Need help to let omni robot rotation around 1 point

[danzhilan]

I made a robot by 4 omni wheels on each sides.
I want to the robot rotation moving around 1 point. The radius can be controlled by the variate. I know the equation for the X and Y axle distance is X?+Y?=R?. But I cannot change it to the velocity of omni wheels at X and Y axle.
Is there any example or idea about it?
Many thanks for your help!

[rouncer]

Get the angle from the centre, and then use the tangent of the circle, to direct the x&y of each wheel.

The easy way to do that, is get the difference of the position of the wheel and the centre of the robot/car,  then simply swap the x and y coordinates around.

That should be the x&y's for each wheel.

Heres a picture of what I mean->
https://scontent-syd2-1.xx.fbcdn.net/v/t1.0-9/31749447_649775965370464_2109055660774653952_n.jpg?_nc_cat=0&oh=604e58cd7b9ef48739b67ea38feea573&oe=5B8C27ED

[danzhilan]

Thanks a lot for your idea.