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Comment by regularfry | Hacker News Reader

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.

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I was looking at electroactive polymers (EAPs) and I could not find a single company with consumer pricing...

I wish there was more visibility here without requiring a PhD.

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."

That's presumably one reason why everyone's so keen on doing all the force sensing from the motor current.

Have to disagree with this. The major limiting factor is the software and lack of applications. If there was a killer application it would be much easier to sell. Then the numbers would drive the prices down.

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.

There are arms using steppers and 3d printed epicyclic or cycloidal drives.

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/

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