[patrickrd]

Let's say we have two different motors mounted to the same drive shaft. If they weren't connected, let's say the RPM's are a slight mismatch. For example purposes:

Motor 1: 100 RPM, 100 N-m torque
Motor 2: 110 RPM, 90 N-m torque

What will the result be? This is not easily intuitive... But the way you do this is you treat one of the motors and how fast it wants to spin the shaft as your frame of reference. For example, if motor one is our frame of reference, we have motor two wanting to spin at 10 RPM with 90 N-m torque. Since power = torque x speed, we have 10 * 90 units (900 units) of power being applied to motor one by motor two. If we look at it from the perspective of motor two, motor one wants to spin at -10 RPM at 100 N-m torque, or 1000 units of power. Thus motor two is losing 1000 units of power to motor one. These motors are acting against each other to a certain extent, and 1000 + 900 = 1900 units of power are being wasted.

HOWEVER, the net result is still great! With both motors combined, we have 100 *100 + 110 * 90 units of power, or 19900 units of power. 1900 are lost, thus our NET POWER OUT is equal to 18000 units. If we compare this to simply using one motor, motor one, we gain 8000 units of power by adding the second motor. Although it is true the RPM is mismatched and the motors do work against each other, for the most part they are still working towards the same goal, and we have a 180% increase in torque.

Hope this helps clear it up.

Patrick