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Low Cost Robot Arm

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Re: Low Cost Robot Arm

#191

Post by Groxx »

boffinAudio wrote: post #83
otikik wrote: post #56

Earlier quoted context omitted.

Oh look someone has already done something like that: https://www.youtube.com/watch?v=04JkdHEX3Yk

I don't know why this can't just be a cleverly laid out arrangement of layered sieves, each one parsing a different object .. I don't see how it needs to be mechanical in any sense other than "pour in the lego junk, out it comes neatly sorted", a la coin-sorting machines ..

The problem with sieves with Legos is that everything goes in the square hole: https://www.youtube.com/watch?v=Nz8ssH7LiB0

Re: Low Cost Robot Arm

#192

Post by robmurrer »

iiJDSii wrote: post #185
robmurrer wrote: post #126

obligatory shout out to Annin Robotics AR4. Here is my build: https://commandpattern.org/2023/03/19/ar4-robotic-arm-build/ $2K USD. 2kg payload. millimeter repeatability (if you build it well :)

Nice build! I always wanted one of those AR robot arms but I'd rather buy it off-the-shelf than assemble from scratch. I don't think anyone sells them pre-built though. This type of 'high level hobbyist robotics' is in a bit of business dead-zone unfortunately, as it's some combination of too small a market and not enough use cases to justify having a company around. Or maybe there's potential there but no one's thou…

this is where my research is going. camera -> llm -> targets -> tasks -> ros2 arm :)

Re: Low Cost Robot Arm

#193

Post by Gracana »

adolph wrote: post #166
mglz wrote: post #152

Earlier quoted context omitted.

Servo + Cycloidal or Harmonic gears are usually the way to go, but to get them backlash-free is hard (or expensive, if you're buying). Once you got that down challenges include: * 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 b…

Do you think there is a way to take out backlash with sensors and software? Something like how additive manufacturing systems can use accelerometers to smooth artifacts from motor movement. [0] Let's say two cheaper cycloidal geared motors running in opposition with a load cell between them to maintain the materially compatible force. https://www.klipper3d.org/Measuring_Resonances.html

The problem with backlash comes into play when the direction of force on an axis changes. If you are applying force in one direction and all the backlash has been taken up, everything is fine -- any force you apply or movement you make will be transmitted to the tool like you'd expect. However, if you have to decelerate, or you've gone over-center, or the tool/load pulls harder than you're pushing, now you have to apply force in the other direction, which you can't do until you take up the backlash.

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).

Re: Low Cost Robot Arm

#194

Post by Johanx64 »

7373737373 wrote: post #69

I'm surprised (or perhaps very unaware) that there doesn't seem to exist a company yet that mass produces cheap, high quality, reasonably standardized robot arms. So many things like 3D printers or CNC machines have entered the consumer/amateur level price realm, but this seems to be something still largely unexplored. Seems to have Arduino/Raspberry Pi scale potential, but I haven't heard of a name/ecosystem that po…

Ask yourself - what problem are you trying to solve? After you've defined it, you'll quickly learn that there's much simpler and cheaper solution than 6DOF robot arm in almost every case. And if you actually do need it, in those cases you'll find that 10-20k is actually pretty cheap all things considered.

Re: Low Cost Robot Arm

#195

Post by leptons »

mtreis86 wrote: post #134

I started working on a similarly sized arm. I've got a use-case, long time friends with a glass blower. I was thinking of using it to make faceted glass pendants. They've got a faceting machine but it is manually operated. 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…

I recently saw this video, using modified servo motors to reduce the wiggle...

https://youtu.be/Ctb4s6fqnqo?si=XP0MS0cpjlK_LMQC&t=8

Re: Low Cost Robot Arm

#197

Post by GabeIsko »

Climato wrote: post #187
mtreis86 wrote: post #134

I started working on a similarly sized arm. I've got a use-case, long time friends with a glass blower. I was thinking of using it to make faceted glass pendants. They've got a faceting machine but it is manually operated. 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…

I think about this regularly just don't have the time to pursue it: 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?

Making and animating a 3D graphics robot arm is trivial compared to building it in real life. So not so much Omniverse, you would want to use a proper simulator like gazebo.

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.

Re: Low Cost Robot Arm

#198

Post by HeyLaughingBoy »

taneq wrote: post #130
7373737373 wrote: post #92

Earlier quoted context omitted.

Agreed, they certainly can be/are useful (and fun!), in a multitude of ways, but all too often I've also encountered peoples' "complaints" that they bought a bunch and now don't have a use case for it/are searching for one :)

That's because a toy engineering project is still an engineering project and will be way more work than you think it is, no matter how much work you think it is. It's hard to maintain that energy for long when it's not your day job (sometimes even when it is, tbh).

LOL. I often tell people online that they're better off downloading the free Arduino IDE or playing around with the Wokwi simulator until they have a good idea of what they want to build and whether or not it's within their capabilities before buying parts.

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.

Re: Low Cost Robot Arm

#199

Post by HeyLaughingBoy »

JKCalhoun wrote: post #107
moffkalast wrote: post #86

Earlier quoted context omitted.

You can use an Arduino for virtually anything though. A robot arm can only move stuff around.

Arduinos are also $20.

$20 will get you a 32-bit processor (ESP32), with Wi-Fi and Bluetooth 5.0 built in and a 2.8" color TFT screen, programmable with the Arduino IDE.

$3 will get you a basic Arduino Nano clone.

Re: Low Cost Robot Arm

#200

Post by jrussino »

otikik wrote: post #116
Max-q wrote: post #91

Earlier quoted context omitted.

I think the easiest way to collect the Lego pieces from the floor is by using a vacuum cleaner. Then look at the sorting as a separate problem :)

We have a “Lego sheet” - just a regular bed sheet that goes on the floor before playing with Legos. When it’s time to collect, you make a “bag” with the sheet, grabbing (most of) the pieces, and then we “pour” them into the final container. The sheet goes in top of the pieces on the same container so it’s also the first thing that comes out the next time.

I guess this was a common enough solution that now you can find products that are essentially what you're describing, e.g.: https://www.amazon.com/SAM-MABEL-Storage-Basket-Play/dp/B0BV...

From the item description: "TIDY UP IN SECONDS: Say goodbye to messy playrooms with our storage organizer! The play mat provides a dedicated area for creative play, and when it's time to pack up, simply gather the handles and tip everything back into the compact storage cube. "

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