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CARA 2.0 – “I Built a Better Robot Dog”

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Re: CARA 2.0 – “I Built a Better Robot Dog”

#61

Post by modeless »

drzaiusx11 wrote: post #29
15155 wrote: post #27

Earlier quoted context omitted.

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.

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.

Mind linking some?

Re: CARA 2.0 – “I Built a Better Robot Dog”

#62

Post by Animats »

regularfry wrote: post #24
lastdong wrote: post #23

Earlier quoted context omitted.

This is pretty cool, thanks for sharing. I wish there was a (mostly) 3d printable Cara mini, but I’ll start with Cara.

The layout is doable with hobby servos, but you'd need to patch in current sensing for that bit of the feedback. It's not terribly difficult conceptually but it's an extra complication that most servo power distribution boards don't give you. You can also strap a capstan to the servo axle, if that's your thing. I've prototyped that myself in the past. You can go surprisingly far with an FDM printer, an SG90, and some…

> The layout is doable with hobby servos

Mostly we're past that. Robotics with hobby servos sucks. Been there, done that, robot arm is in electronics recycling bin right now.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#63

Post by drzaiusx11 »

modeless wrote: post #61
drzaiusx11 wrote: post #29

Earlier quoted context omitted.

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.

Mind linking some?

HAX Ventures (Formerly HAXLR8R) https://hax.co/

TroubleMaker (Conquer! program) https://troublemakershenzhen.com/member/apprentice-membershi...

Seeed Maker Camp https://www.seeedstudio.com/blog/2024/01/15/introducing-make...

I was an alumni of HAXLR8R before the rename.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#64

Post by npodbielski »

layer8 wrote: post #44
npodbielski wrote: post #7

Seeing stuff like this, I am wondering why the hell I am doing software. This is much cooler than CRUD for DB data nth time.

You could do non-CRUD software instead.

Yes, but most of software is like that and by the extent most of the work in software is like that.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#65

Post by pbmonster »

SamBam wrote: post #59
pbmonster wrote: post #9

The jumps are pretty impressive, this thing has some power. I'd be very curious how fast you could get this dog with some reinforcement learning for a proper transverse gallop gait - and if it converges towards a gallop naturally, or if it discovers some other fast gait patterns during learning. Depending on the max speed of the motors/legs, giving it longer foot pads might be necessary for a good gallop. Intuitively…

I wonder how accurate a virtual model could be made of this, which could be iterated on millions of times faster. My first project as a research assistant in AI was doing evolutionary algorithms on Khepera robots, which had a virtual Java implementation. We were able to evolve some pretty cool behaviors, although I don't know what would have happened if we had uploaded them into a physical Khepera robot.

I'd expect pretty good results from simulation until you start bending/deforming the limbs or until the foot pads start slipping.

I also wonder if you can read the impact force from the legs with the ground from the motor controllers (should be able to infer that from motor current + leg displacement). Learning to gallop without "feeling" the legs impacting sounds extremely difficult.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#66

Post by squarefoot »

Animats wrote: post #3

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 t…

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.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#67

Post by layer8 »

npodbielski wrote: post #64
layer8 wrote: post #44

Earlier quoted context omitted.

You could do non-CRUD software instead.

Yes, but most of software is like that and by the extent most of the work in software is like that.

The same is true for hardware development. I’d even argue that it’s easier to do something original in software, because you aren’t constrained by materials and physics.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#68

Post by regularfry »

Animats wrote: post #62
regularfry wrote: post #24

Earlier quoted context omitted.

The layout is doable with hobby servos, but you'd need to patch in current sensing for that bit of the feedback. It's not terribly difficult conceptually but it's an extra complication that most servo power distribution boards don't give you. You can also strap a capstan to the servo axle, if that's your thing. I've prototyped that myself in the past. You can go surprisingly far with an FDM printer, an SG90, and some…

> The layout is doable with hobby servos Mostly we're past that. Robotics with hobby servos sucks. Been there, done that, robot arm is in electronics recycling bin right now.

I agree it's not great but for scale and convenience it's good. If this was going to just get scaled down, what motors would you pick?

Re: CARA 2.0 – “I Built a Better Robot Dog”

#69

Post by coolvision »

cyanf wrote: post #17
barrenko wrote: post #6

Earlier quoted context omitted.

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 frequentl…

thanks for the Xdrive pointer, I just got samples of tinymovr and odrive controllers (with FOC), they seem nice but are more expensive.

Re: CARA 2.0 – “I Built a Better Robot Dog”

#70

Post by regularfry »

regularfry wrote: post #25
Animats wrote: post #3

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 t…

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.

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.
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