I sometimes see the optimal efficiency mentioned of electric motors for R/C cars. These are often in the range of 60-80%. Now Iíve seen that brushless motors may reach higher efficiency scores around 90%.
This may not seem too great of an improvement over the best brushed motors (10%). From this you would expect an increase in runtime of 9/8 = 1.125 times (12,5%). But I was thinking that the increase in efficiency from using brushless motors must be higher when considered through a greater range of speed (RPM). So the difference in average efficiency would greater than the difference in maximum efficiency.
The highest eff. of a motor is usually found at a medium RPM. When going to a higher RPM, brushed motor will experience drag from the brushes. This drag absorbs a lot of energy and will reduce efficiency. (My GM purple bull 15T motor uses 4 Amps unloaded!)
Also, I assume a brushed motor usually can attain a higher RPM. So if you were to gear your brushless motor for the same top speed as you were running your brushed motor, your gearing can be lower. This will decrease the current draw at low running speeds (accelerating). This may not improve actual motor efficiency but I does increase driving efficiency (correct me if Iím wrong).
I figure that R/C cars must benefit most from brushless motors because the range of RPMís in which the motors are used is greatest for this type of R/C application.
Does anyone know a website where I can find data sheets for brushed versus brushless motors. (power output, efficiency, rpm)
Has anyone here geared a brushless motor to stock speed on his car and compared running times. What is the increase in runtime?