Now that it is the off-season (no need for major team spirit) I would do some projects such as building a t-shirt cannon, or a "robotic go-kart" to use that as a teaching lesson. People only really get interested once they start doing things, not making buttons, trust me. Few will want to make buttons after the tested a robo-kart by racing others down the hall and nearly hitting everything in the process.
With that said start these projects with the intentions of specific people working on specific things. If they don't do them, tell others that may have been uninterested in the past that you need their help to get the project done. If they know they are helping it will increase their want to build.
That is about all I can think of, hope this helps
