Subject:
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Re: Electromagnetic device
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Newsgroups:
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lugnet.robotics.nxt
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Date:
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Tue, 16 Jan 2007 04:18:00 GMT
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Viewed:
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10168 times
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In lugnet.robotics.nxt, Geoffrey Hyde wrote:
>
> "Patrick Levy" <patrick@omiccron.com.br> wrote in message
> news:JBxJ1I.En@lugnet.com...
>
> > 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
>
> Well, naturally there's going to be a heavy current drain on your batteries
> when you use an electromagnet with the RCX.
>
> You didn't post the technical specifications of the electromagnet you have
> wired up to the sensors, did it have a data or specs sheet that came with
> it?
>
> It all boils down to what the electromagnet's P = I * V calculations work
> out to.
>
> Quote from HowStuffWorks webpage below:
>
> [quote]
>
> The three most basic units in electricity are voltage (V), current (I) and
> resistance (r). Voltage is measured in volts, current is measured in amps
> and resistance is measured in ohms.
>
> [endquote]
>
> I took a look at various webpages, although howstuff works has a good basic
> explanation of electrical current theory for household appliances here:
>
> http://www.howstuffworks.com/question501.htm
>
> The principles are the same for the electromagnet, once you work out what it
> consumes you can work out what it draws as a load.
>
> It's a lot more complex than it looks, but this should get you started on
> what you need to look for in an electromagnet.
>
>
> Cheers ...
>
> Geoffrey Hyde
I would add that it will take some experimenting to get the parameters correct.
Pick your operating conditions (parallel outputs, or no, etc...) and then given
the supply voltage and maximum current allowance, you know the coil resistance
you are shooting for by Ohm's Law: V / I = R.
Different size magnet wire will have different resistance per foot. So,
different wires will have different total number of turns for the same V/I
operating point. Winding them on an iron core will intensify the magnetic
field, you can experiment with different kids of cores. The resulting "pull in"
power will vary greatly with these parameters, and there is no formula that will
give you the exact answer, although formulas exists that model the first order
effects.
My most recent experiments in this regard were not with Lego, but were aimed at
having my 7 year old daughter and a friend build a telegraph that could be
powered by a single D cell. We were using bent paper clips for the sounder.
The coil, IIRC, was 150 turns of #24 enamled wire on about a 1 inch #8 steel
machine screw. The D cell provides 1.5V, but we were drawing a nasty amount of
current.
#10 machine screws fit quite nicely in Lego Technic pin holes. You might start
with a machine screw mounted to a studless beam and wind your coil on the
machine screw. A google search will turn up several resistance-per-foot tables
for magnet wire. All Electronics or American Science and Surplus or other
on-line surplus houses probably have magnet wire in appropriate sizes.
If you want to try ready-made solenoids, then again start with your operating
voltage and known max current to calculate a coil resistance. Look for coils
with that resistance. Remember, power = I^2 * R, so you want to maximize the
current to maximize the wattage (and thus the proportional pull-in power) of the
magnet. The same surplus houses will have solenoids, or also look at the relays,
because some of the simple open-frame type relays can be stripped down to just
the coil very easily.
-dave
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Message is in Reply To:
 | | Re: Electromagnetic device
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| "Patrick Levy" <patrick@omiccron.com.br> wrote in message news:JBxJ1I.En@lugnet.com... (...) when you use an electromagnet with the RCX. You didn't post the technical specifications of the electromagnet you have wired up to the sensors, did it have (...) (17 years ago, 16-Jan-07, to lugnet.robotics.nxt)
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