Rogue Strandbeest Bike Build

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You typically see these mechanisms with 6 or 12 legs, the Jansen linkage design has each foot at the bottom of its path (where it travels in a straight line) for 1/3 of a crank revolution, so having 3 legs you have 1 foot in contact at a given point in time assuming a flat ground. With 6 legs in the rear it would be smooth and stable with 2 feet in contact with the ground in the rear at all times.

I made this design with a minimum number of legs to test out the maneuverability on a bike, if you have more than one point in contact with the ground then to turn one of the feet has to slide against the ground (skid steer), which works fine on small models but becomes more of an issue at full size when carrying a load (especially with the traction / safety factor / slop in this design/scale specifically).

3 legs on each side with a differential connecting the two sides would be interesting and not have the skid steer problem, not sure if the two sides getting out of phase would impact smoothness

Aluminum tube would probably be the lightest / cheapest aluminum option, it would be plausible if you have a tig welder and wanted lots of welding practice, the relative ease of cnc cutting a single sheet of plywood was one of the design goals in this approach.

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Picked up some aluminum. Wasn’t quite as pricey as I thought BUT way heavier than it needs to be to be practical. It would take some serious lightening and the HAAS to mill it out enough to be reasonably light. Alternative, as Brandon_Green mentioned, Aluminum tubing,
OR two .1" to .125" aluminum plate bolted with .125" wood sandwiched inside. The plate would help prevent impact breaks. With just three legs it looks like quite a bit of force applied when the weight is transferred. The plate is easily cut on the plasma cutter.
If you had 4 legs and they were timed such that two legs were always on the ground, combined with the front wheel you would have three points of contact and that might make it more stable.
The prototype is very impressive. I did not mean to come off all knowing if that was anyone’s impression. I just was wondering if it could be made more stable with simple changes.

Wheels work really really well. :slight_smile:

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I would suggest creating a tab & slot design making the plate interlock with ribbing. This should allow for less welding & more of a robust design.

I’d suggest first starting with real Baltic Birch plywood.
Then, reinforce each side with a layer of heavy fiberglass cloth. (After the legs are cut).
If that doesn’t work, then try a sheet of .032 aluminum cut to match and fastened to each side of the ply using an appropriate adhesive (contact cement).

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Indeed, will write up a post mortem after I get some video during the day time, but using crappy home depot plywood was a large mistake (wasn’t paying attention and assumed 4’x8’ sku would be same plywood type as the 2’x4’ sku I used for initial prototype). Although there will always be a weakest point in the system, and one leg breaking when the mechanism jams is better than bending the frame

Tried riding some more with the repaired leg and the bike leaning issue is a fatal flaw of attempting 3 legs on a bike, if you lean over even slightly then the outside leg coming forward ‘crashes’ into the ground before it starts the backstroke. So I’m calling this project done without achieving the video of riding around smoothly that I was aiming for.

6 legs (3 on each side) with a differential in the middle would make a working steerable / maneuverable bike, but would require a substantial frame and more cost / weight

Overall some successes were

  • Designing in onshape and being able to see the mechanism move ahead of time helped
  • Quickly iterating on design ideas
  • The pressed in delrin bushing and using press fit to retain all the axles on each leg
  • Jigs used during welding frame
  • 3d printing odd shaped pieces to connect frame to bike
  • CNC cutting the leg pieces, being able to in ~30 minutes cut out all the pieces with the critical dimensions all perfect

Some failures were

  • Using poor quality plywood
  • Using bike with front suspension
  • Not realizing how much a bike leans left / right as you ride
  • Bike not functional in the end
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