Easiest and smallest way to do light duty linear motion?

We need a way to lift a claw for our climber, but a winch will be doing the actual heavy duty pulling. So we need a simple and cheap solution for linear motion - hopefully smaller than 80/20 with linear motion kits from REV.
I was thinking about sliding andymark 1/2 hex shaft inside the long hex aluminum spacer stock. The question is what’s the best way to actually move the shaft inside the spacer stock? Obviously pneumatics are the ideal solution here, but our team is not quite ready to implement that this season.

First question is, how long of a linear motion do you want? If it’s short enough, I believe there are some FRC linear actuators.

Generally speaking your non-pneumatic options are going to be:
-Rack and pinion
-rope/string/wire rope/cable/chain (attach one end of the slider to a spot on the chain)
-leadscrew

You could also think about non-linear motion.

Our climbing system has used this in multiple previous years to great success - don’t let the simplicity of using a rope, two pipes, and motor deceive you, it’s an effective combo!



Make a loose fitting telescope out of aluminum square tube, take up the slack with mushroom-head Velcro as so:

image
where the “grey” Velcro is attached to the inner surface of the larger tube and the “blue” Velcro is attached to the outside of the inner tube

Lengths of any single Velcro will probably need to be ~2inches for rigidity (just a guess).

You can use a constant force spring to extend the thing.

one PVC tube inside another PVC tube? :slight_smile:

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We did that way back in '04. You can probably make aluminum lighter, but the flexibility of PVC gives you a lot more room for error. Or someone trying to wrap your telescoping lift around a pole.

I remember seeing robots from 2016 using motorized tape measures to climb
They’d have a hook on the tape measure, use wheels to extend it up to the bar, and then winch themselves up

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you dont always need to have linear motion, 4911 the cyberknighs in 2018 are a great example of this. it can be a lot more simple than making an elevator or arm only for climbing

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Drawer slides with string and pulleys is a pretty thin solution .

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It needs to go maybe 2-3 feet. But the linear actuators don’t go nearly that far.

This seems interesting, but what purpose is the Velcro serving here? I am not sure I completely understand what’s going on there.
Also, does this mechanism have a way to retract or not?

How did you move the inner PVC tube?

We have considered this, but the hooks we will be using are probably a bit too heavy for this solution.
But it’s a really neat idea - thanks for the reply.

This is interesting, I’ll look in the CAD and see if we could fit something like this.

What do you guys think about using a small lead screw?

The mushroom head velcro serves 3 purposes:

  1. takes up the space in between the different sizes of tube such that there is a few thousandths of space for free motion axially (thus making it a linear mechanism)
  2. acts as an end stop when the edges of the “blue” and “grey” touch when at full extension
  3. provides a low friction surface

You could retract this (provided it was sprung to the extended position with a constant force spring or a gas spring) if you ran a string through the center and attached o e end to the inner tube and the other to a winch. I wouldn’t count on this taking moment loads very well though (at least with 1/16 wall, ymmv with heavier gauge)

It had a piece of latex tubing inside, which acted as a spring, and when we moved a pneumatic cylinder that locks it retracted, the inner tube sprang up.

I doubt we’ll use this design this year, because of the difference in robot size and rung height. And the students who came up with and made this wonderful mechanism, have graduated and moved on to bigger and better things.

On your left

Am I correct in thinking that you used the mushroom head Velcro for both the blue and grey parts in your sketch and that it is the same as 3M Dual Lock?

Yes, it should be the same stuff.