Mecanum Rolling Chassis

[Anupam Goli]

Originally Posted by DMike

Why wouldn't mecanum be a reasonable choice for this game? Maneuverability would seem to be a benefit as well as the direct drive. The court is a flat surface with vertical obstacles. We have tested a 6 inch set of wheels on many surfaces including asphalt roads, light gravel, wood, tile, rug, compact dirt and more. The wheels handled it all, they were very durable. The side load from pushing seems acceptable, front and rear a bit less. With some good programming and driving, this should be a good system. It might even roll straight up the tower.

A lot of teams are allured by the whole "manoeuvrability" aspect of mecanum, but in reality it isn't that cut and dry. What you gain with a third axis you lose in traction and power. Since the omnidirectional motion of meccanums is produced by vector summation, you'll always have some sort of power loss in whatever direction you go in. Combine that with the low coefficient of friction, your robot may be able to go sideways, but you won't be going fast, and your drivetrain will not have much power, which is never an ideal combination. A 6 wheel skid drive is proven to be far superior in every category, especially since the traction makes up for the lack of sideways movement. But, let's not turn this into a meccanum bashing thread again, shall we?

The main important reason for your choice was because you thought it would be cool and would be a neat learning experience, and that's all that really should matter when it comes down to it. I also like the paint job on this drivetrain, it definitely looks neat!

[IndySam]

Don't let the haters get to you. They just can't compliment anyone on a nicely built chassis if there are mecanum wheels, on it.

You obviously put a lot of time and effort into this. Congrats on a job well done, especially for a second year team.

[BJC]

Originally Posted by IndySam

Don't let the haters get to you. They just can't compliment anyone on a nicely built chassis if there are mecanum wheels, on it.

You obviously put a lot of time and effort into this. Congrats on a job well done, especially for a second year team.

This-- it really does look classy. Just make sure to get a lot of driver training so you can use it to it's fullest potential come competition.

Best of Luck!
Regards, Bryan

[pfreivald]

The biggest advantage of mecanum drive is something I never hear mentioned on CD: your robot drives exactly as a 1st person shooter.

Intuitive driver control freaking matters, and if anyone can present the math to prove otherwise, I'm all ears.

[EricH]

Originally Posted by DMike

The cool in the design attracts attention and gives us the opportunity to explain the building process and FIRST. It's a solid design, form-function-finish.

This is more what I was looking for, along with the later post. Just saying "it's cool" is like will.i.am saying the 2011 game was "dope" at Kickoff--there are a number of possible meanings. (For example, someone just saw mecanums and said "Oooh, I want some!" is one potential meaning.)

A little more content like this, however--the attention attractor for non-FIRSTers, the testing done so far, and other similar things--and the meaning is clear: you've looked at the alternatives and decided this is the one.

Out of curiosity... is a matching shooter going on top? You've got 4 weeks to perfect that, and a driving base to work with. Or is there something else up your sleeves?

[Akash Rastogi]

Originally Posted by BJC

This-- it really does look classy. Just make sure to get a lot of driver training so you can use it to it's fullest potential come competition.

Best of Luck!
Regards, Bryan

Ditto! Looks like you guys put in a lot of work for this.

How well are the Modulox gearboxes working out for you? The integration is pretty neat!

Again, great start to what I'm sure will be a solid robot. Keep us posted!

[Ryan Dognaux]

Looks great, I can't wait to see what you put on top of it.

Mecanum Haters Gonna Hate™

[lcoreyl]

Originally Posted by Wing

What you gain with a third axis you lose in traction and power. Since the omnidirectional motion of meccanums is produced by vector summation, you'll always have some sort of power loss in whatever direction you go in. Combine that with the low coefficient of friction, your robot may be able to go sideways, but you won't be going fast, and your drivetrain will not have much power, which is never an ideal combination. A 6 wheel skid drive is proven to be far superior in every category, especially since the traction makes up for the lack of sideways movement.

Just posted a whitepaper addressing my disagreement with much of this. The link is in my signature.

But, let's not turn this into a meccanum bashing thread again, shall we?

+1 irony

The main important reason for your choice was because you thought it would be cool and would be a neat learning experience, and that's all that really should matter when it comes down to it. I also like the paint job on this drivetrain, it definitely looks neat!

This part I can fully agree with you on!

The Modulox has worked out very well. everything is Aluminum except the bearings and output shaft. We have discovered that chassis construction is very important to the success of the Mecanum drive. Both frames we have built were very rigid, square and durable. All of our cut dimensions are +- .010 and all of our bends are +-.030. All rivet locations were pre drilled and require very little modification for assembly. There are 125 3/16 blind rivets holding 9 parts together. With the CIMS the chassis weighs in at 43 lbs.

[PVCpirate]

For the pushing match argument against mecanums, how often are you in a straight pushing match during a match? The situation most people describe in making this argument is a six wheel tank drive bot pushing a helpless mecanum drive bot halfway across the field. Any mecanum bot that I've helped build might be pushed some, but with the right driver it would spin away from the pusher and be back down the field in no time.

[NotaJoke]

Originally Posted by Chris is me

Because you have a WIDE OPEN field, and relatively few zones to protect you from defense. There's no tight corners to navigate around, and the main game task really benefits from resistance to pushing that mecanums just can't give you.

Perhaps there is a way to utilize both the mobility of a mec drive and the tenacity of a tank-style drive. Hmm.

Edit: Where are my manors? This is a beautiful chassis, and with the right know how (either mechanical or tactical) could be exactly what a winning alliance needs.

[Billfred]

Originally Posted by PVCpirate

For the pushing match argument against mecanums, how often are you in a straight pushing match during a match? The situation most people describe in making this argument is a six wheel tank drive bot pushing a helpless mecanum drive bot halfway across the field. Any mecanum bot that I've helped build might be pushed some, but with the right driver it would spin away from the pusher and be back down the field in no time.

Not often, but when it counts... (Really, the relative inefficiency inherent to mecanums is what ruled it out for me this year; we favored straight-line speed without using so many of the high-powered motors.)

But frankly, you could put square wheels on this thing and it'd still look boss. I look forward to seeing the whole thing!

[Brandon Zalinsky]

Great job team! That robot looks sick! also, for mecanums, I agree with PVCPirate, not just because we were on the same team. A good mecanum driver can always avoid pushing match with a tank drive and usually will just drive around it.

[dcarr]

Originally Posted by Flak-Bait

Great job team! That robot looks sick! also, for mecanums, I agree with PVCPirate, not just because we were on the same team. A good mecanum driver can always avoid pushing match with a tank drive and usually will just drive around it.

Completely true. What a mecanum driver can't realistically do is initiate a pushing match Sure you can effectively annoy a 6-wheel drive robot, but you can't really move them much.

We used Mecanums in 2011 (good) and 2012 (not so good on the bridge) and this year we're trying a 6-wheel WCD, certainly pros and cons to both as has been addressed many times over.

[Chris is me]

Originally Posted by Flak-Bait

Great job team! That robot looks sick! also, for mecanums, I agree with PVCPirate, not just because we were on the same team. A good mecanum driver can always avoid pushing match with a tank drive and usually will just drive around it.

Still waiting for video of a mecanum drive doing that here... Post if you've got it!

That said, IndySam is absolutely right, that is a gorgeous chassis and I shouldn't have derailed the conversation into yet another debate about mecanum drives. Good luck!