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

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.

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/

> cheap, 800x600 cameras with depth estimation ML algos

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

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

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

Wouldn't be the easiest way to program a robot to "show" it its task by simply moving the arm a few times in the paths it has to replicate afterwards?

In a controlled environment - where the object to pick up, for example, is always in exactly the same location - you could do that. If there is any variation in the location of the object, you need vision to localize it each time. You need a camera, maybe two, and probably some kind of 3d perception, which is an unsolved problem at the moment (well, not solved in a general way, there are some solutions for specific objects).

Yes, they have systems to learn this way, but it assumes the environment is controlled (always) and the task identical (always).

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.

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.

Forward and backward reaching inverse kinematics: http://www.andreasaristidou.com/FABRIK.html