Problem with the physics of the distance traveled by a robot
Kakkonto
Hello everyone,
Thank you so much for the development of Chrono. I have always used the dynamics simulation. I am asking again because my previous question has not been resolved.
I have been struggling with the discrepancy with real phenomena for a long time and would like to ask you a question.
Currently, I am running a simulation with a robot of my own design built in. The structure is based on the curiosity of the robot. The model of the robot is not very relevant, but in addition, I am using the robot model that I use in my own research.
The terrain is based on SCM and NSC, and the robot was moved.
When comparing the distance traveled when advancing a certain time and the theoretical distance traveled derived from w (rad/s) measured from the angular velocity of rotation, the NSC worked fine and the theoretical value > the measured value.
On the other hand, for SCM, the theoretical value < the measured value.
The parameters are the values of the parameters used in Demos curiosity, which are somewhat valid.
What could be the cause of this?
Also, oddly enough, when I decrease the value of K_φ, the sink should become smaller in terms of the SCM model. However, the sinkage became larger.
I would appreciate it if you could tell me what could be the cause of this.
I am very troubled. Thank you in advance.
Kakkonnto
Dan Negrut
Kakkonto – thanks for your message.
Is k_\phi the frictional modulus of the soil? If this is smaller, the sink should be larger – at least that’s what my intuition tells me. If the same pressure needs to be obtained and k_\phi is slightly smaller, the z value should be slightly larger.
About SCM: what happens is you increase the resolution of the terrain? If you have a finer grid for the terrain, that is.
You are comparing \omega r t with the distance travelled by the wheel. You say “theoretical value < the measured value” – how big is this difference? Is it 1%, 10%, 50%, etc. Also, over what distance has this difference been noted? Has the vehicle moved a bit, or a lot before you noted this difference?
Also, what experiment did you run? You mentioned that “the robot was moved.” Was there some constant angular velocity applied to the wheels? If so, which wheels? Also, the Curiosity rover has an odd topology. Could you run the same SCM experiment with the VIPER rover model? Let me know if you don’t have a VIPER model – we can help with a replica.
Thank you,
Dan
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Bernard A. and Frances M. Weideman Professor
NVIDIA CUDA Fellow
Department of Mechanical Engineering
Department of Computer Science
University of Wisconsin - Madison
4150ME, 1513 University Avenue
Madison, WI 53706-1572
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Radu Serban
Better yet, please provide an example reproducing these issues that is based on a Chrono demo and model. That will make it a lot easier for someone else to debug and provide an answer. You could use one of the rover models (the Viper is already available in Chrono, including a demo of that rover on SCM terrain). Even more useful would be to try to reproduce these issues using the single wheel test rig we have available (use a rigid tire with the geometry of your rover wheel); see demo_VEH_TireTestRig.
--Radu
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