Firing 12+ MJG Firewire Initiators with Cobra 18M

[gatorfan5049]

I am trying to design a finale end that has a three volley wall of 36 shot red, white, and blue peony cakes followed by a wall of willow mines followed by a wall of 3" single shot shells. Each of the phases will have 12 pieces going off at the same time aligned in a wall spaced 20 feet apart. My question is if anyone knows of a reliable way to set off 12 MJG Firewire Initiators using a Cobra 18M. Distance from the 18M to the last ignitor will be 300 feet maximum using 18 gauge wire. Was thinking if the 18M didn't have enough current to fire all 12 initiators then I could rig up something using a car battery powering three DC-DC solid state relays triggered by the 18M's cue output. Thanks in advance, any help is appreciated.

[displayfireworks1]

How many total Cobra Modules do you currently have? Trying to shoot 12 MJG Initiators at one time off of a single cue may be pushing the limits past what is recommended.

[gatorfan5049]

I have enough empty cues to split the initiators between and be within Cobra's recommended range but since this portion will be fired manually and not scripted I was hoping to find a way to consolidate everything to one cue per set to keep the amount of button pressing to a minimum. Furthermore I hope to expand this "wall" effect from a straight 240' line this year to a 180 degree arc in the future so something that is modular or expandable is a plus.

[Jay_]

If its lipo, my gut tells me that it will probably fire given enough time between cues. I did 10 volleys of 5 ematches (not MJG's) in .25 second intervals at the end of my show with a lipo 18m last year and it worked like a champ.

Just do a test run. Good luck sticking 12 mjg leads into the spring loaded connectors on the module though :)

[Scotty Rockets]

Only one way to truly have an answer, test it with just FireWire and see if all pop. I have doubts you’ll be able to pop 12 on one module on 300’

[cjurczak]

Typical MJG resistance is ~2 ohms in series that's 24 ohms plus 300+300ft of 24 gauge wire adds another ~16 ohms. So for a ~30 ohm load and minimum all fire current of 600mA you need 18V firing voltage. Recommended firing current of 750mA would require 22.5V.

[esgrillo]

Your idea with a booster battery and relays is a good one. You can also directly plug in a 22.5v hobby battery as an external power source for your 18m. I've done both. cjurczak's info sounds pretty close to reality. The max I was able to reliably fire in the past on the 14v lipo was 7 mjg in series. I did a brief video on my youtube channel showing an effect where I am firing 14 mjg on a single 18m cue over about 750ft using hobby batteries and relays. Unfortunately I did not make the booster, a friend of mine did and he doesnt have a wiring diagram for it, so I really cant give you much detail on it. There is another thread on pyrotalk that I shared the parts list. Also he had to wire everything in parallel to get it to work with the rj45 output on the 18m so I was very conservative on how many matches I had between boosters.

I also know that a show that weller filmed last 4th (huge one) the guy putting it on did a wall of mines with a car battery and I believe a relay as well. There was just a brief clip of it during the set up shots.

[Arclight]

If you don't want to buy dedicated batteries, there are a variety of adapters on eBay that let you use DeWalt, Ryobi, etc. Lithium tool batteries as a general power source. Or just clamp on some alligator clips.

[PyroGyro]

I'm not sure why you are firing manually and not scripted? You could use a STEP script that triggers timed events with one button push. However, you would still need to still space the 3 walls apart by a 10th of a second (100ms) because the Cobra doesn't have enough current to fire all that at the same time. Each volley would all be wired in series, for better continuity check.


COBRA SCRIPT:

STEP
00.00s -- (6) 36 shot red, white, and blue peony cakes
00.10s -- (6) 36 shot red, white, and blue peony cakes
00.20s -- (6) willow mines
00.30s -- (6) willow mines
00.30s -- (6) 3" single shot
00.40s -- (6) 3" single shot

Now the mines and single shots aren't fired at exactly the same time but they are only within 100ms of each other which shouldn't really be too noticeable. All of these fire under a half second.

One more thing, Cobra just did a video(Cobra Classroom Ignitor video) and they talked about this very topic of shooting more ignitors off of a single cue. You'll have to find the spot where they talk about this. https://www.youtube.com/watch?v=6g6ceY8wNjM&list=PLX_-L6sYe4nKal8Fv8dMnwxQePVI7nZTg&index=14&t=0s You can also reach out to Cobra support for help with this.