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Scoob · 01:28 PM

I am looking to learn exactly what makes different turn (KV) motors run the way they do. I usually come here to learn the technical stuff because people here seem to know what they are talking about. I think I have a pretty good handle on this stuff but I'm not sure.
Just let me know if something is incorrect and please explain.

1. RPM times torque = mechanical power.
2. Voltage times amp draw = the total wattage pulled by the motor.
3.Total wattage output by the motor will depend on the efficiency as to how much of the power (wattage) pulled, is put out in mechanical power. Example, A motor pulling 400 W @ 80% efficiency will output 320 W.
4. Given two motors that are the same but with diferent turn and KV, like MM4600 vs. MM7700,the low turn high KV motor should always be capable of more power on low voltage such as 2s lipo. The low KV motor even if geared really tall is limited by higher internal ressistance. You can't force it to make up for the RPM difference with torque through tall gearing, due to the resistance (any other reasons ?)
5. More torque requires more current, so the overgeared low KV motor above would only produce as much torque as it's resistance would allow when over geared. The rest of the current forced on the motor by the load of overgearing will turn into heat so the motor has become very inefficient. In other words, it may pull the same current and therefore the same wattage at that voltage as the higher KV motor but will output a lower percentage of that power.
6. Let's say we have two motors that are geared the same and given a voltage that gives them the same RPM such as a 4600 on 11.1V and a 6900 on 7.4v. The 4600 should run more efficiently as a system because there will be less power lost to heat from the resistance of the system. Starting with the IR of the battery, the resistance of the wiring from batt to ESC, the resistance of the ESC itself, and wiring running from ESC to motor, less current flowing through them means less loss in the high V system.

Thanks for any input.

	(#1)
Scoob RC-Monster Stock Offline Posts: 43 Join Date: Jul 2005 Location: NC	Brushless experts please read - 06.27.2007, 01:09 PM I am looking to learn exactly what makes different turn (KV) motors run the way they do. I usually come here to learn the technical stuff because people here seem to know what they are talking about. I think I have a pretty good handle on this stuff but I'm not sure. Just let me know if something is incorrect and please explain. 1. RPM times torque = mechanical power. 2. Voltage times amp draw = the total wattage pulled by the motor. 3.Total wattage output by the motor will depend on the efficiency as to how much of the power (wattage) pulled, is put out in mechanical power. Example, A motor pulling 400 W @ 80% efficiency will output 320 W. 4. Given two motors that are the same but with diferent turn and KV, like MM4600 vs. MM7700,the low turn high KV motor should always be capable of more power on low voltage such as 2s lipo. The low KV motor even if geared really tall is limited by higher internal ressistance. You can't force it to make up for the RPM difference with torque through tall gearing, due to the resistance (any other reasons ?) 5. More torque requires more current, so the overgeared low KV motor above would only produce as much torque as it's resistance would allow when over geared. The rest of the current forced on the motor by the load of overgearing will turn into heat so the motor has become very inefficient. In other words, it may pull the same current and therefore the same wattage at that voltage as the higher KV motor but will output a lower percentage of that power. 6. Let's say we have two motors that are geared the same and given a voltage that gives them the same RPM such as a 4600 on 11.1V and a 6900 on 7.4v. The 4600 should run more efficiently as a system because there will be less power lost to heat from the resistance of the system. Starting with the IR of the battery, the resistance of the wiring from batt to ESC, the resistance of the ESC itself, and wiring running from ESC to motor, less current flowing through them means less loss in the high V system. Thanks for any input. Last edited by Scoob; 06.27.2007 at 01:28 PM.