Chainless Mecanum Drive

[spiffyspleen]

Our team is looking into trying out mecanum wheels in an off-season competition. Due to time constraints and not wanting to have to mess around with chain, we were wondering if it is possible to have a chain-less mecanum drive. If so, how do we do this? Pictures or diagrams would be great. We are using standard Andy Mark mecanum wheels and the Andy Mark gear boxes. Thanks for your help

(On a side note, as I was looking through the forums researching mecanum drive, I saw some posts mentioning nona drive. However, I wasn't able to find an explanation of it, or any pictures. What is it?)

[whackedwatchdog]

http://www.andymark.com/searchresults.asp?cat=215

That (should be) the link to the "hubs" section of the andymark.biz site. You're going to want to find the size that coincides with the size of your output shaft/key. I wasn't actually around when we got them in and put them on, but unless I'm mistaken, you slide it over the output shaft, and the outer holes correspond to the (long) bolts on the inside of the wheels. There might be another part necessary to keep it on the output shaft, but that would be a good starting point.

(Someone correct me if I'm wrong, I had already left for college when they got everything together.)

[EricH]

Nonadrive (or Neunadrive) is 4 traction wheels, each in a pod with an omni wheel, and a fifth omni wheel in the middle at right angles to the rest. The pods rotate, allowing for traction or agility as needed. Used by 148 and 217 this year.

[BJC]

The nonadrive is the pretty much the coolest new drivetrain in FIRST. It has the traction of a 4 traction wd (normally not used because it can't really turn) and the manuverability of a slide drive (normally gets pushed around alot in the heat of compitition). However, Its arguably on the level of complexity with a crab drive, so its not for the faint of heart. Definatly an offseason project.

lol, beaten to it.

[Alan Anderson]

Direct drive mecanum is trivially easy. You just need the appropriate reduction in your gearbox for the size of wheels you're using. Like this.

[Clem1640]

We designed a chainless mechanum chassis as a mental exercise during the summer of 2008. Included suspension. We never built this design.

Here's the link:
http://wiki.team1640.com/index.php?title=Mecanum

Cheers,

[spiffyspleen]

Thanks! How heavy is a standard nonadrive? Five motors, 9 wheels, and four pneumatic cylinders, that must add up...

[EricH]

Originally Posted by spiffyspleen

Thanks! How heavy is a standard nonadrive? Five motors, 9 wheels, and four pneumatic cylinders, that must add up...

On a sheet-metal chassis, which can be lighter than a more standard box-tubing chassis.

For further questions on the Nonadrive, you might want to take a look at the following two threads (and yes, there are two, one for each team that used it): 217 and 148--and definitely watch the videos that open the threads. (Warning: watching said videos may cause a sore jaw, due to said jaw hitting computer, desk, or floor.) Unfortunately, I can't seem to find tech specs...

But I do know where CAD files can be found!

To echo what Chris said, you need to know what you're doing to try a nanodrive. They'd have had a hanger on their robots in competition if they hadn't decided to reinforce their drive and make other improvements--and that's another scary part, they improved it from the videos.

[kgzak]

Originally Posted by Alan Anderson

Direct drive mecanum is trivially easy. You just need the appropriate reduction in your gearbox for the size of wheels you're using. Like this.

We learned this the hard way. During Overdrive we tried a mecanum drive and our robot would not move. At first it was thought to maybe be a code issue but turned out to be that our gear boxes (stackerboxes) were not geared down enough to move our robot.

[Chris is me]

Not to take away from innovation and technical achievement, but I don't really see the Nonadrive as some kind of new Holy Grail in FRC drivetrains, and it is absolutely not something a team without the engineering resources to design a direct drive mecanum drive should do. It's not exactly a cheap, light, or simple drivetrain.

[spiffyspleen]

So if we're using the 6 in mecanums, what is the appropriate gear box reduction?

[Ether]

Originally Posted by spiffyspleen

So if we're using the 6 in mecanums, what is the appropriate gear box reduction?

12.75:1 seems to be a reasonable compromise between speed and torque (more or less depending on the game, of course)

Just curious, can you share a bit with us about your team's decision process that led you to your decision to explore mecanum wheels?

[spiffyspleen]

Our main reason for trying them now is so that we have experience with them if we decide to use them for the FRC season. We bought them last year but decided not to use them for FRC because we didn't have any experience with them and we didn't think they would work well on the ramp. We want to learn how to use them because they are one of the most manueverable drive trains. From what I saw at the Portland regional last year the teams that used them were able to position themselves very well with the ball and goal and ended up doing pretty good. Basically, we think that they could be advantagous in this years competition and we want to be able to use them if they are.

[EricH]

Originally Posted by spiffyspleen

Basically, we think that they could be advantagous in this years competition and we want to be able to use them if they are.

The key words in this statement are: "could be" and "if".

Right now is a really good time to do a mecanum drive as an offseason project. You get a chance for rookies to build a robot, you test out new technology, and you gain knowledge and experience.

But the problem is that when all you have is a hammer, every problem looks like a nail. When Kickoff shows up, you will be tempted to use mecanum, even if the game is reminiscent of 2002 (where high traction, great pushing and low maneuverability were great benefits). Trust me, you will be tempted.

So, what you do is you take your offseason robot and a competing drivetrain (say, 6WD drop-center, or a 4WD built from the Kitbot) and run them through a series of tests, either individually or against each other with an offense vs defense. Then you evaluate which is better.

I'll let you in on a little secret: 330 has had the capability to use mecanum drive since 2005; development/small-scale prototyping started around 2003, with a full-scale base during the 2005 build season (thanks to the Kitbot frame). The closest they've ever come was 2009 with a turning 6WD system in the middle of their robot. The only time they've used wheels with rollers in competition was omni wheels in 2010, for added agility on a 4WD. They just haven't found it advantageous to use them...yet.

[Chris is me]

Actually, Eric, I'd say they're doing exactly the right thing by trying it now. There's really no better of a time to see if you can get it working and learn about the drawbacks of such a system. I mean, one could say the very same thing about a six wheel drop prototype (ignore for a minute that 6 wheel drop has been consistently very successful).

If I'd say anything it's to make sure you guys are very, very critical of your final project and to make sure the advantages are actually called for in your design process, and that the disadvantages are not absolute. I would say a lot of teams that build mecanum drives get a little distracted by the whole coolness factor and build it without regard to the realities of pushing and whether or not strafing is required.