Manufacturing and Assembly - Mellinger

I recently got a 3D printer, and I thought this would be a great opportunity to experiment with it. I wanted to print each joint and slider so I could learn more about the printer. I also used the laser cutter and Texas Invention-Works to create the frame of the robot.

I wanted the robot to operate smoothly, so I investigated 3D printed bearings and planetary gears. The design on the left is functionally similar to a ball bearing but instead uses herringbone gears. The design on the right is also variation of a ball bearing. The bearings perform well, albeit not as smooth as a machined steel ball bearing. Unfortunately, the printer is not capable of scaling these bearings down to the size of the robot I created. The nozzle diameter for the printer I have is 0.2 mm which is too small. When printing bearings smaller than the ones pictured, the plastic fuses together and can no longer move.

I decided to design a square slider with a press fit pin. The image above shows the design evolution for the bottom half of the slider. Going from left to right: the square edges were filleted to provide smoother motion, the square shape was changed to a round shape to allow rotation in the slot, the press fit pin height was increased to accommodate a larger top, and pin height was increased again to accommodate two washers and the slider top.

The evolution of slider top is shown above. First the hole diameter was increased to improve the press fit to the bottom of the slider. Second the slider height was increased to fit in the slot more loosely to allow for easier rotation.

The design evolution of the input bar is shown above. The square peg in the middle pairs with a shaft that couples to the motor the round hole at the edge is for a shaft that pairs with the long link. The position and hole diameter were changed initially to improve fit between the links. Lastly, the hole was changed to a square so the pin between the input and long link would not slip.