Another chapter to the 6WD vs. Mecanum debate

[MattC9]

So here is my question, If a Mecanum robot and a 6WD robot come in contact and the mecanum strafes out of the way and heads forward can the 6WD catch up after it starts strafing?

[BrendanB]

It all depends on how fast your 6wd base is and how good your drive is. I would imagine that the average 6wd would have no problem catching up to the mecanum robot. I think it would be a cool project to get a 6wd robot and a mecanum robot in the same area and see who can out maneuver the other. I still have my money on the 6wd.

[Chris is me]

There are a lot of variables here that depend on both robots and their respective drivers....

But in general and in my opinion - yes. A mecanum can't get past a 6WD just by going sideways for a second.

[MattC9]

We are going to put them head to head and get a video up by sat. i will post it back here

[goldenglove002]

From experience, a 6WD will push right through a robot with mecanum drive. A good driver could just clip someone with mecanum trying to slide to the side and throw that robot off target.

[Colin P]

Originally Posted by goldenglove002

From experience, a 6WD will push right through a robot with mecanum drive. A good driver could just clip someone with mecanum trying to slide to the side and throw that robot off target.

6WD isn't that much more powerful than a mecanum drive. Of course 6WD is more powerful, but you are exaggerating quite a bit.

The argument pretty much boils down to who the drivers are and what they do. Certain 6WD teams will destroy certain mecanum teams, but certain mecanum teams will run circles around certain 6WD teams. It all depends on the team, the strategy, and the execution. The wheels themselves are unimportant.

[Chris is me]

Originally Posted by Colin P

6WD isn't that much more powerful than a mecanum drive. Of course 6WD is more powerful, but you are exaggerating quite a bit.

Is he? Do you have anything to back this claim up?

[AdamHeard]

Originally Posted by Colin P

6WD isn't that much more powerful than a mecanum drive. Of course 6WD is more powerful, but you are exaggerating quite a bit.

The argument pretty much boils down to who the drivers are and what they do. Certain 6WD teams will destroy certain mecanum teams, but certain mecanum teams will run circles around certain 6WD teams. It all depends on the team, the strategy, and the execution. The wheels themselves are unimportant.

Well, there is "a 6wd", and then a 6wd with high traction wheels, 4 CIMs, and shifting.

One of them is anywhere from mediocre to good, the other is great. The great one will beat a mecanum any day of the week.

[Chris is me]

Originally Posted by AdamHeard

Well, there is "a 6wd", and then a 6wd with high traction wheels, 4 CIMs, and shifting.

One of them is anywhere from mediocre to good, the other is great. The great one will beat a mecanum any day of the week.

I would argue that shifting is not an absolute requirement to build a great 6WD. Other than that, completely agree.

[AdamHeard]

Originally Posted by Chris is me

I would argue that shifting is not an absolute requirement to build a great 6WD. Other than that, completely agree.

A very solid base can happen without shifters, but if you take two 6wds equal in all but shifting, the shifting is superior. It will push harder (while drawing reasonable current) and drive faster.

[Jared Russell]

Originally Posted by AdamHeard

A very solid base can happen without shifters, but if you take two 6wds equal in all but shifting, the shifting is superior. It will push harder (while drawing reasonable current) and drive faster.

True...but if the decision is 6 drive motors w/o shifting vs. 4 with shifting, then things get more interesting.

[Peter Matteson]

[quote=Colin P;1004786]6WD isn't that much more powerful than a mecanum drive. Of course 6WD is more powerful, but you are exaggerating quite a bit.[quote]

Yes it is.

Mechanum inherently wastes ~30% of it's power just in slipping its rollers. That is pure waste of energy that translates to nothing in the terms of pushing force/traction.forward motion. That's not exagerating that's physics.

All else being equal you start yourself at a disadvantage with mechanum.

[Alan Anderson]

Originally Posted by Peter Matteson

Mechanum inherently wastes ~30% of it's power just in slipping its rollers. That is pure waste of energy that translates to nothing in the terms of pushing force/traction.forward motion. That's not exagerating that's physics.

No, it's not physics. It's a myth. There is almost no loss of power at all during forward motion.

When a mecanum drivebase is traveling perpendicular to the axles of the wheels, as if it had traction wheels, the slipping of the rollers is almost nonexistent. There's a teeny bit of roller motion that happens on a compliant surface like carpet, but 30% is a huge exaggeration.

What you do give up with mecanum wheels is maximum pushing force. Because the individual force vectors are in different directions, the sum of the magnitude of the forces on the carpet is greater than the magnitude of the sum of those forces on the robot. The wheels will slip at the same wheel/carpet force as any other wheel having the same surface, but when using mecanum wheels that happens when there is less total force on the robot than when using traditional traction wheels.

[JamesCH95]

Originally Posted by Alan Anderson

No, it's not physics. It's a myth. There is almost no loss of power at all during forward motion.

When a mecanum drivebase is traveling perpendicular to the axles of the wheels, as if it had traction wheels, the slipping of the rollers is almost nonexistent. There's a teeny bit of roller motion that happens on a compliant surface like carpet, but 30% is a huge exaggeration.

What you do give up with mecanum wheels is maximum pushing force. Because the individual force vectors are in different directions, the sum of the magnitude of the forces on the carpet is greater than the magnitude of the sum of those forces on the robot. The wheels will slip at the same wheel/carpet force as any other wheel having the same surface, but when using mecanum wheels that happens when there is less total force on the robot than when using traditional traction wheels.

Emphasis mine.

Because a mecanum drive has less total usable force at any given speed than a 6wd, and power = force * speed, does this not mean that mecanum drive has less available power than a 6wd?

If my interpretation is correct (please correct me if I'm wrong), the power loss in mecanum comes from the force vector cancellation during straight-line driving, not from frictional losses in the rollers.

[Ether]

Originally Posted by JamesCH95

Because a mecanum drive has less total usable force at any given speed than a 6wd, and power = force * speed, does this not mean that mecanum drive has less available power than a 6wd?

Yes. But that's a power limit, not a power loss. This may seem like nitpicking, but it's an important distinction.

If my interpretation is correct (please correct me if I'm wrong), the power loss in mecanum comes from the force vector cancellation during straight-line driving, not from frictional losses in the rollers.

The "force vector cancellation" does not cause any power loss unless you are operating on a very resilient surface at high vehicle force levels and speeds. And then it's not a fixed 30% number but rather a function of the force and speed.

Once a mecanum's wheels break traction (start slipping), then any additional power supplied to the motors is wasted in scrubbing the wheels on the floor.