Subject:
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Re: Power steering for 8448
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Newsgroups:
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lugnet.robotics
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Date:
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Tue, 10 Aug 1999 12:18:38 GMT
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Original-From:
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Philippe Jadin <PHILIPPE.JADIN@spamlessSKYNET.BE>
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Viewed:
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1078 times
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An other way to check the real position of a steering system is to use a
potentiometer instead of a rotation sensor. This way, you have the
absolute position af the steering system, with for example full left at
0, full right at 100 and center at 50. Actually the numbers won't be
that exactly, but once you know which value correspond to the center,
you can hard code it in your source...
The bad thing is the fact that lego didn't release any pot-based sensor.
You'll have to build your own one, but it shouldn't be that difficult
(-:
The good thing is the price : 1$ for 1 sensor isn't bad.
After reading that, you ask yourself : how to build one ?
Have a look at the great "Lego Mindstorm sensor input page" (very good
work made...)
it's at : http://www.plazaearth.com/usr/gasperi/lego.htm
There you'll read at least the following from Mike Gasperi:
"For Touch and Temperature type input, the RCX has a 10,000ohm resistor
pulling up the input to 5V. The sensor only needs to provide some
resistance to create a reading. You can create a fake temperature sensor
by hooking a 4,700ohm resistor in series with a 50,000ohm potentiometer
(both available from Radio Shack). This will read from about -11C to
+60C. With Touch or Temperature sensors there is no reason why you can't
overdrive the input to whatever voltage you want within the 0V to 5V
range."
and :
"You should NOT try to overdrive an input that thinks it has a Light or
Rotation Sensor type on it. Use one of the general purpose analog
interfaces. The RCX has a 120ohm resistor pulling up to about 8V
(probably a diode drop from the battery voltage) to power the red LED
for about 3ms and then looks at the sensor voltage during a short 0.1ms
time. During the short time the sensor is read just like the Touch or
Temperature sensors. The fake Temperature sensor from above will read
Light values from 100 down to about 22 without the risk of damaging the
RCX since it never loads the input with less than 4,700ohms. I doubt any
real damage would occur to the RCX since people could accidentally
connect a Touch sensor where a Light sensor should be or even a motor
output to a sensor input. I can't imagine LEGO letting this destroy the
RCX. Don't say I didn't warn you."
You have been warned : always use passive sensors type (touch or
temperature) when connecting home made sensors.
The author : Mike Gasperi mailto:gasperi@alynk.com
Philippe
Jacob Schultz wrote :
>
> Tilman Sporkert wrote:
>
> > You should be able to get away with just a single rotation sensor. When you
> > power up the RCX, you will not know the position of the steering. Now turn
> > it one way until the rotation stops. You are now at the end point, and know
> > the position of the steering. You might want to consider driving the
> > steering mechanism with a rubber band and pulleys so that the motor can slip
> > at the end position. The only drawback of this approach is that on power up
> > your wheels go through a cycle of rotating back and forth.
>
> Good point! Well I'll have to change my model a bit then - the rotation sensor
> should not go onto the motor axle, but onto the axle driving the rack (stilled
> geared I guess).
> Hmm, what can I use this touch sensor for now?? An extra bumper maybe.
>
> Jacob
--------------------------------------------------------------------------
Philippe Jadin
mailto:philippe.jadin@skynet.be
Belgium, Europe
Simple yet usefull Robot stuff goto
http://users.skynet.be/clairetnet/robot
For low-cost web design goto http://users.skynet.be/clairetnet
--
Did you check the web site first?: http://www.crynwr.com/lego-robotics
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Message is in Reply To:
 | | Re: Power steering for 8448
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| (...) Good point! Well I'll have to change my model a bit then - the rotation sensor should not go onto the motor axle, but onto the axle driving the rack (stilled geared I guess). Hmm, what can I use this touch sensor for now?? An extra bumper (...) (25 years ago, 9-Aug-99, to lugnet.robotics)
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