Subject:
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Re: 110 VAC powered lego motors
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Newsgroups:
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lugnet.org.ca.rtltoronto
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Date:
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Thu, 28 Feb 2002 04:14:39 GMT
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Viewed:
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512 times
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> in some other thread, Mathias said:
It's two "t"'s Mr. Mango :-)
>
>
> > since the
> > motor power is unregulated in the RCX, is a function RCX input
> > voltage, which, in turn, is a function of Hydro line voltage.
>
> I don't follow this.
>
> if 110 VAC (or some amount) goes in, it drops down to 9 (ish) i know
> for a fact that the RCX does not have a transformer, so the regulation
> has to be solid state.....
>
> ergo, somewhere in the brick, there has to be 9vdc
>
> even if the motor outs was unregulated, it would still (logically) run
> off the 9vdc.
>
> what am i missing?
My point here is this:
I was using the Lego train transformer, which is just that: a
transformer (10:1 ie. 120VAC in yields 12VAC out - no regulation, no
filtering)
If the voltage at the wall drops 8.3% (10V) to 110VAC, the output from
the transformer will drop to 11V. I have been told (and my
investigations of the RCX internals can't deny it - ie. I never did
see a 9V regulator) then the power to the motor controller must also
have dropped to 11V, or 10%. Now, unless there's a non-integrated
regulator (zener diode perhaps) then that corresponding 10% drop in
input voltage should appear on the output as well. The motor, BTW will
be controlled by an H-Bridge within the motor controller. An H-Bridge
consists of four transistors with the load (motor) placed between them
(hence the H pattern). To drive the motor, two diagonally opposite
transistors must be switched on, each of which should drop about 1.?
volts. Let's say it's 1.2V - therefor the power to the motor would
ideally be 12V-(2 x 1.2V)=9.6V, or approximately what we would expect.
I can't be sure though without a schematic of the RCX.
Having said all this, I shot down my own theory about the line voltage
at the library accounting for my robot's misbehaviour. I dragged out
my variac (rated at 18A - it ain't light) and powered the RCX with it.
(through the Lego train transformer, of course - although I could have
done it directly, I'm not that crazy)
It didn't effect the robot's performance. The only serious problem
I've encountered, is that my RCX1.0 doesn't want to run on
batteries!?!? I only just discovered this. I had intended to take the
robot over to my bench an test it there, but once I removed the AC, it
died. My IR tower cables won't reach the other end of the house, so I
had to bring the variac to it since I needed to re-load the programs.
My voltage measurements were done with a handheld meter. The meter
does not measure true RMS voltages, and so is only good for the
measuring the AC into and out of the transformer. The power at the RCX
motor outputs are non-sinusoidal so my meter reading will be wrong,
but I didn't observe any change in the "measured" voltage while
varying the variac output. That implies that there is some form of
internal regulation for the motor outputs although I can't see where
it is.
Matthias Jetleb
(who's robot, is once-again, not working tonight)
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Message has 2 Replies:
 | | Re: 110 VAC powered lego motors
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| (...) I am sorry. I was doing it from memory, and i thought I did so well by remembering the combination of "hias" that I forgot the easy part of Matt. As you (and all of Lugnet) are aware, I am a very poor speller. I don't know why, I always have (...) (23 years ago, 28-Feb-02, to lugnet.org.ca.rtltoronto)
| | | Re: 110 VAC powered lego motors
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| (...) If you've ever wondered what newsgroup you're in on Lugnet, and you read "I dragged out my variac", you know you're in rtlToronto, because: a) People here have variacs b) People here know what variacs are c) People are not afraid to say they (...) (23 years ago, 28-Feb-02, to lugnet.org.ca.rtltoronto)
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Message is in Reply To:
| | 110 VAC powered lego motors
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| in some other thread, Mathias said: (...) I don't follow this. if 110 VAC (or some amount) goes in, it drops down to 9 (ish) i know for a fact that the RCX does not have a transformer, so the regulation has to be solid state..... ergo, somewhere in (...) (23 years ago, 26-Feb-02, to lugnet.org.ca.rtltoronto)
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