Those of you who have read my previous Instructable Rapier-Fuego-Retro-Model-Plane will know I promised to do an Instructable on my ignitor. Back when Rapier engines first became available they were supplied with fuses (mid you these could be more of a pain than worth it anyway), unfortunately that is no longer the case so other methods need to be found to light them that are quick and safe.
The best method is to use a hot nichrome wire as used in medical cauterers, these are really expensive and not always easy to get.
Step in The THREAD ZAP II, a cheap tool used in craft for cutting and sealing thread, the perfect starting point for your own powerful ignitor.
Step 1: Materials and Tools
- Thread Zap II
- Thin Copper Sheet
- 28swg Nichrome Wire
- 2 x AA Battery
- Tin Snips
- Small File
- 3d Printer or service
Step 2: Strip the Thread Zap
The thread Zap is a great tool but needs a few modifications and is not powerful enough for what we need.
- Remove the battery cap and keep safe as we will reuse later
- The outer body is coated in paint for insulation which we need to get rid of so scrape the pain off about 10mm of the rear of the Thread Zap
- Remove the tip ready for stage 3
Step 3: Modify the Tip
The wire in the standard tip of the Thread Zap is not long enough to reach the propellant in the rapiers and is also not replaceable.
- Grip the rear of the tip gently in a vice.
- Look carefully at the tip and you can see the ends are crimped over.
- Take a small needle file and gently file off the tips just below the crimp exposing the holes in the tubes
- Test your Nichrime wire for a nice fit
- Take a 1" pice of wire and bend to make a new tip that will have about 1/2 inch to go into a Rapier engine and the ends into the tip tubes.
that's it for the tip you now have a longer and easily replaceable tip
Step 4: More Power!!
We need more power to get the oompf we need so lets add a second battery to the Thread Zap.
- Download the attached stl or open scad file
- Print in PLA
You should now have a nice tube with an internal step at one end, a thread at the other and an internal groove down the length.
Step 5: More Power 2
In order to get the power from the extra battery we need to run something down the 3d printed parts.
- Find some thin copper sheet, mine was what they use to keep slugs out of plant pots.
- Cut a strip as wide as the groove in the 3d printed tube and a bit longer
- Fit this in the groove and bend over the ends to hold in place, make sure there are no sharp bits sticking out.
- Push the stepped end of the tube over the Thread Zap making sure the copper is in contact with the area you scrapped off the paint.
Step 6: Final Touches
Your almost there drop in 2 AA batteries , screw on the endcap you saved at beginning and head off to the flying field
Caution: that tip get seriously hot now so always keep the cap on when not in use.