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Thanks everybody for the explanations!
Everything start to make sense now. I understand that a resitor will limit only
voltage across the circuit, but not current, this is very clear also.
So, i will look for a small electromagnet, (9 volts) because i really don't need
to much power on it, just enough to lift a ping-pong ball with a small iron on
its top. The ideia was to make a grabbing arm with one motor and the
eletromagnet in the same port. So when the motor moves the arm horizontally, the
magnet will be active and grab the ball on its way, Then, when the motor stops
at the end its way, the magnet will release the ball inside the robot. The two
other outputs is for driving the robot along the line following path.
But i realize now that one motor and the electromagnet in the same port will not
be very healthy to RCX/NXT...
Any ideias where i can find this kind of electromagnet? (some electronic device
or appliance...)?
Thanks again!
Patrick
In lugnet.robotics.nxt, Jon Gilchrist wrote:
> Yes, you can use an electromagnet with the RCX. Depends on what you
> want to do with it, but it should work. The device from a disk drive
> might be a 12 volt device, or 5. The RCX puts out around 8-9, so either
> way the device isn't drawing the correct current. It's probably got a
> very high current draw, and causes your batteries to go low. Very much
> like a motor on heavy load.
>
> Finding an electromagnet that doesn't cause heavy drain will depend on
> what you want to do with it. You want a coil rated for as close to 9
> volts DC as possible, and as low power (watts) as possible. Note that
> lower power will mean lower electromagnetic force, so you will have to
> balance low power with whatever you are trying to do. If you're making
> a crane with an electromagnet on it to lift up scrap metal, the power
> level will determine how much stuff you can pick up. If you're using it
> to connect train cars, it will determine how many cars you can pull.
>
> A higher coil resistance will have a lower power at a given voltage.
> Note that putting a resistor in line with the coil will probably not
> help you.
>
> Hope this helps.
>
> -Jon
>
> Patrick Levy wrote:
> > Hi,
> >
> > I was wondering if it is possible to use a electromagnetic device with the RCX
> > and NXT. I tried with this one from a disk drive, and it worked quite well, but
> > a few seconds after it start, the RCX shows the "low battery" icon. (The
> > batteries are OK, and when i checked later, it reports normal 8.0 Mv)
> >
> > 1. May I use some kind of resistor in the wires?
> > 2. Why RCX reports low battery? It seems like motors on heavy load...
> > 3. Is possbile to minimiz/avid this? How this impact in the electromagnetic
> > performance?
> > 4. If i must use a diferent/best electromagnetic device, what kind or
> > specification i must look for?
> >
> > Thanks for any help!
> >
> > This is the electromagentic device plugged in the RCX:
> > http://tdi-ng.locaweb.com.br/patrick/lego/internals/eletro.jpg
> >
> > Patrick
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Message is in Reply To:
 | | Re: Electromagnetic device
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| Yes, you can use an electromagnet with the RCX. Depends on what you want to do with it, but it should work. The device from a disk drive might be a 12 volt device, or 5. The RCX puts out around 8-9, so either way the device isn't drawing the correct (...) (18 years ago, 16-Jan-07, to lugnet.robotics.nxt)
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