Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

CARA – High precision robot dog using rope

aaedmusa.com

Post reply on HN
Print view View original

31–40 of 188 posts

Re: CARA – High precision robot dog using rope

#31

Post by LeifCarrotson »

michaelt wrote: post #27
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.

Well, it probably wasn't that much effort. When you're 3D printing you're going to end up printing everything 2-3 times anyway , so why not dial in the ratio while you're at it? And you can't really declare your design is "high precision" and present yourself as someone others should take transmission design advice from if you aimed for a gear ratio of 8 and achieved "somewhere around 7.9 to 8.2"

It probably doesn't matter so much whether it's 7.913 or 8.186, but it would be important to know the exact value for kinematics. One way to do that is to build an object very accurately, the other is to build inaccurately and then measure the result after the fact.

It's also interesting because competing actuators with strain-wave, cycloidal, or planetary gearboxes will state exactly what the ratio is. The actual gear teeth may not be spaced out perfectly around the circumference, but the number of teeth is an integer with an infinite number of zeros.

Re: CARA – High precision robot dog using rope

#32

Post by taneq »

heap_perms wrote: post #22

Fascinating! I want to get into this type of stuff. But I have no idea where to start, I just have just a CS degree and 3 years experience as a developer.

Arduinos and hobby servos. No, neither of them are "industrial grade" and yeah, you'll reach their limits pretty quickly, but building a physical thing that does stuff is (in my experience) a huge motivator.

Or if you're already all over the basics, figure out what kind of stuff you want to build and then try and build it. :)

Re: CARA – High precision robot dog using rope

#33

Post by munchler »

skeeter2020 wrote: post #9
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.

>> 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.

Re: CARA – High precision robot dog using rope

#34

Post by tonyarkles »

LeifCarrotson wrote: post #31
michaelt wrote: post #27

Earlier quoted context omitted.

Well, it probably wasn't that much effort. When you're 3D printing you're going to end up printing everything 2-3 times anyway , so why not dial in the ratio while you're at it? And you can't really declare your design is "high precision" and present yourself as someone others should take transmission design advice from if you aimed for a gear ratio of 8 and achieved "somewhere around 7.9 to 8.2"

It probably doesn't matter so much whether it's 7.913 or 8.186, but it would be important to know the exact value for kinematics. One way to do that is to build an object very accurately, the other is to build inaccurately and then measure the result after the fact. It's also interesting because competing actuators with strain-wave, cycloidal, or planetary gearboxes will state exactly what the ratio is. The actual ge…

Yeah, I think one of the nice things about making it a "clean" number (either an integer or a rational with a small integer denominator) is that you can easily validate it without needing high-precision measurement equipment: put a mark on both gears (maybe even embedded in the 3D print), line up the marks, rotate the large gear 1 full rotation, and count the number of rotations the smaller gear makes. Check to see if the marks line up perfectly after those rotations.

Re: CARA – High precision robot dog using rope

#35

Post by Paddywack »

taneq wrote: post #32
heap_perms wrote: post #22

Fascinating! I want to get into this type of stuff. But I have no idea where to start, I just have just a CS degree and 3 years experience as a developer.

Arduinos and hobby servos. No, neither of them are "industrial grade" and yeah, you'll reach their limits pretty quickly, but building a physical thing that does stuff is (in my experience) a huge motivator. Or if you're already all over the basics, figure out what kind of stuff you want to build and then try and build it. :)

Can you recommend where to find beginners projects that “do stuff”.

Re: CARA – High precision robot dog using rope

#36

Post by falcor84 »

A4ET8a8uTh0_v2 wrote: post #6
oc1 wrote: post #4

[flagged]

I don't think it is fair to downvote this comment. It is a genuine concern and should be addressed. Amusingly, given that the thought has entered mass consciousness by means of question on 'whether all this is a simulation', matrix ( the animated series ) explored this question a little and it is interesting in how the timeline aligns with what the movie presented.

That's an interesting reference, but do our timelines really align with what was presented in (ani)matrix? Their timelines are quite murky, but it seems that in their universe things only started getting problematic between humans and AIs around 2090 and The First Machine War started in 2139 [0]. With how fast things are progressing, it's not clear to me that we have so much time.

[0] https://screenrant.com/matrix-timeline-year-future-when-sett...

Re: CARA – High precision robot dog using rope

#37

Post by throwawayffffas »

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 look at robotics.

Re: CARA – High precision robot dog using rope

#39

Post by geerlingguy »

dvt wrote: post #21
andrewstuart wrote: post #20

Earlier quoted context omitted.

He might be perfectly happy doing projects and YouTube.

Likely makes more money, too!

For many, no; taking on lots of sponsorships, you can make a good amount of money (especially the ones where you agree to do X posts across Y social media accounts for Z period of time, essentially being fully sponsored across a large swath of life).

But for a lot of tech/engineering channels, it'd be immensely difficult to make the same salary as you could working at a FAANG or the like. (I'm making about half what I made when I had a W-2, but it's enough).

Re: CARA – High precision robot dog using rope

#40

Post by PaulDavisThe1st »

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…

more than 30 years ago I was writing code for a "robotic" device that used motors, directly on the joints.

the motors were so sloppy the company wasted a ton of money [0] having me write heuristics to tackle the errors they accumulated over several hours.

one of his whole points is that by using dyneema (rope), there's almost no elasticity at all in the capstans.

[0] relative to the cost of better motors

Post reply on HN