All-Analog DIY Segway Project 141
An anonymous reader writes "One of the zany hacker-makers here at MIT just finished this DIY Segway project (video). Difference from the others: it's all analog. The controller is built without a microprocessor or even digital logic. It does use a gyroscope like the real Segway. The functionality looks fairly basic, but the fact that the controller works at all is amazing. The guy has a ton of other projects on his site too. Definitely worth a read for people who enjoy building things."
and here we have a hacker (Score:4, Funny)
Old school dork (Score:2)
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would you please carefully read the ENTIRE message including the very last word, please!
SEGFAULT (Score:5, Funny)
Re:SEGFAULT (Score:5, Insightful)
The ultimate SEGFAULT was a sad one, the CEO of Segway dying from running his off a cliff by his home.
http://www.huffingtonpost.com/2010/09/27/jimi-heselden-segway-boss_n_739983.html [huffingtonpost.com]
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The ultimate SEGFAULT was a sad one, the CEO of Segway dying from running his off a cliff by his home.
And dutifully posted on /. [slashdot.org]
Actually, not CEO. (Score:1)
Owner. We didn't have a CEO; we do have a COO. Jimi was never directly involved in the dealings of Segway, per-se.
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Owner. We didn't have a CEO; we do have a COO.
Too bad you didn't have a CSO*
*Chief Safety Officer
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There wasn't any defect in the design or manufacture of the Segway. He had a dangerous location on his own property, an area where one could have just as easily had an accident on a bike or a skateboard. It wasn't a place for any company officer. It's sad that he died, but at least he was doing something he enjoyed. If it were me, I'd rather have gone that way than in a car wreck or hospital or from a heart attack while too fat in front of a television set.
Controllers were analog before they were digital. (Score:5, Informative)
My thoughts exactly (Score:5, Insightful)
Re:My thoughts exactly (Score:5, Informative)
Kids these days couldn't imagine trying to implement a PID controller without a microprocessor. It does make it easy to watch what is going on.
Watching large governors [wikipedia.org] work is pretty cool. No electronics to speak of. Just a properly tuned set of weights and some geometry.
Re:My thoughts exactly (Score:4, Interesting)
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THAT is a worthwhile goal. Price is the only thing that has kept the Segway back.
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I wonder which would last longer? The one with microprocessors or the analog one?
Price might not be the ultimate deciding factor if it could be demonstrated to last significantly longer than the Segway, which would make an equivalent price point seem more attractive.
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A lot of PC motherboards fail because the electrolytic caps wear out, not because the CPU dies.
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That's likely due to using cheap electrolytes instead of solid caps.
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You mean analog/digital, not passive/active. An op-amp is just as much an active component as a microcontroller.
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Price is the only thing that has kept the Segway back.
Not only price of the device, but also price of rethinking the infrastructure that the Segway operates in - too fast for sidewalks, too vulnerable for car lanes, and too damn annoying to integrate into bike path traffic.
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sounds a bit to much like a placebo effect for my taste...
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i was aiming at the coffee requirements, guess i should have quoted...
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Re:My thoughts exactly (Score:5, Interesting)
And I have mod points, but don't give you any. 'Troll' is awfully harsh, I agree. I'd rather give you some 'un-informed'.
The higher part count is surely on the side of the digital controller. Just look at the diagrams offered: analog means direct processing of signals, no A/D. Just some op-amps, pwm, done.
Harder to debug? Nonsense. You debug with a voltmeter instead of a logic analyzer.
You are right with respect to advanced controlling, though, like counting, timing, delays. But none is needed here, some filters are just enough, and filters are implemented easier with some RCs around an op-amp. Also, you need a bridge. A bridge is much more simple if build in an analog manner. So your 'just impractical' is a good reason to not give you any mod points. It might be your opinion, and you sure may have one, but to me, an EE with some experience in developing controllers, it doesn't hold water in the case of a gyroscope.
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How does adding some op-amps and discrete PWM reduce part count ? Have you counted all the resistors and capacitors for the filtering ?
With a digital controller, you can implement the A/D, filtering, control loops, and the motor PWM all inside the same device. You can even avoid some of the A/D stuff by using a accelerometer
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Not a realistic one, though. IOW: tell that to people who code Spice-like modelling software :)
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True, you can't model a realistic RC filter in one line of code, but you can model a perfect one, which is exactly what you'd want in this case.
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Agreed, through there are some people who spend quite a bit of time replicating all the imperfections -- say in the Arturia MiniMoog emulator [zzounds.com] :)
Digital has lower part count (Score:2)
The higher part count is surely on the side of the digital controller
It may look so, until you realize that all the parts in the digital controller are in a single chip.
When I got my EE degree one of the most widely used analog chips was the 555. With an eight-pin chip plus a few capacitors and resistors one could perform a wide range of timing tasks.
Well, it has been several years now since I last touched a 555. Today I use a 12F675 PIC instead. The same eight-pin count, but it can do anything a 555 does, plus a lot more, without any external components. A/D conversion, PWM
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I was speaking to professionally designed products as opposed to just a demonstration of the gyroscope principle. You sound like you have some EE experience but I wonder if you are seriously suggesting that someone would attempt an all-analog control system for such a thing. Even little remote controlled toy helicopters now use DSP for that purpose, and their part count is extremely low.
Sure you _can_ do a gyroscope with a few op amps, but if you're actu
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I know, on Slashdot one is supposed to not agree, ever. ;)
What you write makes a lot of sense to me, now.
Actually, if I wanted to build a prototype to demonstrate the feasibility, I would probably still do an analogue one. I still gobble together parts from my shelf and solder, faster than gobbling stuff together and solder and program.
The very moment even a small series needs to be done, the use of uPs becomes a must.
My comment was motivated by some remarks of some people in here, who seemed to imply that
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Obviously, for someone experienced in electronics, a PID op amp circuits is easy, and needs no debugging.
For someone experienced in microcontroller based digital control, a firmware PID control is easy too, and has no need for debugging either.
Also, this project isn't just a simple PID controller. They also have filters, mixing of accelerometer and gyroscope data, steering, and PWM motor
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Yes and for those the digital solution is better. Just pointing out that it isn't so 'amazing' to have an analog controller. All of the Mercury, Apollo and Gemini controllers were analog. The guidance computer was digital on Apollo but it was pretty state of the art and had only 4k ram.
Filters are actually far easier to design as an analog circuit than a digital one (a low pass is just one resistor and one capacitor). And there is no lag that you would get with a digital filter either.
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building an analog circuit that's programmable means you end up with a digital system
Oh, really [youtube.com]?
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Because such scooters have been developed or to be more precise people tried to invent them before the all digital segway. And they failed. So it is amazing that they were able to do it. It is a little bit an anachronism, because today you try to do all controlling digital. Analog is not precise enough (people think).
Re:My thoughts exactly (Score:5, Interesting)
Analog is not precise enough (people think).
Speaking as a controls engineer, they have obviously not done much digital controls. You have to worry about things like sampling rate, aliasing, round-off error, and digital noise introduced into the (inescapably) analog parts of the circuit. For a simple system, a properly-designed analog controller is much easier to implement, and has advantages like "infinite" sampling rate, graceful failure modes, white (gaussian) noise as opposed to odd frequencies introduced by sampling and clock frequencies, and no programming bugs or crashes.
Analog controllers for simple linear systems (like telescope mirrors) are in virtually every spacecraft ever launched for precisely those reasons. Only recently has the push for miniaturization driven some simple systems into digital FPGA controllers.
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His motor driver chips for example (International Rectifier IRS21184), take standard CMOS digital input signals. Digital input, or digital-compatible input, makes no difference. Somewhere along the line you still need to do what amounts to A-D Conversion. Which brings back most of the problems you mentioned.
Unless I misunderstood, and from the spec sheet I don't think so (the schematic shows Schmitt-trigger inputs, which convert analog input to square wave with h
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What makes the Segway possible isn't its digital control system (that's fairly trivial), it's the sensors. The reason that such scooters didn't exist before is that the consumer-grade accelerometers were not available. Of course inertial guidance systems have existed since WWII, but they were way too expensive and bulky to put in a scooter.
You'll notice that devices containing miniature accelerometers all started appearing around the same time: HD drop sensors (2003), Wii controllers (2006), iPhones (2007),
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He probably "cheated" and designed the whole damn thing on a computer. Anyway, the reason you can't really do stuff like this on an analog system is imo that you'd had to hit a sweet spot with all you're calculations and all the hardware would actually have to do what it was supposed to do; even then the system wouldn't have been able to do proper error checking and recovery if some component went haywire. Yes, he did it with an analog system, but alas it's really of no consequence.
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Have you looked at the circuit diagrams?
What do you mean with proper error checking and recovery in this context? You think a digital controller would not make the thing fall over when the gyroscope fails? Are you sure you know what you are talking about here, or just reproducing what you heard in 101 of digital controllers?
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I'd add a second (or even third) gyroscope and accelerometer, and have the controller compare the inputs. If they are too far apart, the controller goes into "failure mode" where it will cut power to the motor. When they are consistent, you can average the values for lower noise.
Even on the existing design, you can compare the gyroscope and accelerometer.
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Because people are arrogant. They always believe that every generation before them was in the dark ages. Soon they will believe that having no internet was equivalent to living uninformed in a dictatorship.
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"Because people are arrogant. They always believe that every generation before them was in the dark ages. Soon they will believe that having no internet was equivalent to living uninformed in a dictatorship."
Exactly. As opposed to living misinformed in a dictatorship.
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That's partly true... I mean, we aren't really seeing limits where analog loses points. Like, they need to filter that noise out, which will require more than just reprogramming the DSP. What kind of safety limits does it have built-in? Does it change behavior when it heats up or cools down? Do you have to use trim pots every time you go to use it?
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When you've only got one or two control loops, a microprocessor based solution is a lot more complex, costly and failure prone.
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Why is it amazing that an analog control system works?
It's not surprising that an analog system works well, but it does seem to be getting less and less common to find engineers or hobbyists that are skilled at cooking them up. Now days many young people get hooked on computers and games with fewer taking an interest in things more analog like ham radio or building their own audio amps and speaker systems.
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Digital controllers -emulate- analog behavior (at least many of them do). There's a pantload of research and science behind analog control.
At MIT, if you take 18.03 (differential equations), you see an example of a PID controller to balance a broomstick (inverted pendulum) --- in analog -- which, with not too much generalization, becomes a Segway. It doesn't surprise me in the least that this guy is at MIT.
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MIT?? This is kid's stuff. The only difference between your broomstick controller and a $20 DIY backyard sun-tracking sundial is that the broom balancer is 2-axis, and has to be faster. Big deal.
Um, no. Clearly you have not studied this problem which is a (perhaps *the*) classic PID exercise. A simple P term (proportional) will fail very, very quickly. Add the D term (differential) and you get stability, but drift. Finally, add the I term (integral) and you eliminate the drift and turn the meta-stable system into a stable one. If you want stability to external perturbation, or generalization to a broad range of loads, then you need more analysis and more terms.
Designing one of those from scrat
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Systems have been made this way successfully for decades, and still are.
Guidance systems, for example, and even control systems for heat-seeking missiles (which have to be accurate and fast). These have been made successfully for many years without your precious PID. While your example might be one of an idea
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Wow. All I can say is, please do not design any airplanes, power distribution, or life-critical systems. You clearly are far from qualified with that level of understanding of system stability and how it is affected with feedback. Seriously, don't.
PID systems are used everywhere. Even in guidance systems (if you recall, the first cruise missiles had a problem with long-term error accumulation because they didn't have an integral term in the control system). Now not every system needs all three P, I, D
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"Ever designed a feedback network around an op-amp with a capacitor?"
That is an example of an ANALOG solution. So what's your beef?
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Cliff? (Score:2)
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The Land Before CPUs (Score:5, Funny)
Why is this amazing "that the controller works at all"? There was a time before microprocessors, you know, and they did fun things like travel in space without them.
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Sure, but name one moon mission that had and XBox aboard.
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I'm not really sure what to make of this comment. You are aware that the Apollo missions used extraordinary advanced integrated circuit computers, right? The Apollo Guidance Computer was no analog computer...
Re:The Land Before CPUs (Score:5, Interesting)
The computers that flew were digital, but the computers that tested them were analog. My father worked on the Saturn V guidance system, and they built one of the earliest "hardware in the loop" simulation setups to test the software and flight-certify the computers that flew. Digital computers of the day were not fast enough to simulate the inputs and monitor the outputs in real time, so the simulation was built with analog computers.
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No, they didn't. They were obsolete by the time they flew.
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What isn't?
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The pilots?
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No kidding. It's not as if a PID controller is hard to do in analog circuitry.
Females?! (Score:5, Funny)
Re:Females?! (Score:4, Funny)
They are all at MIT?! I'd have studied harder in highschool if they'd only told us.
The MIT recruiting video sent to my high school might have convinced you.
A pair of serious undergrads, one male and one female, are working in a lab. The glassware is very impressive and filled with bubbling food coloring or whatnot. The lights are low to draw attention to the Science. Then the two look at each other knowingly, sweep the contents of a benchtop onto the floor and start making out atop it to the wail of an electric guitar.
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No no they are just robots and avatars of the media lab. Females in CS and engineering? Come on do you believe in Santa Clause? Do you?
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At least one of those was a man.
And the project an excuse to impress women with their apparent skill in awkwardly balancing, slowly scooting, and... badly jousting.
403 Forbidden (Score:5, Funny)
Re:403 Forbidden (Score:5, Funny)
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Very hard to say that it is definitely on fire however. It's just somewhere towards the far right hand side of the "Working <-----> Halted, on fire" continuum.
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Addition http error code, instead of 403 forbidden (Score:1)
I think slashdot needs to apply for a new http error code at w3, something like:
601 slashdotted fault, no server response
602 slashdotted slow, some server response
603 slashdotted dead, fallen over
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Maybe the server could handle the traffic, but 403 is their host's way of dealing with going over a periodic bandwidth limit.
As to your proposal, it seems like they are out of order. Shouldn't it be: some response, no response, slashdotters let out the magic smoke?
I would like to join the chorus (Score:2)
Re:I would like to join the chorus (Score:4, Informative)
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The best part... (Score:3)
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The best part is the shopping cart in the lab holding a jumble of electronics.
I'm an unemployed, homeless software engineer, and those are my worldly possessions, you insensitive clod!
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As seen at MIT:
A Shopping Cart Full Of Roombas. [skitch.com]
Real men do it with op-amps (Score:1)
Analog (Score:1)
What a difference lawyers can make (Score:1)
If you don't have to worry about lawsuits, then you can simplify much of the mechanism: no exhaustive testing, no redundant backup circuits, no fault logging, no record keeping, etc.
However, there's nobody to sue when you inadvertently kiss the front of a moving bus.
Next Up: DIY Apollo Landings and Darwin Awards merge.
I get it... (Score:2)
Instead of spaghetti code, we now have spaghetti hardware :)
http://www.etotheipiplusone.net/pics/seg/seg_102.jpg [etotheipiplusone.net]
Patent infringment? (Score:2)
Hate to point this out, but I'd imagine this project probably infringes on multiple patents on the Segway. The fact that they use different technology isn't a solid defense.
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I guess it just couldn't stand up to all the requests.
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Two MIT profs were arguing which was smarter.
One pointed at a 14" disk drive and said "I can make that walk across the room."
He keyed in something and after a few seeks it lurched onto two legs and walked across the room.
The other one said "That's nothing; I can make it turn around and go back."