MOT_THST_EXPO for T-Motor Alpha ESC's

ArduCopter Copter 4.2
1

I’ve noticed a fair bit of discussion about Tmotor Alphs esc’s having a corrected linear thrust curve. Thus requiring a lower MOT_THST_EXP value. I’m running U8II motors, 12s and Alpha 60HV escs. But unknown to me there’s a new initial setup function in Mission planner that helps estimate MOT_THST_EXP. But it asks if you’re using Tmotor Flame esc’s, there’s nothing about the Alpha units. Is it just the Flame’s that require a lower value? Man, asking Tmotor is like pulling teeth. Then when you finally get a response it’s super cryptic and vague lol!

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We think the Alpha ESCs should use the calculated MOT_THST_EXPO from in MissionPlanner/Initial Parameters (based on your prop size)

You can manually adjust it after you’ve got reasonably stable flight using these rules:

  • set too high you can see instability at low throttle
  • set too low you can see instability at high throttle

If you’ve already Autotuned and have to change MOT_THST_EXPO much you wouldneed to run Autotune again.

1 Like
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I have a question about MOT_THST_EXPO. I am using different ESC’s (HW XRotor Pro 40A) for my quad. Its a 650mm with 17" props, EXPO value is currently .72 as per the calculated value MP says to put it at. But…Ive noticed the more I decrease EXPO to around .3 or even .2, the smoother the transition of motor RPM when slowly increasing the throttle after arming. Its less abrupt. Would this mean that my HW ESC’s are similar to the T-Motor in terms of linearity and should a lower EXPO value be used in my case?

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I dont think that transition from armed to flying is necessarily a good indicator for MOT_THST_EXPO. You might find you are setting it too low and there will be stability issues at higher throttle.
I would be trying more actions with higher throttle and lower throttle, like ascents, descents and resistance to disturbances (wind).
Those HobbyWing XRotor ESCs are not known to do any thrust linearisation. Props and motors could play a role, but I wouldnt expect MOT_THST_EXPO to deviate too far from the calculated value.

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Sorry, I forgot to mention that the spool up test was at my the bench without the props. The motors sounded smoother at lower values. But I will fly the quad like you suggested. Thx.

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That will tell you little to nothing other then the motors spin and in what direction.