# Driving Gearbox in Reverse

https://www.maxongroup.com/maxon/view/product/251601

https://www.maxongroup.com/maxon/view/product/gear/spur/gs45/301171

Consider that this motor-gearbox combination is backdriven so that the motor acts as a generator. My goal is to try and make a relatively accurate simulation of the losses/damping that occur due to the fact that it's driven in reverse. From what I understand, the total inertia of the motor felt by the output of the gearbox (now used as an input) can be calculated by the equation below where $$I_{gearbox}$$ refers to the mass inertia of the gearbox.

$$I_{total}=r^2I_{rotor}+I_{gearbox}$$

I know that motor cogging torque needs to be considered as does the friction in the gearbox, but I am unsure as to how this is done. My impression is that the most resistance comes from the friction within the spur gearbox as it is occuring to the point that it takes grown man strength to get it turning at all.

Are there specially designed gearboxes which are designed to work somewhat equivalently in reverse as well? I know that "planetary gearheads up to two stages or spur gearheads" should work but the efficiency is still low. https://drive.tech/en/stream-content/dc-motors-as-generators

Or would I be better off making a simple gear train with two/three spur gears? The driving torque would be quite low.

Thanks in advance for any assistance

• Hydraulics can provide that functionality... – Solar Mike Dec 5 '19 at 13:36