Hello everyone,i have a problem with assembling a gear with  rack on both upper side and lower side.You can see the picture i attached.

What i want to do is changing the eccentricty by the two driving gears.And the two driving gears is mated with a cylinder with both side rack.

When i put 2 rotation the same speed same direction,the cylinder will rotate with the 2 driving gear.And theoretically, the cylinder would not occur relative motion.

with the 2 driving gears.However the result is opposite.And the animation is discrete and so weird.