Output devices

Group assignment

For group assignment we measured the power consumption of the bushless motor + ESC. Used a multimeter connected in series between the battery and ESC GND.

Used the same code as in Tiago’s individual assignment but with bigger delay in between PWM value changes, to allow the multimeter to stabilize the reading.

The scale of the reading in is Ampere (A). From the video we can see that ~0.28A are consumed to start the engine but at lowest speed then it stabilizes in ~0.8A. Then after incrementing the speed, it reads ~0.41A and stabilizes on ~0.16A. This confirms a characteristic of the brushless motor, it consumes more power when starting and changing speed that when maintaining constant speed.

At maximum speed there is a peak of ~1.20A but it stabilizes at ~0.76A.

But then changing the code to accelerate the wheel from low speed to maximum speed, the result is a bit differente. 

while (1) {
   OCR1A = 1280;
   position_delay();
   position_delay();
   position_delay();

   OCR1A = PWM_max-100;
   position_delay();
   position_delay();
   position_delay();
}

There is a noticiable increase in current consumption from the motor, peaking for moments at ~6.3A

And if we put some load in the motor, like grabbing and stopping the wheel for a moment, it reaches 10A (maximum value that the multimeter can read).

Now calculating the power consumption of the engine, P = I x V.

From Ohm’s law: I = V / R, R = V / I

and from Joule’s law, Power: P = I^2 x R

P = I^2 x R = I^2 x V/I = I x V

P = E/t, E = P x t

  • I – current in amperes (A);
  • V – voltage in volts (V);
  • R – resistance in ohms (Ω).
  • P - Power in watts (W)
  • E - Energy (in this case, consumed)
Tests done in optimal case (without load or friction) Unit
Motor measurement at constant Max Speed (I) 0.76 A
Battery 12 V
P = I x V 9.12 W
E = P x t (1h) 9.12 Wh
E = P x t (3600s) 32832 J
4 Engines running at constant speed 36.48 W
Test done with load by grabbing the wheel Unit
Motor measurement at max speed (I) 10 A
Battery 12 V
P = I x V 120 W
E = P x t (1h) 120 Wh
E = P x t (3600s) 432000 J
4 Engines running at constant speed with load 480 W
Consumption with load increases 1315.79 %

Individual assignment