Cara robot dog

From Leash To Locomotion: CARA The Robotic Dog

Normally when you hear the words “rope” and “dog” in the same sentence, you think about a dog on a leash, but in this robot dog, the rope is what makes it move, not what stops it from going too far. [Aaed Musa]’s latest project is CARA, a robotic dog made mostly of 3D printed parts, with brushless motors and ropes used to tie the motors and legs together.

In a previous post, we covered [Aaed Musa]’s use of rope as a mechanism to make capstan drives, enabling high torque and little to no backlash. Taking that gearbox design, tweaking it a bit, and using three motors, he was able to make a leg capable of moving in all three axes. He had to do a good deal of inverse kinematics math to get the leg moving around as desired; once he had the motion of a step defined, it was time to build the rest of the dog.

CARA is made primarily of 3D printed parts, with several carbon fiber tubes running its length for rigidity. The legs are all free to move not only forward and back but side to side some, as in a real dog. He uses 12 large brushless motors, as they provide the torque needed, and ODrive S1 motor controllers to control each one, controlled over CAN by a Teensy 4.1 microcontroller. There is also a small BNO086 IMU to sense CARA’s position relative to gravity, and a 24V cordless tool battery powers everything.

Once assembled, there was some more tuning of what type of motion CARA’s legs take while walking. There were a few tweaks to the printed parts to address some structural issues, and then a good deal more inverse kinematics math to make full use of the IMU, allowing CARA to handle inclines and make a much more natural movement style. [Aaed Musa] does a great job explaining his approach on his site as well as in the video below; we’re looking forward to seeing his future projects!

CARA isn’t alone on this site—be sure to check out the other robot dogs we’ve featured here.

Continue reading “From Leash To Locomotion: CARA The Robotic Dog”

Capstan Drive Is Pulling The Strings On This Dynamic Quadruped

When it comes to legged robots, it’s easy to think that the complexity and machining costs would keep these creatures far away from becoming anyone’s garage hobby. But, through a series of clever design choices, [Damian Lickindorf] has found a way to beat the odds and give life to Stanley, a low-cost, dynamic quadruped with some serious kick!

As if building a working legged robot weren’t already a tricky task, [Damian] has made some classy design choices to keep the price low and reduce fabrication complexity without sacrificing performance. Keeping up with the latest trend in Quasi-Direct Drive legged robots that started with the MIT Mini Cheetah, [Damian] constructed a small transmission with a gear reduction under 1:9. This choice slightly reduces the amount of heat produced by operating the motor at low-speeds with high torque without sacrificing too much control bandwidth (think: “leg responsiveness”).

Unlike the Cheetah, though, which uses a planetary gearbox, [Damian] opts for a capstan drive, a cable-driven transmission that’s both backlash free and backdriveable: two must-haves for force-sensitive dynamic legged robots. For legs, he’s opting for 2d machined FR4 (think: circuit board material). And for motors, he’s chosen a set of brushless motors with a large gap radius and driven by Moteus Drivers. The result is high fidelity, dynamic build that’s a fraction of the cost of some of the creatures we’re seeing emerge from academic research labs.

If you’re looking to feast your eyes on some action shots, look no further than [Damian’s] YouTube and Instagram presence. And if you’re looking to follow the project, have a look at the Hackaday.io project. While we’re eager to see the project continue to unfold, we’re thrilled by how far it’s come. In the meantime, be sure to take a look at one of the project’s inspirations: the Mjbots Quad A0.

Finally, since we’ve not seen capstan drives much on Hackaday, if you’re curious about these mechanisms and can get past the paywall, these two research papers might be a good place to dig deeper.

Continue reading “Capstan Drive Is Pulling The Strings On This Dynamic Quadruped”