Brushless type config bug

[knmcguire]

Currently there is the following kconfig variable called: ENABLE_THRUST_BAT_COMPENSATED. This compensates the thrust based on the current battery level:

crazyflie-firmware/src/drivers/src/motors.c

Lines 132 to 203 in 39cf2a2

	// We have data that maps PWM to thrust at different supply voltage levels.
	// However, it is not the PWM that drives the motors but the voltage and
	// amps (= power). With the PWM it is possible to simulate different
	// voltage levels. The assumption is that the voltage used will be an
	// procentage of the supply voltage, we assume that 50% PWM will result in
	// 50% voltage.
	//
	// Thrust (g) Supply Voltage PWM (%) Voltage needed
	// 0.0 4.01 0 0
	// 1.6 3.98 6.25 0.24875
	// 4.8 3.95 12.25 0.49375
	// 7.9 3.82 18.75 0.735
	// 10.9 3.88 25 0.97
	// 13.9 3.84 31.25 1.2
	// 17.3 3.80 37.5 1.425
	// 21.0 3.76 43.25 1.6262
	// 24.4 3.71 50 1.855
	// 28.6 3.67 56.25 2.06438
	// 32.8 3.65 62.5 2.28125
	// 37.3 3.62 68.75 2.48875
	// 41.7 3.56 75 2.67
	// 46.0 3.48 81.25 2.8275
	// 51.9 3.40 87.5 2.975
	// 57.9 3.30 93.75 3.09375
	//
	// To get Voltage needed from wanted thrust we can get the quadratic
	// polyfit coefficients using GNU octave:
	//
	// thrust = [0.0 1.6 4.8 7.9 10.9 13.9 17.3 21.0 ...
	// 24.4 28.6 32.8 37.3 41.7 46.0 51.9 57.9]
	//
	// volts = [0.0 0.24875 0.49375 0.735 0.97 1.2 1.425 1.6262 1.855 ...
	// 2.064375 2.28125 2.48875 2.67 2.8275 2.975 3.09375]
	//
	// p = polyfit(thrust, volts, 2)
	//
	// => p = -0.00062390 0.08835522 0.06865956
	//
	// We will not use the constant term, since we want zero thrust to equal
	// zero PWM.
	//
	// And to get the PWM as a percentage we would need to divide the
	// Voltage needed with the Supply voltage.
	float motorsCompensateBatteryVoltage(uint32_t id, float iThrust, float supplyVoltage)
	{
	#ifdef CONFIG_ENABLE_THRUST_BAT_COMPENSATED
	ASSERT(id < NBR_OF_MOTORS);
	if (motorMap[id]->drvType == BRUSHED)
	{
	/*
	* A LiPo battery is supposed to be 4.2V charged, 3.7V mid-charge and 3V
	* discharged.
	*
	* A suitable sanity check for disabling the voltage compensation would be
	* under 2V. That would suggest a damaged battery. This protects against
	* rushing the motors on bugs and invalid voltage levels.
	*/
	if (supplyVoltage < 2.0f)
	{
	return iThrust;
	}
	float thrust = (iThrust / 65536.0f) * 60;
	float volts = -0.0006239f * thrust * thrust + 0.088f * thrust;
	float ratio = volts / supplyVoltage;
	return UINT16_MAX * ratio;
	}
	#endif
	return iThrust;
	}

In Kconfig this setting is on by default, but for brushless types or anything with a different motor, this should probably be turned off. We should add it to the kconfig for the bolt and or other brushless types.

Mind that we now also have the upgrade kit, so that these values are not valid as soon somebody replaces the motors and propellers, but that is more related to #936