When the mecanum wheels came out, there were a number of threads and arguments about whether or not they negatively affected performance as in driving speed and torque. From my experience, they do not seem to make much of a difference in these areas, with the main disadvantage being that they cannot be chained together while maintaining holonomic capabilities. However, strafing with the mecanums requires much greater torque than driving or turning, and our high-speed 393s can trip breakers while strafing with our ~20lb robot. However the mecanums do have other advantages, like being able to turn from the center of the robot without being pushed to the side easily like a robot would be with four omnis.
Does this match up with your experiences with the mecanums? Have anyone, unlike us, noticed the rollers slipping and dissipating any energy while the robot is driving straight?
Our Mecanum wheels line up exactly with what you said. They don’t seem to significantly affect torque or speed. The main issue we have had though is that the wheels are very sensitive to weight distribution, in terms of the strafe acting correctly. Other than that, I really like them and consider them one of the overall best drive train options available.
Of course if we had locking and angle control Mecanums… then they would truly be perfect
I drew up a way to mechanically combine holonomic wheels on each side, but it requires a differential per pair of wheels. Also, it’s very theoretical. I’m not sure if it works during diagonal maneuvers.
The differential mecanum drive is cool and all, but isn’t there a much simpler 6-wheel, 6-motor mecanum chassis you can build? Just have a mecanum at each corner of the robot, and a large omni in the middle of each side. You use all six wheels/motors for driving forward, backward, and turning, but you use only the mecanum wheels for strafing. Technically not as effective as a differential drive, but it’s certainly simpler to build and less prone to mechanical issues.
I think your idea would work. But like you said, not for moving diagonally. You can however, fully power 4 mecanum wheels (forward, reverse, turn, strafe, and diagonal) with only 3 motors using a double adder-subtractor. It requires 4 differentials though. This video demonstrates what I mean. As you can see, it’s VERY complex.
I suppose if you wanted every wheel to contribute to every motion, you could have the omnis be at 45 degree angles like an X-drive couldn’t you?
My team is currently using Mecanum, and we are very satisfied with them. We are using a 4 393 drive geared 2-1 with a robot thats about 17lbs. As far as power issues, we had none at all. We did at first have a problem with weight distribution because a lot of the weight was distributed towards the back. But while the arm is in its home position, we strafe just fine. However, when the arm is raised, we tend to go in a semi-circle path, So we just avoid strafing while the arm is up. If anything, its better than having any other type of wheel
I think that spells issues for driving straight, since you need the omnis and mecanums to spin at the same speed. Plus, you’d probably want to use the 4" omni wheels, and those are kinda wide to put tilted 45 degrees in the middle of a robot.
Forward-facing, independently powered 4" omnis seem (to me, at least) to be the simplest, though maybe not the most power-efficient, way of making a 6-motor hybrid mecanum drive.