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Old 06-12-2017, 10:51 PM   #9 (permalink)
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Join Date: Aug 2010

Something to remember is that the voltage across the motor has to do with how fast the motor is turning; the motor acts as a generator, and produces a voltage that opposes the supply voltage. When a motor sees full pack voltage (100% throttle) at high RPM, the current it flows is much lower than the current it flows at 50% of that RPM. Current may double because the motor BEMF drops in half etc. But two problems here. One is that once the motor sees some (motor specific) high level or current, its magnetic system saturates; more current doesn’t increase the field strength, and huge currents can flow as a result. Another is that heat in the motor is a function of the square of current. So you get dramatically higher heat generation. This is why you don’t fly around at higher power settings at low (relative to Kv) motor RPM- you burn too much current, and create too much heat.

So, you can have a situation where you are geared correctly- and the motor simply cannot produce enough power to generate more thrust. But it may still live within its thermal limits there. Another situation is where the motor RPM drops a bunch, current increases dramatically, and the motor burns up- even if it is producing less output power (more torque, but less RPM, and power is torque * rpm).

Point here is that it depends on how you define ‘undersized’. In one scenario, nothing bad happens. In another, very bad things happen very quickly.
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