In regards to the duty cycle, hit full throttle with the wheels in the air and check the telemetry. Then do the same going half speed or going up a hill. See the results.
39.1v pack voltage * 15.1a battery current = 590.41w electrical
(39.1v pack voltage * 40% duty) * 36.9a motor current = 577.11w electrical
(15.64v effective voltage) * 36.9a motor current = 577.11w electrical
the difference is likely caused by either a combination of iron & esc losses, or possibly decimal rounding inaccuracy of the duty cycle value in the logging app.
Yeah, I know. You’re totally right. Devin’s math was more like:
40 V , 1 ohm = 40 A = 1600 W
10% duty cycle = 4 V * 400 A = 1600 W BUCKED DOWN! LOGIC! WHY CAN’T YOU EXPLAIN WHERE I’M WRONG! I WILL WRITE 4 ANSWERS TO MY OWN POST!
There are probably 3 topics with 300+ post each by devin about this, and I really really really do not want to revive him. He tends to return as @devin2, @devin4… I’m almost scared of speaking it out. Like saying “Candyman” 3 times…
if the winding resistance in this example is in fact 0.01ohm then it seems correct.
((40v battery * 10% duty) - 0v bemf) / 0.01ohm winding = 400a motor current
(40v battery * 10% duty) * 400a motor current = 1600w electrical
(4v effective) * 400a motor current = 1600w electrical
you can calculate the instant back emf voltage to use in this equation by dividing the instant rpm by the kv… for example 1000rpm / 100kv = 10v back emf voltage
so if we assume the motor is 100kv and presently turning 1000rpm, then:
((40v battery * 35% duty) - 10v bemf) / 0.01ohm winding = 400a motor current
(40v battery * 35% duty) * 400a motor current = 5600w electrical
(14v effective) * 400a motor current = 5600w electrical
5600w electrical / 40v battery = 140a battery current
though again, vescs are fail-safe programmed within the firmware to limit motor current below 120a despite any user settings.
^you can estimate the resistance of your motor + vesc by using your throttle with the motor stalled
in this case we have 20a battery current, 78a motor current, 49.7v battery voltage
49.7v battery voltage * 20a battery current = 994w
994w & 78a motor current into the ohm’s law calc (0v bemf - stalled)
this gives roughly 0.163ohm for the motor winding + vesc.
effective voltage for 20a battery current with the motor stalled in this case is ~12.74v effective. (49.7v battery)
the largest source of error in this method is the battery voltage was actually a bit lower than 49.7v while the 20a battery amps were drawn due to voltage sag – so the electrical wattage in this case was in fact a bit lower than 994w while the 20a battery amps were drawn.
Last try, then I’m out. I know that you know that the meaning of DC is not that DC of 10% pushes 10 times more current than DC 100%. And that the power at DC 10% is lower than at DC 100%. That’s all I was saying.