vibrating model


lr101095
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While running the sawyer simulation in intera 5.2, i can see that the model is vibrating.

Calling  rostopic echo robot/limb/right/gravity_compensation_torques, you can see that there are changes being constantly made in actual_position, actual_velocity, actual_effort  and gravity_only.

I compared the same topic to the real robot, and i saw no changes in the output.

Does anyone know why this happens in the simulation or how to resolve it?

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Hi LR,

The caveat when working with the simulator is that it will never perform exactly the same as the real robot. That said, you have indeed encountered a bug with how gravity_compensation_torques are being calculated: one of the KDL::JntArray vectors being used to calculate the gravity torques is being used uninitialized. The uninitialized values cause the calculated simulated gravity torque to vary a fair amount, which causes jitter. I have a fix for this that has not been yet merged into master, but I will hotfix the simulator shortly:

https://github.com/RethinkRobotics/sawyer_simulator/compare/master...kinematics_gravity_torques#diff-3d709d3c805e7153135d0d32960a5b21L449

I will update this topic with details once merged into `master`. In the mean time, if you like living life on the bleeding edge, free to checkout the kinematics_gravity_torques branch on github:
 

$ roscd sawyer_gazebo && git fetch origin && git checkout kinematics_gravity_torques
$ roscd sawyer_robot && git fetch origin && git checkout gravity_inertia
$ catkin build

Best,

~ Ian

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Hi Ian,

I was trying to checkout the kinematics_gravity_torques branch as you suggested, but that branch doesn't seem to exist anymore.
The link you provided also doesn't make comparisons between branches anymore.

I was able to checkout gravity inertia, but there is still a little bit of vibration from one of the joints.

Is there any update regarding the master on git?

Cheers,
Luke

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Hi Ian,

I tried to implement what you suggested, but the joints are still vibrating. In addition to that, I am unable to manipulate any of the joints after joint 3 when trying to run my program. Even when i exit the program, i am still unable to move the robot.

Before running the program, i am able to use joint_position_keyboard to move the robot.

Can you suggest any reason as to why this happens?

Regards,
Luke

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  • 2 weeks later...

Hi Ian,

I've updated as you suggested. However, i'm still seeing unnecessary vibrations in right_j4 when looking at the robot/joint_states/effort through rviz.

The vibrations in right_j4 are also affecting the joint torque efforts in right_j3 and right_j6. The consequential vibrations in right_j6 has a negative effect on the application i'm working on, causing inaccurate readings from a force/torque sensor attached to the end-effector of the robot.

Is there anything you can suggest that may fix this?

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