Igniters
This page and the information on it were provided by David Sparks. Please visit his web site at http://sparksrocketry.com/
Procedure for making reliable electric igniter's and electric matches.
These igniter's should pop just fine on any commercial timer or altimeter but testing is still required to insure reliable results.
Step 1: Cut and strip zip cord or twisted pair wire as shown below. Use 28 gauge or smaller for Estes motors, 22 for F through I motors, and 18 gauge for big stuff.
Step 2: Wrap Nickel Chromium wire on the leads as shown. The application of igniter determines what gauge to use. One-quarter inch of 36-gauge nichrome will pop easily on a nine-volt battery when used for deployment. Heavier wire can be used when using the electric matches for engine ignition on 12 volt systems. The diagram below shows 36-gauge wire.
Step 3: At this point, I recommend soldering the wires. The igniter will work fine without soldering, but for more reliability, I would solder them. You can use regular rosin core electronic solder to do this; but, you have to use zinc chloride based flux like Ruby-Fluid or Stay-Clean. These are available at welding supply stores. After soldering, neutralize the acid based flux with water and baking soda. To clean off the rosin from rosin based solder, use rubbing alcohol. See Charlie Barnett’s suggestions below. This should help conduct the heat from the wire to the primer much better.
After soldering, bend the wire wires down to make the match small enough to fit in the engine nozzle.
Step 4: Dip the match in primer. I used ground black powder mixed with nitrocellulose lacquer. Do not use regular lacquer, polyurethane, or any other wood finish. It is not the same! Nitrocellulose lacquer is used in fine woodwork like musical instruments. It can be found through pyrotechnic supply stores. – you can make your own like I did!
Make Your Own Nitrocellulose Lacquer
This may sound strange, but it really works. Ping-pong balls are made of nitrocellulose, the same stuff as used for gunpowder. If you don’t believe me, cut several small ribbons and light them. They flare up so fast you barely have time to drop them before they burn your fingers.
· Cut up six ping-pong balls and dissolve them in 8 oz of acetone.
· After a few minutes, they will start dissolving.
· After a half and hour of shaking or stirring, they will be nearly completely dissolved.
· Don’t worry if the solution seems a little thin at first. It will thicken as the last pieces dissolve. When done. The solution will seem about the consistency of thin paint.
Andrew Schmidt sent in these comments:
PURE nitrocellulose comes in three forms: Cellulose mononitrate, cellulose dinitrate, and cellulose trinitrate are the forms of nitrocellulose. Yes celluloid was also used to make old film strips. However the celluloid used in ping-pong balls differs from the celluloid used in old film because the mixture ratio and the added pigments needed to be different for different applications. Nitrocellulose is one of the first man made polymers. It was used as any other plastic until it was found that it was too unstable. That is where the camphor comes in. When they added camphor the problem, of detonation when exposed to sudden shock, was amended. Some products that were originally celluloid are now made of other plastics, because of a flammability problem, such as the film strip you mentioned. Others are still Celluloid; like ping-pong balls.
My comments: I have had 100% success using ping pong ball lacquer. Pyrotechnic suppliers like Firefox and Skylighter sell nitrocellulose base powder for making NC lacquer. I purchased a pound of NC base from Firefox. Just a small scoop of this stuff in a pint of acetone will make a lifetime supply of NC lacquer.
Making Igniter Primer
· Use a mortar and pestle to grind the black powder to flour-like consistency. The finer, the better (Work with small amounts at a time!! And wear gloves and eye protection!!!)
· Fill a small bottle three quarters full of black powder
· Add enough NC lacquer to wet the entire mixture to about the consistency of thick paint
· Add a little acetone to make it easy to dip the igniter's in.
Sorry I can’t be more specific right now. I get a lot of people confused on this part. I will place exact measurements soon, but here is the key: The point is to get a lot of black powder on the tip of the match and just enough binder to hold it together solidly.
Mix the black powder and N.C. in a small jar until you have a mixture just thick enough to coat the wire. If you plan on lighting larger motors or hard to light blue thunder loads, mix in a small amount of powdered aluminum or magnesium. Dip the match as shown below.
Alternative to Black powder ( Goex Clear-Shot and Clean-Shot)
I made a batch of primer using Goex Clear-Shot black powder substitute. It works just fine. Grind it up and use just like black powder. The nitrocellulose binder contains the burn and eliminates the problems caused by black powder substitutes that have been observed in ejection charges.
Dark Flash Primer
I read an article on the Skylighter web site that describes a low temperature primer called dark-flash. It is comprised of Antimony Trisulfide and Potassium Chlorate ( I hope I spelled that right) Using the new formula and Charlie’s suggestions below in the chip section, I have been able to make e-matches that pop on a AAA battery. Great for small rockets with tiny electronics.
Step 5: Let the dipped match dry for about a half hour and then dip once more with thin NC lacquer. This will form a hard waterproof coating on the match. I even lit one under water. It was very cool!
Actual Ping-Pong-Ball lacquer shown.
Do not make the lacquer coating too thick. Thinner is better. If the coating is too thick, the igniter will pop like a firecracker and blow off the rest of the ignition source away with little heat or sparks.
Here is a set of finished igniter's. I have lit hundreds of these and have never had a failure yet. I have launch everything from D motors to L motors and have not had a failure yet. .
Here are a few clips of one of the larger igniter's being tested. They go off with a loud pop and a big shower of sparks. I used about a half teaspoon of finely ground aluminum powder in this batch.
These igniters were all lit using a nine volt battery (36 gauge nichrome)
One of eight tests
The above method works well for making a dozen igniter's in an hour. If you want to make hundreds of igniter's in an evening, use the following method.
Step 1: Cut a few ¾ inch strip of double sided blank printed circuit board.
Step 2:Using a straight edge, grind the copper off about 1/8 inch from both edges of one side of the board.
Step 3: You should end up with strips that look like this on one side, and all copper on the other side.
Russ Bruner sent in this suggestion:
You can take an Exacto knife and cut through the copper along each side using a straight edge. Then using a pencil torch, heat one end of the place where you want to remove the copper until it bubbles. Then you can lift the copper off the edge and peel it away along the length of the board. This is much quicker than using the Dremel tool to remove the copper and results in a very neat line.
Pencil torches are all over e-bay for $2-$3 plus shipping.
They are great little tools.
Charlie Barnett sent in these suggestions:
I've done a lot of testing and have settled on 2/32" (1/32" board + 1/32" stripped) for the 47 ga nichrome. It has proven 100% when the bridge wire is completely cleaned with rubbing alcohol after the final soldering.
I've been using tape to temporarily mask both sides of the circuit boards and spring clamps to hold a 7" long piece of angle in place while I cut a 1/32" strip of tape on one side of the board with a razor blade. (If you are not initially satisfied with the cut, you can re-mask and cut again before etching.) Then I peel the tape, remove the angle, and drop all in enchant. The result is a very predictable 1/32" removed. The board must be clean before application of the tape which must be adhered completely on the edges. And it should be neutralized and thoroughly rinsed afterward.
I've been cutting a row of 2 chips off the end of the 1/32" thick board with serrated tin snips and then cutting them apart. It results in perfect chips with almost zero losses.
I have 500 ft of 80 mil tungsten and it works great for igniters but not for chips because it requires too much current and cannot be silver soldered with 3% silver. The 60 mil or smaller tungsten MIGHT be ok on current but there is still the solder issue.
Step 4:Wind 36 gauge around the strips spacing the wire about 1/8 inch apart.
Step 5: Solder both sides completely using acid flux and a “hot” soldering iron. Follow the procedure described in the previous section.
Step 6: Using a Dremel tool and thin cutoff wheel, cut a slot in between each wire.
Step 7: Cut a grove lengthwise through the copper on both sides but not cutting completely through the board. Inspect each chip carefully and break off the good ones. I am usually happy with about 95% of the chips I end up with.
Step 8: Wash the chip in a bowl of soapy water, rinse, dry, and store in a jar. A couple of strips will yield about 400 chips. Enough to make 400 igniter's!
Step 9: This sounds hard, but it actually goes very fast. Strip about ¼ inch of insulation off the end of some small gauge solid wire. Wedge a chip in between the wires, and solder the wires to each side of the chip using regular rosin core solder.
Step 10: Dip as shown above. Done. Using this method, you can make hundreds of reliable igniters in an evening.
Step 11: Success!! This is a ‘chip’ igniter going off on a 9-volt battery. I have lit 25 so far and haven’t had a failure yet. They all go off with a pop and copious amount off flame and sparks. I haven’t even coated them with pyrogen yet.
Lighting large motors reliably especially in clusters presents a new set of problem. Clusters must light simultaneously to prevent the rocket from veering off course. Several methods have been used successfully and will be described below:
The John Coker method: