New features for Absolem robot.

[peci1]

This PR depends on #542.

New features were added to the Absolem robot model:

• relative positional control of flippers
• velocity and torque limits from <joint><limits> are now respected by the flipper controller
• the FlipperControlPlugin was rewritten to use a more reliable implementation of the switching between positional and velocity control

[acschang]

These new features will not be incorporated into the SubT Virtual Testbed prior to Cave Circuit. We will keep this PR open for consideration after Cave Circuit.

[peci1]

I know, that's okay ;)

[nkoenig]

The bounding box for this model is

Min[-0.608707 -0.296315 -0.188594] Max[0.608707 0.296317 0.615689]

[peci1]

I rebased on master and this PR is ready for review.

[peci1]

Review could be easier commit-by-commit as I kept distinct features separate.

To test the relative positional control:

LC_ALL=C LANG=C ign launch -v4 competition.ign circuit:=cave worldName:=simple_cave_01 robotName1:=X1 robotConfig1:=CTU_CRAS_NORLAB_ABSOLEM_SENSOR_CONFIG_1 localModel:=true

# lift up front left flipper by 0.5 rad; calling it for the second time should lift further
# if you issue the command in the middle of another positional command,
# it should treat position relative from where it currently is
rostopic pub /X1/flippers_cmd_pos_rel/front_right std_msgs/Float64 "data: -0.5" 

# push down front left flipper by 0.5 rad
rostopic pub /X1/flippers_cmd_pos_rel/front_right std_msgs/Float64 "data: 0.5" 

Further, the model now respects the pi/4 rad/s velocity limit of flipper joints from SDF. It also sets an explicit velocity limit of 0.8 rad/s in the plugin configurations, but this gets capped by the SDF limit. This should emit a warning on simulator startup, that the plugin is configured for higher velocity than the joint actually allows. If you're not happy about this warning, I can decrease the value in flipper control plugin to pi/4, too. Anyways, issuing a velocity command should get capped by the SDF limit:

rostopic pub /X1/flippers_cmd_vel/front_right std_msgs/Float64 "data: -1.5" 

# verify that the velocity is always between -0.78 and 0.78
rostopic echo /X1/joint_state/velocity[1]

[osrf-jenkins]

Build finished. No test results found.

[osrf-jenkins]

Build finished. No test results found.

[peci1]

I've updated this branch with master (no conflict) and simplified ECM handling by gazebosim/gz-sim#629 (released with ign-gazebo 4.6.0).

[peci1]

@nkoenig @iche033 Friendly ping. I'd like to submit new sensor configs of Absolem, but it'd be more convenient if these changes were already merged. This PR has been open for 7 months now...

[mjcarroll]

Tested out position, relative position, and velocity control with no adverse interactions on my system.

[mjcarroll]

@acschang Can you give this one more pass?

[acschang]

Functionality LGTM. I don't see any adverse behavior with other functionality from the small set of tests I did.

Also, in peci1's example for velocity control, use the following:

rostopic pub /X1/flippers_cmd_vel/front_right std_msgs/Float64 "data: -1.5" 
rostopic echo /X1/joint_state/velocity[3]