Answered: PWM to DC converter

How efficient is the power transmission from PWM to DC with the speed controllers that the vex motors have in them?

Assuming you are asking for the efficiency of the DC part of the VEX motor assembly. The power sent to the motor is highly dependant on temperature, but a typical efficiency of power sent to the internal drive motor vs. power sent to the VEX motor assembly is 88%.

then what is the point of using PWM in the first place? first the batteries are DC so you convert that to PWM (12% power loss) and then to the motors to be turned back to DC again (12% more power loss) so 24% loss. my old Legomindstorms used DC, so why use PWM?

**There is not a 12% power loss from the batteries to create a PWM Signal. The PWM Signal is created from the Microprocessor inside the VEX Controller based on the data received from the Transmitter or values from the Users Code.

After the PWM Signal is received by the Microprocessor inside the VEX Motor, control signals are generated for the H-Bridge. The loss in the output section is about 0.5 ohms for the Current Limit, 0.2 ohms for the High Side Resistance and 0.15 ohms for the Low Side Resistance – assuming 1 Amp @ 7.2V yields about 88%.

The PWM Signal is the industry standard used for Hobby RC Motors and Servos.**