Hubb's Improved Spark Strip

[Hubb]

Some of you may remember seeing my spark strip design under my combustion launcher. I'm in the process of redesigning the launcher and one of the things I wanted to improve was the spark strip, making it more user friendly.

The way it's designed is to allow a spark in the rear, the middle, and the front of the combustion chamber. It has three gaps and each gap is fully adjustable (depending on screw length). The gaps can also be closed, allowing for just one or two sparks (for piezo igniters). It also has a built in fan, which is held in place by a zip tie, allowing it to be removed if necessary.

Here is a parts list:
(2) 10-32 x 3" machine screws
(5) 10-32 x 1" machine screws, including fan electrodes
(8 ) #10 flat washers
(4) small rubber washers
(8 ) wire connectors (I used the ring type and not the fork type)
(13) 10-32 nuts
(1) fan, smaller than chamber (I used a 20mm in a 3" chamber)
(1) zip tie, long enough to go around fan
(1) half piece of 1" pipe, as long as chamber
(1) drill and bit the size of the screws
(1) hacksaw or dremel (dremel works better)

About an inch from one end, cut a notch in the sliced piece of pipe the same size as the fan. Drill a hole under each side of the notch. This is to attach the fan to the strip with the zip tie.

About an inch in front of the fan, drill a hole. Drill another about a half inch in front of that. Move up to where the center of your chamber is and drill another set of holes, then repeat about an inch from the other end of the sliced pipe.

Measure the length between the first and last hole drilled, and drill two holes through the chamber wall. Drill two more through the end of the chamber for the fan electrodes.

Make two pieces of wires with the wire ends. Assemble and shape screws as displayed in diagrams.

To adjust the spark gap lengths, simply tighten or loosen the appropriate screws. To close the gaps, tighten the screws until it touches the adjacent screws.

Try to make gap approximately 1/8". This should allow for any type of ignition source to be used.

I may have left something out (besides pictures; my camera crapped out on me. I'll post when I can).

If there are any questions, please ask.

Oh, and be sure to check out my hybrid spark system.

[starman]

Hey Hubb, nice work on the universal spark strip concept. It would be great if somehow the screws could be adjusted from the outside. You won't be able to get a screw driver inside the chamber so your only option will be to uninstall the whole strip to perform the adjustments.

On the ball valve solution, are you cutting any O-ring grooves into your bushing? Do you believe this solution to be more effective than the typical threaded cleanout?

Nice drawing work...

[Hubb]

That's what I left out (I knew it was something). The spark strip will have to be removed to adjust the gaps. This should not be a real issue once a reliable ignition source is obtained, however (set it and forget it).

As far as the ball valve vs plug goes; ball valves are superior in the fact that they open much faster, open easier, and are integrated into the launcher. With the above approach, it could be removed if necessary. I've only seen one launcher with something similar (I think it was one of Gort's) and this just makes more sense.

There is also another method of faster exhaust (a check valve; seen at advancedspuds.com) but you have to manually hold the valve open, making this superior IMO.

As far as the o-rings, they may not be necessary, but it's better to have them and not need them than to need them and not have them, right?

[starman]

As far as the ball valve vs plug goes; ball valves are superior in the fact that they open much faster, open easier, and are integrated into the launcher. With the above approach, it could be removed if necessary. I've only seen one launcher with something similar (I think it was one of Gort's) and this just makes more sense.

As far as the o-rings, they may not be necessary, but it's better to have them and not need them than to need them and not have them, right?

Yeah I'm a big believer in the ball valve over a plug...just haven't seen a plug design that really turned me on. Gort's plug is effective however.

The only reason I asked about the o-rings...you'll need grooves of some sort to keep them in place. Also the reducer itself is a very tight fit already so any o-ring will have to be mostly buried. Also, finding an o-ring locally that large may be a little challenging...sounds like a McMaster order opportunity...

Oh, you could use a table saw to cut your o-ring grooves.

[daxspudder]

A dremel with a circular routing bit is the best thing to cut o-ring grooves.