Is a constant force spring climb crazy?

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.

Ratchets vary in size, but here is an image of one

Here is the Everybot using a Ratcheting Wrench for their climb.

Everybot links (Click here for drop down)

The 2020 Robonauts Everybot Low Resource Build


thank you this was really helpful

thank you I didn’t realize it all it was was a wrench lol.

You can also use the CF spring to assist the Falcon during the lift. A 40 lb spring working with a falcon is safer than 150+ lb springs and I’d bet it’s faster too. You could try using a combination of springs that are just strong enough to cause the robot to “float” while hanging so all the motor is doing is moving the robot up rather than lifting it up. This is a strategy a lot of teams used in 2018 with their elevators.

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You can also get a ratchet stage on a Versaplanetary gearbox from Vex.

You can, but watch the load ratings on those small planetaries.

You can also do a dog clutch to a solid mount. It’s a little more involved than a wrench ratchet, but has the advantage of being something you can turn on and off at will.


For what it’s worth, we’re considering a similar climb, and will hopefully have it built up and fully tested this week.

Our build thread has CAD and some discussion about why we went with this in the 2nd update.

We tried to do a constant force spring climb for Steamworks. We ran into a couple issues. First, even though we made our climbing mechanism pretty rigid, it wasn’t rigid enough. The springs were so strong that they would always bind up the climber.

Secondly and more importantly, don’t underestimate how scary big constant force springs are. It took two mentors all our might to reset it. I can’t imagine what would have happened if the mechanism released unexpectedly, especially with someone in or around the robot.

We could have made the springs work, but the couple extra seconds saved just wasn’t worth how scary it was.

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