Trying to Build a Launch Controller

I have no previous experience about electrical work, but a couple of days ago I got the harebrained idea of building my own launch Controller. The estes controller I've had since I was 9 is pretty old and crummy. In the past I've only worked on LPR rockets, but I'm about halfway through the Estes V-2 semi scale that takes E motors, so I would need a different controller anyway.

I'm hoping that I can build a controller that I can use for a longer time and for higher power motors as well, when I get there. I know that composite motors need a different type of ignition than the low power gun power ones. If I am correct, certain, larger motors need a higher voltage for the ignitor to work. Is that correct?
Do smaller ignitors fail if the voltage is too high?

In terms of a Power source, I was thinking 12V batteries seem to be a good bet for the power needed for a lot of launchers. Thoughts?

Also, since I'm trying to build a launcher that I will be using for a long time, I'm trying to think of fun and/or cool looking bells and whistles. I know that I need the basic warning light when the ignition key is turned, but I would like to build something that has more lights and switches. I know it's childish, but from my forum browsing it doesn't' seem like I'm the only one. Any suggestions for what I could add to justify this?

I've drawn a schematic for a basic launcher with the one connection warning light. Does my wiring work? I'm not sure the D4 diode is necessary.

(I couldn't think of a way to represent the ignitor, so I chose a resistor symbol. If I'm not mistaken, resistance creates heat, so I'm guessing the ignitors are a form of resistor)

It's not quite correct, and you don't need the diodes.

The removable power switch and the launch switch have to be in series, and the optional continuity light is in parallel with the launch switch. Take a look at this for details. https://www2.estesrockets.com/pdf/2811_Estes_Model_Rocket_Launch_Systems.pdf



This schematic from the above Estes Technical Report shows the simplest type of launcher.

You need a removable on-off safety switch. A simple charger plug works here or you could use a key switch.

You need a momentary push button switch for the launch button.

In parallel with the launch switch you can use either a low current light bulb or a 12 low current LED to check continuity. A LED (in series with a 1K ohm resistor) will draw 10 ma and is safe for all igniters.

Bob

Diodes won't help - in fact they will limit the voltage applied to the igniter and further you'd need pretty beefy ones to keep em from blowing out.

However, instead of a lamp, look into using an LED ( and corresponding current limiting resistor ). It will limit current during continuity tests significantly better. However, if you go this route, then you need to make certain the battery is hooked up with the correct polarity. Nothing bad will happen if it's backwards, but you won't get continuity indication.

Kevin

bobkrech said:

It's not quite correct, and you don't need the diodes.

The removable power switch and the launch switch have to be in series, and the optional continuity light is in parallel with the launch switch. Take a look at this for details. https://www2.estesrockets.com/pdf/2811_Estes_Model_Rocket_Launch_Systems.pdf

View attachment 157916

This schematic from the above Estes Technical Report shows the simplest type of launcher.

You need a removable on-off safety switch. A simple charger plug works here or you could use a key switch.

You need a momentary push button switch for the launch button.

In parallel with the launch switch you can use either a low current light bulb or a 12 low current LED to check continuity. A LED (in series with a 1K ohm resistor) will draw 10 ma and is safe for all igniters.

Bob

Click to expand...

What prevents the ignition from going off the moment the safety key is in? Does the lightbulb/LED resistor sufficiently reduce the voltage/current to prevent ignition?

Yes. When using a light bulb, it has a pretty high resistance, and limits the current. It doesn't limit it very well though and some igniters will light with that much current.

When you use an led, you have to select a resistor which limits the current to something like 20ma. (just guessing here but something like a 500 ohm is right for a 12v system)

When the launch button is pressed, the lamp/led is shorted out of the circuit and the igniter gets whatever current it can handle.

Kevin

Sharpe said:

What prevents the ignition from going off the moment the safety key is in? Does the lightbulb/LED resistor sufficiently reduce the voltage/current to prevent ignition?

Click to expand...

Sharpe

Current, not voltage, activates igniters. A 1,000 ohm resistor in series with a led limits the current to a safe f0r all igniters 10 ma. The incandescent bulb in an Estes launcher draws 0.5 amps and is safe for Estes igniters but not Quest Q2G2 igniters. Either this 12 volt LED bulb https://www.superbrightleds.com/moreinfo/bayonet-bulbs/ba9s-led-bulb-1-led/4/37/ or or this one https://www.superbrightleds.com/moreinfo/bayonet-bulbs/ba9s-led-bulb-1-led-wide-angle/3/19/ are direct drop in replacement 12 volt bulbs for the Estes launchers. They have a resistor built in and drop the current draw for the continuity check to 18 ma making it safe for Quest igniters.

Please download and read the Estes report I linked to. It will answer all your other questions.

Bob

I have only limited electrical know how and went for it with my own controller so go for it, best afvice ai could give would be prototype build it into a woodend or cardboard box to start with so you can get the layout right and make sure that when you do the real thing you drill holes in the right place.

To cope with all possible later needs I built mine with banana jacks for the power supply so mine can launch using either an ecternal 12v battery from a mobility scooter or from a more compact 9v in its own smaller case...yet to build the 9v plug in yet.

Mine is way over engineered but looks cool with various warning lights. Simplistically the battery output both pos and neg goes to a dual pole key switch, qfter the key switch the neg goes direct to the igniter output while the pos line runs through a series of switches each with an LED. The test circuit has its own lines to the igniters and is current limited by a large resistore and and LED in line. The test circuit can be engaged or locked out. I did that to provide for the possibility of igniters that may be too senstive in future. Mine also has buzzers for test ok and final launch warning.

Go for it but as Is ay my advice would be to test it out with just the bits first to get the system clear in your mind.

..and as an added safety measure, test it out with an ematch/Q2G2 ignitor, before assuming it is safe for normal launch duty...

Hello Sharpe,

Another good way to test your prototypes and even finished launch controllers is to use a 12v automobile light bulb in place of an igniter. Works well and you can test with it over and over again without burning it out.

As far as igniting "black powder" motors and/or composite motors, your system will work fine for either. I know a thing or two about launch control systems home-made and commercial for low power thru high power motors and their igniters. The same systems work just fine for both. There is NO difference other than size and volume of ignition initiation material when it comes to igniters.

My own commercially available club sized launch systems ( Wilson F/X Digital Control Systems found at wilsonfx.com ) work just fine for 1/4 A's thru P motors (largest motor lit by WFX that I know of.... so far).

But when it comes to high power rocketry, you really need a club with an FAA waiver. I would also suggest getting away from the regular NAR "misfire-alley" for high power rocket flights. The typical "Miss-Fire-Alley" is barely safe enough for even low power rocketry. When you're ready for high power rocketry get with a club that has a waiver and a club sized launch system. Its safer and one can learn so much from other rocketeers: low-power; mid-power; and high power!

Brad the "Rocket Rev.," Wilson

when I built my launch controller I used two 7.2 volt rc batterys. that makes 14.4 volts at 3300 mah. and it has lit everything from an a8-3 to a g80-7t