Hello Friends
I am trying to adjust the MOT_THST_EXPO parameter for the h11 hobbywing motor using the motor thrust fit.excel found on this page.
I got the table information from Hobbywing website.
In the graph I calculated, Corrected thrust has the least difference with normalized thrust when MOT_THST_EXPO is 0.96 while the site explains that it should not be set higher than 0.8.
This graph corresponds to the value of 0.96:
Every time I use manufacture curves I get data I don’t believe. I have also never been able to get the same results myself. For example, the hobbywing data is below:
This matches an expo of over 1. That means the system is better than perfect as thrust increases.
My suspicion is that the Throttle(%) is not a ratio of PWM command but instead some non-linear relationship to PWM.
As to why I give the advice to not increase the expo over 0.8.
A perfect theoretical propeller provides thrust that is proportional to rpm. RPM is proportional to PWM with a relationship of kv * (pwm - MOT_PWM_MIN) / (MOT_PWM_MAX-MOT_PWM_MIN). This gives the perfect expo of 1.0.
A real system gets increasingly inefficient as the PWM increases. This reduces the expo below 1.0 because the slope of the upper end of the curve is reducing. Further we don’t start the range at zero thrust and again this reduces the expo. The end result is I have not seen measured data with an expo over about 0.8.
Thanks very much for this. I also independently (and coincidentally) received thrust data from HobbyWing (in Japanese) and came to the same result of 1.1 which I knew could not be correct. Garbage in, garbage out I guess. Thanks for confirming this!
