Project Overview

180708: much of this prjt has to do with detecting small-ish fields as well and getting some response from the field(s). Don't forget that the field near the ground is 100v /meter. 180709: and don't forget 'static cling' and that additives exist to nullify it. And Thompson discovered the e- with a vacuum chamber holding a horiz capacitor to which was applied 'several thousand volts' 180410: thinking about making a BIG magnetic field using 2 circular, home-made magnets, separated by ~ 1 foot. The diameter of the electromagnets should be about 8.84 inches, giving an area of 1 over 2pi. No magical understanding here; just sounded cool. And the choice of sizes is a tradeoff between cost, weight, easy of seeing effects on statically charged (styrofoam) 'particles'.
This kind of magnet arrangement is called a Helmholtz coil

mag gallery calculated plots of magnetic fields, 1 or more magnets

visualizing fields with iron filings
contained interesting images plus big excerpt from
wikipedia on Magnetic Field.

wiki/Inductor effects, equations of changing field or current.

There are several magnet-related projects 'below' this project. This project serves as something of
a collection point for procedures and terms.  The terms, if generally useful, will naturally
migrate further to glossary_sci.

namelen dia ohmsawgnotes
mag1_ _ 1.1 24 _
mag21 15/161.259.6624 _
mag31.5" 1.253.8524 _

Teach Magnetism ?

Met math teach 'rebecca' at 2/6/16 robotics contest.
Son 'Forrest' wants to stop a bullet w/ magnetism. (not a good choice).
(deflect would even be tough).
But I thought about lending him some magnets to 'play' with. And a video:
(told mom he'd need a 'bench supply')
        'electro magnets' {show permanent magnet
             electro magnet, spool, iron-ish core,
             pumpkin shape, compasses,
             filings on clear plastic surface above magnet(s),
             poles of a magnet, 'N' etc
             how to pick up filings,
             how to clean up (w/ bagged magnet),
             magnetizing something, hysteresis, bb's, nuts,
             Algebraically adding magnetic field strengths, superposition,
             gluing perm mags to surface (hot glue, epoxy),
             1/r2 (perpen to (invisible) field)
             VOM, induction, Faraday
             motors, solenoids,
             accelerating and decelerating projectiles.
             _deflecting_ projectiles.
No word from them. maybe too awkward.

Project needs or uses

tech tools: Each of the following 6 electromagnets, mag[#], are homemade. References


measuring 'pull force'
measuring the 'pull force'of a test magnet. ?? start w/ a weight (pennies? nickels?) known on a sensitive scale. make an air-core eMag w/ known dimensions, # of turns, wt, and current. attach to weight (by long string(?)), measure how much lighter the weight becomes due to a test magnet. can't let air-core touch the test magnet above it. measure distance. could change current. use bench supply. ?w/ resistor(?) Taking several readings at different currents could circumvent errors.
guessimating nTurns
as done for 'mag2'
The dims of the wound area was 1 15/16" (0.05m) long
and had an OD of 1.5". The ID was approx 3/16".
The wound dim in radial direction was (1.5-3/16)/2 = 0.56"
A separate winding exercise showed about 72 windings/inch.
That's 1"/72 windings = 0.0275" per winding.

So how many windings would stack in 1 15/16" x 0.56"?
0.56" / 0.275 = 20 layers tall
1 15/16" / 0.275 = 70 turns in each layer.
20 x 70 = 1400 turns

If windings lay atop one another, they'd _mostly_ lie in the groove of the layer beneath - though they'd have to 'jump' to an adjacent groove to fit their direction of the helical turning. The wireCenter bottom winding to wireCenter above winding should a 60 degree angle. Sin(60) is .866 so the savings over having the wireCenters lie directly above one another would be 1-0.866 = 0.134 but mag2 windings have gaps in places so nTurns is probably lower. I've chosen to multiply by 1.125

1400 * 1.125 = 1575

mag2 { calc'g expected B0 = u0 N I / len_m
u0 is 4pi * E-7 or 1.256e-6
N  is nTurns // 1575
I  is current in Amps = volts (16v)/ resistance (9.66) ohms)
len_m  is length of coil in meters. 0.05m

12.5 E-7  x 1575 x 1.6amps
  0.05 meters coil length

=  20 x 12.5 E-7 x 2520
=  250 E-7 x 2520
=  630000. E-7 = 0.063 T  // ~1/16 Tesla * 10000 gauss/T = 63 gauss = 126 times SF's field


the following have moved to $pub/glossary_sci.html
H field
Km,relative magnetic permeability
e0, electric constant
24 gauge magnetic wire
    1 ft == 0.3048m; 3.28 ft == 1 m
    24awg copper. 0.0842 ohms/meter
    I expected this to be 24 wire diameters per inch but I get 72 turns/inch.
    Only curious so I can predict the needs of an electromagnet under design.
        - the 'inch' isn't the length that matters. "centimeters"
        - it was spec'd as having a thicker covering and magnet wire has just the enamel.
24 awg, 1.1 ohms. 13.06m (42.6')
24 awg, 9.66 ohms. 114.7m 374')
151008 mag3 is 1.5" long, not 1 15/16. but only 3.85 ohms! dunno why. was end of spool. dif thickness? short somewhere ?(doubt it. pretty tough stuff).
rotatable globe or the like, suspended/supported by mag fields. field changes cause spin.
a simple train 'car' (mechanically?) constrained to float above a 'track'. Ideal would be to shape fields to constrain its position.