Mecanum wheels

[jbsmithtx]

Try VEXpro. They have very affordable yet durable mecanum wheels. The other posters are correct in assuming that unless you are trying to catch, mecanums might not work well this year... However don't believe they are easy to push. We had to play defense with our mecanums last year in matches when our shooter failed and were fine. We could block lots of teams. I know this is contrary to popular belief, but a properly done mecanum drive base can in fact be very strong.

For anyone that wants to question our pushing abilites, we have video...

[Oblarg]

Originally Posted by jbsmithtx

Try VEXpro. They have very affordable yet durable mecanum wheels. The other posters are correct in assuming that unless you are trying to catch, mecanums might not work well this year... However don't believe they are easy to push. We had to play defense with our mecanums last year in matches when our shooter failed and were fine. We could block lots of teams. I know this is contrary to popular belief, but a properly done mecanum drive base can in fact be very strong.

For anyone that wants to question our pushing abilites, we have video...

Mecanum wheels, neglecting friction in the rollers, have an effective coefficient of friction that is a factor of sqrt(2)/2 reduced from that of a traction wheel made of the same material. You can verify this yourself by drawing a free-body diagram of a set of mecanum rollers in contact with the ground.

Whether or not this translates to "being pushed all over the field" depends critically on context (robot weight, weight/drive of opposing robot, weight distribution, manner in which you're hit, etc).

[lcoreyl]

Mecanum wheels are very nice for alignment of your robot even when the driver has not had a lot of practice time. I would imagine this year aligning your robot in order to gain possession of a ball would be important to some teams. Practicing gaining possession in a real-game situation is difficult for a lot of teams, so mecanum can be handy here.

Also, I always throw in my vote for don't believe that mecanum can easily be pushed around. Wait...am i part of the majority on this vote??

[bEdhEd]

At the moment, my team is not a fan of using mecanum, unless it is undeniably the absolute and only way to win matches. With mecanum wheels you can lose up to 50% of your power when doing moves like strafing, whereas with swerve drive, all the power is used more efficiently. Mecanum wheels are indeed expensive, and I don't think that they're worth the price unless you are absolute that they are the best choice. From my experience here in the Californian bay area/central valley, the best teams stick with drop center six wheel drive treaded wheels. Why? They are inexpensive, offer the best traction, best pushing power, least complex in programming and build, easy to fix, and provide all the maneuverability necessary. Name one team that has made it to the Einstein field using mechanum wheels. None, because this has never happened in FRC history, but hey, there's always a first, and it could be anyone!

If your philosophy isn't all about winning, then have at it with the mecanum wheels! Mecanum robots are really fun to drive, too. Still, they are a pretty penny, but 100 bucks per wheel isn't a bad deal. I'm not saying that you can't win with mecanum wheels, many regionals have been won by these types of drive bases, but what I'm saying is that treaded wheels in general are a better choice in my opinion. Treaded wheels are also LIGHTER! And that could be the difference between passing and not passing inspection if you cut it really close with your other robot components.

[efoote868]

Mecanum wheels have a short history in FRC. They tend to have bad stereotypes as being easy to push around and difficult to control, particularly among individuals that have never used them.

The way people write about mecanum wheels, you'd think they were describing casters on an ice-rink.

The easiest drive-train I've ever used in FRC was a set of field-centric mecanum wheels. I've watched mecanum wheels be used for defense effectively, and I've seen times where the maneuverability and ease of use of mecanum wheels won matches.


To answer the OP's question, I think $400 is a bargain for a set of mecanum wheels. Whether your team's strategy calls for them is a different question.

[Ether]

Originally Posted by bEdhEd

...my team is not a fan of using mechanum...

With mechanum wheels you can lose up to 50% of your power...

...Name one team that has made it to the Einstein field using mechanum wheels...

...If your philosophy isn't all about winning, then have at it with the mechanum wheels...

...Mechanum robots are really fun to drive...

...I'm not saying that you can't win with mechanum wheels...

There is no "h" in mecanum.

[bEdhEd]

Originally Posted by Ether

There is no "h" in mecanum.

Haha my bad, there are days when I spell it mecanum, and days when I spell it mechanum. I wrote that post at like 5 in the morning in my time zone. Gimmie a break with the proofreading!!

I'll be sure to edit that, though. You won't see a single extra "h" in my post when I'm done. Thanks for the correction!

[lcoreyl]

Originally Posted by bEdhEd

With mecanum wheels you can lose up to 50% of your power

Originally Posted by JesseK

the default field-centric (or robot-centric with no deadband) control algorithm robs the drive train of power just by the nature of the code.

While as quoted these statements can both be true, I think it can be mis-interpreted as mecanum has less power than 4WD or 6WD. Driving straight forward or backward there is no power loss in mecanum. In any other situation where mecanum has power loss we are talking about motion that 4WD or 6WD can't do at all, so power loss does not say that 4WD or 6WD is therefore a better choice. (alternatively, I could say 6WD has 100% power loss while moving at a 45 degree angle while mecanum only has a 50% power loss) As long as your driver realizes driving all the way down the field with the robot at a 45 degree angle relative to the field would not be a wise use of mecanum, then power loss is not a real concern when deciding mecanum vs. 4WD/6WD.

[Ideal_Nerd]

last year our team loved our mecanum wheels. sadly we where borrowing them. this year we are buying them from vex. they are a lot cheaper with similar performance.
http://www.vexrobotics.com/mecanum-wheels.html

[bEdhEd]

Originally Posted by lcoreyl

While as quoted these statements can both be true, I think it can be mis-interpreted as mecanum has less power than 4WD or 6WD. Driving straight forward or backward there is no power loss in mecanum. In any other situation where mecanum has power loss we are talking about motion that 4WD or 6WD can't do at all, so power loss does not say that 4WD or 6WD is therefore a better choice. (alternatively, I could say 6WD has 100% power loss while moving at a 45 degree angle while mecanum only has a 50% power loss) As long as your driver realizes driving all the way down the field with the robot at a 45 degree angle relative to the field would not be a wise use of mecanum, then power loss is not a real concern when deciding mecanum vs. 4WD/6WD.

I said you can lose up to 50% of power with moves like strafing. I didn't say that you can lose 50% from forward or backwards driving, and you can lose somewhere between >0% to 50% power when strafing diagonally, which is a combination of the forward/back movement and sideways strafing. There is no significant difference in power between forward/back mecanum driving and forward/back tread driving when using the same power source and transmission.

It may be important to be aware that drivers may not have success moving others robots out of the way by turning or strafing, but instead can have success by pushing straight on.

[JesseK]

Originally Posted by lcoreyl

While as quoted these statements can both be true...

Please don't mis-quote me and then poorly attempt to make a counter-point which actually says something completely tangential to what the entire quote said.

[thefro526]

There's a bit of mis-information in this thread, and while I don't want to join in the debate, I'd like to set the record straight for any of the newer teams that might be using this thread for information.

Mecanum Wheels can be purchased from two different FRC Suppliers.

- AndyMark http://www.andymark.com/Mecanum-s/53.htm

AndyMark's Mecanums were first released for the 2007 Season and have been evolving since then. They're offered in FRC relevant sizes of 6" and 8" with a Standard Duty and Heavy Duty version of each. The Pricing Varies from ~$250 for a set of 6" Standard Duty to in excess of $400 for a set of 8" Standard Duty.

- VexPro http://www.vexrobotics.com/vexpro/wh...um-wheels.html

VexPro's Mecanum Wheels are relatively new compared to AM's Mecanum Wheels, but have proven themselves to hold up reasonably well in the FRC Environment. They're a bit Cheaper than AM's Mecanum Wheels and rely on a primarily plastic construction in place of Metal.

As far as Mecanum's implementation in FRC, they're a decent way to make your drivetrain more maneuverable, as well as adding omni directional functionality within a traditional frame. The increased agility awarded by Mecanum wheels should allow you to move around traditional defense to the point where 'pushing' isn't necessarily required.

All of that being said, when comparing two similar drives, with the only difference being that one Uses Mecanum wheels in place of a traditional wheel, the Mecanum Drive will almost always have less traction than the traditional drive train. This is due in part to a couple of factors, the wheels always being in a constant state of slip (in that they're applying force in a non-fore/aft direction) being one of them, and the other being that each wheel's motor is independent. This means that if one of your wheels leaves the floor, or starts spinning, you're not only putting down the power of (3) motors.

[TedG]

We have used Mecanum wheels the last 3 years with great success.
Great for manouvering in all directions without haveing to turn.
Last year we used the 6" dia heavy ones from AM and could push our way around as well as resist being pushed around. It helps if you have a heavy robot though.
And it's a good idea to buy a spare wheel or two, but they are expensive.

[lcoreyl]

Originally Posted by thefro526

There's a bit of mis-information in this thread

yes... yes there is...

Originally Posted by thefro526

Mecanum Drive will almost always have less traction than the traditional drive train. This is due in part to a couple of factors, the wheels always being in a constant state of slip (in that they're applying force in a non-fore/aft direction) being one of them

I've linked a paper in my signature. In the paper is a link to a video showing the worms eye view of the contact patch of a mecanum wheel while being moved as it would in normal forward motion. The contact point doesn't slip. The rollers don't spin.

[thefro526]

Originally Posted by lcoreyl

yes... yes there is...



I've linked a paper in my signature. In the paper is a link to a video showing the worms eye view of the contact patch of a mecanum wheel while being moved as it would in normal forward motion. The contact point doesn't slip. The rollers don't spin.

I don't want to debate this too much since it's going to derail the thread, but I'm still not convinced based on the two videos (Glass table, green backlighting) that the rollers do not spin under FRC conditions. Maybe I'm nit picking, but there seemed to be some sort of displacement of the roller (Looks like a few degrees at most) even on the table top test. At FRC speeds, something tells me that this has to add up into the rollers spinning while the robot is moving in standard fore and aft directions. It's been a few years since I've played with Mecanum wheels first hand, but if I remember correctly, rollered seemed to slip while under load.... But I might be wrong.