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Low Cost Robot Arm

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Re: Low Cost Robot Arm

#201

Post by otikik »

leoedin wrote: post #178
otikik wrote: post #52

Earlier quoted context omitted.

My impression is that the fastest/easiest way to do it would be putting all the pieces inside hopper with the selector at the bottom. Perhaps using compressed air to push the falling pieces into different containers as they fall. I believe there’s already something like that in produce factories, separating vegetables by state/size.

I interviewed once with a company that made rice and grain sorters. They have a massive hopper at the top and pass the grain in a curtain through a machine vision camera, and then decide in real time where each grain goes based on the image. Apparently pretty much every grain of rice you've eaten has been through a machine like that.

That is very interesting! Thanks for sharing. I did not imagine that rice was a good candidate for this

Re: Low Cost Robot Arm

#202

Post by tsycho »

Here's what I want to build:

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.

Re: Low Cost Robot Arm

#203

Post by Yenrabbit »

alex_suzuki wrote: post #68
devsda wrote: post #63

Earlier quoted context omitted.

Unless it has to do something with the print quality itself, can't this be achieved using a stationary phone with its camera towards a monitor displaying 3D transformed barcode images ?

Yes, possibly. But reading from the screen is quite different from reading actual barcode prints, for instance you have to deal with Moirè patterns and such. And frankly it was just a good excuse to buy an arm. Sue me! ;-)

Haha fair play, this is exactly how things should be!

Re: Low Cost Robot Arm

#204

Post by mbrameld »

tsycho wrote: post #202

Here's what I want to build: 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 fr…

An alternative would be a 360 camera and do the cropping in software. It has the advantage of being able to show multiple speakers at once.

Re: Low Cost Robot Arm

#205

Post by willy_k »

tsycho wrote: post #202

Here's what I want to build: 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 fr…

If you can write the code, it could be pretty straightforward. From a quick search, motorized turntables already exist, from $10-100, both with and without remotes. So you could either wire a controller into one, or reverse the remote’s signals. I also found this guide for a DIY one[0], if that’s your preferred route.

[0] https://www.instructables.com/15-Motorized-Rotating-Display-...

Re: Low Cost Robot Arm

#206

Post by jannw »

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…

tight tolerances and repeatability is mostly a combined rigidity and resolution issue, which is functionally equivalent to a cost issue. Add more money. Unfortunately there is a point where programming and hardware costs is higher than a skilled artisan ... hence the profession!

Re: Low Cost Robot Arm

#207

Post by xg15 »

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…

> 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.

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.)

Re: Low Cost Robot Arm

#208

Post by zetalemur »

xg15 wrote: post #207
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…

> 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. 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…

Isn't what you describe a PID-controller: https://en.wikipedia.org/wiki/Proportional%E2%80%93integral%...

AFAIK that is the common approach to solve this problem, but it still needs some degree of sensor accuracy?

Re: Low Cost Robot Arm

#209

Post by ska »

dansitu wrote: post #168
leoedin wrote: post #154

Earlier quoted context omitted.

I worked for a startup developing robot arms for a while. What we found was that giving someone a robot arm - even one with reasonable APIs and no cost to them - didn't really help because the hard part is making useful automations. Mostly people spent a few hours playing with the arm and then put it on a shelf. Every use case is completely different and is a lot of work. Even when you get something working, accident…

It's cool to hear from someone with experience! 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 bo…

This is actually pretty common. But getting enough resolution to improve on what you can do with the encoders isn't so easy.

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

Re: Low Cost Robot Arm

#210

Post by hawski »

Johanx64 wrote: post #194
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.

With my understanding 6DOF robot arms are used when you need to be flexible. Today you do this tomorrow (or in a couple of months) you will need to do something else. The more diverse set of things to do the better. But if you need to do the almost exact same thing many times over for a long time it is better to design a production line that doesn't use 6DOF robot arms at all.
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