Well, I built my first launch controller...

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bsexton

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I took a stab at my first launch controller for our club. I only built a unit that could handle six rockets to get my feet wet with the design and test my electronics skills. I patterned this after the launch controller used by SEVRA. I got most of the parts from Radio Shack as follows:

(6) 275-602 SPST Toggle Switch
(2) 274-1563 DC Power Jack
(1) 274-1569 DC Power Plug (PK 2)
(3) 274-252 1/4" Phone Jack (PK 2)
(3) 274-1544 1/4" Phone Plug (PK 2)
(1) 49-515 Standard Key Switch w/cover (discontinued)
(1) 275-609 SPST Momentary Switch (PK 2)
(1) 273-060 Piezo Buzzer
(1) 270-1809 Project Box
(1) 270-380 Mini Clips (PK 12)
Hookup wire 18 AWG stranded
250' 18/2 stranded wire

The piezo buzzer only draws 5mA and should be safe for all igniters including electric matches. I have tested the unit with Estes Solar Igniters, Aerotech Copperheads, Fire Fly and Davey Fire electric matches with no problems.

I designed the unit to allow for drag races which some people will say is not safe -- I think it is a matter of training and supervision.

I use a Werker 12V, 7.5 AH SLA battery which packs a lot of punch and will even light multiple AT Copperheads with no problem. I used phono plugs to connect the 30' leads to the control box itself and should be easy to maintain.

Please note the diagram has been changed to reflect the proper wiring of the continuity test switch and is attached to a new post in this thread entitled "Updated Wiring Diagram".
 
Can the launch switch handle the current load of a full set of six rockets? When I built mine, I used a DPDT 10-amp relay and ganged the contacts together, for a total of 20 amps, and that was for a single rocket (up to 3 engines). I couldn't find a reasonably priced switch rated for that.

Tip: meters use even less current than buzzers. Mine has a 50 uA meter, set for just over half range (~30 uA to test) for 12v.
 
Originally posted by DJ Delorie
Can the launch switch handle the current load of a full set of six rockets? When I built mine, I used a DPDT 10-amp relay and ganged the contacts together, for a total of 20 amps, and that was for a single rocket (up to 3 engines). I couldn't find a reasonably priced switch rated for that.
I will confess I'm not an electronics guru. I told the salesman at Radio Shack what I was building and he said I should be fine with the parts I selected. That's my story and I'm sticking to it... :D
 
The RS sales folks aren't usually electronics gurus either. I happen to have an EE degree, though, so I don't usually ask their advice anyway.

Igniters can pull up to 20 amps or more EACH. Although my RR didn't blow a 20 amp fuse, so I guess the spike is short enough to not even blow a fast acting fuse. The concern is carbon arcing in the switch contacts - the last switch you close gets a spark across its contacts, which can burn out the switch pretty quickly if you exceed its parameters.

Although, it's possible that the current ramps up slow enough (milliseconds) to avoid a big spark in the switch. Only time will tell.

Another thought is that 30 feet of 18g wire might provide enough resistance to avoid problems. Igniters don't NEED a lot of current, but they'll take it if they can. I use a 16g extension cord for mine.
 
Originally posted by powderburner
Have you done any testing or launching with this yet?
I have tested several types of igniters as well as multiples to simulate a drag race and it has worked flawlessly. I intend to give it a full shake-out at our next club launch.
 
Originally posted by DJ Delorie
The RS sales folks aren't usually electronics gurus either. I happen to have an EE degree, though, so I don't usually ask their advice anyway.
I agree with you in general about the RS folks, but the one I worked with is an EE student at a local college and was also somewhat knowledgeable about our hobby so I felt pretty comfortable with his advice.
 
Originally posted by firemanup
That thing looks great bruce... nice job......
Thanks Jason! Like I said this is my first electronics project and I know there is plenty of room for improvement. It would be nice to add LED's for visual indication and probably a continuity tester at the pad but I think it is a good first try.
 
Can ya build one for me? ;)

Looks great!

Woo! Post 600

Phil
 
I think I have found one flaw in your design. The Test switch totally takes out the safety key and the piezo buzzer doesent use up enough of the current to keep a launch from happening. Lets say you have a rocket set up with the leads connected and you hit the test switch with or without the key, if that rocket toggle switch is on, Up it goes. I would put the key before the test switch.

Am I right???

Dan
 
On mine, the continuity check is between the safety switch and the launch switch. But then, my continuity check only uses 50 uA.
 
Originally posted by Dbarrm
I think I have found one flaw in your design. The Test switch totally takes out the safety key and the piezo buzzer doesent use up enough of the current to keep a launch from happening. Lets say you have a rocket set up with the leads connected and you hit the test switch with or without the key, if that rocket toggle switch is on, Up it goes. I would put the key before the test switch.

Am I right???

Dan
You are correct that the "test" switch can be used without the "safety" switch being on. The logic was I wanted to test the continuity without launching the rocket. The purpose of the piezo buzzer is to draw enough current to "buzz", but not enough to fire the igniter. Even if I put the buzzer after the key switch by your logic you would launch the rocket when you tested for continuity -- right?.

My logic was to test for continuity without the main power switch being on and if that test failed the rocketeer could then go and check the leads. Then the only way to launch the rocket is to have the safety switch on, the toggle on and push the momentary launch button.

To test this I hooked up an electric match (should require the least amount of current to ignite) and toggled on and held the continuity test button for at least 30 seconds - no ignition. I then turned the safety switch on, toggle up and hit the launch switch and it ignited immediately.

Above all I want this unit to be safe. With any continuity test you want to draw enough current to power the buzzer, light the light or operate the meter without firing the igniter. My belief is that a 5mA piezo buzzer will work as intended.

Am I correct or not?
 
Originally posted by bsexton
Even if I put the buzzer after the key switch by your logic you would launch the rocket when you tested for continuity -- right?[/QUOTE]

The point is, at least you won't be standing beside the rocket when it happens, if someone else hits the continuity switch while you're holding the key.
 
Originally posted by DJ Delorie
The point is, at least you won't be standing beside the rocket when it happens, if someone else hits the continuity switch while you're holding the key.

Point well taken - easy enough to change. You do agree that the purpose of the continuity test is draw enough current for the test without firing the igniter (obvious) and while my buzzer draws more current than your meter it should still be safe?
 
I don't know what a safe upper limit is for continuity current. I've seen a lot of people mention 10 mA as "generally safe" but I'm paranoid, and happened to have a 50uA meter available, so I used it.
 
My main concern was that the buzzer might draw enough current to light off an igniter. This will be a good thing to look into. What is the high limit of current to use for a test without getting to close to ignition. But again I still think that the test switch should still be controled by the safety key switch.


Dan
 
My main concern was that the buzzer might draw enough current to light off an igniter. This will be a good thing to look into. What is the high limit of current to use for a test without getting to close to ignition.

Dan
 
A really nice launch controller Bruce, but I do agree with Dan that the continuity checker power should be pulled off after the safety interlock switch to comply with the NAR safety code which requires double redundancy.

Although it is unlikely to occur, should the continuity circuit short circuit, the launch clips could be live even if the safety switch is powered off, and the motor could fire as you were hooking up the clip leads.

The safe curent for an Estes igniter is 100 ma and the all-fire current is 2 Amps. This is a bit high for some low current e-matches. Something between 10-20 ma should be safe for virtually all ignitors and e-matches.

Bob Krech
 
Thanks for everyone's comments. I have updated the wiring diagram to reflect the correct placement of the continuity test switch.
 
Much better. I have started my mod design of your basic system. Ill post it when I get it done.

Dan
 
Okay, I just bought some parts from Radio Shack in order to make my own launch controller! But I am so confused. First, let me talk about my power source. I will be using a 12 volt 7 Ah battery (it just says 12V7Ah) lead-calcium battery.

I am yet to either find a key switch or design my own safety key for the controller.
(1) 49-515 Standard Key Switch w/cover (discontinued)
Bsexton, where did you get it if it's discontinued.

Next up is my switch. I bought a SPSP Momentary Pushbutton Switch from Radio Shack (275-618). The package says, "Rated 3A at 125VAC, 1.5A at 250VAC." Does that mean it will only work with AC, not DC?

Next is my buzzer. I bought the 12VDC Piezo Buzzer (Radio Shack, 273-060). I'm guesing it will work because bsexton used it as well.

Then are my wire clips. I bought the 1 1/8 inch smooth clips from Radio Shack (270-373). On the package it says, "Copper plated, solder terminals, rated 5 amps." Does that mean it can only handle up to 5 amps? My battery says 7Ah on it, does that mean it has 7 amps? If it does, then does that also mean my clips can't handle the amount of power?

Sorry for all the newbee questions, they sound so clueless! Well, I am clueless as of right now.

Thanks,
Matthew
 
I am yet to either find a key switch or design my own safety key for the controller.

I used a momentary SPST toggle switch for mine (because I had one, that's why). Alternately, a center-pinned power jack with matching (shorted) plug works too.

package says, "Rated 3A at 125VAC, 1.5A at 250VAC." Does that mean it will only work with AC, not DC?

No, that means that the ratings don't count if you use DC. The contact spark is different between AC and DC, so the wear-n-tear is different for the same amperage.

Then are my wire clips. I bought the 1 1/8 inch smooth clips from Radio Shack (270-373). On the package it says, "Copper plated, solder terminals, rated 5 amps." Does that mean it can only handle up to 5 amps?

That means they're guaranteed not to melt if you put 5 amps through them for a long time. For the fraction of a second we're subjecting them to, they'll be fine with much higher amperages. I used those same clips for my launcher.

My battery says 7Ah on it, does that mean it has 7 amps? If it does, then does that also mean my clips can't handle the amount of power?

That means if you put a one amp load on it, it would die in seven hours. Amp Hours in a battery is like the letter on engines; it's a total power. Amps is like the number rating, it's a power usage rate.

A 7 amp-hour battery is quite happy delivering anything from a few microamps to tens or hundreds of amps. The amount of current actually drawn depends on the resistance of the load (the igniter in this case).
 
Wow! Thanks so much! Now I can make my launch controller with peace of mind that the parts I bought were correct :)
-Matthew
 
Originally posted by rocketsonly
I am yet to either find a key switch or design my own safety key for the controller. Bsexton, where did you get it if it's discontinued.

Thanks,
Matthew
I got it from Radio Shack. They are officially discontinued but you may find some left in inventory at some stores. It cost me a whole $0.97 but they also had another key switch (don't know the part number) for about $10.00.
 
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