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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Thu, 2 Jan 2003 12:21:58 GMT
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Viewed:
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626 times
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lego-robotics@crynwr.com (Steve Baker) writes:
>
> 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.
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 give you more power.
> 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)
Yes there is, you need to overlap them halfway in the correct way,
take a careful look at the connectors to figure it out.
> that then the voltage to each motor would be just 4.5 volts and it would
> either drive very slowly or not at all.
I just tried it with two power motors in series on a battery box,
(not an RCX), and it's quite interesting.
They are slower than usual as expected, but their load balancing
is quite unstable. If you slow down one the other speeds up, and
they stay that way for quite a while.
Cute, but probably not very useful in practice.
> So, you can drive two motors from one outlet - I wouldn't recommend
> driving more than one from each outlet.
Sometimes you can use two motors instead of a differential.
But I agree that in general it is not very useful, you don't
gain on power by putting more motors on an output.
Jürgen
--
Jürgen Stuber <stuber@loria.fr>
http://www.loria.fr/~stuber/
I åa ä e ö å i öa ä e å.
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Message is in Reply To:
 | | Re: RCX Voltage Question
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| (...) When you connect two devices across a source of electricity, you can do so either in series or in parallel. In parallel: +---...---+---...---+ | | | | | | Battery Motor Motor | | | | | | +---...---+---...---+ In series: +---...---+ | | | Motor (...) (21 years ago, 1-Jan-03, to lugnet.robotics)
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