Need help for noob, willing to pay for some work
jeffjohnvol
Posts: 197
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
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
Comments
Regards,
Quattro
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'Necessity is the mother of invention'
Post Edited (QuattroRS4) : 4/12/2007 11:08:10 AM GMT
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
·
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
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:
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 [noparse]:)[/noparse]. 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!
Regards,
Quattro
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'Necessity is the mother of invention'
-My 2 cents
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
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
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.
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
··· 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.
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.·
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!
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.
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.
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
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.
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
Having the Counter Weight to compensated for at least dead load [noparse][[/noparse]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."········
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
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