Brainstorming for all you Engineers out there

NWCCTV · 2013-10-01 20:16

OK. I have an idea for something but I do not know how to make it work. I figured with all the Engineering brains within the Parallax community someone can come up with a solution for me.

I have a telescoping tri pod. I want to disassemble it and use one of the legs. Here's the tricky part that I am having trouble figuring out. I need the telescoping to be done using either a Servo, Stepper motor or just a plain old DC motor. Whatever I use needs to be as inconspicuous as possible. The legs are hollow so I can run cable through them. I have been thinking of a pulley type setup but I am just not sure how well(or how!!!) that would work. Suggestions and diagrams are all welcome. Thanks all.

Yanomani · 2013-10-01 20:23

NWCCTV

Does something like this do answer your question?

http://www.youtube.com/watch?v=46dZln2JgJE

Yanomani

NWCCTV · 2013-10-01 20:27

WOW. That was quick!!! Yes and no. I need to know how it's done. An antenna would not be sturdy enough but that is the idea.

Phil Pilgrim (PhiPi) · 2013-10-01 20:43

It uses a coil of toothed nylon (like weed whacker line -- strimmer line for you Brits -- only stiffer) wrapped around a drum. As the drum turns, the nylon either pushes on the inner segment of the antenna to extend it, or pulls it in to retract it. There is no control over which sections extend or retract first. That's determined solely by friction.

BTW, the only weight this mechanism has to support is that of the antenna itself. If you want your tripod leg to support more weight, this may not be the best choice of mechanisms.

-Phil

Yanomani · 2013-10-01 20:50

NWCCTV

There is a spool inside it, with an helicoidal track crafted at its outer surface. A semi-rigid steel cable is wound, following the helicoidal track, and fixed thru a hole, at the track start, by means of a short zig-zag path, crafted inside the spool.
The other end of the cable is fixed, sometimes by a welded screw bolt, that is fixed to antenna's top end, by means of a nut.
A DC motor, by means of a pinion-based reduction mechanism, drives spool's rotation, CW and CCW.

I'm searching for some good diagrams, but it seems I'm out of luck till now!

Yanomani

Yanomani · 2013-10-01 20:53

Phil Pilgrim (PhiPi) wrote: »

It uses a coil of toothed nylon (like weed whacker line -- strimmer line for you Brits -- only stiffer) wrapped around a drum. As the drum turns, the nylon either pushes on the inner segment of the antenna to extend it, or pulls it in to retract it. There is no control over which sections extend or retract first. That's determined solely by friction.

BTW, the only weight this mechanism has to support is that of the antenna itself. If you want your tripod leg to support more weight, this may not be the best choice of mechanisms.

-Phil

Phil

He he he

It seems that the antennas I'd saw, dismantled, are many times older than the ones you saw!

I'm becoming older and older, each day!

Yanomani

NWCCTV · 2013-10-01 20:58

Yea, I was thinking along the lines of spring loaded metal strip, wrapped around a drum of some sort. Problem with that is I think it would break after too much use.

EDIT: Does anyone know what the metal spring strip is called and or where to get it?

Just thought of something. I wonder if Fish Tape would work???? I would need a pretty powerful motor though.

kwinn · 2013-10-01 21:31

Look in the plumbing tools for a drain snake, or electrical tools for wire fish tape.

kwinn · 2013-10-01 21:34

If you have to lift some weight take a look at the extension ladders at your friendly neighborhood hardware store.

ElectricAye · 2013-10-01 21:44

NWCCTV wrote: »

Yea, I was thinking along the lines of spring loaded metal strip, wrapped around a drum of some sort. ...

EDIT: Does anyone know what the metal spring strip is called and or where to get it?.....

Are you talking about a constant force spring?

http://www.mcmaster.com/#constant-force-springs/=or7jod

Yanomani · 2013-10-01 21:55

NWCCTV

Even ball and roller bearing based mechanisms do fail, as operational cycle counts and dust (sand, rust) particles piles up inside.
The main concern, as Phil had expressed, is the amount of force to be exerted on the recoil/extend movement.
Multi way threaded axle solutions, ball bearing driven, can be crafted to handle a lot of torque and speed, but they are in no way shorter than half the total maximum extent amount.
And to realize its maximum extensibility of movement, they depend on crafting the ball bearing driver as part of motor's rotor.
Then, some part of motor's lenght must be subtracted from the required linear movement.
That was the reason for the above expressed shorter than half telescopic leg lenght movement limit.
Direct motor drive is possible, where extending forces are not beyond certain limits.
Concentric reduction mechanisms will deal with the amount of torque needed, at the cost of complexity (cost), volume and speed.
All of the above will need some electric current sensing, to limit (and protect) motor driving (even for steppers), as it reaches leg full extending or recoiling and to allow some room for mechanical stalls.

I believe that are not simple solutions to that kind of problem.

Yanomani

ElectricAye · 2013-10-01 22:07

There are linear stepper motors. They tend not to provide very much force and, of course, they don't take side forces. Also, you generally don't get much travel out of them. And they tend to be expensive. I guess it depends on what you want to do. On the plus side, they can provide you with some very controllable small motions, such as those desired in syringe pumps, etc.

Yanomani · 2013-10-01 22:18

ElectricAye

These can withstand up to 3000 N, max. 250 mm/s, but they are huge!!!

They can be found at:

http://www.shsitalia.it/

Yanomani

NWCCTV · 2013-10-01 22:24

extension ladders

Way too big. @ElectricAye. That is what I was talking about. I need about two feet or so. Will check it out. I also like the linear stepper idea but as you said, they are pricey. I also though of Fish Tape but that would require quite a lot of torque to limit the footprint. A coiled drain snake might also work out. I did find the motorized antenna on EBay for $25.00. I might be able to rig one up just for the extension. The forward and reverse motion only needs to be able to push/pull one of these with a stepper motor attached plus the max weight that it is able to carry. Whatever way I go needs to fit nicely on my Wild Thumper.

EDIT: I am also looking at extra strength zip ties. I just need to find one long enough.

EDIT2: After looking at the link @ElectriAye posted, I may have the solution. A tape measure!!!!! Or I may just get some of that material. Thanks all. I think I have some where to start now.

Yanomani · 2013-10-01 22:34

NWCCTV wrote: »

Way too big. @ElectricAye. That is what I was talking about. I need about two feet or so. Will check it out. I also like the linear stepper idea but as you said, they are pricey. I also though of Fish Tape but that would require quite a lot of torque to limit the footprint. A coiled drain snake might also work out. I did find the motorized antenna on EBay for $25.00. I might be able to rig one up just for the extension. The forward and reverse motion only needs to be able to push/pull one of these with a stepper motor attached plus the max weight that it is able to carry. Whatever way I go needs to fit nicely on my Wild Thumper.

EDIT: I am also looking at extra strength zip ties. I just need to find one long enough.

EDIT2: After looking at the link @ElectriAye posted, I may have the solution. A tape measure!!!!! Or I may just get some of that material. Thanks all. I think I have some where to start now.

NWCCTV

You has just banished my wildest thoughts!:frown:

I just now remembered, that even sturdy and speciality crafted tripods will fail, till being wrecked out, under certain circunstances...

Yanomani

NWCCTV · 2013-10-01 22:51

It's only one leg of the tripod that I am using!!! If it fails, I have many more. Garage sales are usually ripe with them!!So much so that if I get this working, I have other great ideas in the back of my head!!!!

Phil Pilgrim (PhiPi) · 2013-10-01 22:59

Here's another technique, a "zipper mast."

http://www.hizook.com/blog/2008/12/22/geosystems-situational-awareness-mast-aka-zippermast

-Phil

NWCCTV · 2013-10-01 23:10

Phil, That is an ingenious idea. Not sure I need anything that fancy but it would be nice to figure out. I am going to order some of the material and see what I can come up with. In the mean time, I think I have a few old tape measures around that might also serve the purpose.

Phil Pilgrim (PhiPi) · 2013-10-01 23:18

It turns out it's not a new concept. Here's an article about a "Fontana mast" from Popular Electricity:

http://books.google.com/books?id=VJMhAQAAMAAJ&pg=PA301#v=onepage&q&f=false

-Phil

NWCCTV · 2013-10-01 23:22

Makes me wonder why the Military never adopted something like this. We use to erect 120 feet of antenna masts up in the air five feet at a time!!!

W9GFO · 2013-10-02 00:27

Photographic light stands often have air cushioning. You could use air pressure to raise and lower them. It would need some type of spring return mechanism if not being used vertically.

xanadu · 2013-10-02 08:53

My initial thought was air pressure via compressor or co2 cartridge but since W9GFO beat me to it and everyone else mentioned probably everything else I'll have to go with micro-hydraulic.

How cool would a robot with hydraulics be?

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=14054

[video=youtube_share;vvaYTVBHHYU]

cswanson · 2013-10-02 15:27

Phil,
I am using Magicdraw to use BuzzToys MyroMagic, Mode C to communicate with the Scribbler Rover in Dr. Russell Peak's SysML class at Georgia Tech. Lately I have become fascinated with the Raspberry Pi and would like to have Mode C download the code to the Pi instead of the Scribbler Rover. I called Parallax and they thought you might be responsible for writing the code for communicating with the Scribbler. How difficult would it be to modify the software to send code to the Pi?

davejames · 2013-10-02 17:47

Hello cswanson and welcome to the Forum.

Mr. Pilgrim can be reached at: propeller AT phipi DOT com.

That would be preferable rather than taking this thread off-topic.

NWCCTV · 2013-10-03 18:22

OK. So after kicking around the different ideas I came to a pretty simple resolution that is also inexpensive. Thanks @ElectriAye for the link to the Constant Force Spring. After reading up on the CFS on the McMaster Carr site a light clicked on. I went to Harbor Freight and for $1.59 I bought a 12 foot tape measure. I currently have the tri pod leg torn apart and I needed to trim just a little material off about 1.5 inches from the end so it would fit the last size of the leg. I thought about using a rivet on the leg end to hold the tape measure in place but the is going to wear out the tape measure fairly quick. So, I am off to Lowe's to get some JB Weld (I usually have some on hand but I used it all on another project a couple weeks ago. I am going to drill a small hole in the leg end of the tape measure and place a pin through it so it protrudes out both sides. Then I will insert in the leg and fill in about 2 inches deep with JB Weld. That should hold it!!!!! After that I need to make a small box with a wheel on the inside to connect a motor to. I will be updating all this on my Wild Thumper Project Page. Thanks everyone for all the great ideas.

W9GFO · 2013-10-03 19:58

I don't understand how you will use this to extend the tripod leg. If you intend to unroll the tape measure, to push it out, it will unravel and bind inside the container. I think you will need a pinch roller external to the tape measure that pulls the tape out and pushes it into the tripod leg. Maybe that is what you are planning?

NWCCTV · 2013-10-03 20:43

Think of a tape measure enclosure but smaller. A hole will be drilled in a small round cylinder to put the shaft of the motor on to. The max weight the clamp on the end will be lifting is no more than a pound so the Constant Force Spring does not need to be a large one. I will be posting pics on my Wild Thumper Project Page in a few days. I was thinking of a pinch roller type set up but since it will not be lifting a lot of weight I decided against it.

Phil Pilgrim (PhiPi) · 2013-10-03 20:49

You may still need a rubber idler wheel pressing against the roll of tape to make sure it unrolls instead of simply uncoiling.

-Phil

NWCCTV · 2013-10-03 20:57

I will keep that in mind. I have several rubber wheels, etc. from printers that would probably work for that.

skylight · 2013-10-04 04:33

Maybe too expensive or not practical but what about a piston within a coil similar to a solenoid but more controllable
or what about a rack and pinion setup?

NWCCTV · 2013-10-04 16:40

@skylight, both are great ideas but I am trying to use items that I have available. Other than the $1.59 for the tape measure, I have everything else that I need. When I decide to do a larger one the piston/coil set up might work well. Rack and Pinion would be quite large.

Brainstorming for all you Engineers out there

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