Constant Force Springs

I doubt this would become a VEX part, but I figured I would ask. Any chance a constant force spring could become available?

For those on the forum that are not familiar:
Vulcan Spring

Like I said, I doubt it, but I figured I would ask, especially with so many teams using high reaching lifts and arms.


The constant force elastic assist is a part of our skyrise plan. We are trying to reduce the shape change of rubber bands by mounting them a certain way and adding more rubber bands. Our goal is to let the elastic force remain relatively constant throughout the lift’s movement. Is this what you are asking for?
Personally, i think that it is only a matter of time for springs to enter VEX. We have tried to use charged pneumatic pistons as springs, but that was a relatively complicated process.

How about the springs inside the clutches? I believe Karthik cleared them for use in the VEX game. I can’t find the thread.

I believe you are referring to this:

Guys constant force springs are not the same as your standard spring as they do not obey Hooke’s law.

Also while I know those springs are pretty strong, they are not very large. They would never work as a counter-balance system, which is what constant force springs are so commonly used for.


Thanks for the product idea! There are currently no plans to release a constant force spring as part of the VEX EDR product line, but we will add it to the list and make sure it gets discussed at our next “potential product” review meeting.

In general additions to the VEX EDR product line are announced at the VEX Robotics Competition World Championship, though we will sometimes release items at other times in the year.

Let us know if you have any other feedback.

Correct me if I’m wrong but i believe there is a constant force spring that is used in the claw kits.

Its a pretty small spring if I can remember correctly but i guess technically it exists?

Okay I’m not sure if you guys understand the difference between a normal coil spring and a constant force spring.

Coil Spring

Constant Force Spring

Example of Coil Spring: Torsion Spring

Example of Constant Force Spring: Vulcan Brand Constant Force Springs

A common example of a constant force spring being used in an everyday application is a tape measure. If you’re curious crack open a tape measuer to look inside.


Just to complement on the explanations from the links, Hooke’s Law (aka most normal coil spring) means the force it asserts is proportional to its displacement. It means the more it’s stretched / compressed, the more force it will assert.

In Math / Physics’s land, this is governed by the equation F = kx. F being force, k being spring constant and x being displacement from equilibrium position.

The product being suggested does not obey Hooke’s Law. The force it asserts is independent of the displacement from equilibrium position (hence “constant force”). Using the example of tape measure provided, it’s a constant force spring because the force it needs to pull the tab out remains essentially the same no matter if you’ve already pulled out 1 feet, 2 feet, or 25 feet.

This is an interesting idea in that it does not require additional hardware to implement. The loop goes around a spacer or shaft and whatever is being spring loaded gets bolted to two or so mounting holes on the end. It does not have the short coming of tension and and compression springs, where many sizes would be needed(not including various k constants) and possibly additional parts for them to operate optimally.

I know there could be a safety issue however depending on the CFS. I know some FRC teams that use them (mostly from Vulcan) design a guard to put over the spring to keep it safe. If a spring becomes loose when extended it can retract violently and be dangerous. That being said, if one was designed like a tape measure, then that would be a much lower risk.