Constant force spring

Where does one put a constant force spring on an elevator lift? It seem a bit dangerous to have out in the open, does it go inside the metal tubing?

Here is a previous thread from Power Up that addresses how different teams used constant force springs on their robot. Constant force Springs

If you’re using a cascade style lift where each stage is connected to the previous, then the spring could potentially be in between any two stages. In a lift with more than 2 stages, moving the spring as late in the elevator as possible will effectively multiply the spring’s force by the mechanical advantage of the elevator and make the whole assembly “lighter”. 148 used a system like this last year and had their spring(s) dead center connecting the top of the third stage to the intake carriage. The spooling part of the spring was within the framing at the top of the elevator.

In a continuous lift, like I believe 254 and 1678 (I don’t think either of these teams used a constant force spring) used, implementing a spring is a bit more difficult because your only option is really to attach one end to the top of your non-moving stage and the other end to the bottom of the first stage on the elevator. Because of this complication, constant force springs don’t provide as much of a benefit in continuous lifts as they do cascade lifts. Both 1678 and 148 posted their CAD last year publicly, so you might consider looking at that for a better idea of what I’m talking about.

As for locating where to put the spring on the elevator, anywhere is fine as long as it is securely attached at both ends and isn’t applying any side loading or torque parallel to the plane of the elevator. I’m not sure how well putting the springs inside the tube would work, but if you were to do that it would likely be best to have a spring on both sides to balance the load equally.

Personally, I really like the packaging and safety surrounding the Constant Force Spring Motor from that thread. The edges of a constant force spring can be very sharp, and any time you fiddle with it you need to be careful it doesn’t let go on you. This packaging takes care of all of that for you, hiding away the spring.


Protip: wear kevlar or cut-proof gloves when handling constant force springs, especially the bigger ones. I got the nastiest cut of my life last season with a 42lb spring–meanwhile my gloves were sitting on a toolbox 10 feet away.

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You can watch 973’s RAMP videos on Cascade Elevators which go over using constant force pull springs:

Thank you all very much.

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We attached it to our fixed stage to our first stage last year. One thing to be careful of and remember is these have a cycle life. We used one with 3,000 cycles I believe. We ran it all season and off season but we ended up snapping it on our comp bot. Usually when traveling or servicing, we disconnected the spring to prevent failures at the wrong time. Luckily nobody was working on the robot when it snapped, but it couldve easily turned bad. It did damage to some nearby components when it snapped too. Make sure you have a procedure for disconnecting the spring (gloves, replace bolts with screw driver or rod to keep control when disconnecting, etc.).

If we run an elevator, we will for sure use a spring again.

Cut-proof gloves at a MINIMUM. The big bulky leather gloves that you can get from Home Depot/etc do make fine movement/handling more difficult, but if the task doesn’t require fine movement (like just holding the end of a spring in place while someone else screws it in) they provide a lot more protection. If you’re going to be working with these springs often, it would be a good idea to pick up some better-fitting leather gloves to make handling easier (I personally have a pair of Mechanix M-pacts and they’re GREAT).

Thanks for the glove recommendation, we will look I to those.