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Re: Rookie team questions on chassis and drive train
Even as a veteran team (our 5th year in competition now), we're using the kitbot chassis. It's strong, light weight, easy to work with, and comes with mounting holes pre-drilled! We made a custom chassis in 2009... while we got everything working just fine, we ended up spending a lot of time on the chassis that we could have really used elsewhere. There is no underestimating the affect of any time saving activities.
I want to second what Al said about the sizing box, and to add to that weight. Both are unforgiving. Pay attention to them both throughout the build season, and actively design your plans with them in mind. Don't aim for a 120lb robot - you'll end up over. Don't aim for a robot that's 28" wide - you'll have bolt heads that stick out. One of the hardest things for a team to do is show up at competition and have to start drastic modifications to get within the height/weight restrictions. I've seen teams spend an entire day (or more!) drilling holes in their robot to try and lighten it enough to pass inspection. I've even seen teams that had to remove their entire manipulator in order to pass inspection.
We always build ours 27"x37" to ensure we fit in the sizing box. We always aim to be at least 10 lbs under weight - then bolt a steel plate onto the bottom of the robot at competition to bring us up to 119.5lbs, once we have the official measurement and know how much we need to add. Probably the worst feeling in the world was weighing in at our second competition last year and being almost 5lbs over... all the students started freaking out a bit. Then the inspector removed his foot from the scale, and we were fine.
One final note about number of motors in the drive train... 2 versus 4 is always an interesting argument, and it relies completely on what capability you want your robot to have. If you feel the need for extra pushing power, use 4. Otherwise, 2 will give you the same max speed and work great - just without that extra oomph of pushing power. If you want to use a CIM motor to power a manipulator of some sort, you'll have to only use 2 on the drive train - the rules only allow 4 maximum on the robot.
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