[buchanan]

Mecanum drivetrains, like every other, have advantages and disadvantages, but some of the disadvantages being discussed here are overstated and/or misinformation.

Even weight distribution is optimal, but not an absolute requirement for straight driving. So long as each wheel has sufficient loading for sufficient traction, it will go the way it's supposed to. The problem only arises when you're at the limit, trying to get more acceleration/deceleration/pushing force than the wheels can transmit. This is true for every drivetrain, though holonomic ones are generally to be more sensitive to it and have more interesting behavior when it happens. The better the weight distribution, the higher the limit, but until there's slippage behavior stays correct.

Concerns about non-flat surfaces tend to be exaggerated for two reasons. One, it's not quite true that loss of traction on one (or even two) wheels guarantees incorrect behavior. The effect of traction loss varies between nothing and complete failure to move, depending on which wheels lose traction and what motion is being attempted; in practice it's usually something in between. Two, this criticism assumes an infinitely rigid chassis. Even if you could make such a thing, it's a basic of holonomic drivetrain design with >3 wheels that you don't try. In practice, even without intentional flexibility/suspension, a basic kitbot type frame has all the flex necessary to keep things like tower base plates from being problems.