3.4/3.5: MOT_SPIN_MIN value unsuitable for many racing copters => MIN/MAX system should be changed

I noticed that the standard parameters are too big too allow a safe take-off with overpowered (racing) copters.
One of my builds worked somehow with 3/4S and suddenly failed with a 5S/6S. Take-off throttle resulted in uncontrollable oscillations. PIDs and vibrations were not the reason. Instead, the controller was not able to achieve a motor output slow enough to keep the device steady. Lowering MOT_SPIN_ARM/MIN did the trick.

Is it actually really necessary to have a system like that? Naively, I suggest to completely remove the MOT_SPIN_MIN parameter. If the controller for whatever reasons lowers the output to 0 instead of whatever is defined by this parameter the worst which can happen is that the PID in the next cycle increases the output again (if there was an effect). In contrast, if the user dares to change the battery and this parameter is too high, the whole copter will sky-rocket (because there is no space for the controller to achieve equilibrium without changing the total throttle) and crash.

In comprehension, I believe the parameter is useless also for bigger copters. I haven’t checked whether the *ARM parameter is independent on the *MIN parameter, but if so there is no reason to be. The line where failure can happen was in my case just ~2 V :confused: So it is not very high.

Many user’s ESCs will soft start if a super slow or 0 signal is sent in flight, followed by a value high enough to restart. That is undesirable.

The max allows the controller to stay in the usable range of the PWM to thrust curve of a particular ESC. If no more thrust is created above 1.90ms, why bother letting the mixer send 1.95ms? Control would be compromised.

These parameters are pretty important, and allow for a wide variety of multi rotors to be setup well.

I believe that SPIN_MIN is forced to be greater or equal to SPIN_ARMED. I also think you’re welcome to set these to 0.

Also, increasing the voltage of the pack on a well tuned multirotor will almost universally result in an overtuned twitchy flight.

Do you know whether every ESC has a different bias upon soft spoolup is starting?