[krisoft]

> Bill likely misspoke or was talking about control error.

Mixing up control errors with absolute errors is a very common form of miscommunication in robotics.

I work with relatively big robots and often my colleagues would say something like this "During the test we had 0.5m cross track error, so we did X, Y, Z ...".

And I always ask them for clarification. Were they looking at the robot and seeing that it is half a meter off where it should be, or were they looking at a screen and seeing that the robot thinks it is half a meter off from where it wants to be? Because those are two very different situations. And both can be described with the same words. (And sometimes it can be both, or just one of them.)

[amelius]

> or was talking about control error.

Control error is defined as the difference between desired value and measured value. So this is pretty good?

Even if they use some crude method to obtain position (e.g. gps), they can still easily refine that using e.g. triangulation using cameras around the landing platform.

[krisoft]

> So this is pretty good?

Not sure what you are talking about. If you are asking if 0.5cm is good controller error for an orbital class launcher on landing? Yes, it is extremely good. Without doubt.

If you are asking about my tangential story where there is confusion between total error vs controller error then no, it is not good. Confusion is never good. Especially if the system is not within the total error budget. Because to improve it you need to know if you are dealing with measurement error or controller error.

> Even if they use some crude method to obtain position (e.g. gps), they can still easily refine that using e.g. triangulation using cameras around the landing platform.

Sure. I doubt that their total error is within 0.5cm, but both of their landings were extremely succesfull.

[meindnoch]

The robot knows where it is at all times. It knows this because it knows where it isn't. By subtracting where it is from where it isn't, or where it isn't from where it is (whichever is greater), it obtains a difference, or deviation.

[mucle6]

Reference: https://www.youtube.com/watch?v=bZe5J8SVCYQ

[dang]

https://hn.algolia.com/?dateRange=all&page=0&prefix=true&que...

[killjoywashere]

This voice sounds like something that Mark Farina should be dubbing into his next album. But it's the first time I've heard this bit. Where did it come from? Is this a classic in engineering circles of some shit Rockwell actually sold to the military?

[yetihehe]

It was already dubbed into a song. https://www.youtube.com/watch?v=_LjN3UclYzU

[rcxdude]

It's from an old air force training video. Best guess I'be heard it that it's an unsuccessful attempt to explain Kalman filters (or something similar) in layman's terms.

It's definitely floated around for a while, but it grew in popularity in the past few years.

[lacrosse_tannin]

this sounds like it's read directly out of the inscrutable text book for the one control systems class i had to take.

[ls612]

I thought it was a Cave Johnson reference before seeing this.

[hedora]

I think this was called "error.wav" when I first saw it sneaking around a campus network.

[scottshambaugh]

> whichever is greater

This always stuck out in an otherwise excellent bit, because you should definitely _not_ be taking the absolute value of your control error.

[m4rtink]

By this point I automatically even read it by that voice. :P

[rascul]

How does the robot know where it isn't?

[exe34]

this only works if the retroencabulator is properly calibrated.