Why is there no friction when the joint is actuated ?

Hello,

I am currently modelling a simplified mobility system of a rover. It has 6 wheels and a body (see image).

I would like to model the rover moving in the sand, to do so I would like to generate continuous high friction while it moves.

However, the frictional force is nul (see image) and become non-nul when the joint stops being actuated (at 5s). Please ignore the first second as the rover spawns above ground and falls which creates high friction.

Finally, plese find below the driveline used. If that can help, the 6 converters are in serie.

Answer 1

[Steve Miller]

Hi Hugo,

The friction law for the Spatial Contact Force block has highest friction near (but not at) zero relative speed between the two bodies it connects. The spike you are seeing in friction force is as the wheel slows down, just before it stops slipping relative to the road.

You may be trying to model rolling resistance. To do that, simply apply a damper across the R and C ports of your Rotational Electromechanical Converter. This will model the resistance the motor encounters as it is trying to fight its way through the sand. This friction will not be measured by the signal you are currently measuring.

If you need a custom friction model at the interface of the wheel and the road, you can create custom force laws in Simscape Multibody. This File Exchange entry includes an example of a disk spinning and slipping on a surface where the coefficient of friction varies based on position. You can create your own friction law.

https://www.mathworks.com/matlabcentral/fileexchange/109680-spatial-contact-force-examples-simscape-multibody

--Steve

[Hugo CASTAING]

Thank you Steve ! It's very clear

[jams]

Thanku so much.