How to change the parameters in the Quadrotor Plant for a different UAV mass?

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Tudor-Stefan Tonca 2022-11-4

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评论： Dennis 2023-4-15

thrust&mass.png

Hi,

I have not had any success in trying to figure out what parameters to chose for a higher quadcopter mass in the quadrotor plant block. After many tries, the quadrotor simply does not take off with different parameters. I would appreciate any ideas on how to calculate the PD gains for a different mass. Thank you!

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Answer 1

Jianxin Sun 2022-11-7

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Hi,

Instead of changing the PD gains on the block, you should increase the commanded thrust to drive a heavier UAV. For example, in order to be able the take-off, the commanded thrust should be higher than the gravity force. So if your mass is 1 and gravity acceleration is 9.8 then the commanded thrust should be higher than 9.8.

Jianxin

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Tudor-Stefan Tonca 2022-11-12

编辑：Tudor-Stefan Tonca 2022-11-12

Hi @Andrew Ouellette, @Jianxin Sun @Sam Chak. Thank you all for your time and interest into answering my question! Since I've read your answers, I have spent a lot of time trying to configure the parameters as advised. I completely understand the formulas for calculating the thrust and it makes total sense to change the parameters as you've said (Initial Thrust = mg, mass = desired mass value). Assuming that I have no altitude error, when thrust is equal to mg, it should work. However, I have tried it countless times and got nowhere..

With the mass = 0.1 and initial thrust of 0, the simulation behaves as expected (see image below).

After changing the mass to 1 and Initial Thrust to 9.81, the simulation behaves as seen below. The trajectory keeps going down, until the smulaton stops. In the QGC, the quadcopter does not appear to move.

I have checked the UAV animation block and can confirm that the Inertial Z direction is set to "Down".

On top of that, I have also tried the following (but with no success):

Chaged DroneMass parameter in the uavPackageDeliveryDataDict.sldd to the same mass set in the configuration tab of the guidance model
Changed Initial Thrust to a very high value to see behaviour - the quadcopter rises initially, then continuously goes down, moving uncontrolled.

N.B. - I have changed the following parameters of the project: uavLatLong, Initial values for the World Position changed to 0 (to eliminate the offset betwheen the Launch and Take-off points in QGC). I am trying to fly a 4-waypoint mission with a quadcopter that has a mass of 5 kg. I have tried both changing the mass to 1 and 5 kg, along with initial thrust according to the formula T = mg, same results..

Thank you once again for your time! I'm really struggling to sort this issue out, but I don't know what I'm doing wrong here, nothing seems to work as expected when it comes to changing the quadcopter's mass...

Tudor

Tudor-Stefan Tonca 2022-11-19

Hi @Andrew Ouellette,

Thank you for the tip. I have tried increasing the saturation, but without success. I have spent much time trying different values for the output saturation limits, because changing only the saturation block for the thrust did not do anything. The best outcome that I've obtained was the quadcopter flying the mission, but missing checkpoints, having random altitudes and flight speeds and not reaching the landing point, but flying past it.

However, I have managed to solve the issue as it follows:

I have added a Gain to the thrust signal, right after the saturation block, calculated as follows: Gain = Desired Mass/Initial mass. For example, for a mass of 5 kg, the gain would be 50.

The same applies for changing the velocity: adding a gain equal to desired velocity/initial velocity (3 m/s) right before the velocity command output.

By adding gain to multiply the thrust as stated, I have managed to solve the issue. I have also tested the method for different mass values and it works perfectly each time.

Thank you all once again for your help. It's very appreciated.

Dennis 2023-4-15

hi Tudor-Stefan Tonca,

I am also trying UAVpackageDelivery, I modified the GCS path but the path is too long, so I hope I can increase the speed from 3m/s. Should I also add Gain in thrust? Or to which part?

Thanks.

Kind Regards,

Dennis

Dennis 2023-4-15