Grippy Mecanums

[IndySam]

Originally Posted by SuperNerd256

Then why are mecanums considered "low-traction" wheels?

They're not by people who understand them.

In a pure pushing match they perform well. They can suffer from gearing problems because they generally have to be geared high for good speed and are rarely used with shifting gearboxes so they can suffer when it comes to power.

Originally Posted by Kevin Ray

This is because most people who say this are merely miss-speaking. What they are actually referring to is the ability of non-powered wheels to roll. For example if an macanum drive bot were to be pushed from the side (straffing) it would "roll" as though it had no traction.

Originally Posted by IndySam

They're not by people who understand them.

In a pure pushing match they perform well. They can suffer from gearing problems because they generally have to be geared high for good speed and are rarely used with shifting gearboxes so they can suffer when it comes to power.

That makes more sense. Thanks!

[Katie_UPS]

If you look at a mechanum wheel or an omni wheel, they have rollers. They achieve omni-directional movement through the manipulation of force vectors (which Ether will be able to explain far more eloquently than I will). The reason they are considered low traction is because the rollers on the wheels are not powered, and so the robot is resting, essentially, on tiny un-powered wheels, which are far more push-able that powered wheels.

The reason mecanum/omni robots can sometimes win in a pushing match is that if the pushing force is parallel with the axis of rotation, then the rollers aren't spinning (and so as the angle of the pushing force approaches parallel to the axis of rotation, the less the robot can be pushed).

I hope that helps

EDIT: It's already been answered, but I hope that adds.

[jblay]

Originally Posted by SuperNerd256

Is there a way to make a grippy mecanum wheel? I know they are usually low traction rollers, and use those rollers to obtain omni-directional movement, but is there any way to add more traction to the rollers, while keeping the fluid, omni-directional movement?

Thanks!

Make a swerve drive setup.

In all seriousness though the real issues with the mecanum wheels in terms of pushing are this:
-They aren't 100% effective at transferring power, a lot of it is lost. This forces you to have to gear higher to be able to go at a reasonable speed which makes you less capable of pushing. It is difficult to do a shifting gearbox with mecanum wheels because each wheel has it's own gearbox and shifting gearboxes are quite heavy.
-They are easily pushed sideways. They are designed to do this so that you can strafe, but most of the time when pushing is done it is not done front of pushing bot to front of bot being pushed but front of pushing bot to side of bot being pushed.

Hope this helps. As a team that used mecanum wheels last year I would advise against them because when the eliminations roll around and you are facing defense, being able to be pushed sideways easily really hurts your chances and it makes winning very difficult.

Originally Posted by jblay

Hope this helps. As a team that used mecanum wheels last year I would advise against them because when the eliminations roll around and you are facing defense, being able to be pushed sideways easily really hurts your chances and it makes winning very difficult.

Trust me, I'm not going to use those things ever in my 4 years as an FRC student. I'm just curious about them, why they are considered "low traction", and how one could manipulate them to make better traction.

Thanks all!

[rocknthehawk]

Originally Posted by jblay

Make a swerve drive setup.

In all seriousness though the real issues with the mecanum wheels in terms of pushing are this:
-They aren't 100% effective at transferring power, a lot of it is lost. This forces you to have to gear higher to be able to go at a reasonable speed which makes you less capable of pushing. It is difficult to do a shifting gearbox with mecanum wheels because each wheel has it's own gearbox and shifting gearboxes are quite heavy.

Hope this helps. As a team that used mecanum wheels last year I would advise against them because when the eliminations roll around and you are facing defense, being able to be pushed sideways easily really hurts your chances and it makes winning very difficult.

Just a few points, as this debate is never-ending every year.

We geared our mecanums 17.5:1 (CIM shaft to wheel), and found this to be perfect. at 12:1 we were TOO fast. The same speed on last year's bot with kit wheels gave us a perfectly capable and quick base.

The weight of shifting 4 gearboxes isn't extreme. We use dewalt gearboxes, with a cim and mount it's under 5lbs each. For comparison, the AM super shifter is 4lbs without CIM's. The problem becomes shifting all 4 at the same moment.

This year is unique, where you've got a large protected area. An efficient mecanum can out maneuver a defensive robot, as we've done many times this year.

[kinganu123]

I just wanted to throw in that the rollers make a HUGE difference to the traction. The new AndyMark mecanum rollers don't have nearly as much traction on our 2011 not as our 2010 robot had (no idea where this were bought from, but it wasn't andymark)