The hard part is repeatability. You need tight tolerances and each joint in the arm adds inaccuracy the further you get from the base. If the base has 1mm of wiggle, the 20cm arm has 4mm wiggle at the end, and the arm beyond it has even more.

You also, for faceting purposes, need much finer resolution than an ungeared servo will have. Gearing it is tricky because you want backlash to keep the join tight, but not so much that it has high friction when moving. You don't really want to use a worm gear because they're both slow and overly rigid. So a cycloidal gear is the best bet for the gears in the arm. You also need real servos with some amount of feedback because grabbing at glass is sketchy at best.

I was estimating 1-2k build cost, bulk of that is in the gearboxes.

And once you manage to get the hardware working, getting a kinematic solver to really work is a massive challenge. Tons of edge cases, real-time feedback to handle and the need to balance usability with reliability. That's where robot companies charge a lot, and rightfully so.

Whenever you can avoid building a robot arm and replace it with simpler kinematics, you should. Hats off to you if you build that thing!

Here's some specifics if you're interested. Depending on the end effector payload requirements, a mix of NEMA34,24,17 can do this (bigger ones for earlier joints). You can go cycloidal/harmonic gears if you have the budget, otherwise each actuator (motor + driver + gearbox + shaft coupling) would run you something like $100-$200 depending heavily on supplier and exact requirements (+$50 or so for closed-loop systems). So not terrible on the price front. Then for the base joint you'd want some wider cylindrical gearbox that distributes the load across better.

If you're able to work with a machine shop I think you can put together something really high quality. Here's some example design inspirations, some of them even better than what I described I was able to put together as a hobbyist:

https://www.youtube.com/watch?v=7z6rZdYHYfc (this one is fantastic; a smaller and lighter version operated more slowly would have even less wiggle from the base) https://www.youtube.com/shorts/II8gdIXPgaE (this is more comparable to the OP) https://www.youtube.com/shorts/_x7P9eZCkVM https://www.youtube.com/watch?v=g9AfhqOd-_I (most professional one I've seen, and almost certainly this BOM would be under $3k, probably under $1k in China. In fact I'll go ahead and email these guys since this is so cool and I wonder if they sell smaller models) https://www.youtube.com/watch?v=iB2NAgfVjIs (definitely check out Chris Annin, American roboticist who imo makes some of the best open source low cost stepper motor robots)

Could this be solved by software instead of expensive hardware?

Some idea I had a while ago was to build an arm out of cheap, "wobbly" components for the large-scale movements, but then add some stages at the end that have a small movement range, but can be controlled very precisely.

Finally, add a way to track the deviation of the tool's actual position from the desired position very precisely, maybe with a tool-mounted camera.

Then you could have a feedback loop in software which tracks the tool's deviation from the desired position and uses the "corrective" stages at the end to counteract it.

I'm not sure if this would work, however.

(There is also the question how long the "counteracting" would take. It's one thing to "eventually" arrive at the desired position at the end of the path - e.g. for pick-and-place - and another to stay below some maximum deviation for the entire path, e.g. for etching or welding.)

Yes.

Imagine a human putting a screw in a hole. You don't follow the "optimal" trajectory, you adapt it on the fly, even do several quick trials to do it.

Humans do it with a combination of vision, touch and planning.

Each of these is currently still a huge problem for AI, nowhere near human level.

If you solve this problem, teaching a robot arm to be accurate should be pretty easy. You would just have stereoscopic cameras that map to a 3d world, and "program" in a trajectory of the object, and the model should use that trajectory to figure out where to move and how to compensate based on visual feedback.

> stereoscopic cameras that map to a 3d world

The current state of the art for this is completely atrocious.

Take a look at this very recent research: https://makezur.github.io/SuperPrimitive/

The idea that robots can "understand" the 3D world from vision is, right now, completely illusory.

Would using something like a stepper motor geared way down with a cycloidal gear box work for a situation like this? (in my mind) It would give you a very controllable and repeatable way to position, with the backlash handled by the gearbox mainly.

Would love to know if I'm wrong though, like I said mostly a software guy trying to venture into hardware!

* How rigid are the links between my joints? Plastic will wobble, metal is better

* How heavy is my arm and how does that limit its movement? If you go for stiff metal castings, you add weight you need to move. The lever arm relative to the base can get really long

* Motors are heavy! Ideally you can mount them towards the base, but then you need drive shafts or belts, which again add flex. (See KUKA arms which have motors 4, 5 and 6 on the elbow often)

* How much payload do you need to move? 5kg is already challenging in ~1m arms and if you need to move it fast the problem gets even bigger.

* Where do you run your cables? Internal is tricky to build, external can get you tangled.

And so on. When approaching this you get a totally new appreciation for biological arms which arae insane in most aspects except for repeatability. And on the software side you can enjoy inverse kinematics :)

> Let's say two cheaper cycloidal geared motors running in opposition with a load cell between them to maintain the materially compatible force.

This might work, but now you have twice the amount of motors.

If your axis has high enough friction, then nothing will move when your actuator is in the decoupled backlash region, so you can compensate by adding the backlash amount to your target position whenever you switch directions. But that means you need more friction than tool force, with bigger motors and drivetrain to compensate. It's often easier just to build a system with zero backlash, then you can focus on tuning for system rigidity/resonance (as shown in your link).

Couldn't you build your arm in Nvidia Omniverse by also adding feedback like a cheap hig resolution distance or angle detector and train an ml model to compensate it?

But beyond that, the kinematics as well as the force dynamics for controlling a serial manipulator are very well understood. So there aren't too many gains to be made by AI. It is difficult to implement in software due to some tricky situations about the nature of motion planning. Discontinuities around orientation approaches in 6-DOF systems for instance. But widespread use of serial manipulators is proof that, although challenging, they are relatively solved. It is always interesting to watch an AI model or genetic algorithm do some path planning, but this is a pretty well trod area of research at this point.

Now, when you want a robot to walk and pick things up at the same time... that is when AI becomes something to consider in order to figure out how the dynamics should work.

1-2k build cost is tiny in this space. I've paid that in individual motors (specialized ones, to be fair).

Every use case is completely different and is a lot of work. Even when you get something working, accidentally shake the desk or crash the arm into something and all your coordinates are broken and you have to start again.

Not to mention the actual mechanics are really complicated - to have a meaningful payload at 50cm reach you end up with really high torque at the base joints (which also need to have super-high accuracy), which requires expensive gears and motors. None of that is cheap.

Then you get to safety - an arm that has a useful payload is also quite heavy, and having that amount of mass flailing around requires safety systems - which don't come cheap.

It's a bit like hardware no-code - you can't make an easy to use robotic arm because programming it is inherently hard. I think the only thing that will change that is really good AI.

Do you know if anyone has tried building an arm that uses spatial positioning techniques from augmented reality, like structured light or pose tracking[1], to understand the position of the arm in space without resorting to "dead reckoning"?

It seems like that kind of approach would increase the physical tolerance and reduce the programming complexity, since you know both a) where the arm is supposed to be, and b) where it actually is.

[1] https://en.wikipedia.org/wiki/Pose_tracking#Outside-in_track...

The more usual application of multi-camera setups etc. is in path planning and scene understanding, not low level control.

I think the limiter on smaller arms is quality servos with real location encoders - this one costs a couple hundred bucks for motors.

Not claiming the software is easy! But I think sourcing parts is (or has been) really hard.

Not a robot arm, but I worked on a project where the customer wanted to use a commercial motion platform as part of a simulator-based training system for boats. They thought they could just put it in the corner of their boat shed and get training but were amazed when they realised how dangerous it could be to passers-by, especially if it moved unpredictably when someone was standing nearby without paying attention. It went from 'we just need some crowd control barriers' to a full metal cage that was also integrated with the building fire alarm system so that it would stop cleanly if there was some sort of emergency elsewhere.

Other motion-platform-based hilarity ensued when it was discovered that the commercial software model they were using to drive the sim could in some circumstances capsize the virtual boat.

[1] https://www.youtube.com/watch?v=UerxNyu147g [2] https://mobile-aloha.github.io/

This typically won't be accurate enough for closed loop kinematics, especially at any sort of speed.

Many medium sized arms are quite capable of generating forces that can kill a person.

Lots of automation works this way, but it actually limits the applications quite a bit.

A robot that can safely work along side people (i.e., a "cobot") and adjust to environment changes and changing work patterns is a whole different beast.

[1] In the order of 1:100, see e.g. https://www.harmonicdrive.net/

These do exist, it's just that "reasonably cheap" is typically low - mid 5 figures for any sort of reach an payload.

Which of those can/cannot be done and why?

The most common designs of six-axis robot arm don't have the 'rotate forearm sideways' joint needed to arm wrestle.

> - Handwriting notes for small jewelry brand?

Possible: https://en.wikipedia.org/wiki/Autopen

> - Drink mixer?

Possible: https://www.makrshakr.com/ (arguably more of a showy entertainment item than anything else)

> - Handing towel when in the bathroom, then getting a new one?

Manipulating flexible materials is difficult. As is navigating through a house with locked bathroom doors and suchlike.

> - Setting up my morning espresso?

Depends if you're willing to broaden your definition of 'robot' to include bean-to-cup machines.

Like arm wrestling a brick wall; if you can push it over then you win, if you can't push it over then you lose - either way there's not much fun in it. And if it can beat the toddler it risks injuring them because neither of them really understand what's happening and what the risks are. The arm can't stop if the toddler says 'ow'.

> "Handwriting notes for small jewelry brand?"

Can be done already with a commercial 2D plotter: https://www.axidraw.com/ . It costs twice as much as this arm, but you don't have to build it and it already has "software for realistic handwriting" and there's a company to get support from.

> "Handing towel when in the bathroom, then getting a new one?"

Is the arm big enough to be useful for that? It appears to be shorter than a typical human arm so it would be cheaper, simpler and quicker to put the pile of clean towels a foot closer to the shower where the robt arm is sitting, and not have the robot arm at all. Plus you wouldn't have to deal with electricity in the bathroom or dripping water on the robotics as you reached for the towel it was handing you. (Are you thinking of a robot arm with cameras for feedback of where it's positioned? Cameras in a bathroom won't be popular with everyone no matter how much you promise they are innocent).

> "Setting up my morning espresso? (grinding the beans and turning on the coffee machine)"

Simpler and cheaper done with a timer mains plug which you can get for under $10. Put the beans in and load up the coffee machine the night before (work you'd have to do anyway) and have the timer start them in the morning. If you expect the robot arm to unseal a bag of coffee beans, measure some out, deposit them in the grinder, close the grinder, and close and seal the bag after, you'll wake up to spilled beans and unsealed bag a lot of days before you get that working reliably. Instead of $250 plus weeks of effort to speed up this 2 minute task(!) you can get a Keurig / Nespresso pod coffee maker for less than $100.

> "Drink mixer?"

How much spilled wasted alcohol, plus time of disassembling and cleaning your robot arm and the surface it sits on, and the floor, or finding the bottles, unscrewing the tops, handing them to the arm, waiting for the arm to slowly pour them which you could have done quicker, then putting the tops back on and putting the bottles away yourself, then putting the drink stirrer into the arm, then waiting for it to mix the drinks which you could have done yourself quicker, before you decide this was not a good use of time or money? (How often do you drink mixed drinks anyway?)

The robot isn't going to learn to do the task better next time like a human could so if you have to get involved in the task at all, you may as well do it yourself. And if it's a 15 second task like "reaching for a towel" what are you doing with your life trying to automate that? Roomba saves a lot of time, a lot of annoyance, it could be worth it even if it does an inferior job - because you can leave it running over and over and over. Same with a robot lawnmower, if you just glance around to make sure there's no pets or children in the way then let it go, it can save you a good chunk of time and if it goes wrong you just get a patchy lawn or dusty floor and it can retry tomorrow. But handing you a towel or mixing you a drink saves you almost no time, but if it goes wrong you get a broken bottle of sticky drink all over or a pile of towels on the floor, which has undone months of 'time saved' in one go.

AND very likely to be completely outdated within a few generations (5 years?) of robotics + AI progress.

I would also not discount how easy it is to sell people on additional cameras in their homes (including the bathroom) for the sake of convenience.

Do you genuinely think they will improve to the point of having finger style grippers, dexterity and adaptability to grind coffee, mix drinks and pick towels, and be on sale to the public, safe for use in the home, for $250 (or $2500) by Jan 1st 2030? I would be very surprised.

(Can you get a robot arm today, for any price, to help a quadraplegic open their mail, bring a drink with a straw in it to their mouth, lift them into a sitting position, hold a book in front of them and turn the pages, or ... do anything helpful? I'm not aware of any, but haven't been looking specifically).

Yes you could probably build a robot today which hands you a towel from a pile, reliably and swiftly, or selects the bottles of alcohol and opens them and pours and mixes a drink - in a carefully controlled and lit environment where none of the lids or corks are stuck and the glasses are all a similar shape and size and nobody is allowed to be near it - I don't say it's impossible with today's tech, but it would cost a lot more than $250. A hundred or a hundred thousand times more, while being far far more limited than a human.

[1] https://arstechnica.com/gadgets/2022/04/boston-dynamics-stre...

Hardware generations are typically closer to a decade than a year. Robotics is moving fast these days, but not that fast.

I've built a lot of custom arduino-based projects for other people and a substantial fraction of them are the "I bought a bunch of stuff, but I don't have time to learn how to program it" types.

$3 will get you a basic Arduino Nano clone.

People think they can build their own robotic arms for leas than a "real" robotic arm costs, but the do not account for wobble or repeatability.

With all due respect to the person who posted a design for a robotic arm made with RC servos on HN, I would like measurements of the repeatability. Have it draw the same pattern on a piece of paper every day for a week. Show me how closely the 7 lines overlap. I doubt that it can draw such a thing; it will tear the paper or get jammed without the strength to tear the paper.

Source: I've been building hobbyist robots since the 1980's, researched robots in the 1990's including a masters thesis, and teaching robotics for most of the last decade.

^Modifying cheap servos so that a robot arm can repeatedly insert a pencil lead. It's a lot of work though.

Most interesting application though fall out of the scope of old-fashioned robotic arms, i.e. when you need to sense the real world in a non controlled context. For instance to develop a robot that can trim wilted flowers, you'll need to measure the real world, and as soon as you do that, you can just sense your robot arm too, no need for fancy, ultra-precise actuators.

Look at this BOM: https://docs.google.com/document/d/1_3yhWjodSNNYlpxkRCPIlvIA...

Do you really need the $6,129.95 & $3,549.95 robot arms for the kind of application described ? I doubt it. I'm not a robotician, and would love some feeback on this idea.

That somebody was 4 decades failing, does not mean that at some point it won‘t be possible. In the last 4 decades the prices have lowered and the quality is much better in the RC world, if you know where to buy.

I did not mean to criticize a hobbyist project for existing.

I meant to say "There is a reason there is no standard hobbyist-grade robotic arm."

When I had leg injury and used crutches, carrying stuff around suddenly became a problem. There are many people with impaired movement. And even without that, I often misplace things and it could help there.

There are plenty of toy robot undercarriages on aliexpress but too small (under 20cm largest dimnsion) to be practical.

So, basically autonomous self-driving mini vehicle. Сompanies spend billions on self-driving cars with quite limited luck.

That's in part because it needs to be very reliable to not kill people.

If the worst that can happen is killing a garden gnome or running over someone's toes you can tolerate more error.

I’m wanting to manipulate a fan in my home gym with some eye tracking to get it to blow air on my face when I work out, but the fan is a few pounds.

Alternatively: any hardware motor suggestions for such a project?

For a heavy fan (don't forget the reaction force from moving air too), you'd be better off mounting it on a some sort of bearing and just using a motor to turn it. That way the motor isn't trying to fight gravity all the time. The robot arm linked here using Dynamixel servos - you could just use one of them to spin a fan on a lazy susan. Much cheaper and less complicated!

I believe it offers higher torque, better precision and ability to just stick to a position with relatively low/or no power due to gearing-side resistance.

I’m sure someone’s written an interesting paper on the ideal sorting algorithm too (i.e. large things > small things vs. ‘just pick up and place the nearest thing’.) I would personally just get it to sort them into basic sets before placing the trays back in their goddamn drawers.

Apparently pretty much every grain of rice you've eaten has been through a machine like that.

Doesn't stop me from wanting one though.

Said like someone who's never tried it :)

For a start you're going to need a camera. Maybe more than one. You want depth sensing? Even an cheap choice like a RealSense is going to add another $250 to your costs. And you'll need a sturdy mount for it, the robot's going to vibrate the table and you don't want to suffer motion blur.

Got the camera in a fixed location, over the area you're picking from? Then the robot's going to block the camera's view when it reaches in. No real-time hand eye coordination for you. Putting the camera on the robot's wrist? Now you've got motion blur problems - and reliability problems, because normal USB cables aren't designed for continuous flexing. You've also got a gripper in view all the time - and now the camera moves, things are always out of focus.

The reach of the arm isn't long enough to give you many bins to drop items off into, considering the number of lego parts there are. The longer you make the arm, the greater the torque at the shoulder joint. Making the motors bigger? Now the elbow motor is heavier. Gearing them down? Now you've got gear backlash.

Your Dynamixels will break, for some reason. Maybe eventually you'll figure out why. In the meantime, $50 each please.

Parts like the small satellite dish https://www.bricklink.com/v2/catalog/catalogitem.page?P=4740... will prove very hard to grasp. And there's like 50 different colours, you're going to need to know your way around lighting and camera settings if you want to reliably tell transparent light blue, transparent medium blue and transparent dark blue apart.

And that's before you get into questions like how to tell a 2x4 stud brick apart from two 1x4 stud bricks next to each other - or how to grasp a brick when an adjacent brick is blocking you from getting in with the gripper.

Every single one of these issues is solvable - but by the time you've solved them all? You could have hand-sorted that lego 20 times over :)

fyi, Luxonis is selling some for $150, I'm still meant to try them but they look quite good

The analysis and disassembly of a combined set of bricks can frustrate even human eyes, brains, and fingertips.

Also, have one to stir pasta in the kitchen.

Viscosities - probably finding a booze's sugar content online would be 90+% of it.

My understanding is e-ink displays will not be suceptible to that.

I might just have given you an excuse to buy a large e-ink display/monitor :)

Side bar: these servos are a game changer.

Downside is when they break, you're out $50 or more - and you're going to break at least one. And the manufacturer wants you to operate them at 11.1v which isn't very convenient. And when it comes down to it, it's still got plastic gears, a plastic case, and enough backlash to be noticeable.

Still got plastic gears though.

A rotatable, table-top round disc base, with a contraption to keep a mobile phone straight and stable. The stand itself will have 4 small unidirectional mics, to figure out which direction (after filtering for human frequencies, ideally) is the sound coming in. And based on that, it will rotate the phone to face that direction (continuosly).

The use case is family video calls that I do frequently from my dining table (my whole family is sitting around the table, hence there is no one good spot to keep the phone). With this self-rotating stand, the phone will auto-rotate towards whoever is speaking.

I can write audio-processing code, but I have no idea how to get started with the hardware. Feel free to steal my idea, but please share with me how you are building it. I just want this to exist, and I want to know how to build it for myself as a fun project.

Just always be aware that these things will never be perfect and don't get anxious because there are so many perfect looking projects on the internet. They most likely went through the same mistakes and might even have more people in the background. Just enjoy the journey

  [1]: https://github.com/adamb314/ServoProject
  [2]: https://www.youtube.com/watch?v=SioCwvR_PYY
  [3]: https://www.youtube.com/watch?v=_4mrb2T706s
  [4]: https://www.youtube.com/watch?v=Ctb4s6fqnqo

if price is a factor then a servo+encoders setup will always be cheaper; there are some dirt cheap encoders out there for the creative hacker. dynamixels offer a crappy value compared to DIY solutions, they're just easy to use off-the-shelf and have nice features that aid construction.. but hardly anything game changing.

Speak for yourself! When I worked on liquid handlers a decade ago the fully integrated servos were at least ten times as expensive as they are now.

Every time I step away for a few years and jump back in, there seems to be at least a half dozen game changing pieces of hardware on the market.

I think I could find some fun projects. I wonder if it could hold my microphone and it turn into an automatic microphone arm...

What payload are you looking for? Cartesian Gantry’s are your next bet if you want to handle higher loads. Eg. Epson vt6l is ~14k but I’m sure you can build a gantry system to handle higher loads for a bit less!

Dobot software sucks though, I ended up programming it in python. It’s definitely not on the same level as say a Kuka or Yaskawa. Epson seems like the best value out of all the higher end arms. Software looks good, the arms are built well, has a long history in industry, and price is decent

The ALOHA project uses the ViperX 300 6DoF, which is around $6500 but uses higher quality dynamixels with aluminum parts and bills itself as "research grade". I have one of these and I'd say it's expensive for what you get, but still cheaper than the "factory grade" robots. I will need a bimanual setup eventually and I'm probably going to get either an Emika or xArm since I'm already hitting the weight limits of the ViperX.

Also it doesn't seems to use springs like GELLO which was a nice add, although the 3D printed parts where the spring was mounted broke quickly.

Lets say the robot that can do that comes out next year for $15 million. Could you afford one? I certainly can't. So pretend that it does, what changes for you and I? Nothing. So the robots that can do that won't be used as robot maids until the price comes down. Which; it will. Open source robotics and model-available AI will force things to be affordable sooner, rather than later, because we'd all like a robot to do that for us. Along with be in the kitchen, doing dishes, cleaning up; cleaning the bathroom, doing yardwork, making my bed.

The industrial versions will be used to do hideously dangerous things. underwater welding, chainsaw helicoptering, manual nuclear reactor rod removal. We already use machines for a lot of those difficult/impossible tasks, it's just a matter of programming the robots.

Which takes us back to today. How far away from that are we? The pieces are already here. Between https://ok-robot.github.io/ and https://mobile-aloha.github.io/ the building blocks are here. It's just a matter of time before someone puts the existing pieces together to make said robot, the only question is who will be first to make it, who will be first to open source it. Who will make it not just possible, but affordable?

In the US or Western Europe, a human worker would cost you about $12-$15 per hour (depending on the actual city and whether they're paying their taxes).

You're looking at roughly 4 hours of work per 100 square meters (the average housing size[1]) per week to get the listed activities done, plus some general cleaning.

So let's call it $60 per week or $3,000 per year. If we estimate the average useful lifetime of such a robot at 5 years, they'd need to cost less than $15k (unadjusted for inflation) to make sense.

This does not take into account that the house owner also would be paying for a small portion of the societal cost of this additional unemployed houseworker. If we assume that there are roughly 1 maid per 500 citizens[2] and that each unemployed worker costs roughly $20,000 to the State per year[3] then our back-of-the-napkin math says the robot worker is generating a socialized cost of $400 per year per household member (2.17 members on average).

So... we need a ~$14,132 fully-automatic, solar-charging bot before your dream can break even.

[1]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8073340/ [2]: https://www.statista.com/statistics/1087472/number-maids-hou... [3]: https://blogs.alternatives-economiques.fr/gadrey/2016/06/19/...

The scenario you described is tough to solve because of edge cases sort of like FSD.

If you want that work done then its cheaper to hire a maid. It would be nice to have complete privacy and have a robot perform all those tasks flawlessly but the price point would make it economical to get a human to do it.

Perhaps you can get someone to drive the robot but that puts privacy at risk.

Same thing with sex robots it is cheaper to hire a sex worker so until something that can get us past the uncanny valley I don't think we will see a robot revolution quite yet. The hardware alone is prohibitively expensive and there is not enough people tinkering at the problem (because to hire humans is always safer and easier and cheaper).

(servos motion is quite jerky, that is why they don't have a video showing off this "robot" operating)

I wonder how smooth one could make a cheap servo-based robot arm operate with decent control algorithms.

Btw I bet your arm's movement smoothness can be improved with some different deceleration rates. It was really fun watching it sort those beans!

My research goal with one of these 'good enough' 1mm repeatability robots would be vision-guided adaptive control to complete tasks after seeing examples of them done via human manual control. Would be a really interesting ML/AI problem. Just need a reasonable hardware platform to get started. Right now I'm leaning more towards simple/smaller servo motors like in the OP of this post (plus there's the cost/time trade-off).