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I'm fairly new to electronics and have been reading extensively into it, but I'm unable to map all the concepts together. My project is a tiny drone involving (four) 4 N40 DC motors, rated 26k RPM at 3V 0.3A, and 42k RPM at 6v 1.68A.

From my understanding, to power the motors at full capacity, I need to provide ~10 Wh, that is (1680)mAh * (6)V = 10.08 Wh each.

I have a set of 3.7V 1,000mAh batteries (3.7Wh), thus I would need four batteries where each two are connected in parallel and then the the circuit is eventually connected in series providing a total of 7.4V and 2Ah or 14.8Wh. diagram describing batteries connection Theoretically, to provide 40Wh to all four engines, I would need to provide total of 7 pairs (14 in total) of batteries connected in parallel to provide 7.4V at 7A leaving me with a bit excess of power. Is my understanding correct as that seems to be a bit excessive?

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  • \$\begingroup\$ You are confused with power and energy : E = P.t \$\endgroup\$ – Long Pham Jun 18 '18 at 16:18
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    \$\begingroup\$ Calculate Watts (voltage and current requirement) to get the required lifting power and use flight time to calculate the capacity (mAh) of batteries needed to achieve the flight time target. \$\endgroup\$ – Jack Creasey Jun 18 '18 at 16:23
  • \$\begingroup\$ Your question is very confuse. Surely you will not connect the batteries directly to the motors, and the motors will not be connected in paralell, so, probably there should be a single connection for each motor, so, the batteries connect to the control unit, and the control unit will control each motor. Someone who is "fairly new to electronics" should try projects simpler than a "tiny drone" with 4 motors. At least, this kind of question shows that you still has to learn a lot before trying this kind of project. \$\endgroup\$ – mguima Jun 18 '18 at 16:24
  • \$\begingroup\$ none of the batteries are connected to the circuit .... what is the point of including a useless wiring diagram? \$\endgroup\$ – jsotola Jun 18 '18 at 23:08
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Total continuous power due to motors running at full speed is say 10 W.

Let's choose a battery of say 7 volts If motor has to run for 2 hours max, then the battery rating has to be 2 * 10 W hours.

It is 20Whours.. Or 2857 mAh.

20/7 is 2.857

So, a battery rated about 2.8 Ah at 7 V will provide you 2 hours of run time for the motor.

Considering conversion losses due to regulator and drooping battery voltage levels when the charge is declining I will ration 30% more.. As my thumb rule.


Unless you run all the motors at peak speed which is doubtful, you will be getting more than 2hours.. What does your device/drone demand finally is the question, just the motor rating alone cannot be considered, I feel.

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