I’m sure this has already been brought up somewhere, but VEX-official mecanum wheels would be awesome. Our team would really love to use mecanums so that we have room for an intake system underneath while still being able to strafe.
I actually preached one of the Vex engineers ears off about a mecanum at the 2008 world championship. I think one day we’ll see it but right now the focus is on the new electronics.
-Cody
New Mecanum wheels would be awsome. For most applications the Omni wheels arn’t that usefull, unless you are doing some forms of skid steer rather than 4WD.
Can someone please explain to me the advantages of mecanum wheels over a good old holonomic drive with regular omniwheels? I really can’t see the difference in performance.
Say you want to drive over a bump AND have a holonomic drive, (this years FIRST competition Breakaway) you’d need a mecanum drive. A mecanum drive also frees up space on the robot chassis, esp if you want to place a mechanism up front (ball grabber, kicker, etc.)
Technic-R-C
The disadvantage of Mecannum wheels is that they don’t have as much traction (grip) as other drive trains do
Packaging in competition robots. Mounting omniwheels at 45-degree angles on the corners of a square robot narrow the possible opening for acquiring game objects at floor level. Mounting mecanum wheels in the traditional fore-and-after orientation allows another inch or two of room between the front wheels which can be critical in designing a competition robot, especially in a game like Clean Sweep which has large game objects.
Realistically, mecanums only save you a few inches of width inside the robot. Your grabber mechanism would have to be as wide as the robot for there to be a problem, and if it is, move it forward some more and balance the back of the robot. Jeesh, there’s not really a problem here in the first place with regular omnis, I think people are just getting lazy. An omni drive should be able to go over a bump, the one I made did. Mecanums also have low traction… so I personally see no advantages (except for saving a few inches of width, which aren’t that crucial anyway).
Well this year, the largest game objects are about 9.5" wide. Giving yourself an extra inch on both sides means you need 11.5". When the large omnis are 4" wide, mounted at a 45 degree angle means 5.6" for the two sides, excluding the metal, motors necessary to mount it; if you wanted a shaft encoder or gearing, it’s even more. In other words, it’s cutting 18" close…
Also, you get more torque moving forwards and backwards. (parallel to the mecanum wheels)
- Mount the encoders on the inside of bot, not outside
- You can change the angle of the omni wheels to adjust for more speed and torque in a particular direction. Turning might have a little bit of skidding to it, but hey, I don’t see those meccanums moving sideways very quickly. Ups and downs…
Alright guys, I’ve been reading through this subject and it seems that there is a lot of misunderstanding about mecanum wheels here. Mecanum wheels work by applying a force on a 45 degree angle in the direction of the rollers. This means by drawing out the applied forces, breaking them down into their X and Y unit vectors and canceling out opposing forces, you can predict the direction and speed in which the robot will move. By doing this, you learn a few things about them. You learn there is a loss of power while strafing(you get about 70% in any direction by taking the sine and cosine of 45 degrees), but that is IDENTICAL to that of a traditional 4 omni wheel setup. This also means that you can strafe in any direction with that 70% power, regardless of the direction(forwards, backwards, left, right, diagonally or anything in between) allowing for the same speed and torque in all directions. The coding for the Mecanum system can also be identical to an X style holonomic drive system. From my experience, a well designed mecanum drive train can result in a drive package just as compact as a standard holonomic drive train, however, because they can be mounted in a standard aligned 4 wheel drive setup, they do usually end up being slightly easier to work with even though they can be wider than a standard wheel. If there are any questions about this, feel free to contact myself or any other member of KTOR, we are all very experienced with mecanum wheels and would be glad to help in any way we can.
Hmm, i thought to drive diagonal with mecanum you only power two of the four wheels…?
These two statements are not consistent.
the following points are based on theoretical analysis of 4-wheeled mecanum and 4-wheeled omni (45 degree) vehicles using properly designed wheels (especially properly designed roller assemblies which have low bearing friction under axial load):
for a given torque supplied to the wheels, you get the same force for a mecanum vehicle in strafe as in fwd/rev.
for a given drive torque tau on the wheels, a mecanum vehicle has a total pushing force of 4tau/r in the fwd/rev and strafe directions, and 2sqrt(2)*tau/r in the pure diagonal direction (in pure diagonal, only two wheels are driven)
a mecanum vehicle has the same pushing force in the fwd/rev direction as a standard-wheel vehicle being driven with the same wheel torque. the mecanum vehicle will however lose a pushing match with a standard-wheel vehicle. the reason the mecanum vehicle loses the pushing contest is because it loses traction at a lower total vehicle force level than the standard-wheel vehicle does, because the reaction forces at the contact interface between the floor and the mecanum rollers is higher than the reaction forces at the contact interface between the floor and the standard wheel, for the same vehicle force. this is true even if the mecanum and standard wheels use the same tread material.
for a given wheel rotational speed omega, the mecanum vehicle has the same fwd/rev and strafe speed, namely omegar. the pure diagonal speed is omegar/sqrt(2) (in pure diagonal, only two wheels are driven)
assuming sufficient floor traction, a mecanum vehicle outputs 41% more total force (in any direction) than an omni vehicle whose wheels are each being driven with the same torque as the corresponding wheel on the mecanum vehicle.
an omni vehicle goes 41% faster (in any direction) than a mecanum vehicle whose wheels are each being driven with the same rotational speed as the corresponding wheel on the omni vehicle.
for detailed analysis of mecanum kinematics and force, papers can be downloaded here:
Quit bring back a dead, old topic! Raww. And btw, where are the mechanum wheels?
JVN, make my day, pleassssssseeeeeeeeeee!
-Cody