Comment by Animats
5 hours ago
3 DOF per leg, so it needs 12 motors and controllers. Getting that under $1000 is nice.
Here's the US$18 motor: [1] Those things are getting really cheap. He did have to rewind it, though, for more turns with thinner wire. The manufacturer mentions that you can order with "custom Kv", which means you might be able to get a different winding from the factory if you order a reasonable quantity. Especially if you tell them that makes them "robot motors".
Motor overheating might be a problem. The dog, just standing, has its motors stalled under load, converting power to heat. Drones don't do that. Temperature feedback would help if this thing has to operate for extended periods. Remember yesterday's article on humanoid robots and their cooling problems.
The motor controller is nice too, and cheap at $49. Needed fixes to the firmware, but that's not surprising at the price. High performance motor controllers used to cost about $1000.
Repurposed drone technology has done wonders for legged robots. We're not quite at the point where limb drive hardware is off the shelf, but it's way better than it used to be.
[1] https://www.xntyi.com/tyi-5008-kv335/kv400-high-speed-brushl...
It doesn't have to stall to stand still. Or squat, at least. With that leg layout it can safely rest against its backstops when the motors switch off. The drive motors, anyway. The hip motors probably still need to hold vertical balance, but that's intermittent, not a stall load.
Could I pursuade you to expand on "Repurposed drone technology has done wonders for legged robots." ? Thanks!
For legged, you want high torque and backdriveability (for shock absorption).
Agricultural drone motors like the eaglepower 8308 are ideal.
They’re cost effective, (~$80 from aliexpress) & you can pair them with a 3d printed cycloidal drive to fulfill both requirements.
Industry actuators are an order of magnitude more expensive than this.
Extra: If you go down this path, you’ll need a driver. The Xdrive is frequently recommended, but there’s a clone that’s significantly cheaper: https://makerbase3d.com/product/makerbase-xdrive-mini-high-p...
This is pretty cool, thanks for sharing. I wish there was a (mostly) 3d printable Cara mini, but I’ll start with Cara.
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Motor: https://www.aliexpress.us/item/3256804897857573.html?gateway...
The 90KV version is what you want.
Look at the original video/article, they used drone motors for the robot dog, by reusing the rotor/stator and rewinding the coils manually.
If you read the epilogue, they weren't able to achieve the under $1000 price goal. Total cost ended up being around $1,450. Pretty good price reduction compared to CARA 1.0 though.
Hypothetically if I were to want a quadrupedal robot to experiment with it's not an impulse buy/build, but getting closer to that point... whereas $3000+ is a hard pass (e.g. Apple Vision Pro territory).
It's $1450 if you discount the construction time, as ever. Which ordinarily wouldn't be worth commenting on, but in this case it means rewinding 12 motors which just sounds like an exercise in tedium and hand pain.
Only because they didn't know how to ask the vendor to do it for them.
I guarantee this vendor would be delighted to make them to spec at a 1ku volume, max. Rewinding isn't even a meaningful SKU distinction or line retool, it's a configuration parameter.
At 12 motors per product, it's easy to hit MOQ.
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