Hi Yohooshi,

What you discribed is an Mechanical Speed Controller (MSC), many years ago used on RC models before what we now call ESC.

http://radiocontrol.wikia.com/wiki/M..._speed_control

I can´t not say that this type of application on a Fight robot is hazardous:

-For be very fragile during combats.
-Most important, if the mechanism "break/stop/stuck/battery disconect" at a "on" position you can´t control the robot moviment, what can result in accidents (I used this solution many years ago on weaponless Hobbyweight ). Same could happen with a ESC, but its a LOT harder to happen. Im not sure if anyone will not allow (even rules) you to compete with this system, its just an advise.

Guilherme