Hello, I have looked all over for an answer to this but haven’t found anything yet…
My question pertains to a fully auto mission. Flying a big hexacopter (about 55lbs) and what I’m finding is that as soon as I initiate a mission on the ground (aircraft is on the ground, motors not even spinning), the motors spool up quite fast and the aircraft launches off of the ground quite fast. It then goes into a nice stable vertical climb.
So my question is not how to slow down the climb rate, which I assume would be (WPNAV_SPEED_UP), my question is how do I slow down the initial takeoff speed itself? Any way to slow down this initial acceleration into flight? The actual climb rate itself is perfect and I don’t want to adjust that.
Running the latest Hex Copter firmware with a 2.1 Cube.
That is the correct method it should follow.
This has been discussed by the Dev’s and the behaviour you see is to ensure there is no ‘I’ term buildup during the spool up and takeoff.
If you let a copter spool up slowly then the Nav controller can build up a slight deviation from position and as the copter attempts to lift off slowly it will try correcting its position, much to it’s detriment and anything around it.
So although the speed of launch is a bit daunting, especially for large copters, it is the best way to achieve a trouble free lift off.
If in doubt, arm in Loiter and try a slow pinup and takeoff.
Don’t be near the copter.
Hey thanks for the reply - much appreciated. I can understand their concern. Just curious if the devs would ever put in a parameter to change this speed? I know it is very possible for this aircraft to lift off gently and smoothly, as it has done it hundreds of other times with ‘other’ flight controllers. Would really love to see this if at all possible…
@rmackay9 any thoughts on a smoother takeoff for Bobby?
WPNAV_ACCEL_Z will decrease vertical acceleration. This can make it a bit less aggressive.
@Anubis’s advice good I think. If you’d like to slow down how quickly the motors spool up these two parameters may help as well:
- MOT_SPOOL_TIME: Time in seconds to spool up the motors from zero to min throttle
- MOT_SLEW_UP_TIME: Time in seconds to slew output from zero to full. This is used to limit the rate at which output can change. Range is constrained between 0 and 0.5.
Thanks for the reply everyone! Will give it a shot and report back…
Hey guys, revisiting this old topic, as I’ve had some time to play around with it again. I have tried adjusting all of the parameters that were mentioned but still no luck.
The best way to describe what I am seeing is that the initial phase of “Spool up and immediately take off” is happening about 2x as fast as I’d like with our bigger drones (55lbs AUW).
I tried changing WPNAV_ACCEL_Z, but that only slowed down the ascent rate AFTER the initial spool up/take off process was complete. The spool up/takeoff process was still quite fast.
I also tried MOT_SPOOL_TIME and MOT_SLEW_UP_TIME, both of which did not seem to have much effect on the instant takeoff into the air.
Anything else I can try? Much appreciated!
I have faced this on my big drones, i think it is caused from a not totally correct MOT_THST_EXPO on big drones. On my drone reducing WPNAV_SPEED_UP and WPNAV_ACCEL_Z helped a bit but finding a proper MOT_THST_EXPO makes an serious improvement.
Hey Bobby. I experience the same issue with our auw of 76 lbs hexacopters. I have tried everything, including in this post with no luck. I wish there was some kind of parameter to adjust it.
Edit: If you set your takeoff off altitude (pilot_tkoff_alt) to say 1000 cm. Put it in Loiter mode and just touch the throttle stick up and then let go of the stick it will do a nice gentle takeoff. However it does not do that in auto mode to do a mission, which has been disappointing. It goes from zero throttle to 100% in a second…shoots off the ground until about ten feet and then settles in to a nice climb.
Thanks for the replies Doug and David.
Doug, I tried all of the parameters you listed with no improvement.
David, very interesting. What we are looking for is the ability to change it in Auto mode. Thinking this may not be an adjustable parameter.
I agree, there is nothing to change it in auto mode. Even a parameter just to adjust how much throttle is outputted at the start would be nice in the initial takeoff. Just surprises me there is now way to adjust takeoff much at all.
Hi Randy. Is anything in the works for helping us out out doing a mission in automode with auto takeoff or just auto takeoff? There is no good way to control the takeoff. Just seems like there should be some way to adjust these crazy fast takeoffs up to 10 feet. I get you want to get the copter off the ground, but no adjustable parameters with this stinks…especially when I have a heavy payload for spraying. Thank you.
Following the topic, i’am currently operating a 25kgs quad.
Takeoffs in auto mode are as describe below. Except for 3 flights where i slide the take off slider and had no reaction. On this case, the flight mode became « guided mode » and i had to slide another time for the drone to takeoff and it was progressive and smooth ! Perfect
Impossible to replicate this behaviour intentionaly.
I run the last firmware with black cube.
Wow cant believe this thread is 2 years old!
This fast takeoff behavior has been resolved in Ardupilot 4.0.7.
For a large aircraft I would also recommend changing the MOT_SPOOL_TIME parameter to 2 or 3 seconds (yes, it says max of 2 seconds, but 3 is also fine). This will allow a slower motor spool up and thus a smooth takeoff on a large aircraft.
Thank you very much.
We have set MOT_SPOOL parameter to 2.
I still have a guided take off random where i can see the difference.
In auto mode, i have still the same behaviour. We test it again today and let you know.
Have a good day.