Full Rotation Static Balancer Using Differential Noncircular Pulleys

A mechanical system with two noncircular pulleys in a differential arrangement is demonstrated in this video. It is able to convert the force from a linear spring into a balancing torque for a rotating payload. Using this system, the payload is essentially floating in space as gravity is cancelled by the mechanism over a full rotation of 360 degrees, a technique known as static balancing. Anti-gravity courtesy of mechanical engineering!
For more technical details, see:
"Differential Noncircular Pulleys for Cable Robots and Static Balancing", by Dmitri Fedorov and Lionel Birglen, ASME Journal of Mechanisms Robotics, 10(6), 061001 (Sep 07, 2018), DOI: 10.1115/1.4041213
Link: mechanismsrobot...
Soundtrack: By the Coast (2004) by Antony Raijekov, licensed under CC BY-NC-SA 4.0.

[@FLORIDIANMILLIONAIRE]

Very cool

[@kurtnelle]

Impressive!

[@heartminer5487]

Would be great if you could adjust the compesation torque on the fly e.g. dynamic loading.

[@PolyLabrobot]

It's possible quite easily by moving the attachment point of the spring (lower right) with an actuated slider or arm. That's beyond the simple mechanism we intended to demonstrate here though.

[@lindaellison899]

cool!

[@vulinhnguyen3170]

great !

[@va7795]

very interesting but I don't understand it

[@PolyLabrobot]

Thanks! Having a look at the original paper might help you: asmedigitalcollection.asme.org/mechanismsrobotics/article-abstract/10/6/061001/367087/Differential-Noncircular-Pulleys-for-Cable-Robots
If you don't have access to the ASME repository, an open source preprint of that work is available at: publications.polymtl.ca/3544/

[@va7795]

Thanks

[@Shocker99]

@@va7795 I haven't read the paper but my intuition is that the shape of the cam stretches the springs to match the gravitational force exerted by the mass, so that the two forces balances out at all angles. Ie. The mass exerts 10N of force downwards, and so the cam stretches the spring so that it also exerts 10N of force but in the opposite direction, therefore the mass doesn't move because the forces are equal. The cam is designed so that the force produced by the springs always matches the force exerted by the mass.
The mass will always rise if it smaller than what the cam is designed for and it will always fall when the mass is greater.

[@zfolwick]

Am I going crazy or is this an application of a Chinese windlass?

[@PolyLabrobot]

You are not far off... the main difference with the Chinese windlass is that our pulleys (drums in the windlass) are not round but have precisely calculated profiles to transform the linear force from the springs into a torque at the lever arm that balances the payload. But the arrangement with two drums/pulleys connected by a cable is indeed common to our mechanism and the Chinese windlass (and Weston's differential too)