Mecanum Wheels

[dudefise]

Does anyone have instructions on making mecanum wheels? Or a source of cheap mecanum wheels? The ones from Andymark seem really expensive...

[Hawiian Cadder]

i cadded a set of mechanums that i calculated would cost less than 50 dollars a piece, but they require a 5 axis mill, and some casting work, i could dig out the cad files if you like. if you want to know all the math involved in making them, here we go:

the most important thing to do is to understand that the profile of the roller is a partial ellipse, where the short dimension is the diameter of the wheel, and the long dimension is the diameter of the wheel divided by the sine of whatever angle the rollers are at (usually 45) after that bit of math there is really not much to designing fully custom mechanums.

http://chiefdelphi.com/media/photos/35738

http://chiefdelphi.com/media/photos/35738

here are the renders of the mechanum wheels that i did, the blue one should cost around 50 dollars, (depending on what casting compound is used for the rollers.

[MattC9]

No sorry, but i'm curious why are you looking at mecanums?

If you want to do an off-season project mecanum might not be the best system for you and your team.

[dudefise]

Originally Posted by MattC9

No sorry, but i'm curious why are you looking at mecanums?

If you want to do an off-season project mecanum might not be the best system for you and your team.

It's for a shifting drivetrain project. It will have mecanum for speed and agility and tank for brute strength (with traction wheels) and the ability to switch between the two.

[pfreivald]

357 has a pretty impressive setup. Michael Crane is probably a good contact person from that team to ask about how they make their own.

[MattC9]

Originally Posted by dudefise

It's for a shifting drivetrain project. It will have mecanum for speed and agility and tank for brute strength (with traction wheels) and the ability to switch between the two.

Nice!!! that sounds sweet!

well i did some searching and the robot shop has some for about 85 for a 4 pack (for the alum. hubs and 75 for plastic hubs) but the O.D. is 2.125. You might be able to do some prototyping with them using vex parts then decide if you want to drop 400 for the AM ones. Our team has done a pure mecanum drive for the last 2 years (we will not go back to it, but the AM heavy duty ones work really well).

Heres the link for the robot shop ones

PS if i did come off as negative, i just don't like a pure mecanum drive.

[Hawiian Cadder]

http://www.thingiverse.com/thing:2473

http://hackaday.com/2010/04/28/print...um%C2%A0wheel/

if you have a 3d printer you could always scale a set of these.

[thefro526]

Originally Posted by EricH

You may want to get in touch with 357 (or, the Behind the Design books from the 2006 and 2007 FRC seasons); they've got casting their own down to a fine art.

Originally Posted by pfreivald

357 has a pretty impressive setup. Michael Crane is probably a good contact person from that team to ask about how they make their own.

I've seen 357's casting method up close and it's pretty awesome, though I don't see most teams being able to do it. 357's wheel body is also it's own work of art - which again is pretty difficult to make, imo.

Originally Posted by Hawiian Cadder

http://www.thingiverse.com/thing:2473

http://hackaday.com/2010/04/28/print...um%C2%A0wheel/

if you have a 3d printer you could always scale a set of these.

I 3D printed a set of Mecanum wheels back in '07/'08 and there's no way they'd stand up to the abuse of an FRC robot.

Not really sure why the OP doesn't want to use AM Mecanums, at $222 a set they seem like a steal.

[pfreivald]

There is that. I'm pretty happy with the AM HD Mecanum wheels.

[dudefise]

Originally Posted by thefro526

Not really sure why the OP doesn't want to use AM Mecanums, at $222 a set they seem like a steal.

I was assuming they were expensive for mecanum wheels; they seem expensive for the materials that go into it. But if they're the best option available, I'll take it.

Also I don't think the printed wheels would survive if we were to use them.

[EricH]

Originally Posted by thefro526

I 3D printed a set of Mecanum wheels back in '07/'08 and there's no way they'd stand up to the abuse of an FRC robot.

Oh? Really?

330 3D printed a set around the 2005 season through one of our sponsors at the time--as a matter of fact, every mecanum 330's played with to my knowledge has been 3D printed. The VEX-scale ones (which were metal) had some problems with fins bending before the roller pins were installed. The resin one had problems with cracking (and staying together--it had a 2-piece hub).

The pure nylon ones held up pretty darn well in our testing. They'd take a full season, I'm certain of it--they took everything we threw at them in testing with zero issues (other than a lack of traction, resulting in some cool tricks we tried with the rollers). 8 rollers, outer rims like the AM ones, not inner ones like 357's, one-piece hub, steel roller shafts (screw-threaded on one end to act like a custom screw, and sprocket attachment points on one side. Sorry, I don't have any pictures--maybe some of the other members of 330 at the time have some, or can get them.

Were the wheels used in competition? No. We considered that a 6WD better fit our objectives that year--and for every year since. As such, to this day, 330 has not used mecanums in competition. They're there, though--waiting to be used if the game calls for them.

[thefro526]

Originally Posted by EricH

Oh? Really?

330 3D printed a set around the 2005 season through one of our sponsors at the time--as a matter of fact, every mecanum 330's played with to my knowledge has been 3D printed. The VEX-scale ones (which were metal) had some problems with fins bending before the roller pins were installed. The resin one had problems with cracking (and staying together--it had a 2-piece hub).

The pure nylon ones held up pretty darn well in our testing. They'd take a full season, I'm certain of it--they took everything we threw at them in testing with zero issues (other than a lack of traction, resulting in some cool tricks we tried with the rollers). 8 rollers, outer rims like the AM ones, not inner ones like 357's, one-piece hub, steel roller shafts (screw-threaded on one end to act like a custom screw, and sprocket attachment points on one side. Sorry, I don't have any pictures--maybe some of the other members of 330 at the time have some, or can get them.

Were the wheels used in competition? No. We considered that a 6WD better fit our objectives that year--and for every year since. As such, to this day, 330 has not used mecanums in competition. They're there, though--waiting to be used if the game calls for them.

What kind of 3D printer did you have access to? I used a Dimension for my Vex prototypes and have played with some parts Made in an FDM machine and I wouldn't trust either machine to make a competition mecanum wheel unless some sort of reenforcement metal was laid into the plastic. (Possible on an FDM machine)

[EricH]

Ask ChrisH--he worked with the sponsoring company for work. I want to say that it was a 3D Systems machine, or something like that, but I could be wrong. Wasn't a Dimension, though. (I'm also guessing that there was some experimental stuff involved--I'm not entirely certain about that--or what was being played with--by any means.)

Nope, no metal reinforcement. Even the steel axles weren't reinforcement. As a matter of fact, the metal VEX wheels has some problems with their "fins" bending during assembly. Though that design would be a REALLY interesting one to take full-scale--it provided a very smooth ride due to the sheer number of rollers. It combined an "internal" hub (like most custom wheels, say 357) with an "external" hub (like the AM wheels), and when assembled was strong enough for VEX-scale use (EDUBot at the time).

The machine type was definitely one that could be used for industrial production.

[thefro526]

Originally Posted by EricH

Ask ChrisH--he worked with the sponsoring company for work. I want to say that it was a 3D Systems machine, or something like that, but I could be wrong. Wasn't a Dimension, though. (I'm also guessing that there was some experimental stuff involved--I'm not entirely certain about that--or what was being played with--by any means.)

Nope, no metal reinforcement. Even the steel axles weren't reinforcement. As a matter of fact, the metal VEX wheels has some problems with their "fins" bending during assembly. Though that design would be a REALLY interesting one to take full-scale--it provided a very smooth ride due to the sheer number of rollers. It combined an "internal" hub (like most custom wheels, say 357) with an "external" hub (like the AM wheels), and when assembled was strong enough for VEX-scale use (EDUBot at the time).

The machine type was definitely one that could be used for industrial production.

I can see how they would've held up then.

The issue I have with telling people to 3D print mecanum wheels is that '3D Printing' is a very, very general term. Most people who have access to 3D printers can only print in ABS or similar materials (Think Dimension Machines, which seem to be the most common), which from what I've seen in my own testing is no where near strong enough to make a wheel from. (Partially due to ABS, partially due to how the machine lays out the layers)

If you're talking about a higher end machine like an FDM or something even better than that that can print in something like Polycarb, Polycarb ABS or Ultem (A plastic used in Fortus FDM machines) then I could see printing a Mecanum as a viable (but somewhat expensive) option. Considering that most teams don't have access to a $100,000 + 3D Printer, I still stand by my recommendation to NOT 3D print wheels, unless you've got the right machine and use the right material.

[Jeff 801]

I have made a set of mecanum wheels that were not for FIRST robotics but used in a high capacity application and the machining of them does not take too much work but more a good deal of time. I can speak more on the machining of the hubs than how to make the rollers because I used a neoprene rubber for the rollers with a nylon core and the neoprene was just too soft. As well as there are much better ways to make the rollers than how I did (CNC Lathe).

As for the machining of the hub I did it in a 3 step process where I started with a 6x6x1in block of aluminium and the first operation I cut out the profile of the wheel hub, the center bore for a FR8 bearing and a 6 hole pattern at 1.875". Then using the 6 hole pattern I used it to mount it to a fixture which stood the hub up vertically and I then used that to cut the fins and drill a hole that I would a #10-32 set screw in. I did 6 fins so that they would line up with the hole pattern and it just made life simpler. I rotated the part to cut each fin one at a time. Then I had another fixture which held the part at a 45 so that I could fillet the corners of the fins and drill a 1/4" hole for the axle of the rollers. The part was also rotated on this fixture for each fin.

I have also uploaded some pictures of the manufacturing process here:
https://picasaweb.google.com/j3ffr3y...eat=directlink

Hope that helps.