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Low Cost Robot Arm

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Re: Low Cost Robot Arm

#141

Post by FrojoS »

regularfry wrote: post #71
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…

There have been a few around, but the limiting factor (as you can see from the BOM in the link) is the cost of the actuators. They get expensive fast.

Sensors too. E.g. force sensors are important for dexterous manipulation and safety. But they are all expensive, bulky, imprecise, or require constant recalibration, or all of the former. Our robotics Prof used to quote his industry peers: "The best sensor is no sensor."

Re: Low Cost Robot Arm

#142

Post by FrojoS »

FeepingCreature wrote: post #125
regularfry wrote: post #71

Earlier quoted context omitted.

There have been a few around, but the limiting factor (as you can see from the BOM in the link) is the cost of the actuators. They get expensive fast.

If they don't have to move fast, could you DIY an actuator with a stepper and a threaded shaft? Steppers are pretty cheap thanks to 3D printers.

For a useful robot arm, you need high forces/torques. Usually, this is achieved by high ratio [1] gearboxes between the motor and the joint. Those are expensive, and inefficient and make estimating the output force via the motor current almost impossible.

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

Re: Low Cost Robot Arm

#143

Post by jollyllama »

deelly wrote: post #111
rini17 wrote: post #98

Why not start with something less ambitious, like low cost robot platform able to follow people and carry stuff around and avoid obstacles. No arms, I am okay using mine to put stuff on and off it. 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 plen…

> low cost robot platform able to follow people and carry stuff around and avoid obstacles. So, basically autonomous self-driving mini vehicle. Сompanies spend billions on self-driving cars with quite limited luck.

100%. Arms are hard. Mobility is hard. Mobile arms are double hard.

Re: Low Cost Robot Arm

#144

Post by monkeydust »

NalNezumi wrote: post #5

I've built my own GELLO setup (the setup the author based it's arm on) and it's quite neat, but as I only use it for teleoperation of an real arm, I wonder how useful this low cost arm really is? Considering limited range, probably backlash, and the limited torque 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.

Cool, how are you controlling it, VR (Quest) type setup or something else?

Re: Low Cost Robot Arm

#145

Post by ectopasm83 »

jfoutz wrote: post #85
Ekaros wrote: post #77

Earlier quoted context omitted.

Also I have understood that robot arms are in real life rather complicated to program to operate correctly. So any process would take substantial effort. Magnitude harder than controlling some relays or reading some sensor data.

I don't know, but I think the big real industrial kind can really really hurt or kill people. 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.

I've explored the idea of using super cheap servos to build a robot arm/tentacle to pick cherry-tomatoes and it seems the only reason you'd want to use location encoders is in tasks that require high precision in an open-loop system (the robot is blind to its environment but has info about his own body). To me it seems you can get rid of this requirement if you allow the robot to sense its environment using cheap, 800x600 cameras with depth estimation ML algos and get away with the accumulated imprecision of sequential servos by coupling to each servo a high accuracy/small angle servo (just modify the servo's gear box). As for the gripper mechanism, you don't need fancy force sensors, just use a kirigami effector [1]. See also mobile-aloha [2].

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

Re: Low Cost Robot Arm

#146

Post by schneems »

Any idea how much weight this could hold?

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?

Re: Low Cost Robot Arm

#147

Post by ectopasm83 »

RobotToaster wrote: post #139
Ekaros wrote: post #77

Earlier quoted context omitted.

Also I have understood that robot arms are in real life rather complicated to program to operate correctly. So any process would take substantial effort. Magnitude harder than controlling some relays or reading some sensor data.

I think the main issue is inverse kinematics and path planning. Which is partly why SCARA is popular with amateur robot arms, the maths is simpler.

[dead]

Re: Low Cost Robot Arm

#148

Post by flutas »

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…

Uneducated in hardware, mostly a software guy for perspective, so I could be way off.

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!

Re: Low Cost Robot Arm

#149

Post by mglz »

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…

One thing that is amazing about industrial robots is how rigid they are when at standstill. Breaking systems start to be a challenge too at high speeds and loads.

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!

Re: Low Cost Robot Arm

#150

Post by leoedin »

schneems wrote: post #146

Any idea how much weight this could hold? 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?

Most of these robots will use servo motors - that gives you dexterity but means that holding any position requires constant holding torque - which means limited payload and a lot of wasted power.

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!

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