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All-Analog DIY Segway Project
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."
a real one that invents and makes stuff...imagine that , quick arrest the terrorist(/sarcasm)
Best. Name. Ever. for this
What one fool can do, another can. (Ancient Simian Proverb)
Digital controllers -emulate- analog behavior (at least many of them do). There's a pantload of research and science behind analog control.
RETURN without GOSUB in line 1050
and the site has been slashdotted.
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.
this is my sig
They are all at MIT?! I'd have studied harder in highschool if they'd only told us.
Divide a cake by zero. Is it still a cake?
I guess the webserver also is running on an all-analog server, which is now in a "halt and catch fire" state.
Why is it amazing that an analog control system works?
Palm trees and 8
as I understand it the sidewinder missile uses a very primitive analog seeker head. I would imagine that it's evolution is a little more than 'closed' so let's see what this different/open parallel effort leads to
--Shaddup and support your local PBS station Plan for it
The original prototypes of the Segway were all-analog; eventually, for lots of reasons, it was decided digital was a better choice. (My source is... me. Yeah, I work there.)
Arguably, it goes a lot further back than that: all that research and science on analog control was done by organisms who would be dead before they hit the ground were it not for evolved analog control/feedback systems by the thousand...
Owner. We didn't have a CEO; we do have a COO. Jimi was never directly involved in the dealings of Segway, per-se.
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
to code or not to code, that is the question.
Asking how it is "remarkable" that an analog device works as intended. Digital, applied to physical systems, is just emulated analog (necessarily so because, of course, the world is analog).
The best part is the shopping cart in the lab holding a jumble of electronics.
"Computer Scientists can count to 1024 on their fingers" (non-mutant, non-mutilatated, human computer scientists)
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.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
For whatever it is worth, my intro controls course lab (in 2006) was taught using an analog computer:
http://www.comdyna.com/gp6intro.htm
Additionally, we were taught the circuitry behind it.
However, it's still cool sort of in the same way as people that launch weather balloons to take pictures of the earth--it's a fun project.
Also, as a control geek, it was really neat looking at the analog controllers on some of the old satellites on display at the Smithsonian air and space museum.
How hard do you think it would be to create an analog version of the part that makes you drive off a cliff?
Just about anyone who took a controls class anywhere is familiar with the inverted pendulum problem and PID controllers. That would be roughly a quarter of EEs in the US and virtually all MEs. That more people don't know about these things is an artifact of control systems not being as glamorous as it once was.
Maneuvering the Segfault would be awkward due to that. It shouldn't be that hard to move the switch and make it steer like a bicycle's steering handlebar, which isn't that hard to do at all.
But all in all, they've made the Segway-like device simpler, thus cheaper and easier to manufacture and service. We'll have stuff like this as christmas presents soon enough.
.sigs are useless; it doesn't protect you from imposters.
Cool, good to know people still do stuff in analog once in a while. Makes you learn those pesky things called differential equations. Of course, all the equations have already been published in about a zillion masters thesis papers... Recreating them in analog circuits just gives you EE street cred.
As an audiophile I proclaim this as proof that analog is better than digital, but only when ordered with the audiophile version 48 kHz motor controllers to avoid the piercing 6 kHz whine, along with fancy hookup wire.
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.
Table-ized A.I.
Instead of spaghetti code, we now have spaghetti hardware :)
http://www.etotheipiplusone.net/pics/seg/seg_102.jpg
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.
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, counters, 4 MHz clock oscillator, everything is inside that chip.
Need a filter? I can design an elliptic IIR filter in a few seconds using Pyhton and SciPy, and implement it in a short routine in the PIC. And if those six I/O pins are not enough you can use bigger chips from the same line. The only analog parts needed is the anti-aliasing filter in the A/D input.
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.
"We have an A-Bomb...what more do you want, mermaids?" --I.I. Rabi, speaking in defense of Robert Oppenheimer
Good luck automatically tuning the analog loop for driver's weight, handlebar bags, quick temperature changes, etc. That's where digital systems show their flexibility.
Still, this makes for one hell of a learning project.
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 scratch, based only on the mathematical modeling, and building it from individual components, while worthy of no more than an undergraduate exercise at MIT, is non-trivial. Designing a full Segway-like system is a generalization of this problem and also non-trivial.
If you think it's so easy, then please build one yourself -- demonstrating all of the calculations -- and post the video.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
Now there is a way for you to look like a complete dork with an analog controller instead of a digital microprocessor!
-- QED
Truly this isnt very surprising. Analog computing has been around a lot longer than digital and for certain things is far superior (read faster). Forcing things into a digital mold just "because" is a terrible mistake. Certain pieces of military hardware that I used to work with were analog and probably still are, it gives a "good enough" answer and does it orders of magnitude faster than equivalent digital devices.
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?
Well, while all the analysis from you lovely ppl is fascinating and a bit over my head, i confess - i DO know this is one cool project... and if i could build/have one i would be a happy geek!!
On the contrary: as long as you have sufficient negative feedback, you can have a stable system without all your glorified analysis. The trick is to have sufficient and accurate negative feedback.
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 ideal system, simpler systems provably work for the kind of task under discussion.
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 terms; it depends on where the system poles are. And, it turns out, that with an inverted pendulum, the inherently metastable system cannot be made strictly stable with just a P term. Ever designed a feedback network around an op-amp with a capacitor? That would be a D term. Ever used a chopper-stabilized op-amp to eliminate offset? That would be a non-linear approach to an I term.
If you insist otherwise, then, please, show us your incredible design that can handle the inverted pendulum system with only the P term. That would be purely resistive feedback, because anything reactive would embody either an I or a D term or both. Really. Post a video. I want to see it.
Put my fist through my alarm clock with its ding-dong death inside my ear. - The Blackjacks.
"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?
More specifically: I erred in saying that it could be done "without all the analysis". What I actually meant, and my only real point, was that it could be done with analog circuitry; digital is not a requirement.
http://demonstrations.wolfram.com/InvertedPendulumControls/
Set the derivative terms to zero and go to town.
If you can't be assed to play around with it to find a solution that goes to equilibrium, try theta = 0.5, K_p_y= 1.8, K_d_y = 0, K_p_theta = 63, and K_d_theta = 0.
I'm not saying this is anywhere near optimal (or robust), but it works.