[Joe G.]

On it being their loss:

I'm a firm believer that the people who show no interest in the engineering experience initially; the ones who are dragged to meetings by their friends, attracted by promises of free food at the first meetings, or just join on a whim, are those who have the potential to get the most out of the program. You can't force anybody into FIRST. But you can give them a gentle push. And sometimes, that gentle push can have powerful results.

On the original topic:

I come from a team where, for a number of reasons, intermittent attendance is a HUGE problem. One of the things I've found very helpful is to step up the team's use of Inventor or other CAD software a lot. "Core" members will likely be most involved in the CAD process itself, although others can also work remotely on it. But once it is finished, having printed drawings of most of the robot's parts makes it MUCH easier for people to "jump into" the process. It's much easier to hand someone a piece of paper with a dimensioned drawing on it and say "make this," than hold a conversation like this:

You: Hey, you're not doing anything, could you make the arm bracket
Them: The what?
You: Oh yeah, you weren't here, the prototype broke so we decided we'll need a bracket for extra support.
Them: how is it designed?
You: well......
*5 minutes of failure to get the design fully conveyed by word*
You: Never mind, I'll just do it.

Also, if they can't attend design meetings, but still want to help, encourage them to come up with concepts, and run concepts by them, outside of meeting time. Members who can attend can then "represent" them.