SprGrf's profile - activity

Thanks for the immediate reply. That was exactly what I was looking for. Thank you very much.

Hello everyone,

I am trying to use the gearbox joint. I found a world example but it seems to be outdated, as the parameters have been renamed, from gear_ratio and reference_body to gearbox_ratio and gearbox_reference_body respectively. However I cannot get it to work, and I do not know if it is my setup's fault, as I am not sure I have understood the way it works correctly, or if it just not supported anymore.

In the case that it is not, does someone have an idea how to transmit motion and torque from a joint to another ?

Thank you all for your time.

That was my experience as well.

Gearbox Joint operation Hello everyone, I am trying to use the gearbox joint. I found a world example but it seems to

Gearbox Joint operation Hello everyone, I am trying to use the gearbox joint. I found a world example but is is seems

Gearbox Joint operation Hello everyone, I am trying to use the gearbox joint. I found a [world example] but is is seem

Thanks for your reply. Unfortunately, this does not seem to work. I tried to load the plugin both from the command line, using the command you mentioned, and the .gazebo file but the result was the same. The clock port does not appear in the list, as I mention on my edited question above.

Hello everyone,

I would like to synchronize Simulink and Gazebo, and for that purpose I am trying to use the YARP clock plugin in combination with the WB-Toolbox for Simulink. However it seems that I cannot load it properly (from myrobot.gazebo file, also using a myrobot.xacro description), as the expected outputs do not appear. My setup includes ROS Kinetic and Gazebo 7.

Has anyone ever used this plugin successfully? Also is there any other way I might achieve synchronization ?

EDIT: Sorry for not clarifying these in the first place. This is the YARP clock plugin (https://github.com/robotology/gazebo-...) and this is the WB-Toolbox (https://github.com/robotology/WB-Toolbox), although the problem seems to originate in Gazebo. The myrobot.gazebo part where the plugin is loaded looks like this:

<gazebo>
    <plugin name="gazebo_clock" filename="libgazebo_yarp_clock.so" />
</gazebo>

This is a possible source of error as I have not found a similar example so I am not sure this is exactly how the plugin should be loaded.

As for the debug process, I have loaded the plugin both from the .gazebo file and using the command line, as MSI suggests below, however the result is the same. When I use the yarp name list command, the /clock port does not appear in the list. The result is that when I run the Simulink counterpart with the simulation synchronizer block I get an error message, mentioning that the block could not connect to the simulation clock server.

I totally agree with you. It's just that if gazebo is using the friction model (a) on the image I included above, there will be no difference between static and kinetic friction. If this is true, the term is, as you mentioned, used incorrectly. I am going to run some simulations to find out how the parameter is implemented. Hopefully I will be able to post some results later.

Finally, I am not sure about the identification. What you are saying could be true (matching just the one case I am working on and not every case). However I can not comprehend how this could happen, and how can the physical parameters be correct for one senario and not for another.

Static friction parameter could affect the final angle of the free fall, depending on the friction model that is used. Consider the following image (case a). After the motion starts there is a constant opposing force that could stop the link earlier. If we add the viscous damping we would end up with something like case b. However I can not understand if the static friction parameter inserts a model like b (so there is no need to add additional damping) or a. http://i.stack.imgur.com/Cb2fN.png

First of all, thank you for the time you took to reply. I know about the steady state error, although in my case integral control is not really useful as the movement has to be very fast (about 200-300 ms). The integral term would not have enough time to "load", thus a large I gain would be required - not recommended. I could increase P but i was trying to see how the gains I am using in the real system would work on sim.

Hello everyone,

i have modeled a real joint that I am using in Gazebo and I am currently trying to set up the parameters (damping, static friction). I let the real link fall from an initial angle only under the effect of gravity and tried to match the response of the model. I achieved that, with parameters close to those I would have imagined (damping = 0.005, static friction coefficient = 0.64). The real and the simulated link stop at the same angle (non-zero, because of the friction and the damping) and fall for the same amount of time.

The problem appears when I use the ROS pid controller. When I give a setpoint to the simulated link, its response is very strange (I have attached a picture). X axis depicts time in seconds and Y is the joint angle.

If I change the static friction coefficient the only thing that changes is the settling time and not the steady state error, which strikes me as weird, as in the case of the free fall this parameter defined where the leg would stop. If i set it to zero the response is realistic but the steady state error is smaller than the real one (that is the reason I used the static friction in the first place).

If anyone could assist me I would greatly appreciate it. If I have not expressed myself clearly or any further clarification or information is required please do tell me.

Thank you all in advance.