Omni Wheels or Mechanum Wheels?

Omni Wheels or Mechanum Wheels?
Which one seems like the best one?

@Supernova Please do not make the same post multiple times on the forum. It clutters it up and makes it hard to navigate. As far as your question goes, it all depends on what kind of drive train you have. This thread has good examples of drive trains: https://vexforum.com/t/best-drivetrain-for-starstuck-poll/35058/1

@wheresmyallen please stop spamming. It’s not funny. @DRow please help.

To answer the question - what are you using the wheels for?

Do you want to strafe and move forward with roughly equal speed, acceleration, and torque in those directions? Do you want to rotate and translate well at the same time? If so, that’s what mecanum wheels do.

Do you not care about strafing? Then there is no benefit to mecanum wheels, and some combination of omni and or / traction wheels will make you a tank drive.

Do you want to strafe, but with most of your torque and acceleration in the forward direction, yet with some ability to go side to side? An H drive is worth looking into.

Efficiency wise, omni wheels are lighter and the movement relies less on the rollers movement. That said, if your drive is high torque, mechanum drives can have better traction in the straight (forward back) axis.

@Chris is me We are using this for the Starstruck competition… We needed to see what kind of wheels would be better for moving fast, but not sliding.

My new favorite is the medium sized omni wheels for holonomic drives. Part 276-3526

Best blend of torque and speed for most robots. If you can apply more motors to your drive then the larger omni wheels will work well.

http://www.vexrobotics.com/media/catalog/product/cache/11/image/5e06319eda06f020e43594a9c230972d/2/7/276-3526-hs-shaft_1_1.jpg

If you have no interest in moving side to side, then you don’t want mecanum wheels at all. You want a combination of omni wheels to assist with turning, and traction wheels to prevent your robot from sliding / drifting when it turns or is hit (if this is something you want to prevent). A popular solution is 4 omni wheels on the outside corners and 2 traction wheels in the center.

“Speed” is a function of both wheel diameter and gear ratio. Top speed and acceleration are also optimized through different means - you get better acceleration with a higher gear ratio, at the expense of top speed, or more motors in the drivetrain (adds power to the whole system). There are diminishing returns on this acceleration, and this depends on factors like your robot’s weight, etc.

If you have no interest in playing with gear ratios for your drivetrain, and you’re just plugging the motors directly into wheels and you don’t care about anything else, the bigger your wheel the faster your top speed will be. Because motors move at a fixed RPM, a bigger wheel moves a greater distance per rotation. A bigger wheel also provides less force to move the robot, which can hamper acceleration. If you adjust the gear ratio of the motor with a small wheel so it moves at the same speed as a big wheel, it will also have similar force / acceleration - gear ratios and wheel sizes are both means to the same end.

Hope this helps and isn’t too confusing. If you need a starting point, lots of teams seem to like four motors, with high speed gearing, running 6 4" diameter wheels. Experiment from there and see what the results are; or do some math to learn how gear ratios and robot speeds change when you alter these variables.