Low torque than expected

I have done some torque tests. But the results are quite underwhelming.
I have tested with a load cell and a fish scale. With different currents and different lever arms - all with the same kind of result:::

From the formula: 8.3*(Current)/(Kv)*6. (the *6 coming from the gearbox that was used)

I should have gotten about 50%more torque. For example, at 30A the torque should be 11.5NM (See graphs below of my testing - one plot is current compared to torque the other one is the power in watts at that current)

Other people that I found for example:
OpenTorque Actuator Test (developed by Gabrael Levine) - YouTube (at 12:00min)
came very close to the calculated value.


  • Motor: Eaglepower 8308 Brushless Motor 130kv
  • Encoder: AS5047P
  • Battery: Li-Ion 5S(running 21V to 15V) and continuous max current 80A
  • Controll USB

Do you have any idea what the problem could be? I also tested Without the gearbox and got the same result with a small margin of error.

Screenshot 2022-06-24 at 18.22.16

Screenshot 2022-06-24 at 18.22.20

Note on testing: For the load cell I just commanded a position about a half turn further then the load cell would let the lever arm go. For the fish scale I just pulled while the motor was in closed loop control.
I also tested different control loop tuning parameters with no difference at max torque.

Thanks a lot for you ideas!

Cheap Motor Kv values from datasheets are largely inaccurate. Turn it with a drill and measure the Kv to be sure

Yes that was the problem. I checked with oscilloscope and the rating from the seller is wrong.

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