Motor Thrust Scaling

Copter includes motor thrust scaling which compensates for the non-linear thrust output of most ESCs and motors.

Tip

The default curve should work for nearly all ESC/motor combinations. Normally the parameters should not be adjusted unless the vehicle’s actual thrust curve has been measured.

Thrust Curves

The curve is controlled by two parameters:

  • MOT_THST_EXPO controls the shape of the thrust curve with “0” meaning a completely linear curve and “1.0” being very curved (see pictures below). The default is “0.65” (the image below incorrectly states the default is 0.5).

Warning

Some ESCs have built-in linearizing curves and the default EXPO value of “0.65” will cause stability issues, requiring thrust stand measurements to adjust the EXPO. Typically, values of “0” to “0.2” will result.

../_images/MotThstExpo_graphs2.png

  • MOT_SPIN_MAX controls the point at which the thrust flattens out near its maximum. By default this is 0.95 meaning 95% of full throttle.

Thrust Stands

The thrust stands listed below can be used to measure the PWM signal vs thrust output for a vehicle’s specific motor, esc and battery. Be sure to use the ESCs rated input PWM range when measuring these values.

Parameter Calculation

A copy of this spreadsheet can be used to calculate the appropriate values from the thrust stand data above.