Morning,
In a project I have to build a simple vehicle model with 7 DoFs (may be 30 DoFs in future): 3 translatories and 3 rotations in XYZ + 1 DoF of 4 wheels from spring damper in Z-axle.
Using V-Rep Pro EDU, Bullet (sometimes compare with Vortex without license).
I'm now focusing on spring damper:
1, in V-Rep model library there is a "spring damper" model with PID controller: P=50, D=250. My supposition is, P-part and Max.torque/force are the parameters for a coil spring otherwise D-part and target velocity for oil damper. Am I right?
2, based on this model two curves could be easily shown on floating view with graphs: joint force and joint position(Z) to time. After the stabilization time (1,5s) the system keeping "jumping". The signal error are about 0,41N (5,7% to bottom plate / 20% to top plate + sphere) in force curve and similar in position curve by simulation time step dt=50ms; if dt=10ms, the error "jumping" force enlarged to 1,5N. Is this a discretization problem or physical problem? Is it related to friction in damper?
3, an individual spring damper model was made with two nonlinear equations: nonlinear coil spring and nonlinear oil damper. This "jumping" problem still exists.
4, if I set the bottom plate as "static", the system would not "jumping" anymore; or I set a weight of 50000kg, the "jumping" force is very small. But considering the real situation, wheels have weight about 20kg and they are not static.
5, if system is simulated with Vortex, the error could be smaller, but still exists.
What leads this problem actually at all? and could it be solved?
Cheers,
Ji
Spring Damper - vibration error?
Re: Spring Damper - vibration error?
Hello,
Refering to the spring-damper in the examples folder, we can indeed notice vibrations with the Bullet engine, but ODE and Vortex do not vibrate at all. Can you confirm this?
Are you using default time steps? (i.e. 50ms for the simulation loop and 5ms for the dynamics loop)
The relationship between the spring constant k and the P parameter of the PID controller is explained here.
Cheers
Refering to the spring-damper in the examples folder, we can indeed notice vibrations with the Bullet engine, but ODE and Vortex do not vibrate at all. Can you confirm this?
Are you using default time steps? (i.e. 50ms for the simulation loop and 5ms for the dynamics loop)
The relationship between the spring constant k and the P parameter of the PID controller is explained here.
Cheers
-
javl0p
Re: Spring Damper - vibration error?
I know this question was posted more than two years ago, but this might be useful for future readers.
I had the same problem, my springs kept on jumping in a rather random way. Make sure you set the parameter target velocity (Scene Object Properties --> Joint Dynamic Properties) to zero. In my case, the vibration issue was solved like that.
Also, try setting smaller time steps, and ODE instead of Bullet engines.
I had the same problem, my springs kept on jumping in a rather random way. Make sure you set the parameter target velocity (Scene Object Properties --> Joint Dynamic Properties) to zero. In my case, the vibration issue was solved like that.
Also, try setting smaller time steps, and ODE instead of Bullet engines.