Like John said, it is all about the geometry. There are three thicknesses we use: .0625, 0.90, and .125. I try to start with .0625 and only go up in thickness as required. For the last few years, the major differences in the basic sheet metal construction between 148 & 217 have been:
- 148 used .090 for the drive base and 217 used .0625
- 148 primarily used 1/4" rivets and some 1/8" rivets and 217 used 5/32" rivets exclusively.
- 148 used flat plates with standoffs for the gearboxes and 217 used bent metal and rivets.
- 217 got most of it's lightening from using .0625 with basic holes and trusses and 148 did it with .090 and a specific focus on visually appealing large lightening patterns.
This year, we decided to try each other' styles and mix and match:
- Both 148 & 217 are using .090 fir the drive base.
- Both 217 and 148 are primarily using 5/32" rivets, but using 1/4" rivets for main structural attachments and in place where we may need a bolt due to rivet gun access. We found a very inexpensive pneumatic riveter that can do 1/4" rivets with no problem. Each team owns 1.
- Both teams are using a bent sheet metal gearbox for the drive directly riveted to the drive base. In addition, our other gearboxes are a combination bent meta / standoffs.
- Both teams are using the 148 style of lightening.
One major difference between the two designs is the choice of fasteners. 148 uses English (where possible) and 217 uses metric (where possible). This posed interesting design challenges to make interface holes to handle English or metric on the few parts that were the same. We standardized on #10-32 (M5) and 1/4"-20 (M6). That has worked out much better than I planned.
I will probably do a joint white paper with John, but it will have to wait until the VEX stuff settles down as John and I are both extremely busy due to VEX's increasing popularity globally.