[Robotgroup] electromagnets

[Marc Emerson]

Don't forget volts...I think the equation is something like
electromagnetism = volts * number_of_windings * some_constant

Also see "bifilar" electromagnets. They have twice the strength of a
conventional electromagnet with the same number of windings.



-----Original Message-----
From: robotgroup-bounces at puremagic.com
[mailto:robotgroup-bounces at puremagic.com] On Behalf Of Leslie Filip
Sent: Sunday, October 15, 2006 6:03 PM
To: Austin Robotgroup Mailing List
Subject: Re: [Robotgroup] electromagnets

When winding coils yourself, there are ways to increase the  
efficiency of the electromagnet while holding the electrical draw  
constant:

1. Use wire with very thin insulation, as thin as possible without  
shorting out. This is why magnet wire is just coated with lacquer.

2. Increase the number of windings. This essentially has to do with  
the total surface area of of the conductors with respect to the size  
of the gap from the insulation between the wires.

3. Use square (or hex, or triangular) wire, as seen in cross section.  
Some motion recovery systems use windings like this. Round wire has  
more space between the conductors, and therefore is less efficient by  
a small amount.

4. When available, use superconductors that are 1 molecule wide and  
separate them by 1 atom of insulation.

Les


On 13 Oct 2006, at 4:53 PM, Gray Mack wrote:

> It sounds like some of us are interested in projects
> involving electromagnets. It seems we don't really
> know much about them.
>
> Here are some websites I found:
>
> http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html
>
> http://www.ndt-ed.org/EducationResources/CommunityCollege/ 
> MagParticle/Physics/ElectromagneticFields.htm
>
> But there is still a lot of unknown things when it
> comes to creating motion with electromagnets.
> It will take some experimenting to figure out what can
> be done with them.
>
> Many questions arise about how strong they can be, how
> much current they draw, how they respond to signals
> such PWM or alternating current, how opposing coils or
> magnets can be used to increase the pull capability
> and provide push capability and how to mechanically
> amplify the motion created since the field strength
> dissipates rapidly with distance.
>
> How does the effort and cost of winding our own coils
> compare with buying commercial solenoids for a project
> that might contain 10, 100, or 1000 coils?
> How do the parameters the coil (# of turns, height,
> radius) affect the distance that it can push/pull a
> magnet?
>
> Some goals could be:
> *making paper butterflies wings flap
> *controlling steel balls on a table
> *creating a tabletop caterpillar robot that moves by
> pushing small angled feet a tiny distance
> *changing the height of an array of tiles making up a
> table
> *assisting pendulums in an art sculpture to swing so
> they don't stop due to friction
> *Cause mirrors to move that reflect laser light in a
> pattern.
> *using the feedback from an optical sensor to keep
> just enough field strength for levitating a metal
> object
> *Interacting with ferrofluid made from printer toner
> and oil
> *Play a musical instrument by controlling valves or
> causing percussion or vibration
>
>
> Cool things about electromagnet coils:
> *Cheaper than servos
> *Can last much longer than servos
> *Can move things quietly
> *Can be sized to the object they are in or drive push
> rods or cables
> *Can be used to generate push,pull, or rotational
> movement
>
> Problems:
> *Use lots of power
> *Must remain energized to maintain motion
> *Need a mechanical (spring,gravity,etc) return due to
> residual magnetism
> *Field strength dissipation allows for only small
> movement of actuator
>
>
> -Gray
>
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