I was testing auto-takeoff a couple days ago. For the most part everything worked great. There were a couple times though where the motor was considerably delayed starting up, resulting in a minor crash.
Upon reviewing the logs I can see that in some instances the throttle is not raised until well after the launch. In a successful launch the delay might be 0.8s, in a failed launch it might be 1.6s. In all cases: TKOFF_THR_MINACC=15, TKOFF_THR_DELAY=0, and TKOFF_THR_MINSPD=0.
Is there a way to allow the motor to run at some low power setting before takeoff? In my case there is no risk of the prop striking anything on the launcher
I figured out the problem. Turns out the problem is that I was launching mid-mission. A short ways off the end of the launcher the AP would decide it was flying and ramp up the motor. By properly restarting the mission each time the problem has been solved.