# Measuring Coil Strength

These are the raw coil measurements I took from a coil I wound. At this point, we're just collecting coilgun data in a spreadsheet. Later, we'll calculate the speed we can achieve.

At each height of the coil above the table, it shows the voltage necessary to barely lift the projectile from the table. This voltage (actually current) will later be increased to the limit of my power supply to hurl the projectile at high speeds. Go here to see the calculated possible forces.

The particulars for these particular measurements in particular are:

• two identical coils were placed closely end-to-end
• each coil is 40.35mm long, total of 80.7mm
• both coils use 228 feet of wire in 790 turns, 5.05 ohms
• two coils are temporarily wired in series
• wire is 24-gauge coated magnet wire
• projectile is 31.6mm drywall screw (about 1 1/4" long)

## Coil and Screw

 Vmax = 12.5 v Lscrew = 31.6 mm Amax = 2.5 A

## Measurements

 Height (mm) Voltage Force @ 1G 38 >12.5 (coil cannot lift screw) 37 12.5 36 12 35 9.8 34 8.1 33 6.7 32 5.7 31 5.2 30 4.6 29 4.2 28 4.05 27 3.6 26 3.3 25 2.9 24 2.8 23 2.5 22 2.3 21 2.35 20 2.2 19 2 18 2 17 2.05 16 2 15 1.95 14 1.92 13 1.85 12 1.87 11 1.9 10 1.9 9 1.9 8 1.9 7 1.84 6 1.85 5 2 4 2.1 3 2.12 2 2.35 1 2.5 0 2.5 -1 2.8 -2 3.1 -3 4.5
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