how to model motor+gearbox

[StevenB]

Time to back up and make sure I understand what's going on. My initial assumption was that the gearbox acts like a constant load on the motor, causing both reduced speed and reduced stall torque. This was incorrect.

If I understand correctly, there are two separate forces acting on the gearbox: One of them (windage) is loosely proportional to the speed of the motor, caused by churning of the lubricant and friction we can't get rid of. The other is loosely proportional to the forces on the gear teeth, and thus to the torque on the gearbox.

Since the power out of the motor is the product of speed and torque, each reduced by their respective loss factors, the product of the loss factors gives efficiency. Thus, when an single efficiency number is posted, it most likely represents both speed and torque loss.

However, the split is not necessarily even - 90% overall efficiency could be the result of 92% torque efficiency and 97.8% speed efficiency, or any other split. Experience is the easiest and most useful way to determine what the separate speed/torque loss factors are.

Is this right, or am I off in the weeds?