Constant force spring alternatives

We are looking for an alternative for a constant force spring for a telescopic arm but we can’t find them here in Israel and importing them will be very expensive.
We are looking for a different way to spring the inner tube up.

While you theoretically could do this with two ropes, and a split drum by winding each rope in an opposite direction and using pulleys to change the direction of force, we have never gotten this to work correctly.

You could potentially do it with a second motor. The rigging may be difficult though.

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You might want to check with local companies that make/sell window products. Constant-force springs are often used to make it easier to open and close windows - for example, something like this:

If they don’t have exactly what you need, they will almost surely know where you need to go to source them locally.

Failing this, I would agree with Mr.R_2 that a second winch is probably the simplest/quickest solution. It can be tiny since it’s only ever lifting a few kilos.


Sourcing them in israel is really tough but you have some options… first of all you can get them from wcp through israeli dealers… also there are places that manufacture them here but this is a maybe timewise and moneywise.

You did get springs in the kop this year and last year so that is enough to build at least one arm,
You can also order them from amazon or some other place using a credit card but that might not be an option to all teams here and also shipping times might be an issue.

The last option i can think of is replacing them with regular springs. I know that its not ideal but it might work given their only purpose is to lift the tube up and not cary any more weight. Just keep in mind that they might add additional load when youre trying to climb so picking the right spring is very important.

We use some rubber bands to replace the springs, be Shure to fix it firmly

The window counterbalance springs are a good idea. Going off of the rubber band comment, you could use surgical tubing or bungee cords. If you need more stretch length than a short piece of surgical tubing can provide you could run a longer piece through a series of pulleys and tie it off at the end. I have seen this done on a fancy backpack. US7931178B2 - Suspended load ergonomic backpack - Google Patents

You can do this if you really need to. In the end, there’s a section that shows how the everybot uses multiple extension springs to replace a constant force spring.

Worth looking into.

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You can scavenge weak ones out of a tape measure too. Industrial folks may be able to sell you a “tool balancer” that contains a power spring.

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