Detect launch on gps speed

[avsaase]

There have been a couple of reports (here and here, and I believe also one in the Telegram group) where launch was not detected but the configured idle throttle was sufficient to sustain flight. When the throttle is raised but before launch is detected, you cannot exit auto launch by wiggling the stick so if you don't think of putting the throttle back to zero you'll have zero control.

This PR adds an explicit check on the gps speed to detect launch, which should make it impossible for this to happen.

[breadoven]

A benefit of #6389 perhaps ... it allows you to exit the launch by waggling the stick because the throttle is already low although it would then need the throttle raising to get the motor to rev but at least you regain full control. It also allows you to do this when Launch is selected by switch rather than as a feature unlike the current method which only allows the launch to be cancelled by stick waggle if it's a feature. If it's switched launch you can only exit by switching it off although in that case you wouldn't need to move the throttle low or waggle sticks ... just find the switch quickly.

[avsaase]

Yes but the problem in these two videos is that they had significant idle throttle configured, which obscured the fact that the launch was not detected. Without idle throttle, the plane would have just crashed a few meters in front of them like any normal failed launch.

I think #6389 will not be very popular with those using idle throttle because it immediately spins up the motor when you arm.

[breadoven]

And the difference between spinning up the motor on arming and when you nudge the throttle stick above min_check is ?

I'm actually interested to understand why people arm when they aren't about to do exactly what they do when they raise the throttle stick before launching. Are they setting up a ground station perhaps or some other gear ... although I can't see why that would require the craft to be armed. Is there anything that requires arming other than immediately before you launch ?

Like the moisture cured Gorilla glue and water based PVA trick in Adam FPV's video. Would have come in useful fixing the AR Sonic wing after it crashed due to the motor mount unsticking itself and falling off.

[b14ckyy]

And the difference between spinning up the motor on arming and when you nudge the throttle stick above min_check is ?

Double safety. If you accidently bump the arm switch while throttle is low, it won't suddenly spin in your arm or face. And if the throttle is high it will refuse to arm anyway. Spinning up the motor on arm immediately will take away a full safety layer.

[breadoven]

And the difference between spinning up the motor on arming and when you nudge the throttle stick above min_check is ?

Double safety. If you accidently bump the arm switch while throttle is low, it won't suddenly spin in your arm or face. And if the throttle is high it will refuse to arm anyway. Spinning up the motor on arm immediately will take away a full safety layer.

Which is why it's an option. I don't use launch idle throttle but if I did I may still prefer to use this method depending on how I assess the risk.

[avsaase]

Guys let's keep the discussion about arming and safety practices in #6389. This PR is just about launch detection.

[digitalentity]

Looks good now, thanks!