my team needs crab/swerve pod cad files

Originally Posted by JesseK

CraigHickman has a good picture of a crab module and a drive train assembly on his site. You could also PM him to ask him how he did some of the more intricate work.

http://www.xtremefury.com/craig/

I too highly recommend that your team does the CAD from scratch. Use a few pictures as reference, but do your own design. Knowing every nut, bolt, washer, sprocket, chain, and spec of dust you put into your drawing will make it that much easier to come up with design improvements. If your team is new to CAD, I would recommend doing the tutorials first, then doing a simple aluminum frame. Then from there you can experiement.

As always, many of the FIRST motors, transmissions, pneumatics (etc) are already available at www.firstcadlibrary.com

Wow, I feel honored to be mentioned...

But anyway, sharing CAD is a tough issue. I normally don't share it unless it's someone I trust, but even then I put in a "security" measure in order to make sure they're doing their homework. Some dimensions will have been slightly changed, not enough for aesthetics, but enough that any attempt to make the part will fail miserably, or will be hell for the machinist.

As for designing your own, I can send you some renders, as well as answer any questions you've got. Please feel free to AIM me any time, or PM me with any questions. Oh, and that old CAD gallery is WAY out of date.... I ought to link the new one...

[Greg Needel]

Originally Posted by CraigHickman

I put in a "security" measure in order to make sure they're doing their homework. Some dimensions will have been slightly changed, not enough for aesthetics, but enough that any attempt to make the part will fail miserably, or will be hell for the machinist.

Ummm...no offense but this seems like a waste of time. The way I see it if you are not willing to share your CAD that is one thing, but messing it up on purpose so it won't work seems like a bad idea. Especially for high school students calculation center to center distances for gearboxes or any of the other precision required dimensions can cause problems even if they design them from scratch. I think it would be better just not to make them public, because once you release virtual files you no longer control where they go and a 3rd or 4th party person who may get them may not even think that they aren't complete. Yes it would be a lesson to learn for the person who just tries to copy but won't you still feel bad when a robot running your design fails miserably on the field....I know I would.

As for seeing unobstructed views of the CAD to get designs from you might have people use auto desk freewheel. http://freewheel.labs.autodesk.com/index.aspx

[JVN]

Hi Will,

Good idea taking a crack at a Swerve drive during the off-season, there is a lot of development involved in something like this.

I don't have Inventor, we do our modeling in SolidWorks. Check the attached ZIP file for a STEP assembly of the Robowranglers 148 - 2008 Coaxial Swerve Module. (The STEP file should import cleanly into Inventor.)

This module was heavily inspired by the Thunderchicken 217 - 2002 & 2003 designs. (Thanks Foof!)

Let me know if you have any questions.
I'm happy to help, and always sympathetic toward a college FIRST team!

Regards,
John

PS - All the dimensions are valid; this is exactly as we built her.

PPS - Don't do a swerve drive for a competition robot.

[s_forbes]

Great files, John! Quick question about that module: What type of bearing are you using for the large turntable? (and where does it come from?) I would have thought that a design with a single bearing like that would put enormous side loads on the bearing that it couldn't handle. Did you have any problems with it at all?

Originally Posted by JVN

PPS - Don't do a swerve drive for a competition robot.

I think we'll take that advice!

[James Tonthat]

Thanks John!

I was trying to figure out how one of the bearing sections worked and what kind of bearing was used (thrust or ball.)

Edit: Err, nevermind

[JVN]

Originally Posted by s_forbes

Great files, John! Quick question about that module: What type of bearing are you using for the large turntable? (and where does it come from?) I would have thought that a design with a single bearing like that would put enormous side loads on the bearing that it couldn't handle. Did you have any problems with it at all?

Yes there are enormous side loads on the bearing, but it handled it fine. The practice chassis deformed but the bearings are fine.

The swerve bearing is a 2" ID, 2.5" OD, 0.25" THK bearing.

It is a KAYDON bearing P/N KA020XP0. You can buy it from any KAYDON distributor. (We got ours from Motion Industries.) If you say you are a FIRST team you can get a discount.

Paul Copioli was the one who recommended it to me, as it is used commonly on the real robots he works with.

After we started production on the swerve parts, I got cold feet. I have never done something like this before, and I am a pessimist by nature. I called Paul up and asked him if this bearing would be able to survive the heavy shock loads caused by our application or if we needed to support the base of the swerve module. He just laughed at me.

These bearings held up great; they were perfect for our application.

It was important to make sure that both the inner race and outer race of the bearing are WELL captivated. You can see in our cross section how we hold the bearing in place. (See above post.)

This may not be the best way to do things, it just happens to be the way we did it.

Hope this helps!

Regards,
John

[James Tonthat]

Wait, so that's a 200 dollar bearing?

[Matt C]

Being able to use a single bearing to mount the swerve module to the robot was probably deemed worth the expense. I believe a normal application would be to have a pair of bearings one to take axial and radial loads, and one to take radial only. This would deal with the moment generated at the mounts. Please correct me if I'm wrong.