Mounting mecanum wheels... please help?
 

This is our first year using mecanum wheels; we have no experience with them. Furthermore, just before the build season, our only engineering coach found out that she pretty much wouldn't be available at any point, so we are short on professional advice.

The attached image is the general frame of our drivetrain, but is definitely subject to change, and is really all the metal we have to use for the drivetrain. It is 32 inches long by 25 inches wide, and this is not changing unless it absolutely has to. We are using the Cim motors that came in the kit of parts and we have enough AndyMark gearboxes to put one on each wheel. Our issue with this is the amount of room available in which to put gearboxes.

The mecanum wheels are 6 inches in diameter and 1.8 inches wide. Right now we are planning to have them roughly 20 inches apart. We would greatly appreciate suggestions on how to mount the wheels and the gearboxes, and if there is an ideal alternative to gearboxes, how to best reduce the RPM from motor to wheel, including specifics of gear size and distance between them. Thanks in advance for any help you are willing to give!

Re: Mounting mecanum wheels... please help?
 

http://www.andymark.com/product-p/am-14u2-mk6.htm
this might be what you are looking for

Re: Mounting mecanum wheels... please help?
 

We mounted mecanums on the kitbot frame, without the kit mentioned above. Distance between the center of the wheels is about 19". We used second stage planetary gearboxes. To mount the gearbox, you will need a plate w/ three holes (for the gearbox) that extends out and mounts to a side of the frame. We used two holes on each side of the plate.

I have attached a two pictures:
http://imgur.com/a/1X2if

and a video of it driving:
https://www.youtube.com/watch?v=uQbVDzJR3bc

Also, a couple of notes on our drive:
There's a ~40lb steel block mounted in the middle to simulate the weight of the actual robot. We started with first stage planetaries, but they didn't generate enough torque to strafe. We switched over to second stage and it strafes fine.

Re: Mounting mecanum wheels... please help?
 

Any thoughts on how structurally stable the side plates will be with those portions of fins removed?

Re: Mounting mecanum wheels... please help?
 

I assume that it would be similar to that of last year's AM14U frame.

Re: Mounting mecanum wheels... please help?
 

http://www.andymark.com/SearchResult...rch=nano+tubes

we love these nano tubes. gear boxes and barrings are within the tube. cims mount directly to them and they work very well for mecanum and other drives. but they are a bit expensive. you may be able to use some of your AM credits towards them.

Re: Mounting mecanum wheels... please help?
 

Assuming that the GB mounting plate is solid aluminium, I'd say the rigidity would be fairly similar. It would be almost unnoticable if you extended the mounting plate so there was ~20mm of overlap with the still existing flanges.

Re: Mounting mecanum wheels... please help?
 

Do you think it would be possible for us to use the AndyMark gearboxes provided in the kit of parts? Additionally, why do single stage gearboxes cause a problem with strafing?

Re: Mounting mecanum wheels... please help?
 

The ToughBox Minis can be mounted with mecanums but it is my understanding that you have to do a lot more machining than if you are using the ToughBox Nanos or 671 or something similar. If you search the forum you can find some pictures of other teams that have done it, but the one I remember mounted the gearboxes below the frame on a seperate plate. There could be easier ways, I haven't looked into it much.

Single stage gearboxes won't cause any strafing problems, just be aware that you may need additional reduction stages to get a slow enough speed. Most single stage COTS gearboxes aren't geared much more than 6:1 or so which, depending on your wheel size, might be faster that you want.

Re: Mounting mecanum wheels... please help?
 

For people mourning mecanums to the AM14U2, how are you securing the other end of the shaft driving the wheel? The corresponding hold in the outer plate has a diameter of 0.675", so you can't put a .5" Hex bearing in there. Or are you cantilevering it?

It looks like the Upgrade kit that AndyMark is selling has the outer plate attached and I'm guessing the shaft isn't cantilevered, but I can't tell by the pictures shown.

Re: Mounting mecanum wheels... please help?
 

They didn't generate enough torque to strafe in our case. We speculate it was a combination of that and our slightly bent frame. Weight distribution/contact w/ground is terribly important with mecanum drive - they need to turn at the same rate and exert the same force.

Re: Mounting mecanum wheels... please help?
 

The shafts on both this year's and last year's mecanum upgrade kits were cantilevered. We didn't experience any issues last year, though, so I wouldn't expect this to be too much of a problem. The shafts are durable.

Re: Mounting mecanum wheels... please help?
 

We're going with mecanums, but with a twist... one pair is direct drive, while the other is chained. Pic of our frame:



Basically, The back wheels are direct driven, and we cut out holes for 1/2 bearings to fully support the wheel, centered on one of the smaller holes along the bottom. The other wheels will be run on a dead shaft in the front, chained to the motors that are in the middle. They are all run using KoP gear boxes (we had two we never used last year and guess what? Same gear reduction!). We're avoiding cutting out any of the flanges on the frame, and instead are building a mount for the gearbox that will stand it off .625" (i think), which is the width of the flange. This also required turning custom axles, as the normal KoP output shaft isn't long enough once we move the gear boxes off the frame like that.

The 6" white wheels in the pic were just used to ensure proper clearances with the front and back frame members... the mecanum wheels aren't in the shop yet.

We used tough box nanos which allowed there to be room but it was a nightmare of drilling. Would run from using mecanum wheels on the kop chassi if you could.

Re: Mounting mecanum wheels... please help?
 

We have cantilevered the wheels off the transmissions with no problems.

We have used Toughbox mini's 12.75:1 with 8" wheels. That's what we plan to use this year. Seem to work OK.

Normally you have to run some rod from the transmissions on one side to the ones on the other side to stabilize the whole setup.

Re: Mounting mecanum wheels... please help?
 

Are the Toughboxes Minis the same gearboxes that came in the kit of parts? I've taken a look, and they look the same, but without being in the shop to really check I can't tell. If they are, do you think they would work the same with 6" wheels? Do you have a video of them working? I would be interested to see the functionality of the toughboxes with mecanum wheels.

Re: Mounting mecanum wheels... please help?
 

The KOP gearbox is a TB Mini, but it's an 8.45:1, not 12.75. Using the 8.45 gear ratio with 6" wheels will be very similar to performance of a 12.75:1 with 8" wheels (about 11% faster).

Re: Mounting mecanum wheels... please help?
 

Another solution would be to provide cantilever support for the wheel by boring out the hole in the inner plate to 1-1/8" and using the KOP hex shaft bearing in that hole. You'd also need a hex shaft collar or two to keep things from walking.