Homemade Launch Controller

hey. I'm trying to make a cheap backup launch controller.[have estes model as primmary] I'm using a old cigar box as case,a electrical on/off switch [used in household apps] and a aux 4 AA battery box from R/C radio spares.I wired everything and tested it using spare motor igniter.thing is it burned the igniter with the switch on off.also the batteries got hot and melted some plastic.I'm using 18gau wire mostly,but the wiring from battery box is smaller.too much current?:confused2: any thoughts? thanks, Dale

Need to post your schematic otherwise it's just speculation.

Steve G

not sure how to do that.I can tell you there are two post on the switch.one post are a battery lead and wire to igniter and the same on other post.

Dale from your description I drew this schematic which explains what has happened. Switch ON shorts battery causing wires to overheat and melt plastic. Switch OFF fires igniter. :y:

Steve G

Steve,you nailed it. Is there a solution? I thought about using a door bell buzzer instead but didn't know if that would help.

The problem isn't the switch, it's the circuit. I recommend some basic research -- https://www.allaboutcircuits.com/vol_1/index.html is a pretty good site.

This diagram by sparkfun is probably worth looking at:

You have to interrupt the flow of electrons with the switch. Currently you have the switch in parallel and when turned on is a direct short.

you guys lost me.I'm not very good at understanding this topic. guess I should stick to the store bought versions,lol

Yeah you probably should ! Melting wires is not a good thing. I am also a rookie when it comes to this kind of stuff but the link in Zeroignites post is very good IMO.

Add a momentary switch like a doorbell button and a LED circuit to show continuity. Then rewire as in the schematic below.
Steve G.

sghioto said:

Add a momentary switch like a doorbell button and a LED circuit to show continuity. Then rewire as in the schematic below.
Steve G.

Click to expand...

This circuit is always alive, I don't like to connect an igniter on a live circuit even if you have a limiting resistor.

And thanks to allaboutcircuits.com I can follow Steves circuit drawing.

No removable safety, is that your objection Gerard ?

samb said:

No removable safety, is that your objection Gerard ?

Click to expand...

Yes can be removable or a switch to power the circuit down for when you plug the igniter

You don't need three switches. If you are worried about the "live" circuit then just connect the LED between the ARM and LAUNCH switches. You should always touch the igniter clips together first before connecting. If the LED comes on, the circuit is safe.

Steve G

I would avoid putting the LED directly in series with the rest of the circuit. Voltage and current draw would either toast it or not supply enough to the igniter. If you made that toggle/arm switch double throw, you could disable the entire circuit when safed, show continuity when armed, and launch the whole thing when armed and shorted with the doorbell switch push.

just connect the LED between the ARM and LAUNCH switches

Click to expand...

I was referring to the connection of the anode of the LED as in this edited schematic, not actually connecting the LED in series with the switches.:wink:

Steve G.

Dale said:

you guys lost me.I'm not very good at understanding this topic. guess I should stick to the store bought versions,lol

Click to expand...

Dale I am not trying to sound like an ass but if you don't understand the circuitry........... You should buy another Estes controller as a backup.....

I'm no electrical genious, but the schematics makes sense to me.
Safe mode would be to disconnect the + or - or both from the electrical soarce physically; Battery cable clamp.
I once built a 5 pad system. 5 door bell buttons is all I used.
Rockets were preped, everyone safely away, battery clamps installed and launch began.
Extremely simple, cheap and effective.
Look into a mirror. that person and only that person is responsable for your safety.