# Building a launch controller...

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#### ActingLikeAKid

##### Well-Known Member
After losing much of the summer to "life events", I FINALLY got back to launching and had a wonderful short LPR launch on Sunday. Everything was utterly textbook. Flew about six rockets and they all came back. The biggest headache was my launch controller. It's an Estes "electron beam", and after about 10 months of use, it's probably time to replace it: The alligator clip springs are getting weak, the battery cover is missing, and I'm using a piece of heavy-duty paperclip in place of the safety key.

So I was thinking... I may actually have access to a location where I can launch HPR on my own, so why not build a controller that's capable of that? And obviously, if it's good for HPR, it's fine for LPR too. Tell me if I'm missing something, but this is what I'm planning.

Supplies:
12v rechargeable security system battery (like https://www.amazon.com/dp/B00A82A4N8/?tag=skimlinks_replacement-20)
16g speaker wire (100 feet)
TBD connectors for wire to box
Alligator clips for the "business end" of the wires
1 push-button switch
1 "key" switch with removable key
small LED for "continuity" indicator
Assorted small electronics connectors

Method:

Install and secure battery in box.
Wire negative lead of battery to negative terminal in box wall
Wire positive lead of battery to one pole of key switch.
Wire the other pole of the key switch to LED to positive terminal in box wall.
Also wire the "second" pole of the key switch to one side of the launch button
Wire the other side of the launch button to the positive terminal in box wall.

With all that done, I should get a continuity light from the LED without it sending enough current to burn the ignitor, but when I push the button, the ignitor burns. This seems like a 1-2 hour fairly easy project. I'm trying to avoid soldering because .... well, because I don't have a soldering iron and don't feel like buying one right now I will, eventually (because there are some Eggtimer projects in my future) but for now, wire nuts and crimp connectors ought to do.

Am I right on this? Is this as easy as it sounds?

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#### NateLowrie

##### Well-Known Member
It's fairly easy. I would use a 3S lipo instead of the battery you specified. I run one on my launch setup and it works great.

Regarding the location for HPR, you can get the FAA waiver right?

#### ActingLikeAKid

##### Well-Known Member
It's fairly easy. I would use a 3S lipo instead of the battery you specified. I run one on my launch setup and it works great.
Any particular reason? Smaller/lighter?

Regarding the location for HPR, you can get the FAA waiver right?
I should be able to. It's 8 to 9 miles from an airport (and we aren't talking ATL or BOS here - we're talking VERY small airports) and surrounded by desert. The HPR thing is an "it would be cool to do maybe sometime" thing, but I think it would be a fun challenge to build an HPR-capable controller.

#### ttabbal

##### Well-Known Member
You might need to run a couple numbers to get the right voltage drop and current for the LED so it lights, but doesn't pull enough current to fire. If you're using a pre-made unit like an automotive type, get the current spec to make sure. For HPR, if you plan to use motors that use an e-match, make sure you design for very low continuity current. It doesn't take much to fire those. There are some sites that list the "all-fire" current for various ignitors, stay well under those.

#### TangoJuliet

##### Well-Known Member
I've been in the R/C airplane hobby for most of the last 25 years and LiPO and LiFE batteries have been the "in" thing for about the last 6-7 years. Yes, they are lighter. They also don't "fall off" as quickly from peak output as traditional NiCD, NiMH, or Lead Acid batteries. But... They do require specialty chargers/balancers, and they can be a bit dangerous (as noted in the current recall of the Galaxy 7 cell phones). If it's something you might not use on a very regular basis, I would stick with the gel cell 12V battery you initially were looking at. I won't keep LiPO's in my house for fear of accidental fires.