pic: Modular Gearbox

[asid61]

Originally Posted by Ari423

The big upside of planetary gearboxes is their huge reductions in small packages. Compared to the maximum 10:1 stage on a VP, the biggest reduction you can get from a spur gear stage with this system is 4.5:1 (9:1 over two stages using a combination of 3/8" and 1/2" gears). That would mean using only spur gear reductions to get up to 200:1 you would need 45 stages, or about a 4 ft wide gearbox.

You're not doing that calculation correctly. Gear ratios are multiplied, not added, so if you stacked 4 stages you would get a 4.5 * 4.5 * 4.5 * 4.5:1 ratio, which is about 400:1. Using a chain reduction for the last stage would give you even more.

[Ari423]

Originally Posted by asid61

You're not doing that calculation correctly. Gear ratios are multiplied, not added, so if you stacked 4 stages you would get a 4.5 * 4.5 * 4.5 * 4.5:1 ratio, which is about 400:1. Using a chain reduction for the last stage would give you even more.

Wow I don't know how I messed up so badly on that. I take back everything I said in that last post (except the thing about VPs not being rated for a CIM at 200:1). Yes, you should exceed a 200:1 ratio on the 4th stage. With the 60:12 chain reduction, you can do it in 3 stages. With the 50:1 VP reduction, you can do it in 2 stages. With both the 50:1 VP and 60:12 chain reduction, you can do it in one stage.