Model Blows Up during Dynamic Simulation

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Astronirav
Posts: 10
Joined: 03 Jul 2017, 06:00

Model Blows Up during Dynamic Simulation

Post by Astronirav »

Hello,
Recently, I created a mock-up of NASA's ATHLETE Moon Rover in V-REP. I created the rover in Solidworks and made a Dynamic Model in V-REP by importing it. When I tried to simulate it, it just behaved in a weird way and blew up (literally!). Here's a video describing it: https://drive.google.com/open?id=0B65Re ... EhFNDMtZUk

I have followed the 'Hexapod tutotrial' and 'Building Clean Model' from the documentation. I have also made sure that the underlying shapes are convex/primitive, here's an image showing that: https://drive.google.com/open?id=0B65Re ... C0zMDlJa2M

What can be possible cause of this and how can I make it behave normally?

PS: I can provide you with the original scene if you want.

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

Re: Model Blows Up during Dynamic Simulation

Post by coppelia »

Hello,

yes, it would be helpful to post the scene file.
I suspect one (or several of the following) happening:
  • adjacent dynamically enabled shapes collide with each other. You can avoid this by playing with the local respondable masks for each of the shapes. Make sure that the model base is flagged as model.
  • the masses and inertias of the dynamically enabled shapes might be too small, or might have a too large ratio. Make sure to read the design considerations 7 & 8 here.
  • the motor controllers might be too stiff
Cheers

Astronirav
Posts: 10
Joined: 03 Jul 2017, 06:00

Re: Model Blows Up during Dynamic Simulation

Post by Astronirav »

Thanks for your reply!

Here is the link to the scene file:
https://drive.google.com/file/d/0B65Reb ... sp=sharing

I tried tinkering with the Mass and Principle Moment of Inertia values but it still behaved the same way.
I have applied the same local respondable mask to all the elements of the robot.

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

Re: Model Blows Up during Dynamic Simulation

Post by coppelia »

if you enable contact point visualization, you will notice that almost all links collide with the other links. And you cannot simply apply the same respondable mask to all links, since they would still collide with each other. You need to apply mutually exclusive masks for adjacent links (or for links that are very close to each other. I recommend that you have a look at some of the serial manipulators and how their respondable masks look like.

Cheers

Astronirav
Posts: 10
Joined: 03 Jul 2017, 06:00

Re: Model Blows Up during Dynamic Simulation

Post by Astronirav »

I think the model is now stable; I have replaced all the colliding links and set respondable masks correctly. But when I simulate the model, it falls down to the ground. It seems as if the joint torques are not able to carry the base (hexagonal ring) of the rover. I have kept Max Torque Value relatively higher (1000) and Mav Vel Value (360 deg/s) but still it is not able to carry it. I tried increasing the joint torque value to 4000 (which I think is okay to lift the base weighing ~4 Kg). What can be the problem now? I think the biggest suspect here is joint torque, is it true? How can I solve it?

In the video, I am trying to gently put the rover down. Please download if it doesn't play.
Video: https://drive.google.com/open?id=0B65Re ... 3BHcDZqRm8
Scene File: https://drive.google.com/open?id=0B65Re ... kZWTF9hd2M

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

Re: Model Blows Up during Dynamic Simulation

Post by coppelia »

You have a mistake in your model: the first joints are attached to shape ATHLETE_Base which is a static shape. You should attach them to ATHLETE_Base0, which is dynamic.

Cheers

Astronirav
Posts: 10
Joined: 03 Jul 2017, 06:00

Re: Model Blows Up during Dynamic Simulation

Post by Astronirav »

Everything works fine! I can't thank you more :)

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