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 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.

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Printed Jig Is A Welding Rig

[NixieGuy] was scheming to build robots with cable-driven joints when the pandemic hit. Now that component sourcing is scarce, he’s had to get creative when it comes to continuous cables. These cables need to be as seamless as possible to avoid getting caught on the pulleys, so [Nixie] came up with a way to weld together something he already has on hand — lengths of .45mm steel cable.

The 3D printed jig is designed to be used under a digital microscope, and even clamps to the pillar with screws. Another set of screws holds the two wires in place while they are butt welded between two pieces of copper.

[Nixie] adds a spot of solder paste for good measure, and then joins the wires by attaching his bench power supply set to 20V @ 3.5A to the copper electrodes. We love that [Nixie] took the time to streamline the jig design, because it looks great.

This just goes to show you that great things can happen with limited resources and a little bit of imagination. [Nixie] not only solved his own supply chain problem, he perfected a skill at the same time. If you don’t have a bench supply, you might be able to get away with a battery-powered spot welder, depending on your application.