From: Roger.Wilfong@umich.edu  (Roger Wilfong)
Newsgroups: rec.models.rockets
Subject: Re: Igniters
Date: Thu, 21 Jan 1993  07:22 edt
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In Article <1jkklvINNf0p@cuda.add.itg.ti.com> "barrett@add.itg.ti.com" says:
> 
>   - Copperhead.  Aerotech told me you need 12 volts and 2amps.  I know
> from experience that you need to make sure your clips are clean since
> they require so much current.  Larger motors require thermalite
> "booster" to be attached.  Care needs to be taken so that clips do not
> pierce two sided clad material.  Innovative design though.
 
The ignitor is innovative; however, the clip could stand improvement.  It 
looses its grip after a while and needs a clothes-pin helper and it needs 
to be disassembled to clean the contacts thoroughly.  Masking tape or 
'Z' foling and micro clips is a more reliable attachment in my experience.
 
> 
>   - Thermalite.  Basic fuse type item that has an internal copper core
> (like the old jetex fuses), with ~1/16" diam.  fuse material.  It is
> wrapped with 5-6 thin strands of nichrome (I think) wire.  If you
> connect your clips to the fuse and send a couple of amps through it it
> will cause the nichrome to glow and ignite the fuse.  Fuse comes in
> three speed (fast, med, slow).  For igniters, most folks put the fuse in
> a teflon sheath so that it will only ignite the motor (core and slot
> configrations) at the top (top of fuse is exposed).  Basic component for
> most flashbulb igniters.  Is used to "augment" copper head and electric
> match igniters.  Sold by the foot.
 
Another way to rig thermalite that requires less current is to remove all 
but one of the thin wires on the outside.  If you're making a short squib 
like ignitor, wrap wire-wrap wire around the ends like this:
  
                 single strand
                / 
          +_______+
         =+=======+=
          +       +         Wire-wrap pigtails
          \       \___________________________
           \__________________________________
 
For a sheathed ignitor, unwrap all but one strand from an inch or two and
when wrap these around the thermalite where it enters the tubing.  Like this:
 
                                unwrapped strands wrapped around thermalite
                               /     single strand
              Teflon sheath         /
            ----------------- +______ 
         =====================+=======
            ----------------- +     ^
                              ^     |
                              |     |
                           clips go here
I have fired thermalite rigged this way using an Estes Solar Launch 
Controller.  It took a couple of seconds to light, but it lit.  Using a car
battery, they light as soon as you push the button.
 
If you are using a car battery, you can put enough current through the 
copper wire in the middle that the pyrogen will almost explode off the wire. 
Rocketflite's early ignitors were nothing more than a piece of thermalite 
that you folded in half and connected to the ends of the copper wire.  
"Bullet" Bob tried this out in his basement and had pieces of burning 
pyrogen flying every whaere.
 
> 
>   -  Flashbulbs.  Necessary for most clusters and 2nd stage ignition.
> Low current (<50ma) and voltage.  Heat from flashbulb will set off
> thermalite igniter.  Dependable, sensitive to static!!
 
On word of warning on bulb selection.  DO NOT use bulbs from the flash-cubes 
intended for use on the Kodak cameras that use the piezo-effect to fire the 
flash.  These bulbs require extremely high voltages to fire.  I spent a long 
time on the range one day trying to get a cluster to light with these bulbs 
before I figured out the problem.  I can never remember which of the various 
types of flash-cubes to avoid so I buy the 10 bulb flash bars for the 
Poloroid SX-70 type cameras - I know they work.
 
- Roger
Newsgroups: rec.models.rockets