Auto and Circle speed limit

Hi. I have a hexa with Cube 2.1 and APM Copter 3.5.4. The drone flies freely at speed up to 20 m/s.

Now the problem: no matter what parameters I set, it does not fly faster than 12 m/s in auto waypoints or 7 m/s in circle mode or loiter turns. I read that firmware has no limits and it should try flying the speed which is set (wpnav speed for waypoints and circle rate for circle).

I set the parameter to slider on tx, but it speeds up to mentioned above speeds max, no more increase has any influence.

Thank you,

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Post a log, let’s have a look.

It was very windy in our city these days. Today the weather was good and I made some tests.

First log is straight flight between 2 waypoints. This time I set them 800 meters apart. WPNav Speed was set to 20 m/s and the drone came pretty close to that speed. So, it should be WPNav Acceleration which was not allowing the drone to go faster, as previous tests were between points 100-200 meters apart. Will test it again with higher acceleration setting.

Second log is circle flights. Does not fly faster than 5-7 m/s. Circle_rate was 30 deg/s and then 60deg/s, which should give me insane speeds on 50-100 m radius circles. Which setting holds the drone this time?

If there is something wrong in the logs, please tell me.

Best regards,

WPNAV_ACCEL is also limiting circle rate.

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You are right. So, because it goes in circle motion not linear, it needs to constantly accelerate towards the center, and wpnav_acceleration limits the speed.

Now, when I set high accelerate it flies faster. But, to achieve something like 12 m/s on 50m radius circle I need to set wpnav_acceleration to 500cm, which is so high, that when the drone flies to the start of the circle mission it pushes way to hard and looks very unstable accelerating/decelerating. When wpnav_accel is lower, it flies slower in circles. Maybe there is a clever way to have faster circles with not so fast acceleration?

Yes exactly. I think of it as centripetal acceleration in circle mode and linear acceleration otherwise controlled by the same parameter. Unless there was some way to break that into 2 parameters I don’t know how it could be adressed.

Where did you get the top speed of 37 m/s if you can’t reach it?

The first log shows 29 m/s and that was it’s maximum possible speed because you had a motor pegged at 100%. It also hit that speed by descending the entire time. Without an airspeed sensor, or without you flying in opposite directions and averaging the two (one straight into the wind, one opposite), you don’t know your actual max airspeed. Airspeed is what you’re interested in, not ground speed which is what the GPS is measuring.

I’ve hit 40 m/s before, but that was with 10 m/s tailwinds. I think you’ve been troubleshooting this issue for so long because there really isn’t an issue. Your drone simply can’t achieve what you believe.

You can do the speed test in multiple directions and check if a different motor is hitting 100% each time (keep the front of the drone pointed in same direction for each test). If it’s always the same motor, replace it. If after replacing the same occurs, you have a weight imbalance/design flaw. My experience with T-Motors is they can vary KV quite a bit.

Thank you for your reply and analysis, Keith. You are right about the air speed and wind. 37 was the speed I achieved once flying with the wind in manual. But it is not the case. I am testing this drone for several months already and know all its characteristics and capabilities. It achieves 20 m/s and maintains this speed freely in calm weather, no wind, tested many times. Actually, the causes of the problems I faced were discussed above and fixes were found. I already have flown several times and the fixes work.

The only problem I face now is the WPNAV_Accel, which limits circles speed. Too high acceleration and the drone goes wild, too slow and the drone flies slow in circles.