VOXL ESC Calibration Voltage Drop

Steve Turner

We are attempting to use the VOXL ESC on our platform and having difficulties driving some smaller brushless motors, not unlike those on the Starling with the EMAX 1306B's.

Standalone with other ESC's we are able to drive our motors without a voltage drop and generate the thrust/RPM we need off of a 2S power supply at nominal voltage of 7.4V.

However, I've noticed when running voxl-esc-calibrate.py that the voltage drops as reported by the VOXL ESC, despite being connected to a constant power source that confirms it is supply a continuous 7.4 Volts.

As a result our curve to calibrate the ESC comes out like this:

Quadratic fit: motor_voltage = a2*rpm_desired^2 + a1*rpm_desired + a0
    a0 = 69.74106389340773
    a1 = 0.24428260831710763
    a2 = 4.98882913108724e-06
ESC Params (after scaling):
    pwm_vs_rpm_curve_a0 = 69.74106389340773
    pwm_vs_rpm_curve_a1 = 0.24428260831710763
    pwm_vs_rpm_curve_a2 = 4.98882913108724e-06

Additionally the ESC reports the following as the last line of calibration:

POW: 89, RPM: 17791.00, Voltage: 6.79V, Current: 2.90A

On our other ESC's with the same airframe we are able to take off no problem and drive the motors at a much lower current for constant voltage.

We will keep digging in, likely an issue on our part but it seems like the VOXL-ESC is not able to maintain voltage and perform in line with the other ESC's we've prototyped against. Appreciate any thoughts or insight!

Alex Kushleyev

Hello stevet,

The reported voltage is the voltage measured by the ESC. In fact all 4 ESCs on the 4-in-1 ESC measure the voltage, you can try to run the calibrate script on others and double check the result. The current of 2.9A for a motor similar to EMAX 1306B is quite reasonable, in fact is probably on the low side (not a concern).

If you are using a power supply that is capable of outputting 7.4V at much higher amps (lets say 10A), then follow these steps to figure out what is wrong:

when ESC reports 2.9A, check to make sure the power supply also reports the same or similar current.
run the calibration on a different ESC id to make sure the voltage measurement is similar to your first test
use a multi-meter to measure the voltage right at the power input pads of the ESC (may need to solder temporary wires to ESC and connect them to multi-meter in order to do it safely.. use your judgement)
the multi-meter voltage measurement should match very closely the voltage measured (under load) in the ESC
the issue is most likely in the wiring between the power supply and the ESC (including possibility of a bad connector or bad solder joint at the connector).

Alex