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CARA – High precision robot dog using rope

aaedmusa.com

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Re: CARA – High precision robot dog using rope

#81

Post by topspin »

throwawayffffas wrote: post #37
fusionadvocate wrote: post #7

Why spend so much effort to achieve an "exact" gear ratio? Having more zeros does not equal to being more "precise". Also, I wonder how resistant this mechanism is to wear and fatigue.

I think it's about kinematics, the more precise your gears the better the model fits the real world. That's why pro crews don't use gears and ropes. At high impulses deformations and elasticity throw the kinematics off what's actually happening. Modeling the deformations and the elasticity is a computational no no. Instead what you see is the motors right on the joints. At least that was the case last time I had a lo…

> At high impulses deformations and elasticity throw the kinematics

Sure. Yet evolution has achieved astonishing kinematics with all manner of deformation and elasticity inherent to the materials, and also constantly changing physical properties, using low resolution data. We cannot build permanently lash free mechanical devices at reasonable cost and reasonable size/weight. Eventually, the answer must be pervasive real-time compensation throughout the kinematic model.

> Modeling the deformations and the elasticity is a computational no no.

Why? Nervous systems do this. That's why you can change your shoes and still walk upright.

Re: CARA – High precision robot dog using rope

#82

Post by BHSPitMonkey »

throwawayffffas wrote: post #37
fusionadvocate wrote: post #7

Why spend so much effort to achieve an "exact" gear ratio? Having more zeros does not equal to being more "precise". Also, I wonder how resistant this mechanism is to wear and fatigue.

I think it's about kinematics, the more precise your gears the better the model fits the real world. That's why pro crews don't use gears and ropes. At high impulses deformations and elasticity throw the kinematics off what's actually happening. Modeling the deformations and the elasticity is a computational no no. Instead what you see is the motors right on the joints. At least that was the case last time I had a lo…

In the video he mentions how the specific type of Dyneema cord he's using is well-suited for the application (compared to other kinds of rope/cord). It's particularly strong, light, and inelastic; a lot of climbing equipment uses a version of it for similar reasons.

Re: CARA – High precision robot dog using rope

#83

Post by dyauspitr »

btbuildem wrote: post #3

I've watched and re-watched Aaed's videos on the capstan drive, it's great stuff. High speed, high torque, compliance, effectively no backlash. It's fascinating to watch a legit engineering mind at work.

How is there no backlash? I can’t imagine a rope drive without backlash.

Re: CARA – High precision robot dog using rope

#84

Post by fitsumbelay »

this guy's work is pretty amazing I whole heartedly believe that I'll own a gang of (armed) quadrapets for home/property/personal protection within the next 10 years. I'm equally worried that once these become commodities they might be worse than an electric scooters have become to us bipeds on sidewalks but on balance I can't wait

Re: CARA – High precision robot dog using rope

#86

Post by [deleted] »

munchler wrote: post #33
skeeter2020 wrote: post #9

Earlier quoted context omitted.

>> Having more zeros does not equal to being more "precise" Isn't having more decimal places the exact definition of precision (vs accuracy)?

The point is that those decimal places don't have to be zeros. 7.893 is just as precise as 8.001.

[deleted]

Re: CARA – High precision robot dog using rope

#87

Post by cryptoegorophy »

How do we make such robots intelligent? Like you only tell it to learn to jump the rope and then it goes through trial and error(s) to figure out a way to do it, and if it can’t and needs a physical upgrade then it tells you that? (Like a certain gear ratio etc)

Re: CARA – High precision robot dog using rope

#88

Post by Animats »

dyauspitr wrote: post #83
btbuildem wrote: post #3

I've watched and re-watched Aaed's videos on the capstan drive, it's great stuff. High speed, high torque, compliance, effectively no backlash. It's fascinating to watch a legit engineering mind at work.

How is there no backlash? I can’t imagine a rope drive without backlash.

Improved materials. Kevlar and Dyneema.[1] Dyneema is about 15x stronger than steel per unit weight. Kevlar toothed belts have been available for many years, and can be used for many of the same applications as this capstan setup. Neither material has much elasticity.

The advantage over gears is that overloads are distributed over much more material. You don't snap gear teeth. This is good for leg landing shocks.

[1] https://www.impact-fibers.com/info/unveiling-the-strength-ke...

Re: CARA – High precision robot dog using rope

#89

Post by scotty79 »

dyauspitr wrote: post #83
btbuildem wrote: post #3

I've watched and re-watched Aaed's videos on the capstan drive, it's great stuff. High speed, high torque, compliance, effectively no backlash. It's fascinating to watch a legit engineering mind at work.

How is there no backlash? I can’t imagine a rope drive without backlash.

It's very non-stretchy rope material. I imagine with enough force you can bend it away from the set position a little bit but it comes back when you remove the force. Nothing like traditional backlash with gears where you can move it with very little force between two adjacent gear teeth.

Re: CARA – High precision robot dog using rope

#90

Post by imtringued »

Lerc wrote: post #30
btbuildem wrote: post #3

I've watched and re-watched Aaed's videos on the capstan drive, it's great stuff. High speed, high torque, compliance, effectively no backlash. It's fascinating to watch a legit engineering mind at work.

I recently found his videos also. It's one of those things that gets my mind bubbling with ideas for things I want to make, never enough time to do them all though (and this breadboard beside me is asking for attention) It does make me wonder about the algorithm, Quite a lot of things I find on Youtube turn up on HN a week or two later. I'm not sure if this is an indicator of the effectiveness or failure of the algor…

I get absurdly niche videos with 33 views in my feed about robotics but most of them have views in the low thousands. The algorithm isn't holding you back.
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