Dynamic simulation of Caterpillar tutorial

Typically: "How do I... ", "How can I... " questions
Post Reply
Satoshi
Posts: 2
Joined: 21 Jun 2017, 09:46

Dynamic simulation of Caterpillar tutorial

Post by Satoshi »

Hello, I am working on modelling of caterpillar vehicle. I used "Caterpillar tutorial" to simulate turning motion. I found strange turning vehicle motion from simulation result. the input was both side of caterpillar velocity. I did simulation with constant value(low speed) for velocity of one side and zero speed for the another side. I expected that turning trajectory was ideal circle and centre of circle does not move. however, result showed that the trajectory was not ideal circle and centre on the circle moved to certain direction. I guess results is wrong. do you have any advice to improve it?

coppelia
Site Admin
Posts: 10339
Joined: 14 Dec 2012, 00:25

Re: Dynamic simulation of Caterpillar tutorial

Post by coppelia »

Hello,

the problem is probably necause your caterpillar is hyperstatic: it has probably at least 4 parallel cylinders. But since we do not have compliance in those cylinders, the contact points can jump from one location to another. The solutions to that problem are:
  • Try with a different physics engine
  • Try to adjust the physics engine's properties for the cylinders (or the floor), so that they appear softer
  • Try to adjust the cylinder's physics engine properties, so that they don't appear that rigid
  • You can also always add some auxiliary prismatic/revolute passive joints, that remove the hyperstaticity
Cheers

Satoshi
Posts: 2
Joined: 21 Jun 2017, 09:46

Re: Dynamic simulation of Caterpillar tutorial

Post by Satoshi »

Hi coppelia,

Thank you for your answer. I have additional question.

-Try with a different physics engine
I tried to use all physics engine, but situation was same. additionally, when I use Vortex, tuning trajectory was not ideal circle. I think it should be ideal circle because tutorial model is symmetrical. where do you think it is coming from?

-Try to adjust the physics engine's properties for the cylinders (or the floor), so that they appear softer
-Try to adjust the cylinder's physics engine properties, so that they don't appear that rigid
please let me know how to adjust physics engine properties to make the contact softer?

-You can also always add some auxiliary prismatic/revolute passive joints, that remove the hyperstaticity
why do you think the auxiliary passive joints can remove the hyperstaticity?

Satoshi

coppelia
Site Admin
Posts: 10339
Joined: 14 Dec 2012, 00:25

Re: Dynamic simulation of Caterpillar tutorial

Post by coppelia »

This really depends on how you modeled the caterpillar. Maybe you can post the scene?

You can adjust the material properties of the cylinders. You will have to play with the various parameters, for each physics engine (e.g. for ODE, try to adjust the CFM: shapes will sink a bit into other shapes)

You can also avoid hyperstatic situations by adding additional spings and masses, as was done in the example model Models/examples/simple ackermann steering.ttm.

Cheers

Post Reply