sympy.physics.mechanics

[Peter230655]

I am trying to calculate some system, a disc rolling on an uneven street, in 2D.
gesamt is a curve in the X / Y plane, the shape of the street, dependent on x (an sm.symbol) and two parameters (sm.symbols).
I want to try these kinematic equations:

kd = [u1 - q1.diff(t) - rhs * gesamt.diff(x)]
where rhs is this expression:
rhs3 = (-u1 * r / sm.sqrt(1. + (gesamt.diff(x))**2)).simplify()

However, I get this error message:
cannot add <class 'sympy.matrices.dense.MutableDenseMatrix'> and <class 'sympy.core.add.Add'>

If I replace rhs with, say, sm.S(10.) there is no error message.

I have no idea, what to do with rhs so the multiplication will work.

Any help is greatly appreciated!

[Peter230655]

forget me question.
It was a simply typo on my part!
Sorry!