Design Rule GuideΒΆ

The following guide is intended to help with designing new parts to extend the kit itself rather than simply using the kit. In practice, this line is blurry, since making mechanical structure is usually a fluid and custom-fit process, and so many applications of the kit will involve modifying or combining existing parts.

The base components and subassemblies were designed with the following set of constraints, chosen for both general purpose utility and simplicity of fabrication. New parts for the kit should generally follow this rules. This list will continue to evolve.

  1. Material: 6 mm Baltic Birch double-sided plywood.
  2. Dimensional grid: part features are generally chosen on a 25mm grid. E.g, the basic straight connecting links are 25 or 50mm wide.
  3. Wooden part fasteners: M6 bolts and nuts. Specific components may require special cases.
  4. Extrusion rail fasteners: M3 button-head socket cap screws and square nuts.
  5. Clearance holes: nominal 6 mm. This is a close fit on an M6 screw.
  6. Bolt pattern: the standard interconnection pattern uses a 25 mm grid with four 6 mm holes at the vertices of a square with 25 mm sides, centered in a 50 mm square area.
  7. Shafts: 6 mm shoulder screws.
  8. Shaft holes: 6 mm drill. This is a free fit on a 6 mm shoulder screw. (This may need adjustment.)
  9. Where parts glue together, provide 0.2 mm glue gap: increase holes in outer surfaces by 0.4 mm diameter, increase slot lengths and widths by 0.4 mm.
  10. Existing tabs are either 15 or 30 mm long. Existing slots are 9.4 mm wide and 15.4 mm or 30.4 long with the glue allowance. Inside corners are 3.5 mm radius. The preferred inside corner design uses a 180 degree arc, but the position varies depending on the purpose.
  11. Bearings: still in flux. Some components will use a 6 mm shaft in a plain wooden hole, some may use a 6 mm shaft in a bushing with 8 mm OD, some may use an 8 mm shaft in a 8x22x7 mm skate ball bearing. The actuated knee designs use a 50x65x7 mm thin-section ball bearing.
  12. SolidWorks parts include Design Tables wherever possible with systematic parametric variations.