Monday, September 1, 2014

The Making of Gertie - Part 2: Early Designs and 3D printing

For some background on Gertie, check out Part 1: Starting Out!

After figuring out what I wanted in the robot's design and function, I decided to start with my first 3D printing experiment. Using Maya, a 3D graphics program, I created a digital mockup of Gertie's motor mount, which would hold the 3 servos (one for each of the delta robot's arms). The print turned out great, and was an eye-opening experience! My digital modeling skills from working in computer animation translated so well to this process. Realizing it made me feel like I'd just evolved into a more powerful Pokemon! You can see below, how closely the print matched the digital model:

Each pair of arms wrapped around one servo. There was a satisfying "click" as each motor fit precisely into its frame! The accuracy of printing, even at a moderate resolution, was very exciting.

I continued to refine the design in Maya, creating a complete digital model of Gertie. Even the parts that weren't 3D printed were modeled, so I could judge the full design and whether the parts fit well.

This model below is one of the earliest versions: you can see the first part I tried printing (it's upside down from the images above). Each of the three legs hooks into the servo at the top, which could rotate quickly and cause the leg to contract and expand to cause Gertie to jump.

This motor mount design wasn't structurally sound in the end because the large motors were very heavy and strong and kept popping out of socket. The motors needed to be secured by being bolted on instead of the previous snap-in method. 

While designing the new motor mount, researching for new motors led me to the consideration of a better weight to power ratio. There were many different servos to choose from, and the most powerful ones were obviously attractive for higher jumps. They were also bigger and heavier, a trade-off that would shorten the jump too. I ended up doing a good deal of research, and created a spreadsheet of the different servos, ranked by power to weight ratio (  Ultimately I chose a smaller motor with better weight to power ratio, the TGY-306G-HV

I created and printed another version, with a new frame design and the much smaller servos:

Getting closer now! In the next post, I'll talk about creating springs for Gertie's legs, and getting to see him finally move.

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