Page 1 of 1
Position Hold Mode
Posted: Thu Aug 03, 2017 10:08 am
by Korrelator
Hello Guys i need your help again.
I'm using a cf2 and want to run a position control. I have seen this post:
https://www.bitcraze.io/2017/04/updated ... an-filter/
and im using the Client with the external tab. I have build a Stereo-System(2 PS-Eye) to track the copter and the kalman filter is giving me good estimations. (I send the external position-data with 5Hz) . Furthermore i changed the Kalman-Estimator. Now my Questions:
1) On the Flight-Tab we have the opstion for Position-Hold. How exactly can i use it and how do i set the Target-Position?
I have seen in the commander-cf-firmware that pitch and roll commands are used as position commands but it doesn't work for me. Where can I check my TargetPosition? I'm using a PS3-Controller with the PS3_Mode_3 Inputmap. Do i have to change something?
2) I have created a new tab where i send CF my Target Positions. For this i have added a new generic Command. This is how the setpoint implementation on the cf-firmware looks like:
Code: Select all
setpoint->mode.x = modeAbs;
setpoint->mode.y = modeAbs;
setpoint->mode.z = modeAbs;
setpoint->mode.roll = modeDisable;
setpoint->mode.pitch = modeDisable;
setpoint->mode.yaw = modeAbs;
setpoint->position.x = -values->x;
setpoint->position.y = values->y;
setpoint->position.z = values->z;
setpoint->attitude.roll = 0;
setpoint->attitude.pitch = 0;
setpoint->attitude.yaw = 0;
setpoint->thrust = 0;
I only send cf a command if a Target-position is changend on the Client-Input. But if i Update my Input the rotor just rotates for a second and then they stand still again. Do you know how i can make this work? Am I missing something?
Thanks
Re: Position Hold Mode
Posted: Mon Aug 07, 2017 10:58 am
by Korrelator
Hey i found the porblem. I was sending my position-command and the client was also sending a rpyt-command to the cf2. Because of this my command has been overwritten all the time. To solve this i just cut out the send call in commander.py. Is there also a better solution to stop the client from send rypt-commans?
But i have a new quetion. How good is the performance of the Position-PID-Controller? Because i couldnt stabilize the copter with the controller. Im sending my external position with 7Hz and have an accuracy about 2-3cm
Re: Position Hold Mode
Posted: Mon Aug 07, 2017 1:11 pm
by arnaud
Hi,
If the position estimate is good, the on-board PID controller should be pretty good. For instance, this video was made with the internal controller:
https://www.youtube.com/watch?v=3lDvWlbDSOA. I also got very good result with AR tag with update at about 20-30Hz.
How does your position estimate look as taken from the kalman filter and are you starting the Crazyflie facing X positive?
As a first approach you could try the position-hold mode integrated in the Crazyflie client, it allows to more easily test if things are working properly (since you keep control on the Crazyflie).
Stereo-vision with 2 PSEye sounds very interesting, Are you planning on pushing the code publicly, I would be very interested to try-out.
Re: Position Hold Mode
Posted: Mon Aug 07, 2017 6:08 pm
by Korrelator
Hey, yes i will make a blog soon and post all my code and know-how about my setup. But basically I have lighted up a Table Tennis Ball with a LED. Then I tracked the ball (color-based) with both cameras and triangulated the position. The power for the LED is supplied by one of the GPIOs of the CF2.
Yes, I'm starting facing X-positiv and also took out the YAW-correction in the controller, because i can't measure the YAW-Angle with the camera right now. So im trying to fly with a constant YAW-angle.
I have moved my cameras now and will calibrate them again tomorrow and post a estimation plot.
Re: Position Hold Mode
Posted: Tue Aug 08, 2017 7:23 am
by arnaud
The kalman filter will estimate the yaw out of the dynamic, but for that to work well it needs to have a good initial yaw estimate, hence the requirement of starting the Crazyflie facing X. So having the yaw absolute at 0 like you are doing or relative at 0 degree per second should work fine.
It will be interesting to see the estimate from the EKF.
Re: Position Hold Mode
Posted: Tue Aug 08, 2017 1:25 pm
by Korrelator
Here we go. At first i made circles in the y-z-plane. Then i moved the copter left to right, followed by up to down and at last i moved it fore- and backward. I have noticed that my x-values are sensitive when i move from left to right. Maybe i should do a better calibration.
And again i dont understand the position-hold mode. I have set the the 'Flight Mode' as 'Normal' and the 'Assist Mode' as 'Position Hold'. How can i make the copter hold his position? Because if i stop giving Trust-input the copter falls down. Am I missing something?
Re: Position Hold Mode
Posted: Wed Aug 09, 2017 8:19 am
by arnaud
Hi,
Yes, you should press the assist button on the gamepad in order to enable assist mode, once you pressed the button you should be able to release all control. It is normally mapped to the shoulder button on PS/xbox controller, you can map it to your controller using the
input device configuration.
Your estimates do not look bad. I guess X is in the depth direction which can explain its sensitivity?
Re: Position Hold Mode
Posted: Wed Aug 09, 2017 10:42 am
by Korrelator
Oh ok thx, yes X is in the depth direction
i have one last question.
How is the coordinate system defined?
1)The x-direction should be positive in the front direction like here:
https://wiki.bitcraze.io/_detail/projec ... 3Aassembly
2)The y-direction is positive leftward
3)The z-direction is positive upward
is this correct?
Re: Position Hold Mode
Posted: Wed Aug 09, 2017 11:11 am
by arnaud
Yes, this is correct, the coordinate system looks like that:
https://www.bitcraze.io/getting-started ... m/#intro19
