Mecanums: Let's Settle This

There’s been a lot of arguing around here about whether the rollers on Mecanums spin and cause a loss of energy when they’re driving forward. Has anyone tested the mecanums out in great detail to effectively confirm or deny this?

If not, I have an experiment to propose, so see whether the rollers are spinning during forward or backward motion on a normal setup:

  1. Build or obtain a mecanum drivetrain.
  2. Put a small, white mark (maybe a piece of teflon tape) on one of the rollers.
  3. Drive the robot forward, and see if the white mark moves. If it does, the rollers roller is spinning; if it doesn’t, then the roller is not.

I want to see this mecanum argument settled once and for all.

I hate to say it, but isn’t this obvious? The wheel just acts as a normal wheel. The rollers have no reason to roll. There is no way the rollers could roll while the wheel is spinning that would result in only forward movement (I think). Also, the method of the tape probably won’t work properly, because as the rollers leave the ground, and make contact with the ground, they are probably spun a little.

EDIT: Actually, to test this, simply put a wheel on a shaft and spin it. Lower it onto the ground. You should be able to see that the wheel moves back and forwards normally, and any movement of the rollers results in sidewards movement.

The arguing has already happened. What The VEX Raptors wants to see is an empirical proof video with a VEX mecanum wheel drive.

Would you want on the wheel or the side of the wheel/cone to be marked? Would a marker work just as well and not affect the wheel’s interaction with the ground?

What about using a go-cam mounted off to the side to look at the wheel as it spun?

Experiment 1 - forward drive
Expeirment 2 - 20 degree right drive
Experiment 3 - 45 degree right drive
Experiment 4 - 90 degree right drive
and so on and so on. Maybe put an LCD screen showing the experiment number to help

I’m just thinking a small piece of teflon tape on one of the green rollers, on a part of the roller that’s not touching the ground. This will show visual proof of whether or not the roller is spinning.

My team might try this experiment at our meeting tomorrow. If we do, I’ll post the results here.

@Telemascope: You could test it with one wheel, but I’ve tried spinning one wheel alone, and it has a tendency to move diagonally on its own. With a full drive, this diagonal motion is canceled by the other wheels. I don’t believe myself that the rollers spin, but theory and practice are completely different. I want empirical proof.

In theory the rollers should spin. When Mecanum wheels roll, there is a force exerted on each roller that has a component not parallel to the axis of the roller so they should spin. It will be interesting to see if they really do.

There is indeed a force on each roller that has a component not parallel to the axis of the roller. However, you forget that on the other side of the robot there is another wheel with rollers at 90 degrees to these rollers. And hence the component of force that is not supported by one roller will be supported by the one on the other side. So the rollers do not spin at all (on an ideal surface with no slippage).

I don’t have a video, but I did a small experiment with our prototype mechanum robot. The ‘rollers’ sometimes have markings or seams. I aligned the seam in a obvious orientation and rolled the robot manually a couple revs, each time the roller I had noted came around the roller was in the same orientation. Not as good as a real drive test, but put me on the side of they don’t roll.
Cheers Kb

While it does not directly address the OP, I believe this video does answer some questions and misconceptions about mecanum wheels.

I saw that video, and I liked it. It was very useful in convincing a teammate of mine that we should use mecanums.

Mecanum wheels will spin if enough torque is applied to them but i don’t think the vex system gives you enough torque (even with 10 393’s) to overcome the mecanum wheel i honestly wouldn’t worry about it you saw the pull off they hold there ground and even if they did slip the slightest bit it wouldn’t effect your drive in a noticeable way. but thats just my take on it.

Any wheel will slip if you give it enough torque.
The difference with Mecanum wheels is that they only need 71% the torque to slip, because the rollers are at a 45-degree angle. The force of friction is therefore 141% the force the motors apply to the wheels, which leads you to that 71% (because 1/1.41 = .71 ).

I think if the rollers move or not doesn’t matter, as long as you go straight.

ummmmm…if your drive train doesn’t go straight…uhhhh…you’re doing something wrong. THe argument is whether the inefficiency is worth the ability to strafe and or is there any inefficiency at all

If a tree falls in the middle of the forest, and no one is there to hear it, does it make noise?

*I am joking.

The rollers indeed do roll when we strafe. last year using them I’ve looked closely at their movements and when I strafed the robot the rollers were still spinning when I stopped and looked. The rollers are not useless because they are the only thing making the mecanums strafe.

This question is null on its face. The premise is that existence is created by perception; if nobody was there to perceive the tree falling, it never existed in the first place.

Of course they roll when the robot strafes. My question is, do they roll when the robot is driving forward or backward?

A little more on the side of the actual use of Mecanum wheels

We had them on our NZ style bot this year with the 393 motors with high speed internal gearing. We found that because of our weight distribution we would constantly tear up our motors internal gears. Because of that we opted to switch over to omni wheels because we could fit a chain between the two wheels. This kept us from tripping our breakers (when we weren’t in pushing fight) and also kept us from breaking our internal motors.

One of the most dramatic changes to our robots speed when we switched from Mecanum wheels to omni wheels is that our turning speed went way up. I believe that you aren’t loosing any of your force using Mecanum wheels to move forward and backward but you might be when you are turning.

This is just from observation and not from anything necessarily back up.

Were the wheels oriented the correct way? The rollers on top of the wheels should be pointing toward the center of the robot. If they aren’t, turning won’t really work. When turning, you shouldn’t have any less force with Mecanum wheels than with omni wheels.