Subject:
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Re: Walkers
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 15 Feb 2001 01:02:24 GMT
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Original-From:
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Josh Herman <MAVERICK@INFOCONEX.avoidspamCOM>
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Viewed:
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572 times
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Hey good points!
What if one took the motor driven pendulum idea and applied it to a gyro to
produce torue counteracting the tilt from stepping forward?
Good point about the distance to ground being nil for detectability,
expecially if you want to walk on slightly uneven terrain.
I bet one could make a bot that "shimmied" forward, like tai chi where one
foot would slide forward, then the other foot would translate the weight to
the front foot. Of course the planar vector of weight perpendicluar to
travel would have to be compensated, like when a person balances on 1 foot.
----- Original Message -----
From: Steve Baker <sjbaker1@airmail.net>
To: Boorman, Mathew <mathew.boorman@admiral.com.au>
Cc: <lego-robotics@crynwr.com>
Sent: Wednesday, February 14, 2001 12:12 AM
Subject: Re: Walkers
> "Boorman, Mathew" wrote:
> >
> > A problem with any 'pendulum' based system will have is that they are
> > effected by the movement of the robot.
> > > From a robot which attempted to balance using 2 wheels I found...
> >
> > From stationary start falling forward...
> > detect pendulum swinging forward
> > accelerate to bring upright again
> > pedulum is pushed back by acceleration
> > detect 'upright', stop
> > fall over really, really hard!
>
> Well, I think your software has to be able to predict (mathematically)
> what will happen to the robot and the pendulum as it accellerates the
> motor.
>
> You can't rely on the simple "if pendulum in middle all is well" thing.
>
> You need to know the accelleration you applied, the torque that'll apply
> to the robot, the consequent rate of rotation, etc. In short, your • software
> has to do the physics to predict what it's actions should produce and
> only use the pendulum to confirm that the error in your calculations
> are not adding up too far in either direction.
>
> I've seen a device demonstrated that consisted of a lever with a free-
> swinging pendulum connected one end - with a motor at the other end
> of the lever. There were rotation sensors at the motor and the fulcrum
> of the pendulum. (This wasn't a Lego device) The software was able to
> jiggle the motor about until both lever and pendulum were
> pointed straight up - and to balance them there indefinitely.
> You could even push the pendulum with quite a bit of force to
> try to knock it over and the system would catch it and rebalance
> the system within a small fraction of a second. The entire thing
> was completely hypnotic because it worked with more speed and
> precision than you'd think possible. It was the robotic equivelent
> of balancing a pencil point-down on the tip of your finger without
> moving your arm...and then letting someone try to knock it off your
> finger without losing it!
>
> This was done by emulating the physics of the system in software
> and applying the precise amount of force theoretically needed to
> exactly halt the pendulum in the vertical position. By recomputing
> this solution about 500 times a second and adjusting the speed of
> the motor accordingly, the system could have the pendulum appear
> to stop dead in the correct position.
>
> I wish I could recollect where I'd seen that - I think it was some
> college student's term-paper project shown at a local science fair.
>
> > A gyro would eliminate that, although I suspect building a compact lego • one
> > would be tricky.
>
> Whilst a gyro helps to prevent the robot from falling, it also makes it
> harder to correct any tilt you do accumulate. However, it may just give
> you more time to react which could be a net win.
>
> > As an alternative I am thinking of using an IR distance sensor to • measure
> > the lean by measuring the distance to the ground.
>
> It would have to be pretty sensitive. A few degrees of tilt won't produce
> a measurable difference in the distance to the ground - so it'll be a
> very insensitive detector of small amounts of tilt.
>
> --
> Steve Baker HomeEmail: <sjbaker1@airmail.net>
> WorkEmail: <sjbaker@link.com>
> HomePage : http://web2.airmail.net/sjbaker1
> Projects : http://plib.sourceforge.net
> http://tuxaqfh.sourceforge.net
> http://tuxkart.sourceforge.net
> http://prettypoly.sourceforge.net
> http://freeglut.sourceforge.net
>
>
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Message is in Reply To:
 | | Re: Walkers
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| (...) Well, I think your software has to be able to predict (mathematically) what will happen to the robot and the pendulum as it accellerates the motor. You can't rely on the simple "if pendulum in middle all is well" thing. You need to know the (...) (24 years ago, 14-Feb-01, to lugnet.robotics)
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