How to simulate a belt driven robot with parallel actuator configuration
Hello everyone!
I'm working on the development of the ROS & Gazebo simulation of the 3-DoF robotic manipulator depicted below. The first joint rotates the whole manipulator around the vertical axis 1, while the second and third are those of the "shoulder" and "elbow" respectively. The actuator of the shoulder joint is directly attached to it, while power from the third actuator is transmitted to the elbow through a timing belt.
The problem I'm facing is the following. As mentioned above, the actuator of the third joint is fixed to the base. That results to a system kinematically equivalent to a 5-bar mechanism (parallel/close chain configuration), as the one depicted below (I am mentioning this to further clarify the problem, as it helped me thinking of it this way). Even though Gazebo has a way of dealing with close chain configurations, it cannot be applied in my case, as the dynamic properties of the two systems are not the same i.e. in the 5-bar there are additional inertial phenomena due to the extra links, which are missing from the belt-driven mechanism.
One solution would be to model it as a 5-bar and assign small masses to the extra links, but from what I've seen this isn't considered a good practice.
Has anyone dealt with this kind of problem? I believe that the only way to solve it is with a custom Gazebo plugin (or maybe a custom transmission in URDF?), but I'd like to be sure that there is no workaround first.
Thank you in advance!
