3 ms·

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 d

by Animats 6mo 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-brushless-motor-for-fpv-drone- https://www.xntyi.com/tyi-5008-kv335/kv400-high-speed-brushl...

rmast 6mo ago
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).
- regularfry 6mo ago
  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.
  - 15155 6mo ago
    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.
    - dezgeg 6mo ago
      Reminder that this was a student project.
    - drzaiusx11 6mo ago
      There are inventor programs that'll literally ship you to Shenzhen to build connections to manufacturing sites and even provide you with a liaison, etc. I only know this because I was once in a program that did exactly this.
      - modeless 6mo ago
        Mind linking some?
        drzaiusx11 6mo ago
        HAX Ventures (Formerly HAXLR8R) https://hax.co/ https://hax.co/ TroubleMaker (Conquer! program) https://troublemakershenzhen.com/member/apprentice-membership/ https://troublemakershenzhen.com/member/apprentice-membershi... Seeed Maker Camp https://www.seeedstudio.com/blog/2024/01/15/introducing-maker-camp-in-shenzhen https://www.seeedstudio.com/blog/2024/01/15/introducing-make... I was an alumni of HAXLR8R before the rename.
    - Animats 6mo ago
      Rewinding drone motors for high torque and lower speed seems to be a popular thing. Here's the commercial process of machine winding motors like that.[1] That's a medium-volume machine, loaded and unloaded by hand, and adjustable for different wire and motor geometry. Here's a hobbyist version of a similar winder.[2] And another automatic hobbyist winder. Those wind under uniform tension, and with wire positioning, so you get a smooth, tight winding. This matters if you're going to use the motor much. Doesn't matter as much for short-lived toys. There should soon be enough convergence that low cost, high torque, low speed models are off the shelf items. It's a great time to be building robots. Used to be all uphill on the parts side. [1] https://www.youtube.com/watch?v=cMk2qFFcSho https://www.youtube.com/watch?v=cMk2qFFcSho [2] https://www.youtube.com/watch?v=486nUU2FjGU https://www.youtube.com/watch?v=486nUU2FjGU [3] https://www.youtube.com/watch?v=e-tAsM0K7Sg https://www.youtube.com/watch?v=e-tAsM0K7Sg
barrenko 6mo ago
Could I pursuade you to expand on "Repurposed drone technology has done wonders for legged robots." ? Thanks!
- franciscop 6mo ago
  Look at the original video/article, they used drone motors for the robot dog, by reusing the rotor/stator and rewinding the coils manually.
- cyanf 6mo ago
  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-precision-brushless-servo-motor-controller-based-on-odrive3-6-with-as5047p-on-board https://makerbase3d.com/product/makerbase-xdrive-mini-high-p...
  - cyanf 6mo ago
    Motor: https://www.aliexpress.us/item/3256804897857573.html?gatewayAdapt=glo2usa4itemAdapt https://www.aliexpress.us/item/3256804897857573.html?gateway... The 90KV version is what you want.
    - JKCalhoun 6mo ago
      "The 90KV version is what you want." You mean the "KV90 color" of course, ha ha. That we live in an age where "agricultural drone" is even a word pairing…
  - lastdong 6mo ago
    This is pretty cool, thanks for sharing. I wish there was a (mostly) 3d printable Cara mini, but I’ll start with Cara.
regularfry 6mo ago
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.
- regularfry 6mo ago
  Oh, just thought in addition to this: you could define a standing locked position, too, if you drive the capstans to full rotation inwards so the knees only just reverse, and put extra backstops there. Not sure what that would do on uneven ground, I think you'd need to balance centrally over three legs and let the fourth hang loose.
Tade0 6mo ago
> Motor overheating might be a problem. The dog, just standing, has its motors stalled under load, converting power to heat. The Nao robot[0] had this exact problem and of course no way to fail gracefully. I recall checking its basic functions with my lab partner in college. I looked away for a moment and that was when it went down hard. Me and the other guy locked eyes in an "oh fuck" moment, as the robot was expensive and our thesis supervisor went through quite a lot of paperwork to have it funded. Fortunately it was intact and none of us mentioned this incident to anyone. [0] https://en.wikipedia.org/wiki/Nao_(robot) https://en.wikipedia.org/wiki/Nao_(robot)
JKCalhoun 6mo ago
"Temperature feedback would help if this thing has to operate for extended periods." Rather than thermistors all over the place, perhaps an onboard program could calculate motor temperature by integrating current sent to each over time—assumed some degree of cooling (and perhaps here a single temperature sensor might measure ambient temperature of the environment… or could just assume "indoor temperature").
- fennecfoxy 6mo ago
  I would rather just have temperature sensors over the place. More reliable.
  - deleted 6mo ago
    [deleted]
  - Animats 6mo ago
    For a toy, you might just have a simple thermal fuse.[1] ($0.78 from DigiKey, plus "tariff may apply if shipping to the United States". About $0.15 on Alibaba, if you order enough.). For a working machine for field use, you want feedback to the controller, so it can slow down or rest or something when it overheats. [1] https://www.digikey.com/en/products/detail/cantherm/RT121/28383650 https://www.digikey.com/en/products/detail/cantherm/RT121/28...
- rmast 6mo ago
  Train it like Disney’s Olaf where it can adjust how it walks/stands to keep motor temperature under control.
- Gracana 6mo ago
  That’s how industrial VFDs do motor overload protection, they just keep track of heat accumulation (based on current) vs dissipation (based on fan speed) and fault when a threshold is reached. Probably there’s more nuance to it, but that’s the gist of it.
squarefoot 6mo ago
Not my field so I'm likely using the wrong name for the concept, anyway, don't stepping (bistable) brakes exist? I mean, one pulse to one pin engages and one pulse to another pin disengages, just like step relays, with the current consumption being zero when it's not operated so that the robot can be kept indefinitely in resting position without wasting energy to keep motors stalled.
- Animats 6mo ago
  Stepping motors are not good at stationary power consumption. They use power even with no load on them. Brakes for robot joints are common in industrial robots. They're usually part of the emergency stop system. If power fails, the controller crashes, or someone pushes the emergency stop button, spring-driven brakes lock all major joints to stop all motion.[1] That might be useful in a quadruped, which can park without active balance. [1] https://www.techbriefs.com/component/content/article/28812-choosing-the-right-brake-for-robotic-applications https://www.techbriefs.com/component/content/article/28812-c...

by Animats 6mo ago

rmast 6mo ago

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).

regularfry 6mo ago
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.
- 15155 6mo ago
  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.
  - dezgeg 6mo ago
    Reminder that this was a student project.
  - drzaiusx11 6mo ago
    There are inventor programs that'll literally ship you to Shenzhen to build connections to manufacturing sites and even provide you with a liaison, etc. I only know this because I was once in a program that did exactly this.
    - modeless 6mo ago
      Mind linking some?
      - drzaiusx11 6mo ago
        HAX Ventures (Formerly HAXLR8R) https://hax.co/ https://hax.co/ TroubleMaker (Conquer! program) https://troublemakershenzhen.com/member/apprentice-membership/ https://troublemakershenzhen.com/member/apprentice-membershi... Seeed Maker Camp https://www.seeedstudio.com/blog/2024/01/15/introducing-maker-camp-in-shenzhen https://www.seeedstudio.com/blog/2024/01/15/introducing-make... I was an alumni of HAXLR8R before the rename.
  - Animats 6mo ago
    Rewinding drone motors for high torque and lower speed seems to be a popular thing. Here's the commercial process of machine winding motors like that.[1] That's a medium-volume machine, loaded and unloaded by hand, and adjustable for different wire and motor geometry. Here's a hobbyist version of a similar winder.[2] And another automatic hobbyist winder. Those wind under uniform tension, and with wire positioning, so you get a smooth, tight winding. This matters if you're going to use the motor much. Doesn't matter as much for short-lived toys. There should soon be enough convergence that low cost, high torque, low speed models are off the shelf items. It's a great time to be building robots. Used to be all uphill on the parts side. [1] https://www.youtube.com/watch?v=cMk2qFFcSho https://www.youtube.com/watch?v=cMk2qFFcSho [2] https://www.youtube.com/watch?v=486nUU2FjGU https://www.youtube.com/watch?v=486nUU2FjGU [3] https://www.youtube.com/watch?v=e-tAsM0K7Sg https://www.youtube.com/watch?v=e-tAsM0K7Sg

barrenko 6mo ago

Could I pursuade you to expand on "Repurposed drone technology has done wonders for legged robots." ? Thanks!

franciscop 6mo ago
Look at the original video/article, they used drone motors for the robot dog, by reusing the rotor/stator and rewinding the coils manually.
cyanf 6mo ago
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-precision-brushless-servo-motor-controller-based-on-odrive3-6-with-as5047p-on-board https://makerbase3d.com/product/makerbase-xdrive-mini-high-p...
- cyanf 6mo ago
  Motor: https://www.aliexpress.us/item/3256804897857573.html?gatewayAdapt=glo2usa4itemAdapt https://www.aliexpress.us/item/3256804897857573.html?gateway... The 90KV version is what you want.
  - JKCalhoun 6mo ago
    "The 90KV version is what you want." You mean the "KV90 color" of course, ha ha. That we live in an age where "agricultural drone" is even a word pairing…
- lastdong 6mo ago
  This is pretty cool, thanks for sharing. I wish there was a (mostly) 3d printable Cara mini, but I’ll start with Cara.

regularfry 6mo ago

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.

regularfry 6mo ago
Oh, just thought in addition to this: you could define a standing locked position, too, if you drive the capstans to full rotation inwards so the knees only just reverse, and put extra backstops there. Not sure what that would do on uneven ground, I think you'd need to balance centrally over three legs and let the fourth hang loose.

Tade0 6mo ago

> Motor overheating might be a problem. The dog, just standing, has its motors stalled under load, converting power to heat. The Nao robot[0] had this exact problem and of course no way to fail gracefully. I recall checking its basic functions with my lab partner in college. I looked away for a moment and that was when it went down hard. Me and the other guy locked eyes in an "oh fuck" moment, as the robot was expensive and our thesis supervisor went through quite a lot of paperwork to have it funded. Fortunately it was intact and none of us mentioned this incident to anyone. [0] https://en.wikipedia.org/wiki/Nao_(robot) https://en.wikipedia.org/wiki/Nao_(robot)

JKCalhoun 6mo ago

"Temperature feedback would help if this thing has to operate for extended periods." Rather than thermistors all over the place, perhaps an onboard program could calculate motor temperature by integrating current sent to each over time—assumed some degree of cooling (and perhaps here a single temperature sensor might measure ambient temperature of the environment… or could just assume "indoor temperature").

fennecfoxy 6mo ago
I would rather just have temperature sensors over the place. More reliable.
- deleted 6mo ago
  [deleted]
- Animats 6mo ago
  For a toy, you might just have a simple thermal fuse.[1] ($0.78 from DigiKey, plus "tariff may apply if shipping to the United States". About $0.15 on Alibaba, if you order enough.). For a working machine for field use, you want feedback to the controller, so it can slow down or rest or something when it overheats. [1] https://www.digikey.com/en/products/detail/cantherm/RT121/28383650 https://www.digikey.com/en/products/detail/cantherm/RT121/28...
rmast 6mo ago
Train it like Disney’s Olaf where it can adjust how it walks/stands to keep motor temperature under control.
Gracana 6mo ago
That’s how industrial VFDs do motor overload protection, they just keep track of heat accumulation (based on current) vs dissipation (based on fan speed) and fault when a threshold is reached. Probably there’s more nuance to it, but that’s the gist of it.

squarefoot 6mo ago

Not my field so I'm likely using the wrong name for the concept, anyway, don't stepping (bistable) brakes exist? I mean, one pulse to one pin engages and one pulse to another pin disengages, just like step relays, with the current consumption being zero when it's not operated so that the robot can be kept indefinitely in resting position without wasting energy to keep motors stalled.

Animats 6mo ago
Stepping motors are not good at stationary power consumption. They use power even with no load on them. Brakes for robot joints are common in industrial robots. They're usually part of the emergency stop system. If power fails, the controller crashes, or someone pushes the emergency stop button, spring-driven brakes lock all major joints to stop all motion.[1] That might be useful in a quadruped, which can park without active balance. [1] https://www.techbriefs.com/component/content/article/28812-choosing-the-right-brake-for-robotic-applications https://www.techbriefs.com/component/content/article/28812-c...