For those like me looking to understand team update # 3 from last year, the update reads
calculate servo max power as stall torque x no load speed
and then they give an example for the HS-322 which, at 6v, has a stall torque of 3.7 kg/cm and a speed of 0.15 sec for 60 degrees, and they give the final formula as
torque = 3.7 kg/cm = 0.36 Nm
RPM = 0.15s @ 60 degrees = 66.7 RPM
and the result is
0.36 * 66.6 * 0.1046 = 2.5W, and thus under the 4.0W limit.
But where did some of those numbers come from I/you ask?
Well 1 Kg/cm = 0.0980665 Nm which you know from looking it up, say at
http://www.onlineconversion.com/torque.htm, or from basic physics. A newton is the measure of force necessary to move a mass of one kilogram a distance of one meter in one second. The force of gravity on 1 kg is about 9.8 newtons, depending on your location, etc.
So that is how 3.7 Kg/cm * 9.8N/kg * 1m/100cm = 0.36 Nm
RPM is just algebra, no physics... 60 degrees is 1/6th of a circle so 0.15sec to travel 60 degrees becomes 0.15*6=0.9 sec for 1 revolution.
1rev/0.9sec * 60 sec/min = 66.7 rpm
So far we have N-m * Rev/min and we want an answer in watts. Ah, a watt is by definition one N-m/sec.
The last item is 0.1046 which, again, we know from a conversion table like at
http://www.micromo.com/motor-calculations.aspx, but what it represents is the conversion of RPM to radians/second.
I hope this explains how stall torque x no load speed, or 3.7 kg/cm * 0.15s @ 60 degrees, became the equation 0.36 * 66.6 * 0.1046
Let me know if I messed any math or physics. Ignore me if I caused more confusion than I resolved.