# Gear down Motor or Gears?

So, to get around a 4:1 gear ratio, should I gear down with a gear box then run the chain system off of this with the same size sprockets, or should I gear down with the teeth on the sprockets in a 15 teeth to 60 teeth gear? Does it matter?

I don’t think it matters. The purpose of a gearbox is to put all of that long, chaining through sprockets down to a smaller size.

Ah okay thanks! I was worried with the CAD draw up that I would have to change it… ugh. lol So your saying I can achieve the same torque/RPM change with a 4:1 gear ratio in the sprockets as I would get from the gearbox?

You can. Efficiencies can vary dramatically from case to case.

What’s that mean? Because I used the formula T = Ts - (N Ts ÷ Nf)

where T is the torque at the given rpm N, Ts is the stall torque, and Nf is the free rpm.

edit: marked by asterisk

It means that how you gear a system up or down can have very different efficiencies. Case-by-case analysis is the only way I know of for determining which is best.

Okay thanks! :] so basically, even a 4:1 gear down can somehow produce way less then calculated? by http://www.gizmology.net/motors.htm

T = Ts - (N Ts ÷ Nf)

where T is the torque at the given rpm N, Ts is the stall torque, and Nf is the free rpm.

Some energy is lost to things like friction, heat and vibration in every stage of your gearing.

Spur gears and sprockets and chain are both very efficient if built properly – as high as 98% or so. That means that 98% of the energy input on one end comes out the other.

Losses due to inefficiency occur at each stage of gearing – so a system with two stages would be ( .98 * .98 ) efficient, for example.

Cool! and… disheartening… but, with 96% effieciency, that still falls within our range which is about a 75% wiggle room.