Target not reachable by the robot about unity-robotics-hub

[SDBonhof]

I managed to fix it myself. I raised the target a bit so that it falls onto the table when I press play. Perhaps the target was clipped into the table slightly or something. Still not sure why that would be a problem for goal reachability but at least it works now.

[LaurieCheers-unity]

Thanks for the feedback; glad you were able to fix the issue. The Robotics Hub project is under active development and we will be looking into this case to see why it wasn't working initially.

[NathanielRose]

@SDBonhof What did you raise the target to. Its seems as if I am having a similar experience.

[SDBonhof]

@NathanielRose It is a bit sensitive, but I can get the tutorial working when I place the target at

-0.218, 0.805, 0.199

Upon further inspection, placing the target at the same x,z coordinates but lowered onto (or even slightly into) the table still results in a successful pick and place. Restarting the ROS nodes with the launch file did not change the outcome.

Placing the target back at my original locations as shown in my original post results in a failing pick and place again.

It seems to me like the robot is unable to reach targets that are on its left. Placing a target at around 8 o'clock causes the robot to swing left to go to the target and reaches it. But placing it closer to 9 o'clock causes the pick to fail. from about 9.30-10-ish towards 12 the robot is able to reach the target again.

I find this quite strange behaviour since the robot is able to swing past 9 to 8 (from 12) but it supposedly isn't able to reach 9?

[mrpropellers]

@SDBonhof Collisions with the table should be a non-issue, as the MoveIt solver, which is computing the trajectories, doesn't know of the table's existence, so whatever is happening here is not necessarily the robot failing to reach the location, but the solver failing to compute a valid path for those start/end points.

I'm going to log your observation that the solver fails specifically when the Target is on the left and TargetPlacement is on the right - that seems to be the key factor is what causes the path-planning to fail... Could you confirm, when setting up the scene initially, did you drag the Target and TargetPlacement objects into the Scene view, placing them on the table manually, or into the Hierarchy? When dragged into the Hierarchy, they should show up in a default location in the view that is (presumably) guaranteed to work, and should look something like this:

[SDBonhof]

@mrpropellers What you say about the MoveIt planner makes sense.

IIRC I dragged the objects into the scene directly instead of into the hierarchy. Nevertheless, the location should be reachable either way, so I am happy you are looking into it.

[mrpropellers]

Just to provide an update: this issue has been noted internally but it hasn't made it to the top of the list yet. There's a few tasks ahead of it but I will find time soon to try and root cause this and determine whether it's an issue within our stack that we can fix. If it's a problem inherent to move-it we can at least note the exact conditions under which planning would be expected to fail.

[SDBonhof]

Thanks for the update. For me this issue isn't pressing as I am not using Unity at the moment, but maybe others experience this issue too, idk.

[mrpropellers]

So I finally had some time to check in on this and was unable to reproduce. I was able to identify a region directly behind the arm that was (correctly) reported as unreachable, but with Ubuntu 18.04 and the Target and Placement objects at the coordinates specified, trajectory planning succeeded:

While investigating, I saw there was a confounding issue which caused the trajectory planner to break when it failed to find a path so I've submitted a fix for that: #155

Hopefully this issue was resolved incidentally by some previous code change. I'm going to close since we can't repro, but if this crops up again feel free to either re-open or submit a new Issue!