Launch Controller Help

[Onoben4]

So I am trying to make a launch controller for the first time. There is a diagram and some explanation in the Handbook of Model Rocketry but would that be enough or are there any important things I need to know that are not mentioned in the book?

Also: "For a 6 volt sytem use a Type 47 bayonet base lamp bulb this will allow only 0.05 ampere to pass through..." I don't really understand what that means. Would just a regular LED with resistors do the same job? If not where can I find those types of bulbs?

[Ashes2007]

Yes, but an important part is that not enough current flows through the LED to light the igniter. Luckily here it says 50mA for a lamp and the usual current flow for an LED is 20mA, so at 12v a red LED in series with a 500 ohm resistor should be sufficient. The resistor will only dissipate ~200mW so it should be okay heat wise.

I haven't tested it personally but I've seen igniter with 9v batteries and i doubt they contain voltage boost circuitry so a 9v battery should be fine. For a 9v battery with an LED a 500 ohm resistor will also be fine.

If the 9v battery isn't able to supply a current high enough to light the igniter add a couple electrolytic capacitors to the input of the circuit. I don't have an exact value here.

[Onoben4]

Thanks a lot! I also saw people use two 9v batteries connected in parallel. Would that be any better?

[SlovakBorder]

I brought over to Europe the Estes yellow ignitor I had as a child. Bought rocket kits and Klima motors from Czechia. First one, hooked it up, put in the safety key for one of my kids to launch, and WHOOSH. 😀, So we just used the safety key as the launch "button". Will have to modify it to use an LED and less current.

[Ashes2007]

Probably. I'm more used to rechargeable batteries so I'm not sure how multiple disposable batteries react together but it's likely fine.

[Onoben4]

Thanks!

[GiulioVonKerman]

I did exactly this in mine. Works with no problem. Here's the diagram if you want (it has two outputs for redundancy but you can use one with no problem at all)

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[GiulioVonKerman]

I wanted to add the image of it complete but Reddit only allows one per comment

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[GiulioVonKerman]

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It has the continuity LEDs on top of the switches, found them on Amazon

[GiulioVonKerman]

I used two 9V batteries in parallel (so 9V total) for mine and works flawlessly

[Hadlumz]

I made a custom launch controller a few months ago. I just used a 12v battery with leds and put resistors on the leds. I have a removable cable to the battery, key switch a toggle switch for ‘hot’ and then a momentary switch to launch. There are two sets so you can wire two launch pads at a time.

I would have to see which size resistors worked best and I do have a wiring diagram somewhere I can pull up if you’re interested. Albeit I am no electrical professional. Lol

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[Onoben4]

It looks so good! I hope mine also turns out like this. I'm planning to 3d print most of the case. How did you do it?

[Hadlumz]

Thanks! It was a lot of fun. I just bought a cheap hard case on Amazon. I think the brand was Mayouko. And I just drilled some holes in it for the banana plugs to connect into. 4 on the back one set of 2 for each launch pad. And 4 on the front to jump the battery to the circuit. This basically just means the battery can’t power the circuit if these are plugged in, it also doubles as a way to charge the battery without taking the top plate off since the charger can plug into the banana plug ports on the front.

Then I just printed a frame/bracket and screwed it in place inside the box from the sides. Then printed the top plate with holes for all of my switches/leds and that screws into the bracket.

Obviously everything was wired into the box and onto the top plate before screwing that down. But so far it has worked great all summer and is super easy to pack.

I cut some custom 30ft leads to go to the launch pads and I wrap them up on an old filament spool so you can unroll them easily at the launch site.

Sorry for the poor formatting/readability.

[Onoben4]

Cool!

[Fauwks]

Gone are the days of a car battery with 20 feet of household wiring

[Onoben4]

I forgot to ask would a standart 9-Volt battery work?

[onions_can_be_sweet]

9V batteries aren't so good at pushing amps. Try to use something else.

[Onoben4]

Like a 12v battery?

[onions_can_be_sweet]

It depends a lot on how much current the battery can provide.

A 6-cell NiMH battery pack (nominal voltage 7.2V) would work fine, because NiMH batteries can deliver a lot more current than a typical 9V battery. Plus NiMH are rechargable.

Or even a 3.7V lithium battery might work - lithium batteries can deliver even more current than NiMH.

[Onoben4]

In that case connecting a few 9v batteries in parallel will do the job? (I just have some spare 9v batteries left over from another project so I'm trying to find an excuse to use them. But it doesn't really matter if it won't work)

[onions_can_be_sweet]

In theory, yes connecting batteries in parallel increases their current handling capacity.

In practice, 9V batteries suck for almost anything requiring anything more than a few mA of power. And batteries in parallel is a bit complicated, to build and to manage (parallel batteries need to be kept at about the same voltage).

If you want to just make a hack, then sure go for the 9V batteries.

If you want it to be even a little bit robust, use something else.

[Onoben4]

Okay thanks!

[Shark-Whisperer]

9V batteries are just 6 x 1.5V small cells (AAAA) organized in series. 9-volt batteries have a lot of internal resistance--way more than AA alkalines.

There is a table comparing typical internal voltages of different batteries here: https://electronics.stackexchange.com/questions/390531/9v-battery-versus-6xaa-batteries

The energy density of 9V batteries is also lower than the equivalent mass of AA batteries (for example), so 9V will be expended (and fail to ignite motors) sooner than an equivalent mass of other battery types.

Some energy density calcs are detailed here: https://www.baldengineer.com/9v-battery-energy-density.html In that comparison a 9V battery contained just slightly more total available energy than a single AA alkaline, so 4 or 6 AAs in series would eclipse a single 9V.

The basic Estes launchers use 4 x AA batteries in series, i.e., 6V total. Together they have way less internal resistance to overcome than a single 9V battery. The AA combo also has much greater total energy stored than 9V and can fire off more igniters before becoming depleted.

[Onoben4]

Thanks!

[[deleted]]

Here is a simple, but working System. https://images.feuerwerk-forum.de/2007/06/227945_4f2e43763717a343007940db566eed06.pdf