This is a classic problem. Gearing to a master actual position will result in the noise of the master being propagated to the slave, and depending on the gear ratio, can even be amplified. This makes is difficult to tune the axis tightly, especially the differential gain and feed forwards.
Some common methods of dealing with this are:
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Filter the actual position
Filtering will cause some delay. If the master axis is a control axis, this can be problematic, since delay causes problems with control, and then the master itself may have control issues. The RMC200 has several filtering options that do not cause as much delay as the filter in the RMC75 and RMC150. -
Detune the slave axis
This is of course not always an option. -
Gear to a smooth target position
If you have the option, always gear to a target position that is generated by the RMC, since it will usually be very smooth… However, when the master axis is in open-loop control, the target becomes the same as the actual, so the same problem can exist, as mentioned in the first post.
There is also certainly a chance the I-PD may work better. It depends on the system.
Another option is to use gearing with velocity and acceleration limits. This means the slave axis will not follow the master exactly, but its motion will usually be smoother. Use dynamic retargeting or the Tracking command, but the Tracking command can be a bit finicky.