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Old 06-23-2016, 04:52 PM   #221 (permalink)
Krager
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Join Date: Dec 2014
Location: Seal Beach, CA
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You can actually shut off the over-current detection through the CastleLink software. In that case it will put out current until the switches burn out. You wouldn't know it until the ESC quits working permanently. Still I believe in having some head room. I'd rather take the weight penalty and provide some margin to be assured things will stay cool. It's also better for efficiency. I get pretty good flight times with the motor and ESC I'm using even though it adds 15 or 20g.

For example the motor I'm using has about 30mΩ resistance compared to 75mΩ for the stock motor. At 20A that's 30W wasted in copper loss for the Align motor versus 12W wasted for the 4000Kv motor I'm using. There's also the difference in heating which further adds to the disparity in resistance. All in all it's enough of a difference to have a pretty noticable impact on flight time. The same is true for the ESC, the Talon 25 has lower resistance than the Talon 15, but not to the same degree as the motors.

Another limitation comes with the Kv of the motor. The best you can do is about 90% nominal voltage times Kv. On 3S the stock 3600Kv motor even with a 16T pinion is not going be able to put out more than about 4800 rpm head speed and that will fall off as the battery discharges and voltage gets lower. The only way to increase speed after that is to increase Kv with a motor rewind or use a higher voltage battery. Anyone who is saying you can get 5500 rpm head speed with the stock motor on 3S is either full or it or has found a way to defy the laws of physics.

There's also the issue of gearing. Surely you could go even higher than 16T to get a speed theoretically higher, but that just won't work. You get to a point where torque delivered to the rotor is not adequate to overcome drag created by increasing head speed. There's also the electrical issue of increasing currents as torque demands increase. There's a point of no return where current keeps going up without any increase in torque. As it is the stock gearing takes it to the limit at 8:1. With the bigger, higher torque motor I could probably run 7.5:1, but I won't go that tall. The torque for it really isn't there even with a bigger motor. Running that tall ratio takes a bite out of efficiency since you get to where current goes up with less increase in torque.

Last edited by Krager; 06-23-2016 at 06:20 PM..
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