Rhombot 0.3 alpha
See an animation of it on YouTube: http://www.youtube.com/watch?v=zSeg-Th1tRw
The Rhombot is a printable XYZ stage based on 3 chains of rhombus shapes. It is currently just an early alpha version. It's a rough sketch of the idea. See one of the two .MOV videos for how it is intended to work.
The Rhombot can be used with Makerbot motors, electronics, and extruders. All parts can be built in a Makerbot, or in itself. The Rhombot has no rods, belts, pulleys, nuts, threads, screws (other than the screws on the motor), sarrus hinges, moving towers, or moving motors.
That last point is important. The XYZ motors and extruder motor are all fixed. The X motor does NOT move a carriage carying the Y motor. The Z motor does NOT raise a platform carrying the extruder motor. Instead, all 4 motors can be permanently mounted. This means it will work with motors that are arbitrarily large and heavy. That should help when we start printing motors, since the early ones are likely to be large and heavy.
The green build platform has a Z coordinate that is the sine of the rotation angle of the NEMA17 stepper motor under the light blue panel. X is the sine of the dark blue arm's motor, and Y is the sine of the purple arm's motor. To use this to print, it would be necessary to modify Skeinforge to take the extra sine into account.
The build volume is large enough to print all its own parts. The animation even shows it building 4 of its own parts, as well as building a cube large enough to hold any of its own parts. The build volume actually extends beyond this cube, but is an odd shape. The cube in the video is the largest cube that fits within the build volume, oriented that way.
This has now been printed on a ZCorporation ZPrinter 650. It glues powder together to give an object similar to sandstone. This means the pieces are extremely rigid, but break easily. The printed Rhombot has hinges that move smoothly, with almost no slop at all in the direction of the hinge, nor orthogonal to it. The smooth movement is surprising, since the surface feels like sandpaper.
If you hold two panels that should stay parallel and try to twist one, it seems to allow almost no twisting at all. The small amount of twisting that it does allow seems to be from some of the hinge pins that are too thin. The hinge pins are wooden toothpicks, and don't have uniform diameter. They will soon be replaced with segments of 2.4 mm diameter aluminum rod.
The next step is to build this in plastic. It will be far stronger, but it may start having problems with panels bending and twisting. That's the big question. There are also several design changes that should make it into the next version.
Print everything in the stl_to_print.zip file. Each filename tells how many to print. Connect them with hinge pins that are 3 mm in diameter.
The pieces actually have the build directions engraved on them. Two edges connect to form a hinge if they have the same number on that edge. For positive numbers, they should face the same direction, as if the hinge was formed while both panels were sitting on a table face up, with the writing visible on both. The numbers are negative if they face opposite directions, as if the hinge was formed while they were lying on a table with one face up and the other face down, hiding its writing. If a hinge has two sets of holes (so it can connect to two other panels), then there are two numbers given, with the first number referring to the highest hole (the one farthest away).