Subject:
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Re: RCX Voltage Question
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 1 Jan 2003 23:07:55 GMT
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Original-From:
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Steve Baker <SJBAKER1@AIRMAIL.NETsaynotospam>
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Viewed:
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629 times
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Pengy wrote:
> If you connect two motors to the same output port, will they each get 4.5
> volts, or will it take current from the other outputs?
When you connect two devices across a source of electricity, you can do
so either in series or in parallel.
In parallel:
+------------------+--------------+
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Battery Motor Motor
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+------------------+--------------+
In series:
+------------------+
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| Motor
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Battery |
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| Motor
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+------------------+
When you connect two motors (or lamps or anything else) in SERIES,
the voltage is halved but the current stays the same.
When you connect them in PARALLEL, the voltage stays the same - but
the current demanded from the battery doubles.
When you just stack two Lego wires onto one RCX output and connect
one to each motor, you are connecting them in parallel - so the voltage
remains at 9 volts and the amount of current pulled from the circuit
needs to double.
If your batteries are good, the RCX can provide enough current to drive
two motors from one outlet without affecting the other outlets. However
there will come a point with three, four or more motors where the RCX's
batteries won't be able to provide enough current and either the voltage
in the RCX will drop (which could cause the computer inside to stop
working just as if the batteries had gone flat) - or the thermal regulator
inside the RCX will cut out and none of the motors will get power. Either
way, if that happens your robot won't work - but the RCX and motors
won't be permenantly damaged.
It's not easy to connect two motors in series using the clever
design of the Lego wires (but I *think* there is a way) - if you did do
that then the voltage to each motor would be just 4.5 volts and it would
either drive very slowly or not at all.
So, you can drive two motors from one outlet - I wouldn't recommend
driving more than one from each outlet.
Bear in mind that your battery life will be much shorter.
---------------------------- Steve Baker -------------------------
HomeEmail: <sjbaker1@airmail.net> WorkEmail: <sjbaker@link.com>
HomePage : http://www.sjbaker.org
Projects : http://plib.sf.net http://tuxaqfh.sf.net
http://tuxkart.sf.net http://prettypoly.sf.net
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Message has 2 Replies:
 | | Re: RCX Voltage Question
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| (...) Actually the motor control chips in the RCX limit the current, which will limit the maximal power that can be drawn from a port. I don't know how many motors it takes (I'd guess one) to reach the limit, but from then on extra motors will not (...) (21 years ago, 2-Jan-03, to lugnet.robotics)
| | | Re: RCX Voltage Question
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| "Steve Baker" <lego-robotics@crynwr.com> wrote in message news:3E1374CB.70000@...ail.net... (...) Just a minor quibble... The current for two identical resistive loads in series will be half that of just one of the loads when connected to the same (...) (21 years ago, 2-Jan-03, to lugnet.robotics)
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Message is in Reply To:
| | RCX Voltage Question
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| If you connect two motors to the same output port, will they each get 4.5 volts, or will it take current from the other outputs? (21 years ago, 1-Jan-03, to lugnet.robotics)
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