How can this 6 axis robot have a static accuracy of 0.05 mm? (2021) [video]

He goes into detail on the control algorithm of the project on the github. It's rather complicated... https://github.com/adamb314/ServoProject/blob/main/Doc/Theor...

Be aware, per erratum 9, that you’ll need to include external pull-downs instead of using the internal ones

It’s relatively old at this point, but I’m still getting excellent performance from the Teensy 4.1. It’s a little more expensive, around $30, but runs Cortex M7 @ 600MHz and includes a generous compliment of I/O and protocols.

> (...) the new Raspberry Pie Pico 2 is both orders of magnitude more capable than the chip used here and also around half the price.

That's cool and all but what are the tradeoffs?

Of what use are the primary encoders then?

But they're not the same motions? The second move is to the other side.

You have oversimplified the Boeing one: their goal was to create an efficient plane to compete with Airbus without needing the expense and delays of a new type certification.

To do this they needed bigger engines on the same frame, which in turn needed to be mounted further forward affecting flight characteristics and requiring retraining. Retraining would be a sales killer so they hacked on some software systems to attempt to make the plane fly like an older 737.

Then they can just use an iPad training course for pilots to upgrade. The augmentation had to avoid the pilot knowing about (I think) the plane getting stuck in a stall at a too high AoA (this is where my memory might be off...) so the MCAS software uses AoA sensors to nose down based on the detected AoA.

The AoA sensors were never designed to be used for a direct life and death critical use case and sometimes they got stuck or failed. MCAS only used one as an input. If MCAS incorrectly asseses a nose down is required and the pilot follows their 737 training they are having their last day. That plane is going down.

Bascially people were murdered by Boeing so at every stage of this wretched plan they can make more money.

I think you are right but Boeing was more of perhaps the worst possible asshole design, and deserves it's own league.

Regarding applications for robots that have to move very precisely without carrying a load, there are robotic measurement systems: https://en.wikipedia.org/wiki/Coordinate-measuring_machine

Look at this later videos where he has the servo lift a weight on a long arm.

I haven’t watched the whole video, but I’m assuming what they were showing was ‘move x from 0.00 to 10.00’ with the gauge showing the final move was to (actual) 10.05.

Which with how floppy that rig is, is pretty impressive.

Notably though, those gauges do need to be ‘preloaded’ (compressed into their ‘positive’ range) to be able to measure negative direction shifts, and while it looks like that was done, I can’t be 100% sure without analyzing it far more than I want to do right now.

Also, those gauges provide a degree of preload (not much, but some), which might be taking a bunch of slop out of the system and giving overly rosy accuracy numbers.

Yes. The sphere at the tip has a certain radius, and the indicator will show zero (again) when the sphere has been deflected by its radius (i.e. the contact point is exactly at the center line). When out of contact, it's essentially telling you that you're missing at least a whole millimeter to the point where you should be.

Often there is a second needle indicating which of these situations you're in, but I assume it's not considered necessary because if you're 1mm off, the situation is (in the contexts in which these devices are used) very obvious.

It’s the compromise between a gantry vs arm design

Yes but they're not robot arms so it's not as fascinating. The length of the arm amplifies error so if you made a "mechanics and steppers" arm with the same positional accuracy as a printer, the motors would have to be much more precise or if you geared them down, the backlash extremely low like an industrial robot arm.

I'm curious what would be the best way to replicate an x/y (optionally z) system with 0.05mm or lower accuracy? Without sacrificing speed of course.

Feynman brings up some problems with pantographs and precision in https://calteches.library.caltech.edu/1976/1/1960Bottom.pdf (page 6-7). I haven't thought about it myself, though.

Pantographs are mostly useful in 2 dimensions and any robot only needing two dimensions can just use rails which will be more accurate

What their video demonstrates is mostly same-direction repeatability, not absolute static accuracy. They can correct for with backlash at individual motors, but not slop or bend in the linkages.

This uses DC motors. If you use modern 3-phase servomotors, you know more of what the motor is doing.