1/20 Design Notes

Here are a bunch of little ideas that I haven’t gotten onto paper in an organized way, but I want to catch them before they blow away. You can ignore all this if you have many things to do, or read it if you have time to share your thoughts for improvements.

  1. 1) We need to have a way to turn the steering lock-to-lock to facilitate bumper changing. It would be inconvenient to be obliged to power up the robot to defeat the locking worm drive steering just to reach the bolts.
    And yes, the bumpers will require a mess of bolts compared to earlier years’ designs. This is because we will be relying on the plywood in the bumpers to add structural stiffness to the frame perimeter. (And why not? It’s going to be there.) It will be easy to swap them out IF the holes align and they are placed to allow a screwgun to reach them from inside the (enormous) wheel wells.
    Alignment can be facilitated like this: The bumpers will be two C-shaped (or even 4 L-shaped) units, with studs on one side and pockets for bolts on the remaining sides. Running the studs into holes on the frame should position the remaining bolt holes in alignment.
    There should be a non-colinear pattern of bolts into the bumper backing. (3 points determine a plane.) This will amount to an upper and lower row of bolts, with at least two bolts into each face of the bumpers. This will be 16-18 bolts. (Because these bolts don’t just hold the bumpers on, they make the robot frame as stiff as the 3/4″ plywood the bumpers are made of.)
  2. The frame perimeter will also have an upper and lower set of bumper bolts. Major attachment points should be where the internal frame hits the frame perimeter: Center front, center rear and on the frame sides just behind the front wheels (ditto rear) where the transverse members hit.
  3. Conceptually the frame is triangulated like this.

    In practice, parts of the rollbar framing and the skid-keels could be made of sheet metal triangles rather than tubes.
  4. Use one strong gearmotor to wind both the catapult and the climbing winch, using two ratchets in opposite directions. When running say clockwise, the catapult spring is wound up and the winch ratchet is freewheeling. In the other direction, the opposite happens. To work well, the motor would be winding the “fixed” end of the catapult spring, so as not to interfere with the catapult release.
    What is a suitable type of catapult spring for this? Twisted surgical hose? Garage door spring?

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