One of 'em, Diane, is in it because she's chasing Caleb, one of the central characters. I don't want to follow romance tropes; they don't eventually get together. Caleb gets involved with somebody else, and Diane eventually goes off by herself to straighten out her head, and succeeds in so doing, building an eventual platonic friendship with Caleb -- and a more important one with Andy, the most-central character.
That leaves the ones I've been thinking of as the Two Small Boys. Ted is Andy's little brother, but that doesn't explain how and why he gets involved with the robot. And Tom is Teddy's "little shadow", which again explains why he's *here* but not how he gets involved with the project. Hmm. The robot-wreck is currently hiding in the garden-shed at Teddy's house; Teddy could spend some time working on it and do some drawings of what he's found inside. For the moment, Tom is still just a tag-along, but he'll turn out to be a champion scavenger later. (Teddy's eleven; Tom is ten.)
And now I need to figure out a technical detail: The robot is *not* electronically controlled. So how do signals get from the mechanical brain to the hydraulic actuators? Fiber optics are out, they weren't invented yet. Some form of analog mechanical communication. Geeks of LJ, any ideas? The predominant form of controls at the time would have been cables, which can be pulled or pushed varying distances for varying durations -- is that enough bandwidth to provide sufficient signal for a bipedal robot to maintain physical balance?
Back on Diane: Her motivation at the moment is that she's chasing Caleb, and she gets to hang around with the group because Andy and Teddy's mom Faye thinks teen romance is cute. So she's not looking for a way to be involved in the robot project because she's into robots, but still needs a way to make herself useful to the project.
However, she doesn't need to be useful from the very beginning. Her main skill-set is social rather than theoretical (Andy), physical (Caleb), or mechanical (Teddy). So before we get to that point, I have to figure out whom in the story she's charming to get what.
All of which generates no text. Right now Caleb has a contact sheet from Andy's dad Dale, and can spend the week calling people and talking with 'em. Andy herself is going to have a long and very informative talk with her grandma. Zari is going to ask *her* Dad for help, and will bring a report back of what he has to offer, which isn't going to turn out to be immediately useful. And Ted cracks the robot open and identifies a two-stroke engine, a hydraulic pump and reservoir, and an amazing network of valves.
Back to work.