Rubberbands on Elevator Lifts

Our team built an elevator lift, and it works really well; however, we would definitely love to make it stronger by adding rubberbands. The problem is, we’ve done all the brainstorming we can and cannot figure out a way to have rubberbands that stay taut all the way up. We’ve been able to connect the top of one stage and the bottom of the next, but after the arm goes up, the rubberband is no longer tight, and it doesn’t help the robot when the arm is at the top, one of the places we need the rubberbands the most.

Does anyone know of any way to attach rubberbands so they can assist the lift no matter where it is? We’ve tried two, 3, 4 attachment points, different shapes, etc., and nothing has helped.

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Something you could possibly try is latex tubing. Raise the lift all the way up and tension the tubing so that it is still taunt when the lift is raised. I’m not sure if the tubing would handle the strain when the lift is all the way down but it might if you play with it right. Other than that, I’m not sure if there is a way to counterweight it to still have upward tension at full height.

Double up the rubber bands so that 1 rubber band makes 2 loops? Otherwise, all that yiu can do is attach them in places that are farther apart when the lift is all the way up. Really the rubber bands are always going to get less taught as the lift goes up; that’s how they work. If they didn’t, then they wouldn’t be assisting the lift.

Back in Clean Sweep, we built a rather unique robot, with 2 parts:
“Wall” had no motors, but rolled to the dividing wall under rubber band power, then deployed a wall, blocking the other team from scoring.
“Floyd” fit inside of Wall, and deployed (tethered by a wire) to perform 10-motored offensive duties.

I’m currently looking for an image of the rubber band drive on Wall, but here’s a summary:
The colored circles are “barrels” which the rubber bands wrap around.

Yes, it’s rather large, but could achieve the same thing you’re trying to do: making a constant-force spring out of rubber bands. You would simply attach the output of barrel 2 directly to your lift motors, and let it go.

We had a few issues with repeatability at high tensions, but I’ve got a feeling with a little tweaking, you could get it to work. We used 84-tooth gears for the sides of our barrel, but there’s no reason you couldn’t use 36-tooth gears, depending on how much energy you want to store.

30th post!

Thanks for all of your replies!

Actually, our tournament is in 2 days and we wouldn’t get it in time, but we’ll definitely look into that!

Yeah, we just somehow need the bands to provide some sort of assist when the lift is at it’s highest. Right now, they’re just loose and do not help at all.

Hmm, that looks really complicated but also a really good idea! A question, though, it looks like this doesn’t have to be vertical to work, so is it possible to put it in any orientation? With our current design, vertical wouldn’t work very well, but I just checked and we can fit something like this in horizontally.

Yup, orientation doesn’t matter! And you can exchange total size for a different gear ratio. Note that wrapping tensioned rubber bands around a barrel (we used standoffs screwed between two gears) will create a huge compression force (twice the tension for each full wrap).