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Quadrupeds

I’m working on a new quadruped over spring break, where I will have much time (alone with no food). CAD it up and make a small model if 3D printing allows. It will focus on a biometric tensegrity structure, which mimics mammalian skeletons and ligaments. Instead of direct drive in torque based joints, I will try to support structures with ligaments and partially tensed tendons.

Here’s what I have done so far with CAD. The tendons are not added in yet and I still need to design the spinal structure for the left/right motion. I also need to accommodate for the rotary sensors/flex sensors for the spine. For this robot, I want to integrate a two degree of freedom flex sensor inside the spine. I was inspired to try building a running quadruped by the cheetah robot by Boston Dynamics. The video of it’s record breaking running speed is circulating on the internet.

For now, I plan to have it electronically actuated, as pneumatics are way out of my price range. Three degrees of freedom per joint, two for the spine, two for the neck, and two for the tail. Then the walking gait generation fun begins again. And once again as inspiration, I have Zoids:

My fox project’s namesake, the Shadow Fox.

On a more relevant note, the other quadruped I’ve been working on is nearing completion. After a long lull of waiting for the university to deliver parts, I need to calibrate the sensors and servo motor settings, but then hopefully it will take its first steps.

So I’m back at school again, so I returned to where I left of with the dog. The chassis has been sitting around in CAD form for a while, two days ago I printed this thing. It’s my first time using one of the commercial 3D printers. It’s the same 3D printer I keep seeing at universities, of the Dimension brand, that prints extruded plastic with a weaker support material.

For a job the size of the quadruped, the print time was 44 hours. The chassis had to be put on its side and diagonal across the printing bed to even fit.

When it was done printing after 44 hours, it was a piece of plastic encased in a support material block. For the fancy Objet printer in the other lab, the support material seems like a powdery material you have to pressure wash off. This material you had to peel off with your fingernails and some metal picks resembling dentist’s picks.

And after some frustration and an hour or so of picking away, it looks like this:

The little gaps will need some creative sanding, and I’ll have to re-bore the holes. Otherwise, I’m getting closer to mounting the motors, legs, and valves. The next step is to 3D print the precision valve parts with the UV resin Objet printer.

I’ve been interested in quadrupeds for a while, since my sophomore year of high school. Or maybe way longer than that, since I watched Zoids: Chaotic Century years and years ago. Riding a Liger Zero with Jager high speed armor was and still is a goal I strive towards (that and driving a tank).

My research for this semester is to design a hydraulically actuated quadruped with two motors. The motors individually drive the front or back legs, and can support the entire robot in the event of a motor failure. These motors are hydraulic motors from large-scale model airplane landing gear from some far away country, and are extremely expensive, at over 600 dollars each (Cornell funding).

My design as of now looks like this:

Once again with the 3D render option in SolidWorks, making it look like a commercial for an Apple product.

The legs use cylinders, though I would one day love to expand to hydraulic muscles. Those four blocks are the valve manifolds that are servo actuated. The entire chassis will be 3D printed on the standard commercial extruded plastic printer, while the precision parts for the valves will be printed on the UV resin Objet printer.

Maybe if I study hard enough in school, and with enough time, blood, and sweat, it will someday look like this: