add ability to control uavcan hardpoint by MAV_CMD_DO_GRIPPER

[PonomarevDA]

Describe problem solved by this pull request
This PR allow to control a gripper based on uavcan via mavlink MAV_CMD_DO_GRIPPER command in both mission (as waypoint) and manual (by just sending the command) modes.
The old version of uavcan/hardpoint was supposed to be used via mavlink console that in my opinion was not user-friendly. It was even removed from uavcan_main.cpp recently.

Describe your solution
I extended navigator a little bit. Now uavcan/hardpoint periodically checks vehicle_command. If it is VEHICLE_CMD_DO_GRIPPER, it starts sending uavcan/hardpoint message with a small rate.

Besides changes in PX4-Autopilot firmware it is also necessary to ublock Gripper waypoint in QGC. It might be fine to implement some additional widget to manually control a gripper (I attached an example of such widget in the video below).

Describe possible alternatives
During the real tests it was found out that it's a bit uncomfortable to manually add delays before and after each of the gripper command. As I see, the next step might be:

1. Wait for hardpoint feedback on PX4 side while the gripper is ready
2. Add a parameter with delay duration and wait for it before and after each gripper command on PX4 side
3. Somehow make the gripper waypoint in QGC to be a comlex item that contains 3 waypoints (delay before, gripper cmd, delay after) or even extend MAV_CMD_DO_GRIPPER parameters.
   But as for me, current solution is enough for the beginning.

Test data / coverage
Manual control was tested on this branch: video.
Mission was tested in the uavcan simulator based on cuav v5+ on test branch: video illustration and log.
We also have several real tests on v1.12.1 with this feature.

[junwoo091400]

Wow totally missed this! Gripper support was added in #19963

@PonomarevDA

[PonomarevDA]

@junwoo091400 Thanks that you notified about it. Probably, I could leave only dronecan related part in this PR.

[benjinne]

Hey @junwoo091400 does gripper support uavcan control or does that still need to be added? I couldn't find documentation on canbus with gripper

[junwoo091400]

Hey @junwoo091400 does gripper support uavcan control or does that still need to be added? I couldn't find documentation on canbus with gripper

It only responds to MAV_CMD_DO_GRIPPER as vehicle command. Not sure when related UAVCAN message is received, it gets translated into that vehicle command. If that's not the case it isn't supported yet.

[PonomarevDA]

Hi, @benjinne. I've rebased the branch.
I've sent MAV_CMD_DO_GRIPPER and it seems to be working fine because an autopilot starts broadcasting the hardpoint message as I expected.

I don't have an EPM v3 device, but I have a node that can subscribe on the hardpoint message and control a servo. I uploaded this branch to cuav v5+ and reset everything to default. It works as I expected as well. On this video I send commands to release and to grab: https://youtu.be/1npnHknUpq8.

Can you please give a try to this branch with your device? Is it what you need?

[PonomarevDA]

I couldn't find documentation on canbus with gripper

I rely on https://dronecan.github.io/Specification/7._List_of_standard_data_types/#uavcanequipmenthardpoint
It is similar to https://mavlink.io/en/messages/common.html#MAV_CMD_DO_GRIPPER

[hamishwillee]

@PonomarevDA When this goes in, can you please add a docs update?

Docs affected by gripper are:

• https://docs.px4.io/main/en/peripherals/gripper.html
• https://docs.px4.io/main/en/flying/package_delivery_mission.html
• https://docs.px4.io/main/en/peripherals/gripper_servo.html

We'd also add specific hardware to this list: https://docs.px4.io/main/en/dronecan/#supported-hardware

And last of all, a line to https://docs.px4.io/main/en/releases/main.html to record the change

Ideally you might have a topic like https://docs.px4.io/main/en/peripherals/gripper_servo.html - but what I'm mostly after is making sure that we make it clear how you configure a uavcan gripper for use via MAVLink and in a package delivery context. If it can't be used in package delivery we need to make that clear.

[PonomarevDA]

@hamishwillee Sure, I can add it. First, I will improve the docs of the mentioned device (the device itself is just a CAN-PWM converter, and a gripper is one of the ways how we can use it). Then I will add it to the PX4 docs.