R/C Tech Forums - 80amp ESC for 1/10

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It is not a constant power situation with a given motor, the 13.5 originally asked about, as you acknowledge a couple times later in your post. But for discussion, achieving the equal power, and equal A-B times, with significantly different voltages likely requires a different motor to accomplish the current change.

I did not say that you would be faster or slower with different voltage, and I am not necessarily using 100% of my capacity, so it does not matter what your voltage is. Bringing an object from A to B require the same energy every time regardless your system as long as weight and time is the same. This is just physics. In any other application using any electric motors, you will always lower you amps with increased voltage if your load is the same.

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The original question is about sizing the ESC, which needs to handle the peak amps involved. Peak amps occur at stall where the more complex aspects of a motor are not terribly significant, and it is mostly resistance. But even at higher RPM where back EMF comes into play, effectively creating complex impedance and reducing current, Ohm's Law still works, just requires complex math to work out and it varies with RPM. Trends remain the same.

Motor equations: Yes, with steady state condition (stall) you can simplify the equation. Ok, if we actually had to take all this into consideration when picking a ESC then there would not be any sold. So either you do the calculation with 8,4 or 7,2 with the size of the motor as simple as that. Again, there is not a lot of option when selecting an ESC.

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Much of it is due to the greater capacities. With lipo at least in racing cells are frequently not drained very far with a 13.5 in typical race heats. Wasn't always the case with lower capacity nickel cells combined with less efficient brushed motors which used more. A situation where say only 30% of the pack is used compared to 80 or 100% makes a big difference all by itself, regardless of cell chemistry

For a 13.5, I agree. But all my car has lower motor turns with a voltage drop in the 1.0V - 1.2V range.

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that's not the way ESC's work

That is exactly how a ESC works (ref. PMW). If you get 8,4V or 7,2V I do not know. However, you can use a true RMS meter or a oscilloscope to measure it.

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equal a lower KV motor has a lower watt capability at a given voltage. Reference the Novak chart linked earlier.

Sorry, got this mixed up. Lower Kv yields less wattage not more. The reason for 6S versus 4S. It's not practical or legal for racing. So why would you use 6S?