I understand that you are trying to differentiate your position signal to get a velocity signal and then feed that into a velocity source, but you are getting drifted position due to small inaccuracies.
While using the derivative block, the model needs to follow a specific set of guidelines which are mentioned in the below link and if not possible there are certain alternatives mentioned to reduce the number of inaccuracies which are observed in the results –
Also, try implementing a feedback control system that uses a PID controller to ensure the position tracks the desired trajectory by comparing the actual position with the desired position and adjusting the velocity input accordingly.
For further information, refer to the documentation links below:
