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I would like to build a simple homemade gravity battery (a weight is pulled to a high height and is then dropped to turn a motor and generate electricity.) My plan is to have a 5kg weight pulled to 2 meters, testing this example and then increasing the weight to 10kg and height to 4 meters.

I was originally thinking of using a gearbox of some sort, in order to reduce the height required to drop the weight, and increasing the RPM at which the motor-generator rotates (due to many motors I’ve found needing between 100-2000 rpm.) After reading a related post on this site about using pulleys to lift a weight, though, it has made me consider whether pulleys would be a better fit.

TL;DR - Would using pulleys, a gearbox, or a combination of the two be beneficial in decreasing the rope used when lifting/lowering a weight and increasing the RPM of the motor-generator?

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    $\begingroup$ Gears: no slip but friction. Pulleys can have both slip and friction. $\endgroup$
    – Solar Mike
    Aug 28, 2022 at 12:46
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    $\begingroup$ @DKNguyen I was planning on using either river or rain water as a weight $\endgroup$
    – user39077
    Aug 28, 2022 at 20:58
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    $\begingroup$ Warning: the total potential energy storage depends on the height to which you raise the weight, and nothing else, so you can't reduce the vertical dimension regardless of gearbox design. $\endgroup$
    – Carl Witthoft
    Aug 29, 2022 at 14:01
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    $\begingroup$ @CarlWitthoft I had assumed OP wanted gears to match the load characterostics to match the generator, but maybe not. $\endgroup$
    – DKNguyen
    Aug 29, 2022 at 14:41
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    $\begingroup$ @DKNguyen good point. $\endgroup$
    – Carl Witthoft
    Aug 29, 2022 at 16:37

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The most efficient power transmission is chain and sprockets. These work very well at a nominal cost.

Gears are probably next, but at a higher cost due to gear fabrication. The closed nature of a gear box should help longevity. Be sure you have gears that run both ways if you're planning on lifting with the gear set - some don't, like worm gears.

Belted pulleys would be next, just a little less efficient. This seems like it would be hard to manage, belts are generally continuous, though I guess they can be bought in length. Pulleys with ropes will be last due to rope friction, but are probably the cheapest option here.

All the above will be affected by the bearings used, simple bushings will be less efficient than good quality roller bearings.

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    $\begingroup$ Yep, plus you can get chain+sprockets cheap from a bicycle salvage pile :-) $\endgroup$
    – Carl Witthoft
    Aug 29, 2022 at 13:59
  • $\begingroup$ Gears can be 3d printed for cheap these days. $\endgroup$
    – Drew
    Sep 13, 2022 at 9:17

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