Plane Auto TakeOff : Idle Throttle / Missing feature?


Most of my wing build (Z89, SonicModel HD Wing, AR Wing Pro) are using folding propeller.

Take-off is kind of “very” risky with that kind of frame using arduplane Auto Takeoff because if motor is not spinning before launching the plane (Idle Throttle is equal to 0% by default), there is a high risk that the ESC has to retry its “startup procedure” due to the torque required at startup-time ( if propeler is folded or unbalanced) . causing the propeler to have a 1-2 sec delay before really spinning… leading to some crashes… because wings have fewer attitude authority than t-tail plane

What’s-more if the propeller itself is heavy or just big, the torque required to speed-up the motor will generate some roll at launch-time, what is very unwanted at takeoff, causing loss of lift… leading to some crashes…

INAV has a parameter for that issue : nav_fw_launch_idle_thr
Here is the associated documentation for folding propeler :

It can be very stressful for your motor, props and even fuselage if a folding propeller is spinning instantly to 100% power if it is folded. So, you can use a low value like 1100 to make sure the prop is open and in balance before launch.

My proposal is to implement a param TKOFF_IDLE_MODE with 3 values possibles:

  • MODE=0 throttle when idle is equal to 0%
  • MODE=1 throttle when idle is equals to param TKOFF_IDLE_THR (static value, in % of motor PWM) . The motor should start to spin when RC MOTOR INPUT >1500 for safety reason.
  • MODE=2 throttle equals RC MOTOR INPUT (eg channel 3), limited by the upper value define by TKOFF_IDLE_THR (in % of motor PWM).

so basicaly, MODE=0 is the current behaviour, MODE=1 is the INAV feature, MODE=2 allow the pilot to take manual control with its RC on the motor startup, with a predefined “security” limit .

To sumup my main feature request is to have a “balanced folding propeller” BEFORE launch time… and the only known way is to have a 10-30% throttle when the plane is IDLE. INAV have this feature for this specific prupose.

Does enyone has some more ideas on that “TakeOff : Idle Throttle” feature ? any other mode in mind ?

Are you looking to get a low idle, but not go to full power until after the launch? If you don’t mind going to launch power while you’re holding the plane it is possible to do “shake to spin up motor” with ArduPlane:

yes i am looking for a low throttle when idle, just before capapult / bungee launching, but also for a more secure hand launching (lower throttle means lower risk to get hurt by the propeller)

Launching a wing by holding the leading edge is only possible if the wing has a low AWU at takeoff.

I my case I have heavy loaded wings (due to electronics for FPV long range + telemetry + lidar) , thus aving a AUW near the max the wing can handle, and in the case you cannot take the risk of a delayed propeler startup… otherwise you hit the ground for sure…

The additional benefit is to ensure a maximum level of thrust in the shorter time possible.

I use the shake to wake with all my hand launch planes (wings and conventional). The only crashes with that mode have been because I messed up the throw.