Is a constant force spring climb crazy?

our team had the idea to use constant force springs to hold our climb. I don’t know if it has been done before or at least I can’t find anything like it. it would be an elevator brought up by falcons and then the cf spings would pull the bot up. Is this actually do-able, if not how are you guys holding your lift at the end of the matches?


Using CF springs are certainly doable. We did it in 2018, had 2 50lb springs on our elevator. supported our robot of 119.9lbs (before bumpers and battery) and another 140lbs+

We also considered using locking pins that would engage to help lock our elevators in case we started lowering. Turned out we didn’t need them.

Our locking pins were basically metal rods tapped on one end, screwed onto pneumatics. Drilled holes in elevator so the metal rods would hold the bot in place.

I should ask, do you plan on having the springs connected to your elevator? it sounds to me that you are using falcons to extend elevator, then somehow using the springs to pull the bot up…

This definitely could work although I’m concerned that the spring tension might start to deform the frame of the elevator over the course of the season. Ideally once the elevator is in the “closed” position the springs would no longer be in tension.

If you do this, look into ways to cover the springs so that in case they break they’re contained and don’t hurt anyone.

I like this idea a lot because it could allow for a buzzer beater climb.

Together we rise.


One idea is to use the constant force spring to deploy, and then winch it back in with a ratchet. Depending on if you have pneumatic, you could have a cylinder release a latch and extend the climber up.


We had the inverse last year. We used a constant force spring to hold the climbing mechanism in place until we turned on the motors to climb.

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Are the springs only under tension when you raise the elevator to hook onto the rung? If there is some tension in the springs after climbing, then it would be wise to have some way of ensuring it is safe for the people around it as it is being removed from the rung at the end of the match. The RI’s will be looking at that. Please refer to I7 for the relevant rule.

honestly not completely sure but it seems like we will have the spring mounted to the base, and then when lift is brought up by the falcons, then the springs will have enough force to pull the bot up by themselves when the lift is positioned.

thanks i’ll make sure of that

So based off of that, you are relying on the springs to “naturally” pull up the bot. Why not reverse the Falcons?

I like that idea although my team has very little experience with pneumatics. I’ll definitely propose it next meeting.

i think the idea was so that we would be held after the match

I think you’re over complicating this. If you reverse the mechanism so that the cf springs pull the mechanism up and then the motor spools it down, all you need is a ratchet to prevent the motor from backdriving.

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Oh yeah. Any locking pins will have the full lifting force acting on them so releasing them could require quite a high force. The other people who have actually used CF springs might be able to give more insight.

Any reason your are not using the Falcons to extend AND climb? Checking the numbers using the JVN calculator might be an enlightening and beneficial exercise that may lead you to a much simpler solution.

thanks, i’ll definitely make sure this is done safely

I can see why and where this is coming from. The backdrive on the motor was our fear too.
If you rely on the natural retraction of the springs, they may not be enough to pull you up resulting in a failed climb. It would also mean a slower climb, if you get off the ground at all.

Spinning a motor both ways, while having the springs on shouldn’t be a problem. As others pointed out, putting a ratchet works too.

PS If you go the route of motor to extend, rely on springs to retract, a tip is to make sure the elevator is SMOOTH. Just a bit of something and that elevator will want to stay stuck.

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We definitely could use the falcons to lift back up I guess we hadn’t really thought about that yet.

thank you, i’ll definitely talk to the team about the ratchet, are there any examples of it?

Read through this post then do the calculations using the Rotary Mechanism tab of the JVN Calculator. You may find you have to try different gear ratios. I suspect that you will be very pleasantly surprised.

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yeah this will be the first year our team has a climb so we definitely have been cautious.