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  #31   Spotlight this post!  
Unread 23-11-2008, 22:12
CraigHickman
 
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Re: pic: Mecanum Musings

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Originally Posted by Brandon Holley View Post
I've spent some time designing mecanums (on a smaller scale), and I have my own method, but I was wondering if you would share the method you used to create the curvature of the roller. Specifically in CAD terms (I'm very familiar with any CAD system), what you did to ensure your roller curve was as effective as possible.

Thanks in advance!
Brando
Sure thing. Start with a center line that will serve as an axis to revolve the roller around. Next, draw your edge lines on the left and right edges of the axis. Put a third in the center, higher than the first two. Draw two arcs connecting these outer lines to the center line. Let me know if this is confusing and I can upload a drawing for you.

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Originally Posted by Hell918 View Post
The only question i would ask would be if they were to be bumped into would they break easier or would they still have enough strength.
They're quite solid as they stand, but I don't like leaving a wheel uncovered for any reason. For that reason I'll probably enclose the wheels, most likely in 1/8th aluminum sheet on which the bumpers will be mounted.
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  #32   Spotlight this post!  
Unread 23-11-2008, 22:28
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Re: pic: Mecanum Musings

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Originally Posted by Speedfiend View Post
Sure thing. Start with a center line that will serve as an axis to revolve the roller around. Next, draw your edge lines on the left and right edges of the axis. Put a third in the center, higher than the first two. Draw two arcs connecting these outer lines to the center line. Let me know if this is confusing and I can upload a drawing for you.

I believe I understand what you are saying, it is similar to what I do as well, but a picture would not hurt... thanks!
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Unread 23-11-2008, 22:35
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Re: pic: Mecanum Musings

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Originally Posted by Brandon Holley View Post
I believe I understand what you are saying, it is similar to what I do as well, but a picture would not hurt... thanks!
Well, here's a Paint version... I don't entirely feel like booting into windows right now, so I can swap this image out for a screencap of the sketch some other time.



Then you revolve it around that bottom line. After that you put a hole through the center for the bolt, then put recession into the roller for bushings.

Last edited by CraigHickman : 23-11-2008 at 22:39.
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Unread 23-11-2008, 23:45
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Re: pic: Mecanum Musings

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Originally Posted by Speedfiend View Post
Well, here's a Paint version... I don't entirely feel like booting into windows right now, so I can swap this image out for a screencap of the sketch some other time.



Then you revolve it around that bottom line. After that you put a hole through the center for the bolt, then put recession into the roller for bushings.
Yes i'm completely with you there.

To be a little more specific, I was referring to how you designated the actual arc on your sketch. Was it simply a large radius? A spline? If so, what did you use to define that spline, etc... Any more info would be awesome! Thanks again
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Unread 24-11-2008, 00:12
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Re: pic: Mecanum Musings

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Originally Posted by Brandon Holley View Post
Yes i'm completely with you there.

To be a little more specific, I was referring to how you designated the actual arc on your sketch. Was it simply a large radius? A spline? If so, what did you use to define that spline, etc... Any more info would be awesome! Thanks again
Gotcha. It's drawn as a Center Point Arc. The arcs were each 5 inches in radius (I think. I might be off a little.), and the entire roller is 2.75 wide. I'm still doing some math to see if really using an Arc is the right move. I might end up moving to a spline, who knows right now. I do know that we'll be pouring our own wheels into molds that we get 3d printed!
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  #36   Spotlight this post!  
Unread 24-11-2008, 00:13
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Re: pic: Mecanum Musings

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Originally Posted by Speedfiend View Post
Gotcha. It's drawn as a Center Point Arc. The arcs were each 5 inches in radius (I think. I might be off a little.), and the entire roller is 2.75 wide. I'm still doing some math to see if really using an Arc is the right move. I might end up moving to a spline, who knows right now. I do know that we'll be pouring our own wheels into molds that we get 3d printed!
Funny you say that....I use splines when I've designed mine

I actually have my wheel 3d printed already and am making a silicone mold of it, and then using that mold to cast my own hubs and rollers!
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Unread 24-11-2008, 08:54
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Re: pic: Mecanum Musings

I would strongly suggest that you make your rollers out of some non-lubricating plastic, then dip them in a rubberized coating to make them sticky. You can get the coating dirt cheap at any hardware store (it's what you dip tools in to rubberize them).

I say that because machining softer grade rubbers can be a real headache for the machinists. They tend to tear - even the harder durometers. So they end up having to freeze them then rush them to the lathe to get them done before they thaw. Like I said - real pain in the neck.

Plastic would be easier to machine, and in the end probably it would probably be cheaper too.

A step up from that would be to have a machine shop machine a female mold that you could pour your own rollers from. That'd be cool and not too hard - heat plastic in pan till liquid and pour in. A bit like pouring those old lead army men into casts.
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Unread 24-11-2008, 10:20
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Re: pic: Mecanum Musings

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Originally Posted by Tom Line View Post

A step up from that would be to have a machine shop machine a female mold that you could pour your own rollers from. That'd be cool and not too hard - heat plastic in pan till liquid and pour in. A bit like pouring those old lead army men into casts.
From what he said, I believe he is going to do some sort of casting.
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Unread 24-11-2008, 15:37
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Re: pic: Mecanum Musings

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Originally Posted by Tom Line View Post
A step up from that would be to have a machine shop machine a female mold that you could pour your own rollers from. That'd be cool and not too hard - heat plastic in pan till liquid and pour in. A bit like pouring those old lead army men into casts.
In the past our team has had molds 3d printed by the local community college. We would probably do the same this year.
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