We need help... A lot of it

Hey guys Im Sam from 2869 and we have some major issues. We “finished” the elevator system today only to find there is a couple of fatal flaws.

Basically the wheel that is supposed to make the wire move slips and does not actually move the cable. Another issue is the elevator platform is so tight on bot that it barely moves unless you put a good amount of force into it.

Its too late now to do anything on the bot and yes we bagged and tagged it. So we have to work with the 30 pounds.

Another thing to consider is the bot already weighs 117 pounds.

We have the funds necessary (Just recieved sponsorship money) the real issue is having enough time. Our regional is on March 27th.

Another thing to consider is our lack of resources we have in our lab at our hands. We are working with bar stock L bracket and Lexan. We have no 8020 no alumium sqaure or rectangular tubing ect.

Heres the Sketchup model of what its supposed to look like


and here are some pics of the “finished” product.






Extra high quality pics for download (Much better pics)

Thanks for your support and ideas hope your stop build day went better then ours. - Sam

Out of curiosity why did you bag it now instead of much latter at night like 10?
The extra hours of bug fixing might have been nice.

Is your wire/cable tied off through the wheel? OR is it just wrapped around?

Not sure how the system is failing from the pics.

Our mentor wanted to go home at 5:30

It’s just wrapped around. The biggest problem area is the slipping wheel (the one connected to the motor at the bottem left and right.

The elevator might be getting stuck due to the rails not being parallel to each other.

How many wraps of cable do you have around your winch? I believe the recommended number is 2-3, looks like you don’t have that many.

This would be a quick, light fix, involving a longer cable and whatever you use to attach the cable to the drum/terminate the cable. That’s all you’d need. Depending on your setup, attaching the cable to the winch could work very well too.

It is because the elevator is too tight basically the easiest fix imo is to dremel out a slot on the bar stock and slide over the bearing blocks. The issue is we can’t throw sparks in the competition and I am not sure if there is a machine shop. So we may have to drill out 4 more holes but it will be hard.

It’s one continuous cable and they terminate connected to the elevator plate. There is only one cable but the way it’s setup I don’t know how you would use more then one cable.

I think I need to find more detailed pics that show the pulley system better. Because I think it’s slightly confusing what we actually tried to do.

You don’t need to use more than one. You just bring in a longer piece of cable.

As follows:

  1. Unterminate one end of existing cable.
  2. Terminate one end of new, longer cable where previous cable used to be.
  3. Run new cable and unrun old cable along the same path, until you hit the winch drum.
  4. Wrap new cable around drum about 3 times.
  5. Continue #3 above until you reach the other termination point.
  6. Terminate new cable (probably want to do a temporary termination here, and make it permanent later). Make sure old cable is gone.
  7. Test.

Nope, I think I understand you. The cable is terminated to a moving plate on the elevator, on both ends, and the rest of it moves through associated pulleys to the drum, where it wraps around once and continues to the other termination point via more pulleys if needed. See my last post.

the part where I am losing you is the drum. What do you mean by drum? Do you mean the small wheel connected to the motor.

I am starting to catch some sort of drift. will wrapping the cable around the moving wheel make it so theres tension to make it contact the wheel and actually move? Our imediate reaction was we needed something to make the wheel more grippy.

A second cable is only needed if your lift plate is too light, or your friction is too heavy, for the lift to lower itself. As I read your posts, your first cable (pull on lift) is also your second cable (pull on lower). If this is correct, you can pretty much ignore the “second cable” posts.

Also, if this is correct (that is, your cable is doubly terminated on the chassis end), you can make your system more repeatable/reliable by adding more wraps to the shaft/axle/spool on the lift side. This basically means making a somewhat longer cable in the shop (add one or two wraps around that spool), including it in your WITHHOLDING ALLOWANCE, then replacing it on the Thursday of your competition.

Yep. Often for winches, that’s a bit larger and drum-shaped.

I am starting to catch some sort of drift. will wrapping the cable around the moving wheel make it so theres tension to make it contact the wheel and actually move? Our imediate reaction was we needed something to make the wheel more grippy.

It’s more of a “hold-in-place” on the wheel, giving it more cable to work with (having the same effect as a grippier wheel, theoretically). You’d have a tensioner (turnbuckles work well) elsewhere in the system and run a pretty tight cable for this trick to work, but it should be. Given that you’ve got a small(ish) wheel width-wise, you might be able to get away with 2 wraps.

I’m going to suggest following the procedure I posted earlier, with the cable not permanently terminated until you get the lift working reliably. It might take extra cable wraps or some grippy material or both, but it should give you some working room.

Thanks guys its such an easy fix Im mad we didnt get to do it today. The good thing is our mecanum wheels are working and I had a little bit of driving practice getting a good feel for this years control layout. We should be able to make all the fixes necessary in an hour or 2 on practice day of the comp. Thanks all :wink:

Enjoy your competitions.

My favorite thread of the season.

Always glad to help. I hope we ally with you on Einstein ;->.

Miracles are real… I think

You might find the capstan equation interesting: http://en.wikipedia.org/wiki/Capstan_equation

Basically having a few wraps around the moving part of your winch increases the maximum pulling force exponentially.

You might see a few photos of 5742’s robot with a 6" diameter steel pulley on the front of it. There are three wraps of 1/8" plastic coated wire rope around there, and it does not slip. http://www.chiefdelphi.com/media/photos/41356?

With two wraps it slipped a bit.

With one wrap is just spun uselessly.

You’ll note that there is an eyebolt at the top of the 5742 lift to adjust tension in the cable. That also helps improve traction.

As far as linear slides are concerned, IGUS (the cool plastic bearing people) have some information on designing them at http://www.igus.ca/wpck/6109/TechTalk_Overview Check out the “2:1 rule” and “How to Eliminate Binding”

Good luck,