Help with a Custom Made Launch Controller for G motors / HPR

[ThisGamerAlex]

Hello fellow rocketeers, I hope you are doing well. I am currently designing a rocket that will fly with a G or H motor but I have a problem. Because I live in Spain and here, rocketry isn't commonly known like in USA and around, it is very hard to find and buy certain elements. Today I'm struggling with the motor ignition. Because e-matches can't be shipped from different countries due to hazards, I'm planning on making my own following the steps that Richard Nakka states on his website, but that's another thing. What I really need help with is to get myself a decent launch controller to be able to ignite and launch HPR motors.
I have found just a few rocketry websites around Europe but the few ones that have launch controllers, they are:

1- not suited for launching HPR motors
and or
2- too expensive

So, bearing in mind that launching rockets isn't going to be a day to day thing for me (at least for now), I thought of building my own, following serious tutorials of people that know what they are doing (I really don't have that much knowledge about electronics, sorry). Some minutes ago I found this custom made launch controller that seemed pretty simple and efficient enough for it's purpose but I have some doubts and I want to hear the opinion of the really experienced and talented people around here.

The first is: is this launch controller build reliable? Would you recommend me to build and use it?
And second: As far as I'm aware, when you launch HPR motors you need to stay at least 100 feet apart (30 meters) and the original build uses less length so, could it be changed to have 100feet of cable length to be suitable for launching G/H+ motors? And if so, any tip on how to do it?

As I said, my knowledge on electronics etc is really basic and ofcourse I'd love to just buy some e-matches, an "official" launch controller and go safe but the costs of building the rocket itself are pretty high and even tho I still need and want to spend some more money on the launch controller (ofcourse), I prefer to go for something that can launch HPR for this launch and future ones, and that doesn't cost me my hole wallet (also, I can't find them..) .

Thanks in advance for any help, info and tips provided.

Take care and have a good day!
Alex

 

[ThisGamerAlex]

Update: As soon as I posted this, I saw the post Mike Haberer did on a custom LPR/MPR Launch Controller Build so I will take a look but I still want to stay with the easiest build option possible and that still matches the requirements.

LPR/MPR Launch Controller Build from Mike Haberer

 

[waltr]

That controller and many others work fine on HPR ignites IF you use a 12V battery with enough current capacity.
That means almost any 12V lead-acid (car/motorcycle battery) or a 3S LiPo without protections circuits built-in).

As for ignites, these are really easy to make. Ematches are typically not used for motor ignition but are used for ejction deployment charges (Dual Deploy with Altimeters). Ematches are also used for fireworks so may be available through fireworks sources.

A twin 24 gauge wire and some 30-36 gauge nichrome wire then a pyrogen mixture.
Read about this here: http://quickburst.net/qb/

The chemicals should be available in Europe. Ask about them at rocket clubs over there and ask what others are using.

Most motors do come with an iginiter so you would not need to make them.

Which G & H motors and brand are you considering?

 

[ThisGamerAlex]

That controller and many others work fine on HPR ignites IF you use a 12V battery with enough current capacity.
That means almost any 12V lead-acid (car/motorcycle battery) or a 3S LiPo without protections circuits built-in).

Okay, that's some usefull info to know. Do you know if something of the circuit he presents would need to change in order to use a larger length for the wire? So that I can fire it from a safer distance.

As for ignites, these are really easy to make. Ematches are typically not used for motor ignition but are used for ejction deployment charges (Dual Deploy with Altimeters). Ematches are also used for fireworks so may be available through fireworks sources.

A twin 24 gauge wire and some 30-36 gauge nichrome wire then a pyrogen mixture.
Read about this here: http://quickburst.net/qb/

The chemicals should be available in Europe. Ask about them at rocket clubs over there and ask what others are using.

I was planning on buying some e-matches and then making some changes (adding a pyrogen mixture as you stated, for example) both for motor ignition and chute deployment with an Eggtimer Apogee. I really tried to find them locally but the only pyrotechnic related thing I could find are fireworks, it was impossible for me to find e-matches or something even similar, that's why I decided to craft them. Thanks for the website!

Most motors do come with an iginiter so you would not need to make them.

Which G & H motors and brand are you considering?

I am hesitant to mention it because I'm aware that the "research" type of info is restricted for certain members but I will build my own motor from scratch (ordering the custom designed pieces to a CNC machining business etc), making a lot of research and taking all the safety measures possible always. The propellant is a sugar-based one so not as dangerous and APCP for example. I hope I'm not breaking any rule or anything by saying this.

 

[sghioto]

An easy to make igniter is a .125 watt, 10 ohm carbon film resistor as the bridge wire covered with a some sugar propellant. No additional chemicals required. Fired using 12 volts.
Similar to this drawing:

 

[ThisGamerAlex]

An easy to make igniter is a .125 watt, 10 ohm carbon film resistor as the bridge wire covered with a some sugar propellant. No additional chemicals required. Fired using 12 volts.
Similar to this drawing:

View attachment 529343

So you are using the resistor to heat up and eventually ignite that bit of propellant around the resistor so that it starts the motor? I'm not sure at all about if I understood it right. Probably messed up with the function of the resistor there haha.

I do have to say it looks pretty easy and straight forward. Thanks!

 

[sghioto]

So you are using the resistor to heat up and eventually ignite that bit of propellant around the resistor so that it starts the motor?

Exactly.
12 volts connected to a 10 ohm resistor draws 1.2 amps but the dissipation is 14.4 watts. The resistor will heat up in less then a second to ignite the sugar propellant pyrogen.

 

[waltr]

That would work. 14W in an 1/8W small resistor will get very hot.
If not then use 4 turns of 30-36gauge Nichrome wire instead of resistor.

Do make some then ground test with the battery and leads you will use to launch. Then you'll know for sure.

Ematches can be make with very thin nichrome wire. I use 40 gauge to make ignites to airstart composite motors from an Eggtime Quark on 2S 300mA-Hr LiPo. The Eggtimer Apogee will do the same with a 1S LiPo. Again build some and ground test.

Use the method in link but only do 2 turn of nichrome instead of four turns. Link: http://www.jacobsrocketry.com/aer/homemade_wire-wound_igniters.htm

 

[ThisGamerAlex]

Thanks for the fast replies and useful info about this! Really helped me out.

 

[tsmith1315]

Do you know if something of the circuit he presents would need to change in order to use a larger length for the wire? So that I can fire it from a safer distance.

No change needed. Be sure the wire size you choose can handle the current for that length of run- from the controller to pad and back to the controller would be 200 feet.

As an example, I use a 100 foot outdoor extension cord rated for 15A, because I already had one. Standard AC outlet jacks repurposed at the controller and pad to plug it into, which makes it easy to replace or exchange for a different length.

 

[Voyager1]

Nice idea. You could just wrap and fold the leads rather than soldering.

 

[StuartL_UK]

One of the easiest ways of solving the long wire problem is to use an automotive relay at the pad end as the switch. A "relay" (sometimes incorrectly called a solenoid) has two key components in one casing:

1. A switch, often capable of switching very high currents.
2. An electromagnetic solenoid, when current passes through this solenoid coil the switch is turned on.

This means that you can wire the switch in at the pad end as if you were stood next to the pad (not advised ) and power the solenoid from the real switch at the end of the long wire.

Automotive relays are a great source for this for three key reasons:

• Demand is high, hence they're cheap and available *everywhere*
• They are 12v, but tolerant of a wide variety of voltages (because car circuits are very rarely at 12v)
• The pinout is identical for every single one of them, making it easy to wire them up

All automotive relays will have at least four pins numbered 30, 85, 86 and 87. If you have a five pin relay the fifth pin would be 87a and this pin should be unused (unconnected).

Pins 85 and 86 are your solenoid coil. Pins 30 and 87 are the switch.

While the following seems daunting, it's not as bad as it seems and gives you the ability to run *very long* (or cheap/underspecced ) wires without sacrificing ignition performance. To those reading this retrospectively: This design is OK for individual use, but you'd want more safety features if you were making a club launcher.

The simplest way to connect the automotive relay is as follows:

1. Get a switch, preferably a key switch or other isolation switch that you can install at the pad end. This acts as your master isolation switch and is how you make everything safe while people are putting rockets on a pad. Connect one side of this switch to your battery + terminal and the other to the relay pin '30'.
2. Connect one end of your long wire so that one core is connected to pin 30 and the other is connected to pin 85.
3. Connect a switch to the other end of your long wire.
4. Connect one end of your igniter wire so that one core is connected to pin 87 and the other is connected to pin 86.
5. Connect the igniter clips to the other end of the igniter wire.
6. Connect the battery - terminal to pin 86 on the relay.

With the master isolation switch 'off' the battery is disconnected from the circuit and everything is 'safe'. With the master isolation switch 'on' positive power is applied to pin 30 (one side of the relay switch) and to the long wire that goes into your hand. Negative power is connected to the igniter and the 'bottom' of the relay solenoid coil. No current flows because a) the switch in your hand is 'off', so nothing can flow through the relay solenoid coil and b) the relay solenoid coil is de-energised, so the relay switch is off and nothing can flow through the igniter.

When you connect the switch in your hand two things happen almost immediately:

1. Current flows through the long wire, back to the relay solenoid coil and back to the battery. This energises the coil and immediately...
2. The relay switch is turned on. This allows the battery to provide current to the igniter.

Because the automotive relays are designed to work near 12v your best choice of power source is probably a fully charged 3S LiPo battery. Fully charged these put out approximately 12.6v, half discharged they put out about 11.1v and fully discharged they put out about 9.6v. LiPo batteries are much smaller and lighter than lead acid (car/motorcycle) batteries and are readily available from a very large number of online sources. If you are unfamiliar with LiPo batteries then PLEASE take some time to learn how to charge, discharge, store and use them safely. They can be a serious fire risk is misused.

 

[sghioto]

Here's a modified electrical diagram for the description above from StuartL_UK.

​

​

 

[StuartL_UK]

Here's a modified electrical diagram for the description above from StuartL_UK.

View attachment 529610​

​

Thanks for the enhancement @sghioto . My only concern with that diagram is that it pulls the igniter high immediately, the power for the continuity test is 'north' of the arming switch. This could mean that if someone has connected their own ignition circuitry south of this (e.g. they're using a timed ignition circuit to trigger multiple motors with different pressurisation curves) that circuit could be triggered immediately upon connection. I'd much rather have that continuity test 'south' of the arming switch so that the worst case scenario only occurs when that switch is flipped, not when someone connects the ignition.

 

[Handeman]

Thanks for the enhancement @sghioto . My only concern with that diagram is that it pulls the igniter high immediately, the power for the continuity test is 'north' of the arming switch. This could mean that if someone has connected their own ignition circuitry south of this (e.g. they're using a timed ignition circuit to trigger multiple motors with different pressurisation curves) that circuit could be triggered immediately upon connection. I'd much rather have that continuity test 'south' of the arming switch so that the worst case scenario only occurs when that switch is flipped, not when someone connects the ignition.

I'm not sure what you mean by pulling the igniter high? When connected, the 12V drop would be divided between the 470 ohm resister, the LED and the igniter. Assuming a 12 volt source and a 1 ohm resistance in the igniter and 20 mA current with the 470 ohm resister and LED, the high side voltage on the ignter at that current level would be about 0.021 volts. That is still a low.

 

[StuartL_UK]

I'm not sure what you mean by pulling the igniter high? When connected, the 12V drop would be divided between the 470 ohm resister, the LED and the igniter. Assuming a 12 volt source and a 1 ohm resistance in the igniter and 20 mA current with the 470 ohm resister and LED, the high side voltage on the ignter at that current level would be about 0.021 volts. That is still a low.

On the assumption that only an igniter is ever connected there this is a safe approach, but if there was a circuit connected there instead of an igniter (for example the gate of a MOSFET or a digital input to a timing circuit) the leakage from resistor and LED could feasibly be high enough to trigger that circuit.

I'm not saying it's likely, it's just a risk that would need to be mitigated with some degree of control of what's being connected there. Even if you were to make the change I've recommended, should someone connect that kind of circuit it will still trigger when the arming switch is closed, which is hardly 'safe'

 

[StuartL_UK]

Clarification: By the last sentence I mean that using any kind of circuit connected to a launch controller this way is unsafe, not the design that @sghioto proposes.

 

[sghioto]

The reason I like to connect the LED that way is to confirm continuity before the system is armed. True an additional circuit not designed to certain parameters connected to the igniter leads could be an issue. I have done something just like that a few times. We used the igniter output to control another relay about 250 ft down range from the main field relay box. This auxiliary unit had it's own battery for the igniter but the relay coil was driven directly from the 12 volts from the main box which required 120 ma to activate so the 15 ma through the LED circuit was not a problem.

 

[ThisGamerAlex]

Sorry for answering a bit late! Even though I don't understand much about electronics, the design that @StuartL_UK proposed seems like a nice solution that also doesn't involve much difficult thing. I'll ask for help to a university teacher I know that does all sorts of electronic things at home, so that with his help I'll probably be able to build it.

Another thing: if I understood correctly, the diagram that @sghioto uploaded is the diagram for the design of Stuart but with some changes or is it literally the same?

Sorry for my lack of knowledge on the subject, it seems a bit hard to me but I try my best to learn it haha.

Thanks for your help, hae a great day.
~Alex

 

[sghioto]

Correct the schematic is mostly the same except for the connection of R2. I prefer it as shown connected to the junction of F1 and Sw3. StuartL_UK prefers it connected to the right side of Sw3 at the junction of Sw3 and R1. It's your choice. If your not going to be connecting anything other then an igniter to the ignitor leads then either way should be fine

 

[ThisGamerAlex]

I'm just planning to connect an igniter, so there shouldn't be any problem then. One question about this: depending on the igniter I use, could it be a problem? I ask this because I'll probably need to craft them myself as I can't find any on Spain and they can't ship them internacionally.

 

[sghioto]

I don't see a problem as long as they are constructed according to the suggestions given here.

 

[ThisGamerAlex]

Perfect then. Thanks a lot for the help!

 

[waltr]

I would mod the circuit slightly.
I also don't like the continuity LED always connected and some current flowing while connecting the igniter.
The change I would do is add a button switch in series with the LED. Then igniter clips are DEAD while connecting. Step away from rocket and push the continuity button to check connection.

 

[waltr]

I'm just planning to connect an igniter, so there shouldn't be any problem then. One question about this: depending on the igniter I use, could it be a problem? I ask this because I'll probably need to craft them myself as I can't find any on Spain and they can't ship them internacionally.

There could be an issue if your igniters only require a very low current, Ematches or Flash bulbs.
If you make the ignites (as I posted in your other threads) with 30-36 gauge nichrome then this launch circuit will not ignite them will a continuity check.

But Always Test before loading into a motor.

 

[sghioto]

Ematches and flash bulbs still require much more current then the LED and resistor can provide. The resistors (R1 and R2) can be increased to 1K ohm, that will reduce the current to appx 10ma. If igniters are firing at 20ma or less they are way to sensitive.

 

[waltr]

Yep, probably ok at 10mA BUT always doubt and then Test.

 

[StuartL_UK]

The change I would do is add a button switch in series with the LED. Then igniter clips are DEAD while connecting. Step away from rocket and push the continuity button to check connection.

I like this as the best of both worlds.

 

[sghioto]

Added optional momentary switch to continuity indicator in post #13 for those concerned.
The standard way of connecting igniter leads is #1: verify the Arm indicator is not ON
#2: short igniter leads together. Verify no "sparking" and if the continuity indicator lights up then it's safe to connect leads to the igniter.

 

[ThisGamerAlex]

I would mod the circuit slightly.
I also don't like the continuity LED always connected and some current flowing while connecting the igniter.
The change I would do is add a button switch in series with the LED. Then igniter clips are DEAD while connecting. Step away from rocket and push the continuity button to check connection.

I'll for sure try to add that into the circuit then!

There could be an issue if your igniters only require a very low current, Ematches or Flash bulbs.
If you make the ignites (as I posted in your other threads) with 30-36 gauge nichrome then this launch circuit will not ignite them will a continuity check.

But Always Test before loading into a motor.

Perfect, I'll have that in mind but for sure, always doubt first and test.
I still haven't decided what kind of igniters I'll be making, the ones you guys suggested or ones from R. Nakka. I'll take a look at them again and maybe he says how much current they need.

Ematches and flash bulbs still require much more current then the LED and resistor can provide. The resistors (R1 and R2) can be increased to 1K ohm, that will reduce the current to appx 10ma. If igniters are firing at 20ma or less they are way to sensitive.

Should I increase the resistence of R1 and R2 to 1K ohm from the start then to be on the safer side?

Thanks for your help and dedication