ME: Paper

Process

Getting into the specifics of the design, paper and imagination was absolutely the fastest way to find basic flaws in construction. It's far faster than CAD or building it even if you're trying to make clean drawings.

Once the design is a bit more final, CAD seems like a solid choice again. This time, not using a bunch of exacting math or trying to model it all but instead just using the values you know you will and trying to get things close. I'll add more to this cad drawing as time goes on.

The problem I was solving

Lets imagine how the grabber will work. There's the threaded rod. On either side of the rod are bearings. On one end there's also a gear that the motor connects with to turn it. Sliding along the rod will be the actual grabber arm and it's electromagnet.

This poses already several questions:

#1. What keeps the grabber arm from just rotating as the rod does? We could give the arm bearings to slid along some flat surface. I think instead it's probably easiest to just connect it to the other arm. They're supposed to move in tangent anyways and the cables to power the electromagnets on either side will have to go to both of them anyways. Also, that's just a lot simpler than bearings, which are either a pain or expensive.

#2. Just how close to the user can the table get? Will the fetcher be able to bring the shelf from all the way stowed to right next to the user? Not really. So how closer? If the bearing is there, that's 1.5" and then the arm will actually have to extend over the gear, another bearing at the other end, and the length of the electromagnet. All that will be 4" at least. Now the table is 6.5" away from the user at a minimum.That's getting to be a bit awkward. We'll have to cut out any connection on the far end of the fetcher arms. Either side will extend out a bit but the center will only connect farther back. This also makes the threaded rods more convenient; we won't have to cut those and they only come in 24" while the plan for the table is to be 18" deep. Of course, given that we decided on having a cross piece in #1, we will have some offset. Probably just the width of the cross piece and the electromagnets themselves. 2" seems tolerable.