I've had several false starts on the drive system upgrade. At one point I thought I would be able to attach a gear to my old wheels and use my old drive frames and add the NPC motors in, but after I got the parts from The Surplus Center I could see that that wouldn't work. So I reconsidered.
I've been really impressed with Mike Senna's drive system ever since he developed it. So I've resolved to give it a go with some modifications. I searched around Sacramento a bit for wheels and found a place that
sold me these:
Next I have cut 4 trapezoidal side plates. I'm following the Senna planes on outside dimensions. (I've mentioned it before, but the Senna plans are part of the "Files" attachments to the R2 Builders Yahoo group. Go down to Senna files, then look in the Senna Drivetrain folder.) The side plates are going to bolt onto the channel top plates above to make the frame.
So I clamped these side plates into position on the U channel to mark and drill the holes for mounting in exactly the right spot, drilled them out, and then the bolts went through no problem. My bolts were a bit long and protruding into the space inside, so I trimmed them off with the Dremel tool.
Here's the result. I've put the plates on the inside but they can be easily be mounted on the outside to make a little more room. So there's a bit more versatility with the interior width here than working with the rectangular tubing. The drawback is that the bolts can work lose. So I'm going to add some locktite to them on final assembly or superglue. When the rest of my materials get shipped here next week, I'll start laying out the axle locations, add some bolts across the bottom for bracing, and so on. More details then. I'm excited to get those NPC motors in there.