4) Manufacturing and Assembly - RA

Our build consisted of laser cut and 3D printed parts. The base and mount were built using wood and 3D-printed brackets. Atlas was entirely 3D printed including the gears, body, and limbs. Finally, we cut 2mm steel rods to connect the various parts to each other.

Our initial prototype was manufactured using PLA and PETG. While the mechanism worked, many of the parts would collide or rub against each other while moving. This caused jagged movements when running:

The vibrations and significant play between the links would sometimes cause the mechanism to fall apart. We addressed multiple reasons for these issues.

The first issue was using PLA and PETG to manufacture small parts. This caused warping and made press-fitting difficult. This also left imperfections on the part surfaces, increasing friction. 

The second issue was imprecise measurements of the steel rods. We used the CAD model to measure the rod lengths for the gears and limbs but estimated the motor transmission rod due to time constraints. This caused a poor connection between our bevel gears. 

Finally, our initial assembly was poorly done. We did not adequately plan the order of assembly. Press-fits had to be done multiple times to correct assembly errors, such as when a part needed to be press-fit while already attached to the mechanism. This degraded the quality of our prints. 

For the final assembly, we used SLA prints. The higher resolution of SLA printers meant that the resultant prints were more precise. This meant tolerances were better for press fitting, and connections between parts (such as the gears) were cleaner. We also increased the size of the end caps which held the limbs to the steel rods. Finally, we used precise measurements for cutting the steel rods.

Below figure shows the difference in the quality of the bevel gears:

Gear printed in PLA                   SLA printed gears

As a result, the motion became much smoother: