Quantcast

Building a launch controller...

The Rocketry Forum

Help Support The Rocketry Forum:

ActingLikeAKid

Well-Known Member
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
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?
 
Last edited by a moderator:

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
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
Joined
Nov 17, 2015
Messages
1,133
Reaction score
13
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
Joined
Jan 19, 2009
Messages
1,082
Reaction score
22
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.

3S lipos are great, if you have a charger etc.. They require special chargers, do not attempt to charge them directly from a car battery etc.. They are small, light, and pack a punch. Some versions can deliver more current than the booster pack type SLAs. They are also more fragile, and more temperamental. So if you want to use one, please read up on them a little. You can get a good charger for them from HobbyKing for $20 or so. You might consider a low voltage alarm as well, they do not like being drained low and can be permanently damaged if you do. Not saying they aren't a good choice, just mentioning possible issues you need to be aware of when working with these unprotected lipos. If you're willing to treat them right, they are great.
 

NateLowrie

Well-Known Member
Joined
Jun 28, 2016
Messages
667
Reaction score
4
Any particular reason? Smaller/lighter?



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.
Much smaller and lighter and also cheaper. I have a relay launch controller from QuickBurst and use this 2200mah battery with it. The battery is capable of 66A for 10 sceonds or 44 amps sustained and it'll fit in the palm of your hand. Get yourself a set of Deans connectors and solder them on instead of alligator clips. Then the battery plugs right in. You could even build the battery into the box and have a power switch on the positive side (just make sure it can handle the current).

That battery and controller was able to cluster launch 5 rockets with the old current hungry copperhead igniters in it. Motors all lit within a second of each other.

I use this charger to charge it. I cannot stress enough how important it is to use a charger specifically designed for lipo packs.
 
Last edited by a moderator:

Handeman

Well-Known Member
TRF Supporter
Joined
Jan 18, 2009
Messages
7,776
Reaction score
364
Location
Stafford, VA
Smaller and lighter is a good thing with batteries. But.... You might want to consider a car starter. They are 12V, put out all the current you will need, only need an extension cord to recharge (they have built in chargers), usually have built in lights, USB charging ports for phones and other devices, a cigarette lighter socket, etc. It's like having all the functionality of your car's electrical system that you can carry around.

I use my starter to run my charger that charges my LiPos, even at home since the LiPo charger requires 12VDC. It can also get a car started if you or your friends sit in a field all day with the radio etc. going and run the car battery low.

My launch controller is a small box and wire that I hook to the car starter. Here's the schematic and a pic. The way I did it, as an added safety feature, you have to hold the ARM switch On while pushing the launch button. Since it is a hand held device and could get set down in any position and I sometimes forget to remove the safety plug, I didn't want a single button to launch with. That is also why the coiled wrist bracelet is attached to the safety key.
Schematic.png 0701161216.jpg 0701161217.jpg

Notice how the black power wires are different lengths? If you move the controller and pull the wires, the two power clamps won't hit together and arc. That was learned the hard way.

You would probably have to do a little soldering to build one like this, but it works great. As for the car starter, I've started cars at launches and used it as an emergency replacement for a dead battery on the club's HPR pads.

BTW you will need a much lower wattage soldering iron for the Eggtimer then you will need for soldering this. You should be able to get a 25W or 30W soldering pencil for less then $10 to solder this, av-bay wires, and most home projects. A good soldering iron with controlled heat that you can use for surface mount components on the Eggtimer will cost you more.
 

TangoJuliet

Well-Known Member
Joined
Jun 26, 2016
Messages
1,239
Reaction score
9
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.
 
Top