Crazyflie Bolt unable to hold altitude above 1.5m

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cfnewbie
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Crazyflie Bolt unable to hold altitude above 1.5m

Post by cfnewbie »

Hi,

My build is a quadcopter with crazyflie bolt, and currently having this problem position mode.
Whenever i flew the drone above 1.5m manually or using script, the drone will start to have "bouncing" motion but it holds altitude well when flying low.
The beacons were set up in a 4x3x3m square.

Is there any parameter that i can change to improve the z axis performance to allow the drone fly stable at a higher altitude.

Thanks in advance
kristoffer
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by kristoffer »

Hi!

Which type of positioning system/mode are you using?
cfnewbie
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by cfnewbie »

i am using UWB with flowdeck and 8 loco positioning beacons in twr mode
tobias
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by tobias »

Sounds like the noise from the VL53L1 laser ranger sensor is going up and that it is causing instability. The height measurement is handled in zranger2.c. You could try to increase values in the STD model here as a first step. You could also try to switch VL53L1 mode to VL53L1_DISTANCEMODE_LONG
cfnewbie
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by cfnewbie »

Thanks Tobias, it works better now after increasing the value.

May i know what is the difference between expPointA and expPointB?
tobias
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by tobias »

The ExpPoint values are creating an exponential STD function based on the distance. The longer from the ground the less the kalman filter will trust the data. The function looks like this:
zranger2_std_function.png
cfnewbie
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by cfnewbie »

i tuned the values and it's working fine in TWR mode, able to fly stable at 5m, however when i switched mode to TDoA3 the same problem happen again, may i know why?

And is the possible for crazyflie fly above or outside the area enclosed by the beacon in TDoA3 mode?

Thank you!
tobias
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Re: Crazyflie Bolt unable to hold altitude above 1.5m

Post by tobias »

Good question. I think it is because the TDoA is a bit more noisy and depending on the anchor positions often Z is the most noisy. Is it different then if you would only use the Loco positioning, no flow or z-range?

In TDoA the position estimation will quickly become worse outside the enclosed area. I recommend to read up a little about TDoA to get a better understanding.
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