Change max velocity of gimbal

[ClementLeBihan]

Hi,

I’m would like to change gimbal max velocity ? I want to send gimbal position but I don’t want gimbal to go too fast. I would like to know if we can configure CamController with something like DEFAULT, SOFT, AGGRESIVE, DYNAMIC, etc.

Best,
Clément

[MattMgnParrot]

Hi,

You could directly set the desired position and velocity by selecting POSITION_VELOCITY as ControlMode for AxesCamController.

https://developer.parrot.com/docs/airsdk/messages/messages_list.html?highlight=axisreference#_CPPv4N13CamController8Messages13AxisReference9ctrl_modeE

Best regards,

Matthieu

[ClementLeBihan]

Thank you for your quick answer @MattMgnParrot.

I didn’t undersand POSITION_VELOCITY was a position command with max_velocity.

Is TrajectoryPoint works the same (Messages list - 7.2) ? x is the position you want to reach, and dx and ddx are the max acceleration and the max velocity ? I thought it was a target point where we want the drone to reach it with the state [x, dx, ddx].

[ClementLeBihan]

I tryied your suggestion @MattMgnParrot and it seems like it doesn’t work.

Here is the code I use :

            self.output.has_front_cam_reference = True
            fcam_ref = self.output.front_cam_reference
            fcam_ref.yaw.ctrl_mode = cam_cm_pb2.VELOCITY
            fcam_ref.yaw.frame_of_ref = cam_for_pb2.NED
            fcam_ref.yaw.velocity = 0.0
            fcam_ref.pitch.ctrl_mode = cam_cm_pb2.POSITION_VELOCITY
            fcam_ref.pitch.frame_of_ref = cam_for_pb2.NED
            fcam_ref.pitch.position = - math.pi/2
            fcam_ref.pitch.velocity = 0.01
            fcam_ref.roll.ctrl_mode = cam_cm_pb2.POSITION
            fcam_ref.roll.frame_of_ref = cam_for_pb2.NED
            fcam_ref.roll.position = 0.0

Unfortunately, with 0.01 rad/s in pitch.velocity, gimbal reach -90° in few ms …

Any ideas ?

Best,
Clément

[MattMgnParrot]

Hi,

Did you filter the axis? It is required to take velocity into account. If not, it could be done with:

 def configure(self, msg, disable_oa, override_fcam, override_stereo):
        ...
        self.output.front_cam_config.pitch.filtered = True

Matthieu

[MattMgnParrot]

An other point: the filtering process takes into account position and velocity but it does not involve to accurately match the given velocity. To precisely reach a velocity value, VELOCITY ctrl_mode should be used.

[ClementLeBihan]

Hi @MattMgnParrot,

Where can I find the doc about filtered and locked boolean meaning ?

Anyway, I set the filtered to True and the gimbal seems to go more slowly.
Unfortunately, I still don’t understand how the POSITION_VELOCITY works.

I tried 2 different code (starting from -90 and target is pitch = 0°) :

            fcam_ref.pitch.ctrl_mode = cam_cm_pb2.POSITION_VELOCITY
            fcam_ref.pitch.frame_of_ref = cam_for_pb2.NED
            fcam_ref.pitch.position = 0
            fcam_ref.pitch.velocity = 0.0001

Here is the result

            fcam_ref.pitch.ctrl_mode = cam_cm_pb2.POSITION_VELOCITY
            fcam_ref.pitch.frame_of_ref = cam_for_pb2.NED
            fcam_ref.pitch.position = 0
            fcam_ref.pitch.velocity = 1.0

Here is the result

When I set velocity to 1, the gimbal move the same velocity as when I put to 0.001, but now final position isn’t 0° …

I tryied an impossible configuration (from -90° to 0° with a negative velocity) :

            fcam_ref.pitch.ctrl_mode = cam_cm_pb2.POSITION_VELOCITY
            fcam_ref.pitch.frame_of_ref = cam_for_pb2.NED
            fcam_ref.pitch.position = 0
            fcam_ref.pitch.velocity = -1.0

and here is the result :

Do you have an example where POSITION_VELOCITY works ?

Best,
Clément

[MattMgnParrot]

The position velocity relies on an internal dynamic model that realize state integration (such as drone TrajectoryPoint), so position and velocity must be consistent. Also the given velocity in POSITION_VELOCITY doesn’t represent the maximal value.
If you want to set a maximal velocity, you could set the following parameter while sending a POSITION reference:

def configure(self, msg, disable_oa, override_fcam, override_stereo):
	self.output.has_front_cam_config = True
	...
	self.output.front_cam_config.pitch.max_vel = math.radians(10.0)

Matthieu

[ClementLeBihan]

Thank you for this max_vel argument. Where is the doc of this argument ?

Moreover, I understand POSITION_VELOCITY doesn’t represent the maximal value, but do you know why in the three examples I sent just above, the position target is 0° and regarding the velocity value, the end position of gimbal is different in the three examples …

Also, where can I find the doc about filtered and locked boolean meaning ?

Best,
Clément

[Ronan]

@ClementLeBihan

Thank you for this max_vel argument. Where is the doc of this argument ?

Hello,

The doc is here:

https://developer.parrot.com/docs/airsdk/messages/messages_list.html#_CPPv4N13CamController8Messages10AxisConfigE

(but the generation of the documentation was not handling the comments correctly. It will be fixed in the next release).

Here is the source of the AxisConfig message:

// Axis configuration.
message AxisConfig {
    // Specify if axis reference will be used or discarded.
    oneof optional_locked {
        bool locked = 1;
    }
    // Enable filtering to have a smoother movement.
    oneof optional_filtered {
        bool filtered = 2;
    }
    // The filtering magnitude applied to the axis.
    oneof optional_smoothness {
        float smoothness = 3;
    }
    // The maximum velocity of the axis.
    oneof optional_max_vel {
        float max_vel = 4;
    }
}

Thanks,

[ClementLeBihan]

Thank you @Ronan for the doc of AxisConfig !

I still don’t understand why the three examples of POSITION_VELOCITY don’t reach same 0° target, but at least I know the max_vel parameter, and it was the main question on this issue

Best,
Clément