[Robotgroup] electromagnets

[Gray Mack]

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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