Custom 4 wheel robot going backward
Hi, I've made a custom robot model in gazebo with 4 wheel. I used gazebo_ros_control to control 4 wheel separately. here is one of the example:
<transmission name="${name}_transmission" type="SimpleTransmission">
<type>transmission_interface/SimpleTransmission</type>
<joint name="${name}_joint">
<hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
</joint>
<actuator name="${name}_motor">
<hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
<!--hardware_interface/EffortJointInterface-->
<mechanicalReduction>10</mechanicalReduction>
</actuator>
</transmission>
when i launch the gazebo, robot goes backward a bit by bit, very slowly.
header:
seq: 1778
stamp:
secs: 35
nsecs: 973000000
frame_id: ''
name: - left_back_wheel_joint
- left_front_wheel_joint
- right_back_wheel_joint
- right_front_wheel_joint
position: [-0.003141305783456616, -1.1831937287709593e-05, -0.0019454167338839312, -4.350494892335632e-06]
velocity: [-0.000171673603876349, -0.00015815614100299791, -9.107017547230386e-05, -0.00012163253784832723]
effort: [0.0, 0.0, 0.0, 0.0]
here is my pid example:
right_back_wheel_controller:
type: velocity_controllers/JointVelocityController
joint: right_back_wheel_joint
pid: {p: 10.0, i: 0.01, d: 0.1}
what is the problem there?
I had a same issue and the reason it was happening was the Gazebo world. I had one world where there was no drift backwards and another one where I had the same behavior that you describe. So the reason was something with the physics inside the .world file. Try another world and see if that changes
it still gives some,
header: seq: 5362 stamp: secs: 6031 nsecs: 66000000 frame_id: '' name: - left_back_wheel_joint - left_front_wheel_joint - right_back_wheel_joint - right_front_wheel_joint position: [-0.00895766188413738, -0.00010029614281670263, -0.0037137861694445107, -5.215430933613874e-05] velocity: [-1.790139788460453e-09, 0.00015371939159806736, -6.087800114257582e-10, 5.4862705390444695e-05] effort: [0.0, 0.0, 0.0, 0.0]
Hi @ridwan,
The robot is "technically" going backwards but that is not the result of the controller but as @kosmastsk, is a problem of you Gazebo world. You will need to configure properly Gazebo contacts and wheel params. Nevertheless, you will always end up with those kind of values since it is the nature of the Gazebo contact computation algorithm.
hi @Weasfas , so what can i do to prevent this type of problem?
Hi @ridwan,
In order to decrease this type of behaviour you can do several things:
mu1andmu2as well askpandkd. You can check what those values mean here and here. As well as in the SDF documentation.ERPandCFMused to balance the inestability of the simulation. You can learn more about his params here.And finally from the physics tag of SDF format you can try to adjust the
itersparameter. The higher the more precission the engine have when calculating contacts.All this will let you tune your enviroment to try to decrease this behaviour but you need to know that it is very common to see this this when dealing with Gazebo contacts.