Launch Controller Mod

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Dbarrm

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This is a modification to the launch controller that bsexton posted. With his ok i have done some modifications to it and would like a second set of eyes to look it over and let me know if I have set this up correct.

Dan
 

DJ Delorie

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If you close more than one arming switch, continuity on any jack will light all the continuity lights. You need diodes to prevent backfeeding power, or use relays to switch each jack independently.
 

Dbarrm

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Can you explain the current path on that??

Dan
 

DJ Delorie

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Ok, close the first two switches. Now, you can trace a path from J1's hot side, down through its switch, to the common rail, through the second switch, and up to J2's hot side. Thus, the two jacks are electrically connected together.

For diodes, you'd need to put one for each jack to isolate the launch side of its arming switch to prevent this backfeed.

For relays, you'd have one relay (or at least one set of relay contacts, for quad-pole relays) for each jack to provide launch power.
 

Dbarrm

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Im not seeing it. Maybe I just dont understand the path your trying to show.

Dan
 

DJ Delorie

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This shows the short between the two jacks. When shorted, the continuity lamps can't tell which igniter is which.
 

Dbarrm

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Ok I see your point now. So if only one was good but lamps would light do to current path. If I used diodes I can control the flow of current.

Dan
 

DJ Delorie

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Yeah, but remeber that (1) the diodes will have to be big enough to carry the launch current, and (2) diodes will drop the voltage 0.7 volts or more for that size diode (minor, but plan for it).

Relays are better but more expensive. Three high-current dual pole relays would add about $25 to the cost, not including sockets if you plan for eventual replacement.
 

Dbarrm

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Wow your making my head hurt. now I have something to do while I wait for glue to dry. Let me look this over. I want to figure it out myself. If I get to stumped ill come asking for help.

Thanks

Dan
 

Dbarrm

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What kind of current are we talking about. I think I have figured out where the diode needs to go but not sure how big of one I need.

1N4001

Dan
 

DJ Delorie

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Search the other threads for a link to a PDF where someone tested a whole bung of igniters. Some pulled over 20 amps, but only for a fraction of a second. 1N4001 is only rated for 1 amp, which might work for a while, but I'd at least use 3 amp diodes (like 1N5400). Note that 1N4001 and 1N5400 drop 1.1-1.2 volts.

For more excitement, a power schottky diode is better - 16 amps at 0.6v drop, or dual 20 amp at 0.3 volt.
 

Dbarrm

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Is this what I need to do to fix it??

Dan
 

Dbarrm

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So I need to find a diode that can handle the current. Put it in the same leg for each jack and all should be ok.

Thanks for all your help.

Dan
 

Dbarrm

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Ok here is the updated schematic.

Dan
 

Ted Cochran

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Originally posted by Dbarrm
So I need to find a diode that can handle the current. Put it in the same leg for each jack and all should be ok.

FWIW I used a very similar circuit.

https://www.mn-rocketry.net/masa/tech/tedcontroller.htm

I used the same 6A rectifier diodes that Radio Shack sells, which cost about $.50 each retail, except I got them at a surplus store. It's not a safety critical part in that if you burn out a diode you'll just lose continuity testing on that circuit. Buy some spares, solder on some quick connects, problem solved. I've had to replace two over the past four years or so, always after some ridiculous thing like a seven AP motor cluster....

However, I do have some suggestions.

First, you might want to put a relay between the launch button and the firing circuit. As it stands, you're using the launch switch--which IS a safety-critical part-- to handle all of the launch current, and it's going to have to be a very beefy and expensive switch to take that kind of abuse. If you instead get a 30 or 50 amp relay (a car horn relay would be just fine), you can use a pretty switch (mine's an old arcade game switch) for the launch button.

Second, it is always possible to get a welded relay, so to avoid nasty surprises you might consider putting a buzzer across the firing relay so it yelps if the relay is closed.

Third, consider splitting the console box and put the relay box (and the battery!) at the pad. You can connect them with 50' extension cords, which are about the cheapest wire you can find anyway. If you want, you can have continuity at the console, and still only need five extension cords to run six pads. You can use 110 volt plugs and receptacles for easy maintenance and relatively low cost.

Good luck with the project!

For what it's worth,

--tc
 

Dbarrm

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What is the advantage of splitting up the system? Is it to minimize the current loss do to the long length of wire??

Dan
 

Dbarrm

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So something like this with a relay??

Dan
 

DJ Delorie

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What is the advantage of splitting up the system? Is it to minimize the current loss do to the long length of wire??
Yes. Plus, each rocket gets its own battery that way - more current available.
 

Ted Cochran

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Originally posted by Dbarrm
What is the advantage of splitting up the system? Is it to minimize the current loss do to the long length of wire??
Yes--the primary firing circuit can be in a loop of 5-10 feet of heavy gauge wire at the pad. Otherwise you need bigger extension cords.

Also, I'm not a EE, but all the EE's I know hate long wires. They cause issues with maintenance, inductance, all sorts of things. Probably not a big deal for a standard 12 v relay system with mechanical switches, but definitely worth worrying about when you upgrade to MOSFETs or other razzmatazz :)

It also reduces the bulk of the console, if that's a concern.

Cheers,

--tc
 

Ted Cochran

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Originally posted by Dbarrm
What is the advantage of splitting up the system? Is it to minimize the current loss do to the long length of wire??

Yeah, that's it. Now put a buzzer in there that sounds when the relay is closed, and you'll be in great shape.

--tc
 

Ted Cochran

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Originally posted by DJ Delorie
Yes. Plus, each rocket gets its own battery that way - more current available.
Alternatively you can put all the relays in a spider box, and have that box feed a rack of pads with (short) leads. Then you can use a tractor battery or some such at the pad side relay box.

Otherwise you'd have to connect all the pad side boxes to each other, or have a select relay and a firing relay in each box. That's what NASA does, I think :)

--tc
 

Dbarrm

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Wow so much info. Its 9:39 and im still at work, got off at 4:30 but was working on this. I think its time to go home. Tomorrow Ill do some more on my design and post what I come up with. Thanks all for your inputs and help. This is going to turn out great.

Dan
 

Dbarrm

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Ok I have redesigned the system into a two part controller. The dotted line separates the two sections. Pad & Launch Station. Now I’m no engineer so I might have not done this correct so can you people with the know take a look and let me know if you see any flaws.

Dan
 

Dbarrm

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Well this has gone through a lot of changes and im sure it will get a few more. Right now it shows bulbs but that will be changed to add LED's soon.

Dan
 

Dbarrm

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Im not sure if I stated this but dashed line seperates the two different boxes of the launch Controller. I have added a second safety switch to the pad box along with a power LED. All bulbs have been changed to LED's

Dan
 

Dbarrm

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I would like to give a big thanks to bsexton for letting me mod his original design.

I would also like to give a big thanks to DJ Delorie for all his help with the mod, without his help my mod project would of been dead in the water.

Thanks to both of you. :D :D :D :D :D

Dan
 

Dbarrm

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Well here is what the front panel of the launch controller will look like. It will look much better when the finished product is made but this will give you an idea.

Dan
 

Dbarrm

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Well here is what the front panel of the launch controller will look like. It will look much better when the finished product is made but this will give you an idea.

Dan
 
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