I’ve build robots with X-Drives and with mecanum wheels. Both can be very good if built well. However, the much more critical thing to get right when using any kind of holonomic drive is to have even weight distribution. If you don’t have that, then the robot might move sporadically when accelerating, and be very inconsistent in autonomous.
That being said, X drives are generally better on a function sense, although they take up more space inside the robot, are harder to build, and even harder to build well. In my experience good alignment between all four wheel is key to a consistent autonomous. Also mecanum wheels tend to strafe sideways at about 87% the forward speed due to friction on other losses. X-Drives on the other hand handle strafing much more smoothly and there are much fewer losses due to friction.
If you do build an X-Drive, I would highly recommend making polycarbonate gussets. It’s easiest to cut them on a CNC router I’d you have access to one, but if not they can be cut out of hand with a printed template. If you cut them by hand you should use a center punch to ensure all the holes are perfectly aligned. Using robosource shoulder screws and drill bits as close to the shoulder size as possible will ensure good alignment. I built our X-Drive without shoulder screws and found that the play in the screws was sufficient to skew the drive enough to negatively effect the performance. One other note for CNC cutting polycarbonate, it works very well to use carpet tape or other strong double-sided tape to pulled down the polycarbonate to a sacrificial sheet of wood to hold the parts down when cutting.
(Please ignore the keps nuts and poor build quality)
