pic: Pigmice Northwest Drive

This is the first CAD model i have had the guts to post to CD. Quick specs
-4in Performance center wheels with dual omni outside
-Pneumatic Supershifted with optional gear ratio for high speed of little under 14 fps and low gear of 3.6 fps.
-Custom chain tensioners allow for easy chain maintenance, as well as allowing any of the four outside wheel to be unbolted and replaced in a matter of minutes.
-Designed to be built within the first week of competition requiring minimum machining.


Looks good! Only question I have is you called it “Northwest Drive”. Is this any different from West Coast Drive? If so, what are the differences and advantages/disadvantages? I’m assuming the duel omnis on the corners are for ease of turning, and that there is no drop on the center wheel because of that.

This chain-path is on the outside of the frame rails. Traditional WCD has an inside chain-path. This also doesn’t look like it has the characteristic bearing blocks of a real WCD.

Just curious, why the 4 inch wheels? The smallest I’ve heard of in the past are 6 inches. Also, don’t be nervous about posting stuff on here. It looks really good and you should be proud of your work. We may ask questions, but we try not to be too scary.


254 used 3.5" this year and 233’s wheels were smaller. In recent years, small wheels have been one of the defining features of “west coast drive” robots such as this. Just look at the robots of two of the current world champions. :stuck_out_tongue:

bout 2.75in rims on the corners last year.

next year expect possibly 2.5in rims for packaging reasons.

I do believe that there have been WCD robots with the chain in both locations and even a few wit it inside of the frame rail. The real distigushing feature here is that this robot has omni-corners and no drop on the center wheel. ALL true west coast drives have droped center wheels and none use omniwheels.

Why though? What is the functional advantage?


-Less Weight
-Cheaper Material
-Less Machine Time
-Less Gearing, 233 may get away with only one stage of gearing?
-Better acceleration
-More efficient.


Less, and thus lighter, gearing results in the same effective ratio, also the wheels are smaller. the weight savings might be enough of a reason,** but smaller wheels and the associated gearing allow the motors to operate at a different, possibly more efficient part of the performance curves.**

That is not strictly true. While at the same rpm the smaller wheels would go at a different (slower) speed, the gear ratio could be used to compensate. While there are fewer gears necessary to get the same speed,there isn’t a change in the fact that, with enough gears, you can gear for any speed

I like it, but how are you attach your SS? and why did you make a “V” in front instead of adding a front rail because the rules for the bumpers this year would not allow that. How exactly are you planning to mount the bumpers to the 1’ alum. tubing on the sides? and do I spy a custom center wheel? last question I promise, hex axle or keyed axle?

But looks great keep up the good work

There is no single distinguishing feature for a real WCD IMO, I only consider 254 based drives to be real WCDs.

Thanks for the responses. I knew there was a good reason just couldn’t figure it out. I still have my reservations about such small wheels, but that is probably just because they are new to me.


I’ve been thinking of a similar design, but I was planning on using 4 plaction wheels in the center with the 4 omnis in the corners. I believed this would help increase stability from being spun by other robots.
8 wheel - 4 plaction center, 4 omni corners for stability and forward pushing. No drop.

Anybody think the 4 wheel center would actually do anything to fight being spun from other robots pushing your corners?

Highly doubt it. You’ll still get spun easily. If you want traction and maneuverabilit take a look at 148/217 2010 setup.


Many times it has been said that you shouldn’t bother shifting if you are gonna have omni wheels. It’s fairly accurate. You can do the math if you like, but it will be easier to spin the wheels and you won’t win many pushing contests.

One other note: Low gear is defintely too slow. This past year we ran a similar speed w/ 13fps and 3.5fps. In low gear we could push without issues, but it took a very long time to get anywhere. It really wasn’t worth it. Try gearing your low gear closer to the traction break point. Which will probably comeout to be 7-8fps.

When you’re driving around trying to get to places, shouldn’t you always be in high gear?

I know our driver stayed in our 17fps high gear 90% of the match, if not more.

This post I made in another thread (and some other posts from others in that thread) describe more benefits of small wheels.

Agreed. I could probably count the number of times we used low gear in 2011 on one hand. Low gear is one of those things that is rarely needed in everyday match play. However, when we need it, we really need it. You can probably make low gear faster than 3.6 ft/sec, just make sure it’s traction limited.