I’ve thought a bit more about my model and I think that instead of a conveyor belt, a hollow cylinder the inside of which depicts zodiac/ecliptic and which can be spun on the X axis using a single motor (DC or continuous rotation servo, I don’t know) will be so much better. This way, the motor does not have to be bi-directional either.
The model Saturn and the camera will be housed inside the cylinder. The shape of the cylinder and the width of an annual depiction can be controlled to calculate motor speed(s). I can’t believe how simple this seems. Rob?