Subject:
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Re: moving in a straight line with two motors?
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Newsgroups:
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lugnet.robotics
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Date:
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Sat, 14 Nov 1998 03:08:00 GMT
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Original-From:
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Daniel Miller <danielmi@expert.cc.purdue(NoSpam).edu>
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Viewed:
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2288 times
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On Sat, 14 Nov 1998, Patrick Gili wrote:
> The answer lies with reactive design. Think about the way we
> drive a car. We "close the loop", providing the feedback that
> enables the car to drive a "straight line" (or more to the point,
> "follow a path"). When we drive, we watch the road and constanly
> make adjustments to the steering wheel to ensure that the car is
> following the path. There are just too many factors that will
> not allow a car (which does have excellent mechanical tolerances)
> to drive itself in a straight line, some of these factors don't
> even have to do with car, but can be external in nature (e.g.,
> the terrain, rocket-propelled grenades, other vehicles, etc).
1) You've been playing too much Carmageddon.
2) Control theory is relatively new (it paces the development of
computers). There are quite a few good textbooks available, but a
professor is a much greater help. Familiarity with calculus and dynamics
is required.
Not to say I'm an expert (I got a "c" in AAE464 and I was grateful) but it
should be pretty possible to implement proportional and derivative
control. Integral control may be harder... but it would be needed to
eliminate steady-state error (i.e. keep it straight!). Lead-lag control
would be damned impressive.
Here's an exercise for someone with an RCX: Create a chassis that
consists of one drive motor to the wheels and an angle sensor geared to a
2-d inverted pendulum on top. Write a program that moves the chassis to
keep the pendulum straight vertical.
And finally: It's quite possible to create a car that drives itself. It
still needs human control for things like parking. Same goes for
aircraft; the main purpose of the pilot in a current production A320 is to
park the airplane and make the passengers feel better en route.
There are some cases where the control system has failed. On a flight
from Warsaw to New York, the pilot told the passengers they could see
Ireland out the starboard side. The ensuing rush to the starboard
windows was too much for the autopilot, which disengaged. Later, the
cause of the crash was determined to be a problem with the flight
computer; it seems there were too many Poles on the right hand plane.
Sorry, controls engineering joke.
Another: "Welcome passengers to the first flight of the Boeing 2707, the
world's first totally robotically controlled airplane. Please do not be
alarmed; the systems have been tested to the tightest imaginable
tolerances and we guarantee that nothing can go wrong go wrong go wrong go
wrong..."
Daniel "Dan'l" Miller Senior, School of Aeronautics and
danielmi@expert.cc.purdue.edu Astronautics, Purdue, Indiana
danielmi@cartoon.ecn.purdue.edu
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Message has 3 Replies:
 | | Re: moving in a straight line with two motors?
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| Daniel Miller wrote in message ... (...) What? (...) This is all fine and well, but I was thinking about something a little less complex. The RCX doesn't have the power to perform image processing and sophisticated feedback control. What I was (...) (26 years ago, 14-Nov-98, to lugnet.robotics)
| | | Re: moving in a straight line with two motors?
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| (...) Believe it or not, I've been working on exactly this problem for the last few days. I built an angle sensor using a 500K potentiometer wired directly to an RCX input port. (Lego's angle sensor doesn't have sufficient angular resolution unless (...) (26 years ago, 14-Nov-98, to lugnet.robotics)
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Message is in Reply To:
| | Re: moving in a straight line with two motors?
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| Ardjan Besse wrote in message <364c7d42.4532817@lu...et.com>... (...) "Straight" is a relative term. For example, while the alignment might be 0straight, the wheels might not provide the bot with the ability to travel in a straight line. I believe (...) (26 years ago, 14-Nov-98, to lugnet.robotics)
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