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The hip bone's connected to the leg bone

A project log for Tardygrade

3D printed quadruped with a tiny BOM

dejan-risticDejan Ristic 07/09/2021 at 13:360 Comments

Each of the robots legs hinges at two points. One is at the "hip". The other one is at the "foot", which connects the lever that pushes the leg back and forth. 

If using screws to join these parts that would add up to a total of eight. Those screws adds weight, they look dumb, and the threads might eventually wear down the plastic around it.

Older leg design with M2.5 screws.

I had experimented with using 1.75 mm filament in place of the screws. But a major problem was that the filament would start slipping out sideways after continuous movement. 

Also, each leg consists of left and right halves, which would be held together by the lower screw. Substituting filament for that screw would let the leg halves wedge apart, which is no good.

The solution I finally came up with gets assembled in four steps:
  1. A lower joint filament pin is fixed inside channels within the two leg halves, with no holes on the sides for it to slip out of. 
  2. The leg halves are joined with a filament "shoelace" to prevent them from wedging apart. The shoelace channel has a slight bend to it, which keeps the filament from coming loose. 
  3. Another filament pin hinges the leg onto the hip joint.
  4. Finally, the hip pin is prevented from slipping out by a sleeve built into the robot body.

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