Winch winding with a fusee

[nixiebunny]

Back in the 1700s, watches kept time better by using a fusee to compensate for the weaker spring as it wound down, by changing the 'gear ratio' between the spring and the works. The fusee is a cone with a track for a chain, so that the sprocket's effective diameter changes as the mainspring's winding-down progresses.

I thought today about making a fusee for our winch, to stretch the surgical tubing 'spring' faster at first, then slow down (increase the reduction ratio) as it gets further along in the stretching process, as the force required increases.

Am I nuts? Could I print a fusee on my 3D printer and stick it on the winch shaft?

[Bryce2471]

I like the idea, but in my opinion, it's not worth the extra complexity for a marginal gain in reset speed.

Also, in the beginning their is less load from the tension part of the mechanism, but their is more inertia to overcome as the motor and gear train spin up. So I'm not sure how much difference it would make. Very cool concept though.

[Nate Laverdure]

Totally doable. You can think of the fusee as just a multiple-turn cam, where the spiral is pushed out-of-plane into a 3rd dimension, forming a helix. And as Ether brought up the other day,

Originally Posted by Ether

One nice feature of a cam is that, with a little math, you can derive the equation for the spiral so that the torque required to drive it remains constant as it is pulling back the arm. Then you can use that equation to cut out the cam.