Questions about crab/swerve drive.

[hillale]

Originally Posted by BenX02

2) This is going to sound like a dumb question, but I have heard that a water jet/computerized mill is necessary for building a crab drive system, may I ask why? The machine shop our team meets at has one, but in the past they have not let us use it.

Precision is key when building a bulletproof swerve drive. This cuts down on everything from chain play to drift. Our 2007 swerve (handmade) was down for some reason or another (thrown chains, etc.) every few matches. Our 2008 swerve (waterjetted) made it through 3 regionals and champs without the need for a fix (until IRI when one of the axles wore far enough to lose it's snap ring which was a less than 1 minute fix with our design).

If you want more info, pm Aren_Hill

[BenX02]

Originally Posted by hillale

Precision is key when building a bulletproof swerve drive. This cuts down on everything from chain play to drift. Our 2007 swerve (handmade) was down for some reason or another (thrown chains, etc.) every few matches. Our 2008 swerve (waterjetted) made it through 3 regionals and champs without the need for a fix (until IRI when one of the axles wore far enough to lose it's snap ring which was a less than 1 minute fix with our design).

If you want more info, pm Aren_Hill

I see. Did you machine your wheel hums out of one piece of metal? I'm guessing not, but it's an idea.

[sgreco]

You definitely don't need a CNC to make a swerve drive, if it's going to be coaxial and you're going to use bevel gears, you probably want to find a shop to help you out. My team made a full swerve on a manual Bridgeport mill in 08.
We used a 4-axis CNC this year, but you certainly don't need that to make it good.

For sensors, my team finds hall effect sensors to be the best because they are absolute sensors which saves time centering the modules(the reading is usually more accurate for us than we found with pots and encoders).

Although you are only allowed 4 CIMs, you probably wouldn't want it for steering anyway. They are too fast. I would use the globe motors. My team used the Denso motors and they worked fine as well.

If you have any questions feel free to PM and I can answer any questions you want about mechanical aspects of swerve.

[R.C.]

Here are some pics of some modules and dt's:

http://www.chiefdelphi.com/media/photos/33368
http://www.chiefdelphi.com/media/photos/33336
http://www.chiefdelphi.com/media/photos/33335
http://www.chiefdelphi.com/media/photos/33334
http://www.chiefdelphi.com/media/photos/32573


CAD:
http://www.chiefdelphi.com/media/photos/32520
http://www.chiefdelphi.com/media/photos/32444
http://www.chiefdelphi.com/media/photos/31626
http://www.chiefdelphi.com/media/photos/31078
http://www.chiefdelphi.com/media/photos/29415
http://www.chiefdelphi.com/media/photos/29412
http://www.chiefdelphi.com/media/photos/28568
http://www.chiefdelphi.com/media/photos/25328

These are just some images and stuff on CD. If you contact the creator, they will for sure help you out. There are a ton of iterations. You just have to find one that fits your needs. On sensors, since MadTown will never do Crab (I mean NEVER). I don't know. But someone will post a link soon hopefully

[sgreco]

This a is a swerve I drew up during the build season with the specific intention of not needing a CNC machine. However, you do need a rotary table for your mill with this design.



The sprockets for powering are not shown, but they could simply be attached with a keyed connection. The steering sprocket is shown, but the motors for steering aren't because we didin't know what method of actuation we wanted or which motors we would need elsewhere. I would recommend steering the front wheels together and the back wheels together for a little bit of flexibility in steering modes.

The CIMs can also be down into the frame. The only reason they a sticking up is because of a few specific wiring issues that pertained to my team's 2009 bot.