Top Speed + BottleNeck Calculations

The controller that we’re using is a kellycontroller which has a max of 40000 electric RPM. Electric RPM = Mechanical RPM * Motor poles, or half your motor poles if they’re activated in pairs. Essentially, Electric RPM is the number of times a minute that the kellycontroller can flip the current from wire to wire. We conducted a series of top speed tests to figure out if batt-mobile’s top speed was limited by the battery voltage or the controller.

We set a 50m course on the back lane of N52 and batt mobile scored 6.5s (6.49,6.51,6.51), which works out to about 7.7m/s, probably due to the really low gearing and slightly-larger-than-sprocket-wheels.

Jocose on the other hand scored 5 seconds flat, probably due to their significantly higher gearing.

Following from 7.7m/s, and given that our wheel radius was 2 inches, we can calculate the rps of the wheels: 7.7/(0.02*2.54*pi*2)=24.1 RPS = 1447.4 RPM

Given that the sprocket mounted to our wheels had 42 teeth, and the sprocket mounted to our motor had 12, we can derive that the motor RPM is 5066.

GIven that we have 7 poles, the electric RPM is 35462. Not sure if this is close enough to the kellycontroller max of 40000 electric RPM for the controller to be the bottleneck.

On the other hand, the voltage of the battery pack varies between 26-28v, and we can assume it was at 28 since we did the test after a full charge. Given that the kv of our motor was 149we should have a theoretical no load rpm max of 149*28=4172.

So….. I guess I’ll try increasing the voltage and measuring the top speed again =/


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