# Body CS in SimMechanics

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Marco De Simone on 10 Jun 2013
Is it possible to have CS coordinates in a Body block of SimMechanics 1st generation, that depends from a parameter?
For example
CS1 = [L*sin(teta) L*cos(teta) 0]
Thanks for your time and help.
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Marco De Simone on 10 Jun 2013
Hi Ryan, thanks for your help. I need to be able to change the cs of a body as the simulation starts. In other words my x and y must must not be costants but variables x= x(input parameter) and y= y(input parameter). Hope you can help me.

Ryan G on 11 Jun 2013
Well if you change at the very start of simulation a parameter should work, where you define it in your workspace. So CS1 would be a variable, x, and CS2 would be a variable y. Where x and y are defined in your workspace.
If that doesn't work, what is the error you're seeing?
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Ryan G on 12 Jun 2013
You could try using a point curve constraint. This would allow you to define a trajectory that the other connected body is allowed to follow. There are similar blocks that may be more applicable in the constraints and drivers sublibrary.
Can you elaborate on what your design challenge is here? The current way you are trying to do this is not possible (changing CS points while simulating) but that doesn't mean there isn't a way to do it.

Marco De Simone on 12 Jun 2013
Hi Ryan G. I'm trying to replicate, through the application of a force field on a wheel, pure rolling. Instead of using the already known blocks from the Contraints & Drivers sublibrary or using appropriate combination of forces and torques to replicate the condition of pure rollingwanted to use the fields of forces in the point of contact. So my goal is to apply a force field at the contact point between wheel and plane. To do this I needed to be able to vary the coordinates of the point as a function of time and angular velocity. Thanks a lot
Ryan G on 12 Jun 2013
Have you considered the gear constraint where the radius of the base would be the radius of the earth? You can also model a rolling wheel with simulink and connect the forces from rolling to the simmechanics model. If you wanted to model the actual forces of the wheel (braking/accelerating like in a car) then you would would need to model the contact friction curve as well.

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