Is there a way to ramp up the throttle slower on takeoff?
Our Hexacopter flies perfect with auto missions, loiter, auto land…
But when we try auto takeoff, arm in stabilize on the ground, switch to auto, then bump the throttle, it shoots up into the air very aggressively. It’s not a huge problem, but it would be preferable if takeoff could be adjusted.
try to change the throttle to a curve in your radio which is flat a the hover point. It also helps to hover in stab mode.
Thanks for the suggestion. I am talking about auto takeoff though, where the multirotor is switched into auto while on the ground, armed, and then as soon as the throttle is blipped, the autopilot takes over. It is a little aggressive, I was hoping there would be some parameters to change to slow down the throttle increase rate.
[1:32:07 AM] Randy Mackay: there should be a slow start in the code…
[1:32:39 AM] Randy Mackay: i wonder if perhaps the copter is not sitting on the ground long enough to recognise that it’s landed
[1:32:48 AM] Randy Mackay: I’d have to see a log and look for the landed event.
[1:32:56 AM] Randy Mackay: the slow-start only works if the vehicle thinks it’s landed
[1:33:12 AM] Randy Mackay: and i believe there’s some code in AC3.1.3 that resets the landed flag to false when you change modes
[1:33:24 AM] Randy Mackay: so it can take a few seconds after switching for it to realise that it’s landed
[1:33:57 AM] Randy Mackay: there are no other paramters
Thanks for that info. I’m not sure land detection is the problem here tho because we are only doing auto takeoff after a power up and arm. We have also tried after auto land and disarm and results are the same.
We found that ramping up the throttle in stabilize to just before takeoff then switching into Auto helps a lot and it throttles up much smoother.
It’d be really nice to have a takeoff throttle ramp speed parameter but it sounds like there isn’t one so that answers my question
How high does it jump?
There is actually something in the program which makes the copter try to jump to 20cm altitude when it first takes off. This is done because it was felt that it’s safer to get the copter up and clear of the ground ASAP. This prevents problems where the landing gear are dragging in the grass as the controller starts to pitch/roll to hold position.
Some people like it, some don’t. It’s one of the compromises we have to deal with.
However, if it’s jumping more than that, like 1+ meters, then there is definitely some issue that we would need logs to diagnose.
Thanks, that’s really useful information.
We’ve changed the parameter so that the motors spin when armed, then when switching to AUTO and bumping the throttle for takeoff, this seems to takeoff a little less aggressively.
My guess is because we are using large, slower motors it takes longer for them to start up from stopped, so by the time they are spinning, the APM is outputting high throttle percent to make it get up to 20cm. If the altitude is PI controlled, the I term would build up while the motors are starting. Maybe that’s not the case and it’s just P control.
Anyway, we are really happy with the takeoff procedure now with the motors spinning on arming. Thanks for all the hard work!
Yes, that could be a factor. I believe there is an I-term in effect. Also keep in mind, the final PID operates in the acceleration domain, not altitude.