Mecanum Wheels
 

I have searched and searched for some specific information on Mecanum wheels. This is not for a FIRST team, but for a class I'm taking. (If any of you are familiar with Square One, that's the program its through. To read more: http://www.squareonenetwork.org/inno...ign-challenge/ ) And we are actually doing this research and testing for our robotics team in the future. Kill two birds with one stone.:D


So back to the information we need:

What is the suggested RPM for Mecanum wheels?

What motor has had the best outcome?

Which is best for motor reduction? (ex: gearbox, chain, belt, etc)

Any other helpful tips about building with mecanum wheels?

P.S. We are really only building a chassis to mount to the bottom of the jeep, and everything is autonomous.

THANKS IN ADVANCE!!

Re: Mecanum Wheels
 

RPM depends on how fast you want to go. Just do the normal calculations. You can use JVN's spreadsheet.

The simplest gearbox motor combo would be direct drive with AndyMark Nano's and CIM motors.

Nano

AndyMark is also a great resource for using Mecanum wheels. Call them and get direct advise. It's summer they're just sitting around :)

http://www.chiefdelphi.com/media/papers/2755

Sounds like fun, please keep us updated with your results.

Re: Mecanum Wheels
 

I'd probably go with VersaPlantery gearboxes and BB775 motors if you are looking for the simplest motor and gearbox combination. It's not for an FRC robot, so hopefully you don't plan to stall these motors too often. If you do then CIMs into a single speed gearbox would work as well.

Think about how you want to ensure all 4 wheels maintain contact with he ground at all times. If they don't your autonomous navigation is likely to be much harder.

Re: Mecanum Wheels
 

Is this driving out in the environment?

Re: Mecanum Wheels
 

You really aren't giving us enough information to realistically tell you what to do. I think the simplest thing for you to do is to go for a kitbot with mecanum wheels, make a basic frame to mount these (http://www.andymark.com/product-p/am-0482.htm) and just put mecanum wheels on the output shaft or just buy one of the mecanum platforms andymark already sells.

Q:
What is the suggested RPM for Mecanum wheels?
A:
what size wheel do you have and how fast do you want to go?

Q:
What motor has had the best outcome?
A:
Not enough information. Is this FRC specific? What limitations are you working with in your class? Most teams in FRC use 1 CIM motor per wheel but other teams have gone for 1 CIM + 1 miniCIM per wheel as well. I will withhold my opinion on the competitive outcome of mecanum based robots in FRC other than that the faster ones with better drivers are visibly better.

Q:
Which is best for motor reduction? (ex: gearbox, chain, belt, etc)
A:
Not enough information. This depends on your implementation and design. This year, on their respective tankdrives, 254 had all gear reduction, 1114 had gear+chain reduction and 67 had gear+belt reduction. Most mecanum drives I see are all gear.

Q:
Any other helpful tips about building with mecanum wheels?
A:
Excessive rigidity is bad. Uneven weight distribution is also bad. You want all wheels to have equal traction at all times. Unless the floor is flat and fairly smooth I'd avoid using mecanum wheels.

What budget and manufacturing resources do you have access to and what surfaces are the bot going to be driving on?

Re: Mecanum Wheels
 

Using andymark 6 inch mecanums you can gear for 20 FPS+ but beware the rollers start falling off with higher frequency as your speed increases. We geared for 15+ and had to replace a roller for every 2 hours of run time. Sometimes substantially more depending on conditions.

Cims. They have pretty good acceleration compared to mini cims as well as a larger thermal mass.

Gearboxes. My team built 5 mecanum robots all using the toughbox nano directly bolted to the wheel and the motor with out a single failure.

Built your chassis slightly floppy. This allows all the wheels to touch the ground on imperfect terrain (like carpet.)

Re: Mecanum Wheels
 

I can imagine that a "barbie jeep" will be operating on something distinctly different to the industrial carpet we are used to (or smooth warehouse cement floors either). I would, without further knowledge, assume you will be driving on a road surface, like a concrete or asphalt parking lot.

As such, I will warn you that Mecanum wheels made for FRC, such as Andymark and VexPro wheels, will likely have very poor tread durability operating on the sandpaper-like ground. The durometer of the tread on the rollers is quite soft and will wear down quickly, particularly during strafing.

Re: Mecanum Wheels
 

At IGVC a few years ago I saw a team that built large custom mecanum wheels out of razor scooter wheels. They seemed to have a tendency to get clogged with grass. Pretty awesome nonetheless.

From an autonomous perspective, are you going to really have enough sensors to take advantage of the strafing motion? It seems like you'd need to be able to align your sensor array with your direction of travel.

Re: Mecanum Wheels
 

We used the nano tuff boxes with the long shafts. We put a bearing on the outboard end on the shaft so the wheels were not cantilevered. The nano box were a little slow. I would look at decreasing the reduction with different gears. We used chains on one end of the robot because of clearance issues. Otherwise chains just add weight.

Re: Mecanum Wheels
 

Yes, It will be driving on asphalt.

Re: Mecanum Wheels
 

CTRE had a demo bot that used mecanums (AM 6") using Nano Tubes. It ran at MakerFaire for 2 days (near constant running) with no noticeable degradation of the wheels. There was an issue in which a stone got into the gearbox but aside that I don't recall many issues due to different surfaces.

Re: Mecanum Wheels
 

I have driven mecanum wheels aggressively on concrete and noticed the same (or less) roller wear and not a single falling off in contrast with driving on carpet.

Re: Mecanum Wheels
 

Did you have any problems with traction or strafing?

Re: Mecanum Wheels
 

We haven't gotten very far into design yet, so we might not have enough, but I'm sure we can figure it out somehow.:D

Re: Mecanum Wheels
 

How smooth is the asphalt it will be drivng on? As previously mentioned, meacnum wheels from AndyMark and VexPro are designed for FRC, and the concerns about using them in an outdoor setting extend beyond tread wear. In order to function properly, all four mecanum wheels need to be in contact with the ground at all times*, and have roughly equal normal force exerted on each wheel**. Driving on uneven asphalt has the potential to cause significant issues if you don't design some sort of suspension to accomodate for it.


*or at least any time that wheel is spinning

**or at least have some control method to account for uneven forces transmitted by each wheel in the situation where it's not even

Re: Mecanum Wheels
 

the times we've built mechanum, we've discovered its been really important for all four wheels to be on the ground. If your 'after school project' has the ability to have independent suspension, I recommend it. We built a robot with simple gas struts on the four corners and it kept the wheels on the floor. Even with a flat floor, when you corner, stop, etc, you can lift wheels and lose control.

As for which gearbox, even when we've done Andymark wheels it made sense to use Banebot planetary gear boxes. Since you need a motor on each wheel anyway, these work great and make a nice installation. Unless you need more power, like two CIMS on each wheel. http://banebots.com/c/P80K-S4 just something different to consider.


And as for motors, everyone here is used to FRC rules, so we don't suggest alot of motors that aren't FRC legal, but there are many motors out there. The CIM at a mere 337 watts isn't close to the most powerful available. It's just what we know. Most scooters are in the 500w range and hub motors go alot higher. Depends on what you need power-wise. CIMS are a great value, but don't be afraid to look around.

Re: Mecanum Wheels
 

The asphalt is like the PIT area of a nascar track.

Re: Mecanum Wheels
 

Just a little 'looking around' flushed out this motor--peak 3.8 HP works out to 2800watts. wow.

http://www.robotmarketplace.com/products/0-A40-300.html


But price of $330 is pretty high too.

Re: Mecanum Wheels
 

SSS 5694:
http://www.horracing.com/product_inf...roducts_id=609

If you use 3-4 lead acid batteries in series, they should produce enough voltage for it to really pump out the power. They need a brushless speed controller to go with them, but they're pretty good value.

Re: Mecanum Wheels
 

Given that the bot is driving on asphalt, I wouldn't trust any of the frc intended mecanum wheels to last any reasonable amount of time. Couple that with the fact that the asphalt likely isn't perfectly flat and you've got a complicated, expensive, heavy, high maintenance and badly performing platform as compared to tankdrive or front wheel steering like what's on the jeep originally.

Even on carpet I wouldn't really trust mecanum wheels with more than 700w per wheel, they just aren't intended to either go that fast or use that much force (depending on how you're geared).

Also what manufacturing resources do you have? this is still a really important question.

If you really want to strafe, swerve or crab drive is probably the easiest/best way to do it well. 1640 has good code resources and you can buy good KOTS swerve drives and a chassis to mount it to.

Re: Mecanum Wheels
 

[quote=Scott Kozutsky;1399804] Also what manufacturing resources do you have? /QUOTE]

We have a pretty advanced shop to work in. So a lot is possible. There are only 2 of us working on it, which in turn doesn't give us much flexibility on what we can custom manufacture.