A Few Words on “The Segfault”

Okay Make, I have an axe to pick and a bone to grind with you guys.

My experiences with Make Magazine and the affiliated blog have been extremely positive in the past. Everything from LOLrioKart to a certain 3D printer to even Fankart has been on the blog so far, and MITERS generally has contacts with people pretty closely associated with Make anyway, so just about everything we do ends up on there. But I have some pretty big reservations about the description of Segfault up there, in this month’s Make (volume 26). Basically the story is a few months ago I was contacted by a journalist for a quick interview about Segfault’s construction, which I obliged to. Now, I don’t blame John up there at all – I know that the guy knows his shit, and he’s in fact the person who puts alot of our stuff on the blog. So I think in this case, he was only reporting on information relayed to him. And boy was that faulty – so since the given address seems to link directly back to this site, I might as well open the valve a little, so to speak.

In a nutshell, those are all the fine little details that nobody cares about being treated as headline news. It has 9 inch scooter wheels!!! And GEARMOTORS!!! No, I’m not just bitter because the gyro and accelerometer functional description is wrong and I’m not sure how it was distilled from the description I gave it. No, what I’m really peeved about is the fact that

Segfault is analog.

That was like, the entire point, man.  Fact #1 about Segfault is always that it’s analog. Not a single line of code runs to keep the vehicle stabilized. Your segway runs on 14 lines of code, mine runs on op amps. Real op amps.  FOUR HUNDRED OP AMPS.

Okay, so more like 11. I think they’re starting to wear out and their gains need replacing soon, but OP AMPS!!!

The signal processing occurs in continuous time.

Instead of waterjetted aluminum chassis (which is nice and all), that line should read ANALOG!!!! I’m not particularly proud of the fact that it uses rudimentary and rather obsolete technology to accomplish the task, but the fact that it was one hell of a control theory learning experience, especially since the final build really occured over like 48 hours. Porting a transfer function to op amps!!!!! is about the closest you can get to just double-fisting the raw theory.

It doesn’t have an Arduino.

Or an ATMEGA chip, or a MSP, or a Cortex. Or anything for that matter. I guess the twin Class D switching amplifiers running the motors are kind of digital.

It also doesn’t work like that.

I’m not sure where the “gyroscope prevents the accelerometer from overcorrecting” bit came from, but it’s way more like the gyro and accelerometer complementing eachother and working in synchrony. In fact that’s so true that it’s even called a complementary filter. It’s a very common and simple sensor fusion algorithm, and if you actually want to know what one is, Segfault’s second most recent build post goes over why I use the two sensors this way in the Adaptive Face Forward Compensator.

Okay, that’s enough for now. Ya’ll should go build Segsticks. Maybe I should start writing for Make or something, eh?!

2 thoughts on “A Few Words on “The Segfault””

  1. Hey, chill, it’s just Karma – for not sticking with brushless motors on the BearLandSharkMan, I suppose… but yeah, I do get the point and the difference. Don’t sweat it. Excelsior!!! ;)

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