Make IMU, GPS, pinger and ball shooter joints fixed

[stepanove]

This is a proposed fix for the issue #866.
I'm new to VRX, but as far as I understand, the ball shooter is not supposed to be actuated. Actually, the current joints configuration is wrong anyway, it has two joints both rotating around Z, the second joint should rotate around Y, I suppose. It's obvious that IMU, GPS and acoustic sensors should be fixed. It looks like all of this is just a kind of a copy-paste mistake.
So my suggestion is to make all the following joints fixed:

• wamv/ball_shooter_base_joint
• wamv/ball_shooter_launcher_joint
• wamv/gps_wamv_joint
• wamv/imu_wamv_joint
• wamv/receiver_pinger_joint

[stepanove]

[gazebo-1] [Err] [BallShooterPlugin.cc:158] The frame 'wamv/ball_shooter_launcher_link' does not exist

I noticed an error from BallShooterPlugin, it turns out that Gazebo merges links with fixed joints by default. I pushed a fix to prevent it.

[stepanove]

Hi @caguero , did you have a chance to take a look at this issue?
Is there some hidden reason in keeping those axes revolute that I'm missing? If the problem is only in the fixed joint lumping, then it would be better to use "preserveFixedJoint" option, I suppose.

[caguero]

Hi @caguero , did you have a chance to take a look at this issue? Is there some hidden reason in keeping those axes revolute that I'm missing? If the problem is only in the fixed joint lumping, then it would be better to use "preserveFixedJoint" option, I suppose.

I need to check old issues but I remember we had a problem with a fixed joint related with joint lumping and this was the workaround.

[caguero]

I need to check old issues but I remember we had a problem with a fixed joint related with joint lumping and this was the workaround.

Here's one related issue.

[stepanove]

I need to check old issues but I remember we had a problem with a fixed joint related with joint lumping and this was the workaround.

Here's one related issue.

I see, thanks! I added "preserveFixedJoint" option to all joints I made fixed previously.