pic: Skunkswerve Module Cross Section

[big1boom]

We also had at 3 axis controller. X and Y for crab steering, twist for warthog.

[keehun]

Excuse my lack of knowledge on Crab Drive, you only needed one CIM because all the wheels move in the same "direction" but the wheel base themselves turn?

[big1boom]

Under normal traction circumstances you need at least 2 CIM's, but with the Regolith 1 CIM is adequate for our team at least.

[Dave McLaughlin]

With a crab drive all of the wheels are oriented in the same direction relative to the field, and all wheels are powered so that the robot moves in that direction. With a pure crab drive there is no way to change the orientation of the robot relative to the field, so most teams implement a turreted manipulator (Team 118 in 2007 and 2008 are good examples). A pure swerve is where all wheels are powered independently AND steered independently so that each wheel can be facing a different direction relative to the field. Our "half swerve" has the front and rear wheels steered together, and the left and right wheels powered together.

[big1boom]

Just wondering, did your team do any prototype in the off season? Or were you like us and decide that tank will not work this year in the middle of week 2.

[Dave McLaughlin]

We had kicked around a swerve last year until we went to CMP and saw how much machining it took to make a proper one. This year necessity drove our design like it always seems to do

[big1boom]

We decided that tank would be inadequate this year, so we CADed up parts and CNCed them on our 20+ year old machine.

The amazing thing is, that we really only started assembling at the end of week 3 I think

[Dave McLaughlin]

We decided in our initial brainstorm that swerve would be the way to go. After that we CADed our brains out and sent out parts to be water jet cut and welded for our frame in week one (Thank you Omax). The modules 4"x4" (1/4 W) was cut into segments and sent to another welder along with the 1/4" al. plate to be welded into the modules initial shape. From there they were taken to a new machining sponsor (Puget Sound Precision) and were machined on their 9 axis CNC mills. We got them back and assembled them during week three and were driving at the end of week 4

[big1boom]

Nice. We had the plates CNCed in our small little shop out of 1/8" plate. It took a long time.

[Aren_Hill]

Originally Posted by big1boom

Or were you like us and decide that tank will not work .

wait...tank doesnt work? did i miss a memo...

[big1boom]

Tank works, we just decided that this year would be a good year to start swerve, and that it would help a lot with the trailer.

[Swttrt224]

Big1Boom....their modified swerve is what we call a twerve....nice job guys, that's a very creative idea. i had a similar idea last year but have never been able to actually implement it. If i may ask, how is that working out for you perfomance wise?

[Sam N.]

Surely you are running closed-loop position control for your steering motors. What type of sensor are you using on them?

[Dillon Carey]

Originally Posted by Dave McLaughlin

I envy how easy it must be to get your hands inside the module for maintenance.

we had the same problem with our first swerve drives, one somewhat simple thing you can do is to move the chain and sprockets connecting the wheel axle to the upper axle to the outside of the module. As long as this doesn't cause your module to become wider then the diameter of the wheel it shouldn't hit anything. this makes tensioning and replacement of this chain much easier, also it opens up more room on the inside of the module.

http://www.chiefdelphi.com/forums/sh...=swerve+module

This is our teams last swerve design, one other thing we did as far as maintenance was use hex axles and snap rings to make everything very easy to change. Our '08 bot,which used these modules,never broke in competition but it was way better than '07 when we had to get 4 people and sit for an hour to get the wheels out and replace the tread, now it only takes 1 person 30 minutes or less to replace all 4 wheels.

[Sam N.]

I think all of the wheel modules I've seen online have had their main housing either welded together or machined from solid.

Our modules are bolted together using aircraft-grade 6-32 machine screws.

http://www.chiefdelphi.com/media/photos/32573

Don't get me wrong though, I'm a big fan of welding. It just seems to me that it would be easier to do service work on a given wheel module if it could be taken apart. Using screws to fasten the parts together does offer a serviceability advantage IMO.

I also believe that the weight of bolted housing is comparable to the weight of a welded housing - our modules weigh less than 4lbs each.

Still, the best wheel module is one that's so reliable it doesn't need to be serviced very often, or even at all!