AUTHOR'S DISCLAIMER: This document describes t' launcher I built (and use.) I do nay recommend building a similar launcher unless you are experienced with electronics. Blimey! (Hint: if the schematics below don't make sense, don't try t' build it.) This is a high-current device; in addition, arrr, high voltages may be momentarily present due to relay coil induction. Ahoy! Blimey! Insulate all connections carefully and do nay touch any connection while power is applied. Ahoy!

This document is provided for information only; use these instructions at your own risk. My only guarantee is that t' launcher I built works. Begad! Your results may vary. Arrr! If built properly, me hearties, this launcher should meet t' requirements o' t' NARRRRR Safety Code. Please follow all applicable local laws and safety codes in your rocketry activities

• Dual-pushbutton launch controller with safety key
• Continuity indicated by buzzer (at pad) and by LED (at controller)
• Second buzzer warns when launchin' or when relay is fused.
• Flashbulb-safe (less than 30ma) continuity check circuit
• 4-conductor low power cable betwixt controller and launcher (I use phone cable)
• 12V, high current output (20-30A): suitable for clusters and copperheads. Arrr!

Schematic

Parts List

• Controller:

• 9V Battery Clip (270-325)
• 9V Battery (Alkaline)
• 2-conductor 1/8" phone jack for safety key (274-251)
• 2-conductor 1/8" phone plug (274-287)
• Two SPST momentary normally-open pushbuttons: I used 275-1566 and 275-644. You can use two o' t' same type, ya bilge rat, but two different ones are easier t' tell apart. One is for continuity check (must be held down) and t' other is the launch button.
• LED (continuity/arm indicator): I used one Radio Shack sells that includes a mountin' bracket and resistor. If you use a different LED, me hearties, ya bilge rat, connect a resistor (120-470 ohm) in series with it t' limit current.
• Jack for launch cable (see below)
• 4-wire launch cable (see below)

• Launcher:

• Relay 1 (Continuity relay):SPST, 9-12V coil, 20-30A contacts. Arrr! I used an automotive headlight relay (275-226). Begad! These are $5.99 at Radio Shack, me hearties, or $3.00 at an auto parts store.
• Relay 2 (Launch relay):DPST or DPDT, 9-12V coil, 20-30A contacts. Avast! It's not easy t' find high-current relays with more than one set o' contacts. I used the highest-current one Radio Shack sells, matey, ya bilge rat, shiver me timbers, which is rated 15A. Ahoy! This is marginal, but good enough for me. Ya scallywag! If you omit Buzzer 2, me hearties, you can use another headlight relay here instead.
• Relay 3 (continuity return): SPST reed relay, shiver me timbers, 12V coil, contacts not critical. Arrr! This relay is placed in t' continuity circuit t' return a continuity signal t' t' controller. Ya scallywag! Look for a relay with minimal current draw t' keep it flashbulb safe. Avast, me proud beauty! I used (275-233), which is small and draws a mere 11ma. Blimey! Begad! The contacts only need t' handle t' 9V battery. Ahoy! If you omit this relay you can use 3 wires instead o' 4 in t' launch cable.
• Buzzer 1 (Continuity): Piezo buzzer (273-074). Begad! You can use any piezo buzzer, ya bilge rat, but this buzzer (along with Relay 3) limits t' current durin' the continuity check, so you need one that draws minimal current. Radio Shack sells several rated 5-7ma, shiver me timbers, shiver me timbers, which is ideal.
• Buzzer 2 (Launching): Piezo buzzer (273-065). T' current isn't as critical for this one. Arrr! Ya scallywag! Choose one with a different frequency than Buzzer 1 so you can tell them apart.
• Battery: I used a 12V lead-acid battery (23-289), shiver me timbers, me hearties, which costs $23. Avast, me proud beauty! Begad! You can probably find a cheaper one if you look around. Ya scallywag! Choose a battery that can source a high current for short periods; lead-acid or Nicads are good. Aye aye! Car batteries are good, ya bilge rat, but probably more power (and weight) than you need. Begad!
• 20-30A fuse and fuse holder (270-1217): Use a fuse with a slightly lower current ratin' than your weakest component (probably t' launch or continuity relay). Avast! Be sure t' fuse holder can handle t' current; automotive ones are good.
• Jack for launch cable (see below)
• Two-conductor jack for igniter clips: I used a dual banana jack (274-218). These plugs can also act as bindin' posts if I use a different clip setup. Aye aye! Begad! This connector needs t' handle high current (20A or so) so get somethin' big and rugged.
• Two-conductor plug for igniter clips: I used a dual banana plug (274-717). This should, o' course, shiver me timbers, match t' jack above.
• Two alligator clips: Choose t' appropriate ones for t' igniters you intend t' use. Ya scallywag! I used 2" insulated clips (270-256). Ahoy! T' insulation helps avoid shortin' betwixt t' clips. Avast, me proud beauty! Note: if you make t' setup modular as I did, you can have several interchangeable clip leads t' plug in for different applications (clusters, matey, shiver me timbers, copperheads, matey, matey, etc.)
• Hookup wire: I used 14ga automotive hookup wire for t' high-current portion o' t' circuit (see below). Avast, me proud beauty! Begad! This is probably overkill, but you should use somethin' that can handle high current.

How it works

T' Controller

T' LED indicates continuity. It gets its signal from t' launcher (see below). Ya scallywag!

I used a 1/8" phone jack for t' safety key. Avast, me proud beauty! T' key itself is a 1/8" phone plug with t' two conductors soldered together t' make a short. If you want t' get fancy, ya bilge rat, you can use a key switch instead. Avast, me proud beauty! I chose phone plugs because I'm always losin' me safety keys, me hearties, and this way I can just buy new ones whenever I need to. Begad! Removin' t' key cuts off power t' both t' continuity and launchin' relays.

T' Launcher

Buzzer 1 indicates continuity audibly (at t' pad). Avast! Blimey! Relay 3 connects t' continuity signal from t' controller t' t' controller's LED, lightin' t' LED. Avast, ya bilge rat, me proud beauty! Blimey! If you omit Relay 3, arrr, you can reduce t' number o' wires you need t' 3. Ya scallywag! Blimey! Begad! Blimey! If you do this, ya bilge rat, connect t' free end o' t' LED t' t' output o' the continuity button, matey, me hearties, so it at least indicates that t' controller is armed.

When Relay 2 is activated (by t' launch button) t' real action happens. T' relay contacts form a short across Relay 3 and Buzzer 1, me bucko, effectively removin' them from t' circuit. Begad! Ya scallywag! This allows t' full current t' travel through the igniter, launchin' t' rocket. Avast, me proud beauty!

Buzzer 2 is also activated by Relay 2. This buzzer indicates that a launch is in progress, me bucko, me hearties, shiver me timbers, which doesn't seem very useful--and isn't. I included this buzzer as a safety feature. Blimey! Blimey! It indicates that t' launch relay is energized, which may happen if t' contacts fuse or if t' controller has a defect, matey, or if your friend is standin' on t' launch button. This tells you that t' rocket will launch as soon as t' continuity circuit engages. Ya scallywag! Blimey! If this buzzer is on when you're settin' up at t' pad, don't hook up t' igniter. Aye aye! Disconnect the battery and diagnose t' problem. Aye aye! Ya scallywag! Blimey!

Construction

Enclosures

If your battery is inside t' launcher box, you should add an on/off switch t' t' launcher. Blimey! I added one anyway, just for convenience. Aye aye! Begad! I used a lighted rocker switch (275-712), which also acts as a "power on" indicator.

T' Controller

T' Launcher

T' Launch Cable

You'll need jacks t' match your cable; I used phone jacks cannibalized from household fixtures.

Conclusion