12V Controller Homebuild

Cobalt11235

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I started having some reliability issues with my small Estes controller and decided to start building my own. Ha, turns out the Estes controller had a bit of crud on the clips, and works fine after a quick sand… but I was already keen on the idea of a build.

First, this site has been a great resource to get ideas. There was a few functions I wanted from this:

1. Two big launch buttons that both need to be depressed to fire. With two young kids, I thought it’d be fun for them to launch together.

2. I wanted the controller to disarm itself after every launch.

3. I wanted to look kinda cool. Lights, buttons, etc…

This was my first electronics project, so there’s probably better ways to do it, but here’s how this one came together.
The controller uses (8) AA rechargeable batteries to get (less than) 12V. It uses two DPDT 12V relays to get the functionality I wanted.

Relay 1 is the continuity relay. The coil resistance is about 160 ohms, so it limits the continuity current to the igniter to below 75mA. Once there’s continuity, the relay closes and sends power to the continuity light and to Relay 2.

Relay 2 is the arming relay. There are two momentary switches (one N/C and one N/O) to arm and disarm leading to the relay coil. This one is wired as a “latching” relay, which keeps the relay closed once the momentary arming switch is hit. But it opens the relay whenever power is disrupted (either by no continuity at the igniter or by breaking the circuit with the disarm button).

Once Relay 2 is closed, both green momentary mushroom head buttons must be pressed (or slammed!!) to fire the rocket. This completes the circuit and sends the full battery current through the igniter.
2377DA41-BBBD-431A-B414-EE5BF7C2F107.jpeg

At some point I’ll add a charging circuit and plug so I don’t have to open this thing up to charge… but for now, it’s ready for launch (once the Ohio winter decides to end).

To do it over, I’d probably go for a few bus bars like I saw in another build. The wires in this thing are a mess, and that would help a lot. I also bought a lot of switches that didn’t end up working for one reason or another, so lesson learned (sometimes Amazon is your friend, sometimes not)
View attachment IMG_4063.MOV
. But whatever. It was fun.
I’ll have to update and post the schematic next. I made some changes on the fly, so my original napkin schematic isn’t so accurate.


Components:
mxuteuk 2pcs DC 12V Coil 8 Pin...

APIELE 22MM Mushroom Head Push...

TWTADE 16mm IP65 Waterproof...

DaierTek 1032L Looper Guitar...

CESS Dual Binding Post Terminal -...

uxcell 12mm 2 Positions Key...

https://www.westfloridacomponents.c...V+Panel+Mount+Pilot+Lamp+Indicator+Light.html

LAMPVPATH (Pack of 2) 4 AA Battery Holder, 4 AA Battery Holder with Leads, 4 AA Battery Holder with Wires
 

Cobalt11235

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Some more pictures, including the wiring mess under the lid and the preliminary schematic. This one only shows one relay, before I realized it’d need two to do what I wanted. But it does show how the latching circuit works.
896979A2-728E-4E15-A38F-F2848CE172CC.jpeg 0F345135-0706-4048-A11E-608A0FA258BF.jpeg E915901D-5CF0-46C4-AC1C-B8B09BC2429E.jpeg 834B8D4E-DB64-4FAB-A5FA-57697B8C0687.jpeg 190E65C3-D7CD-407F-AB6D-14A398DE8B13.jpeg
 

therling

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A bit of advice on electronics components. I usually order from Mouser or Digi-Key, depending on pricing and/or availability. They have much better quality control, far wider selection and lower prices than Amazon. For example, a key lock switch from Mouser (https://tinyurl.com/4bb9n83t) at $3.61 is less than half the price of the Amazon item. Customer service is excellent from both too. Mouser tends to charge a little more for delivery so I usually compile a sizable order to make it cost-effective. The online catalog system takes a little getting used to but worth the extra effort.

If you really want to save money, there's a hack for Digi-Key. If you print out and mail your order and pay by check or money order just like olden days, shipping is free, though it takes a little longer than ordering directly online. You can find a mail order form here:

 
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