not engage at the top or bottom because some type of physical barrier would stop that process. I think that might work.
My dad runs a panel shop in Chattanooga.· They use those buttons all the time in all of their work.· I'll try to find out the name of the supplier and will let you know.· I think it could be from Grainger.

The remote control is actually a small panel that has those buttons wired into a linearcorp remote, which has 4 buttons.· We currently only use 3, but I hope to put a center stopping point, so we may need to add a button to it.

Thanks.· Jeff

jeffjohnvol
04-18-2007, 10:33 AM
MORE REASONS TO USE A STAMP.

We are adding a lower deck area for the cart to stop at (near bottom of the house for firewood etc).· The cart now either goes all up, or all down.· At the bottom of the lift, there's a button to bring the empty cart down, and vise versa at the top.· We do all of this with the motor controller which although it is very powerful, is somewhat limited in conditional processing.

If we have a midpoint stop, I need a way to "call" the cart to the new landing.· I don't want my kids to go through the decision process of "Up" or "Down".· I need one button to bring it, so somehow I need some logical process to decide, to send up, or send down.

Therefore, using a stamp with a Hall Sensor I can determine the RPM for the original problem proposed, as well as determining the location of the cart (there are 42 spool rotations from top to bottom).· If I know the location, via relays I can:

inactivate the UP button if it is near the top (we have some safety here already, but I'd love to have the added safety feature). inactivate the DOWN button if it is near the bottom. control whether to activate the stop switches at a new mid point. track the last 10 positions when the the upper or lower RTS switches are hit (these tell the cart to slow down and come to a stop) so that if the value is passed by with no RTS, it can assume there is a fault and execute a shutdown. I have 4x20 LCD display.· We can display current RPM and location of the cart, and perhaps fault conditions that we detect.

Dad and I have discussed it, and we are going to have a series of relays that will allow us to "switch over" to a stamp solution.· In otherwords, if our stamp fails, we can turn off a switch and it will go back to the current operation which seems to work fairly reliably.

My research has shown that the PLC BS2 panel is the one for me.· The control box already has a 24volt bus.· Now I need to figure out which of the stamps to get, the BS2 at a minimum.

I hope that now I've decided to go with a stamp, I can get as much good help·on my stamp development as I have on other potential solutions!http://forums.parallax.com/images/smilies/wink.gif

kelvin james
04-18-2007, 01:23 PM
Looking around the net for manufactures of hoist trams, i found some interesting things. Looks like there is a safety code for these devices, but i guess as long as an inspector doesn't come around where you are, or you are not worried about insurance issues, you are okay. Take a look at the safety features on the link provided, they do have the clutch brake, and a lot more than that. Don't take for granted that your cables and motor drive are accident proof.


www.munsonworks.com/munson/products.html (http://www.munsonworks.com/munson/products.html)

jeffjohnvol
04-18-2007, 07:31 PM
kelvin james said...
Looking around the net for manufactures of hoist trams, i found some interesting things. Looks like there is a safety code for these devices, but i guess as long as an inspector doesn't come around where you are, or you are not worried about insurance issues, you are okay. Take a look at the safety features on the link provided, they do have the clutch brake, and a lot more than that. Don't take for granted that your cables and motor drive are accident proof.


www.munsonworks.com/munson/products.html (http://www.munsonworks.com/munson/products.html)
Yes, you are referring to ASME code A17.1, section 513.·

I have seen many of those sites, but hadn't seen that one before.· I liked that cable track design where the cart sits in between.· I can only imagine how much concrete they would need to keep those cables tight.

We initially priced some of those systems, but they wanted close to 30 grand for a complete system (installation not included).· We built ours for under 7k.

Loopy Byteloose
04-18-2007, 08:38 PM
I find the Munsonworks system interesting in what it is lacking.

It doesn't have a second cable. And it doesn't have a counterweight system.

I still prefer having the counterweight as it really will conserve on your power bill as well as reducing stresses on the primary drive systems to a minimum. In the long run it might actually recover its own costs.

I live in Taiwan and we have many [likely thousands] of small low tech elevators that rely on a single winch system. The tracks actually lift away from the ground floor to allow auto parking. Many building owners use these as freight elevators to store goods up to 5 floors about a ground store outlet. It seems to work fine as long as the traffic is not intense and the users are aware of the limitations.

Forgive me, but I assumed that this was an main entry point into the home, rather than backyard access. I happened to have a cousin that had a home on a sea cliff which did have such a main entry lift that delightfully ran above a rhodedenron garden as it decended from parking to the main entry.

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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········


···················· Tropical regards,····· G. Herzog [·黃鶴 ]·in Taiwan

jeffjohnvol
04-18-2007, 08:50 PM
Kramer said...


Forgive me, but I assumed that this was an main entry point into the home, rather than backyard access. I happened to have a cousin that had a home on a sea cliff which did have such a main entry lift that delightfully ran above a rhodedenron garden as it decended from parking to the main entry.




No, its access to my boat dock, and hopefully access to my subbasement if I can add another landing platform.· We have the first floor (and a 2nd) where the tram starts, a basement level, and a subbasement level which is like 2 floors high.· From the base of the house, you climb 3 flights of stairs to get to the first floor.· And thats once you are at the base of the house.· Its quite a climb up the hill just to get to that point.· The tram gets us up 90 feet in the vertical plane.· I might add a counterweight later on, but currently (no pun intended) the electric bills aren't that high.· By using 220 volts 3 phase with PWM, its pretty efficient.

Robert Kubichek
04-18-2007, 10:04 PM
jeffjohnvol said...

bennettdan said...

jeffjohnvol,
What you need to do is have a mechanical brake setup on the cart itself and you can use a braking system like on a old elevator its the same principle as a steam engine govenor. The balls on the end of the vertical rod spin because its linked to the shaft that has the wheels on it if it spins to fast the balls will pull outward and push down on the rod inside of the shaft and apply the brakes. I hope you can understand how it works with such a plain drawing.

bennettdan, yes, I have seen one of these work before and I understand the drawing. Part of the problem though is the rail is 2.5" schedule 40 pipe. Getting traction to spin the wheel on that pipe for a regulator like that may be difficult to manage. The current wheels are just casters, so there is no drive shaft to attach to. The attachment is a picture of the wheels I put on this weekend, and got rid of those other single wheels.

Given the fact that the pipe could be wet, rusty, dusty or some other situation that could prevent traction in an outdoor environment, I would be worried about tuning such a mechanical control system. Plus, given the fact that I can adjust the speed through the controller, I might have to fine tune when changing speeds. In theory that regulator would work, as an incremental brake or pulling a pin, but I would prefer a more exact solution, hence RPM measurement at the top.

Thanks!


Looking at the pics, you could add 4 more wheels to keep the cart from "bouncing" off of the rails;
...T.T.T
....\.l./
S--.O.--S ...."periods are for screen formatting"
..../...\
...B...B
Leaving just the bottom center wheels off for rail support, the two bottom sets would not have to be as tight to rail as well..


Some one liked the switches you used, here is a source for totally waterproof digital ready switches for industrial use.

The technology;
www.itwactivetouch.com/pdf/ITWActiveTouchBro_R1(0806).pdf (http://www.itwactivetouch.com/pdf/ITWActiveTouchBro_R1(0806).pdf )

The actual switches;
www.itwswitches.com/pdf/activemetal_catalog.pdf (http://www.itwswitches.com/pdf/activemetal_catalog.pdf )


Bob



http://forums.parallax.com/images/smilies/scool.gif

jeffjohnvol
04-18-2007, 10:25 PM
Robert Kubichek said...

·


Looking at the pics, you could add 4 more wheels to keep the cart from "bouncing" off of the rails;
...T.T.T
....\.l./
S--.O.--S ...."periods are for screen formatting"
..../...\
...B...B
Leaving just the bottom center wheels off for rail support, the two bottom sets would not have to be as tight to rail as well..


Some one liked the switches you used, here is a source for totally waterproof digital ready switches for industrial use.

The technology;
www.itwactivetouch.com/pdf/ITWActiveTouchBro_R1(0806).pdf (http://www.itwactivetouch.com/pdf/ITWActiveTouchBro_R1(0806).pdf )

The actual switches;
www.itwswitches.com/pdf/activemetal_catalog.pdf (http://www.itwswitches.com/pdf/activemetal_catalog.pdf )


Bob



http://forums.parallax.com/images/smilies/scool.gif
Thanks Bob.· Actually, the angle iron that the pipes are welded to prevent us from putting wheels underneath the pipe.· If you look at the picture that I attached on an earlier post, you can see that I've increased the wheels from 4 total to 40.· They are very stable and don't bounce at all.
I'll save that link for other switches should I need them.· The ones I am using are industrial grade and rainproof.·

Loopy Byteloose
04-18-2007, 10:48 PM
By the way,
since this is not part of a main entry, I suspect that you can merely claim it as 'not for passenger use' -- just a 'dumb waiter hoist'.

The should satisfy local buiding inspectors and insurance people.

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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········


···················· Tropical regards,····· G. Herzog [·黃鶴 ]·in Taiwan

jeffjohnvol
04-19-2007, 12:01 AM
Actually, when I got my permit for the dock, I forgot to put in the request for the concrete pad that the rails are on. So, I told TVA (local lake authority) that the pipes were electrical conduit for my power. And it doubles as a road for my cart, lol. They were okay with it. I would never be able to sell these of course, and they don't have building inspectors where I'm at.

jeffjohnvol
04-19-2007, 12:39 AM
DiablodeMorte said...
I realize this is a little off topic so I'll try to add something worthwhile at the bottom of my post:

Where did you get those buttons? I want some! By "Those Buttons" I mean the buttons on your control box, very professional looking!


From my dad:
Jeff,
The switches are made by C3 Controls in Beaver, PA.
Phone 724-775-7926, fax 724-775-5283.
They are NEMA 4 rated and can be provided with Class 1 Div. 2 explosion proof contacts.

kelvin james
04-19-2007, 12:41 AM
Here is an "idea" that no one has probably considered yet. This would be for a self contained safety brake system on the tram itself, independant of the drive system. Since it is outside, a gps could monitor the rate of acceleration and decent of elevation. The gps data would be watched by a stamp, and depending if the maximum values are exceeded, the stamp would activate an electric brake on the tram itself. You could have the tram stop if the gps lost the signal also, as an extra precaution. If you have a portable gps, or can borrow one, take it on the tram with you and check the location and elevation resolution, as the tram is moving down the track ( like how fast the info is being updated ) WAAS should be around 10 ft with a good signal fix. A 12 volt car battery has plenty of amps to hold a brake ( solenoid ), and holds the charge for a good time if not being used, other than powering the electronics if required. There are variables like the elements and mechanics to be considered, but it may be an idea to keep in mind. Lots of gps info on the forum here.

jeffjohnvol
04-19-2007, 12:54 AM
Thanks Kelvin. That could work, but it would defeat my goal not to have any battery or something I have to charge on the cart. Solar charging isn't much of an option either, because we are behind a mountain and under a lot of trees.

I also have additional reasons now to use a stamp other than the safety issue as discussed above.

Thanks.
Jeff

kelvin james
04-19-2007, 01:27 PM
Some other thoughts, ---- Instead of the hall effect sensor, consider an industrial type optical quadrature encoder, such as sealed Grayhill to monitor the drum shaft. You don't need a high count per revolution one, possibly a 64 or less will do. This will give the option of detecting which way the drum is turning, which will come in useful, and give a faster response time. Also, the mobo stamp may be worth a look, it has coprocessors to read an encoder ( Parallax can correct me if i am wrong ) or other sensors, freeing up the stamp to do other things.

jeffjohnvol
04-19-2007, 07:44 PM
kelvin james said...
Some other thoughts, ---- Instead of the hall effect sensor, consider an industrial type optical quadrature encoder, such as sealed Grayhill to monitor the drum shaft. You don't need a high count per revolution one, possibly a 64 or less will do. This will give the option of detecting which way the drum is turning, which will come in useful, and give a faster response time. Also, the mobo stamp may be worth a look, it has coprocessors to read an encoder ( Parallax can correct me if i am wrong ) or other sensors, freeing up the stamp to do other things.
Kelvin, I've been googling quadrature encoders and am very interested in this.· I hadn't considered determining direction.· I'll keep looking for ones that would be easily mountable to my situation (huge, industrial equipment).· Thanks!

jeffjohnvol
04-19-2007, 09:35 PM
Kelvin, the 2pe Motherboard looks interesting, but I need at least four digital inputs and up to 6 digital outputs, and that doesn't include the encoder (which, as you point out, would be handled by the DVR daughterboard processors).

I wonder if with using the StampPLC with a 2px I would be able to measure 2 sets of pulses, with a minimum pulse width of 1/64 of a second (60 rpm max, = 1 rps, with 64 position encoder).

And I like the PLCStamp because it works with 24 volt source and switch values, but I'll have to find a way to step some 5 volt inputs up to 24v, I guess with some transistors.