Multi Motor Drivettrains

[Joe Johnson]

A similar analysis of motor current and motor effeciency (by which I mean the ratio of the mechanical power out divided by the electrical power in) would make it clear that it is incorrect to assert that current is somehow mis-directed if not sent through the drill motor.

Generally speaking, motors are more effecient when lightly loaded. Given that you have multiple motors of approximately balanced power ratings (namely the drill, the Chiaphua, and the Fisher-Price), for a given load (i.e. torque at the output shaft), you can choose gear ratios that would make the torque on the motors be 1/Nth the torque it would see if it was doing all the work on its own.

This means that instead of running at 3/4th of the stall load for the drill for instance, if you are the TechnoKats, you run the drill, the Chiaphua, and the Fisher-Price each motor at 1/4th of their stall loads.

Let's be clear about how big a deal this is: At 3/4th stall, the drill is about 25% efficient -- it turns 3/4ths of the electrical power put into it into HEAT!. At 1/4th stall, the drill motor is over 70% efficient -- that means that it generates about 1/3rd the heat per unit of mechanical power you need at the output shaft -- believe me, this is a good thing.

I don't want to belabor the point, but think about it, the Chiaphua's and the Fisher-Price motors are going to have similar gains in efficiency. AND THESE EFFECIENCIES DON"T MULTILPY as most cases they do so basically your drive system is going be 3 times as good at turning electical power into mechanical power. This means that you are generating 1/3rd the heat for a give amount of power you need. AND... ...HERE IS THE EVEN MORE IMPORTANT THING... you have THREE motors not ONE to dissipate that heat.

Bottom line: 3 motor systems like the Technokat's drive are going to have much longer battery lives and have a much easier time staying cool than those that use only one motor per side of their robot.

Joe J.