what's the use of torque arm for gear motor

[ITBT]

Some of the hollow shaft worm gear motor requires a torque arm at bottom. Can anybody tell me what's the use of it?

Thanks

 

[dvd]

It keeps the gearmotor from spinning around on the shaft as the inertia of the gearmotor is usually less than that of the driven object.

 

[sacem1]

In order to be able to make the shaft turn with the shaft mounted gear reducer you have to have a fixed point to transmit the torque introduced by the gear. The motor usually is bolted to a base that sits on top or besides the gear reducer so it would spin also with the gear reducer. You might think that if the motor is sitting on a diferent base you could forget the torque arm but that is not the case as the belts and pulleys, even if they are located in the proper direction are not designed to absorb the torque forces involved.
sacem1