Hey,

I got a motor model based on the following equations:
J * ddot(theta) + b * dot(theta) = Kt * i - T
L * d/dt(i) + R * i = v - Ke * dot(theta)
where 
dot(theta) : first derivative of motor angle
ddot(theta): second derivative of motor angle
L: motor inductance
R: motor resistance
Kt: motor constant
i: current
Ke: back emf constant
b: motor damping
J: motor inertia
T: effective torque output
v: motor voltage input 

If i now use, for example, a simple mass test object, and I run the simulation, then everything work perfectly fine.

Next step is to add a pitch n=0.0016 to the motor. So now we substitute in the equations above:
 theta = 1/n * x
F = 1/n * T

If I now run the model, Ill get an error message because the integrator in my model grows to fast.  Of course the problem is the big factor 1/x = 630. 

Is there a way of solvign this problem? I think this is a common scaling problem or something that should be solvable?

many thanks in advance.
Bob