XRobots’ James Bruton, a robotics engineer and 3D printing YouTuber, has commenced work on V3 of his 3D printed robotic dog.
Dubbed openDog, the open-source project has been running for a couple of years now and is intended as a more accessible, cost-effective alternative to Boston Dynamics’ Spot (which retails at ~$75,000). Besides the motors, bearings, and a few other components, the robot can be 3D printed entirely on a low-cost FDM system like the LulzBot TAZ Workhorse Bruton happens to use.
Bruton said, “Many of my regular viewers will have seen my robot dog development over the last few years. The last working robot dog I built is openDog V2, which works okay. So it’s time for openDog V3 – this version uses my Cycloidal Drives which I’ve developed over the last few months. I will eventually publish the CAD and code as open-source when it works.”
openDog V2 vs openDog V3
So what’s changed since openDog V2? During the development of the previous iteration, Bruton discovered that the most agile robotic dogs were the ones that had back-drivable gear trains. These allowed for a natural spring in the dog’s legs, almost like the suspension of a car, except the springiness could also be controlled in real-time by altering the way the motors were driven using software.
However, to make the back-drivable gear trains work, he needed quite a lot of torque as the drive reductions ideally need to be less than 10:1. V2 of the open-source dog relied on a conveyor belt-based reduction system because that was the simplest solution Bruton could design at the time, but the system only delivered a 5:1 reduction due to the physical space constraints of the belts and pulleys.
For openDog V3, he had to implement an entirely new, more compact gearbox solution. Bruton wanted to keep the hardware as open and accessible as possible, so it needed to be 3D printable as well as being durable and able to move quite fast. Eventually, he settled on a cycloidal drive gearbox, which uses cycloidal discs instead of conventional gears.
The engineer said, “I’ve done quite a bit of testing with these reductions, including having one push me on a skateboard for a few miles with no visible wear, and it was all printed in PLA. I’ve already built a test robot dog leg using two cycloidal drives. This time, we’re going to build 12 of them and put them all in a mechanical assembly for openDog V3.”
The power of open-source 3D printing
Having protoyped most of openDog V3 already, Bruton is optimistic about the outcome of the open-source project. The new cycloidal drive has hardly any backlash, making for a sturdy and robust build. The robot is also foldable into a clean, compact form, meaning it can be packed into a flightcase for transport.
Without any electronics in the body, V3 currently weighs around 20kg but is expected to reach 25kg by the time it is complete. This is significantly lighter than Boston Dynamics’ Spot, which comes in at around 32kg. Additional features of the openDog V3 include extra battery space for double the battery life, carbon fiber tubing for a reinforced frame, and 3D printed TPU feet for impact absorption.
The open-source 3D printing community is often a source of great innovation, yielding low-cost projects that you just don’t see in industry. A student YouTuber by the name of Lucas VRTech has previously designed and 3D printed a pair of low-cost finger tracking gloves for use in virtual reality. Named LucidVR, the open-source gloves cost just $22, and grant users the ability to precisely track their fingers without the use of dedicated VR controllers.
Elsewhere, 3D printing YouTuber Teaching Tech designed and 3D printed his own open-source version of a rare antique fractal vise. Dubbed ‘the coolest tool you didn’t know you needed’, the 100-year-old fractal vise is near impossible to purchase these days, and is capable of morphing to grip virtually any object, regardless of the complexity of the geometry.
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Featured image shows James Bruton next to openDog V3, which is still in development. Photo via James Bruton.