New Homemade Launch Controller

[paparoof]

Sorry for my wordiness on this one, but I figure when safety of children is involved, more detail is better then not enough.

Okay here's the project: new homemade launch controller.

I'm not an electrician by any means, but I'm very logical and I certainly grasp the general concepts of DC power. I know what a resistor is and what a capacitor does, I just don't know how to do the math to figure out which ones to use.

So like any project, I gotta start with a list of problems I'm trying to solve:

I currently have and use a homemade controller.

Problem #1:
I ALWAYS have the kids take turns pushing the button cause they love it and it frees me up to hold the camera. the current launcher is too big for my kids little tiny hands.

Problem #2:
I'm convinced that the majority of launch failures I've had were due to weak power at the ignitor and I've had no failures since I began bringing my boat battery to launches. Of course, my current launch controller was designed for an internal battery, so I already had to muck it up in order to adapt it to an external battery. It has blinking status LED's with inline resistors, but that math was done by a Radio Shack clerk and it was done based on a 9v power source, so the LEDs don't behave properly on the 12v power source.

Problem #3:
I'm not sure if it correctly complies with the NAR safety code. There is no dedicated "removable saftey interlock". The wires that run out to the pad can be unplugged from the controller so we treat that as the "safety interlock". Before I connect the clips at to the ignitors, I turn around and say to my daughter "show me the wires" and she has to hold them up and show me that they are disconnected from the controller before I'll connect the clips to the ignitors. There are also two momentary push buttons ("arm" and "launch"). Both buttons must be pushed in order to launch (holding down the "arm" button makes the LEDs start blinking). I figured that would make it far less likely to fire accidentally. So I'm confident that our implementation is safe but like I said, I'm just not sure is sure it's officially compliant.


So main goals...

1. Designed for the kids to use; safe, small, easy (in that order).
   
2. 12v ignition.
   
3. NAR compliant.

BTW: the kids are 6 (girl) and 8 (boy). Both have a very solid grasp of the necessary concepts.

The idea so far:
So I started messing around in Visio this morning to come up with a new circuit design using a relay out at the pad to switch from the 9v in the small hand controller to 12v coming from the big boat battery that will be sitting in a wagon next to the launch pad.

The removable safety interlock in this case is a 1/4" stereo phone plug (like headphones USED to use back in the day). The plug will be worn on a lanyard around the neck of whoever is the official "launcher-person". This should help assure that it will always be disconnected immediately after the launch when the launcher wants to go run after the rocket, but finds their neck physically connected to the controller. All the conductors in the plug will be shorted to each other, so it just acts as a switch between the three conductors in the female jack.

Plug the plug into the jack and the LED begins blinking - I could add a buzzer there as well, but I'm not sure I want to annoy others that much. The controller has only one momentary launch button. Push the button and 9v are sent out to the relay which closes the 12V circuit to the ignitors and fires the rocket. I could still have two launch buttons but it's really unnecessary and might mean I have to use a bigger box than the small one I have planned for it now.

I apologize right away for my lack of knowledge in drawing circuits, I'm sure I broke all sorts of rules with proper symbols etc. but you should be able to get the general idea from this picture:

So now after all that, PLEASE ADVISE ME on whatever issues you see with this plan. Go ahead and tear it apart, I'm an adult - I can handle criticism pretty well.

And for all you electricians out there, the LED I bought is rated for 3v DC. with a 9V battery, what resistor should I put in front of it? should that resistor go on the + or - side of the LED or doesn't it matter?

 

[paparoof]

followup question:

Staring at the diagram, I see that when the phone jack is plugged in, there actually IS a closed circuit sending voltage out to the relay even before pushing the launch button. but the voltage is whatever's leftover after having passed through the LED. so with a resistor knocking it down to 3V for the LED, does that mean the voltage going out to the relay will not be enough to trip it until I DO push the launch button?

The coil on the relay I have is rated for 12vdc, but a brand new Duracell 9v trips it quite nicely. I suppose once the resistor is in place with the LED I could just test wire it and see if it will trip the relay, but I'd feel much more confident if someone who actually knows what they're talking about could confirm that this is or isn't something to worry about.

 

[bobkrech]

There's a few problems with your circuit.

1.) There's no power switch between the relay contacts and the battery.

2.) There's no continuity check.

3.) There's no fused relay buzzer or indicator light.

Attached is an example of a relay controller with just about every safety feature your would want. It's not the simplest one, but you can use a cheap 4 wire phone cord to connect the relay box to the controller. If your clever, you can reduce the number of conductors to 3 or even 2.

Bob

 

[paparoof]

Thanks for the reply Bob - gonna haveta stare at your diagram for a little while to see how it works.

Are the little zig-zags that say "1K" next to them resistors?

Is there no battery in the hand control unit at all?

 

[Micromeister]

The Idea behind the removable key is that this prevents anyone from rearming the controller while someone is at the launch pad. simply disconnecting a plug, doesn't cut it unless your going to take the plug and wire all the way to the pad with you.

The disconnect 'key" can be as simple as a plug and jack in line with the control circuit. I use this method on every system i've built over the years. Some use a 1/4" photo plug & panel jack ,but most use an 1/8" panel jack and a piece of salvaged 1/8" stainless launch rod as the plug.

You can add this jack/plug Safety disconnect to your circuit very easily, without much trouble at all

 

[DaveCombs]

Bob: If I may ask... Is the reason you can use phone wire because the control circuit is on the "low-current side" of the equation? Most people would suggest using 16 or even 14 gauge wire, because of its current-carrying capacity.

 

[paparoof]

MM: perhaps you didn't notice this paragraph - that's all in the plan. Being around the neck of the launcher is going to make is uncomfortable enough for that person when it's connected that it will only be connected when it HAS to be.

Or are you only saying that I should be the one holding the plug while I'm out at the pad connecting the clips to ignitors, then hand it back to the kid when we're ready for launch?

The removable safety interlock in this case is a 1/4" stereo phone plug (like headphones USED to use back in the day). The plug will be worn on a lanyard around the neck of whoever is the official "launcher-person". This should help assure that it will always be disconnected immediately after the launch when the launcher wants to go run after the rocket, but finds their neck physically connected to the controller. All the conductors in the plug will be shorted to each other, so it just acts as a switch between the three conductors in the female jack.

 

[DaveCombs]

Or are you only saying that I should be the one holding the plug while I'm out at the pad connecting the clips to ignitors, then hand it back to the kid when we're ready for launch?

That's how the current Estes "Electron Beam" controller works; the safety "key" is tethered to a launch rod cap for exactly that reason. You have the key in hand while you walk to the pad, place the cap on the rod so you don't put your eye out irate:, and the key's away from the controller so they can press the button all day long (figuratively) and you're safe.

 

[paparoof]

I just checked the NAR website and it doesn't even say "removable" next to "safety interlock". Huh.

I'm gonna make it removable anyway...

So how bout them resistor values? Anyone wanna take a crack at that?

How about explaining the continuity check to me a little better? I'm staring and staring at Bob's diagram and it's just not clicking in my head.

 

[Micromeister]

The Launch officer "Can" be the one holding the Key. but the Idea is to have the key AT the Pad. so there is No way for the controller to be activated or energized while anyone is loading their rockets.

and to answer Daves question:
Your correct as the contoller ciircuit in this application is only closing a relay. it can be almost any conductor as all as it only as to carry enough current to energize the relay coil.
That's one of the reasons there is no "continuity buzzer" or lamp as it might be just enough bypass current to close the coil. There are ways around this problem and a continuity lamp can be installed on the Launcher side to confirm igniter continuity without tripping the relay.
Here's a diagram I've used for years on my Relay launchers.

 

[Micromeister]

Drat wrong dwg! try again

 

[shreadvector]

Current Estes controllers (for the last several years!) have not had the key attached to the cap. The key is not spring loaded (rubber grommet-like "spring") and it is tied to the controller body. It cannot be left in accidentally since it ejects itself.

If your key is not self-ejecting, it should be able to be removed and put in your pocket as you approach the launch pad to prevent anyone from energizing the circuit.

N.F.P.A. 1122 says removeable interlock.

That's how the current Estes "Electron Beam" controller works; the safety "key" is tethered to a launch rod cap for exactly that reason. You have the key in hand while you walk to the pad, place the cap on the rod so you don't put your eye out irate:, and the key's away from the controller so they can press the button all day long (figuratively) and you're safe.

 

[DaveCombs]

I just checked the NAR website and it doesn't even say "removable" next to "safety interlock". Huh.

I'm gonna make it removable anyway...

So how bout them resistor values? Anyone wanna take a crack at that?

How about explaining the continuity check to me a little better? I'm staring and staring at Bob's diagram and it's just not clicking in my head.

1. The "removable" interlock: don't go there... (You can't imagine how many arguments have been started over this one.)

2. I'd love a complete parts list from you, Bob!

3. Micro: Thanks for clearing that up. I'm also no whiz at DC electronics, but I "get it" for the most part. I just need an occasional clarification.

 

[DaveCombs]

Current Estes controllers (for the last several years!) have not had the key attached to the cap.

Fair enough; 2 of my sons got Estes RTF sets maybe 4 or 5 years ago, and the keys in them are as I described.

 

[bobkrech]

Thanks for the reply Bob - gonna haveta stare at your diagram for a little while to see how it works.

Are the little zig-zags that say "1K" next to them resistors?

Is there no battery in the hand control unit at all?

A 1000 ohm resistor in series with a led limits the current flow to ~10 ma with a 12 volt lead acid battery.

The current required to pull in most 40 amp automotive relays is ~ 100 ma.

The total current for the hand unit is ~130 ma which is easily carried by 4 wire modular phone cord over a great distance eliminating the need for a second battery.

The high current flow in the circuit is limited by the 20 amp fuse which could be increased to 40 amps if you use a 40 amp automotive relay (which are actually good to over 100 amps.)

Bob

 

[bobkrech]

1. The "removable" interlock: don't go there... (You can't imagine how many arguments have been started over this one.)

2. I'd love a complete parts list from you, Bob!

3. Micro: Thanks for clearing that up. I'm also no whiz at DC electronics, but I "get it" for the most part. I just need an occasional clarification.

That's a plan I pulled off the web years ago as an illustration of a well made controller. I dont have a parts list for it.

Here another one from https://www.info-central.org/support_relaylauncher.shtml that has a complete parts list.

Bob

 

[DaveCombs]

Got it. Thanks again, Bob!

 

[jadebox]

I just checked the NAR website and it doesn't even say "removable" next to "safety interlock". Huh.

They used to say "removable safety interlock." But, if you think about it, you'll realize that doesn't make sense. The safety interlock should always be part of the controller, not removable. It may be implemented using a key or plug which is removed, but the safety interlock itself is still a part of the controller's design.

-- Roger

(Sorry, Dave.)

 

[RimfireJim]

There's a few problems with your circuit.

1.) There's no power switch between the relay contacts and the battery.

2.) There's no continuity check.

3.) There's no fused relay buzzer or indicator light.

Attached is an example of a relay controller with just about every safety feature your would want. It's not the simplest one, but you can use a cheap 4 wire phone cord to connect the relay box to the controller. If your clever, you can reduce the number of conductors to 3 or even 2.

Bob

A nice feature of this circuit is the "Test" switch, which allows you to perform a test to see if the relay contacts are welded closed before connecting an igniter. Not fully fail-safe, but better than most, which don't have a provision for this at all.
Radio Shack's 4-pin microphone cord connectors work well for connecting the 4-conductor phone cable to either the control unit or the pad unit. I put one on each end, but that is not really needed and runs the risk of a bad connection compared to being hardwired. The connectors are sturdy enough for reasonable hobby use, and have a threaded locking ring.
The 4-conductor phone cable comes in 50 ft. coils at Home Depot and the like. I just used the whole coil, as I like standing back as far as I can for a better view of the launch.

 

[mike_bar]

Attached is an example of a relay controller with just about every safety feature your would want. [Snip]
Bob

Bob's attachment:
https://www.rocketryforum.com/attachment.php?attachmentid=41308&d=1183483911


Hi Bob,

I like all the safety features in that relay controller.

Two questions:

1. What is below the "Warn LED" on the Pad Unit circuit? Is that a small battery?


2. What happens if the relay contacts are welded close AND the "Test" button is pressed AFTER the igniter is installed? Will this launch the rocket? This may be a dumb question but I have seen dumb things happen.\

Thanks in advance.

Mike

 

[DaveCombs]

1. What is below the "Warn LED" on the Pad Unit circuit? Is that a small battery?

It's a ground (the inverted broken arrowhead thing).

 

[mike_bar]

Thanks Dave.

 

[paparoof]

I appreciate the responses on this. I don't want to argue whether something is a good idea or not. Frankly, I think every suggestion I've seen so far is valid and makes good sense. Of course I can't implement them all or I lose the "small" and "easy" parts of goal number 1.

To that end, I'd like to separate out the "shoulds" from the "musts" here. Once I have adhered to those that MUST be followed, I will make my own judgment about the "shoulds" that I'm going to add in to the system.

The "removable" thing is a good example. I referred to NAR's rules, ShreadVector is referring to a totally different body: NFPA. I think everyone here will agree that NAR's rules go in the "must" category. In which category do I put NFPA's rules?

What about all the other aspects that have been mentioned? Should or must?
continuity check
power switch between the relay contacts and the battery
fuses
buzzers

 

[mike_bar]

I appreciate the responses on this. I don't want to argue whether something is a good idea or not. Frankly, I think every suggestion I've seen so far is valid and makes good sense. Of course I can't implement them all or I lose the "small" and "easy" parts of goal number 1. [Snip]

This is a great project and I am sure you will succeed at your implementation.

Most all of the suggesting fall in to your "should have" category since a relay system is not required by the NAR or NFPA.

I would like to make one small note (opinion).

A relay system is not necessarily small or easy to build (or use?).

A simple, small, hand-held six or twelve-volt system can be fashioned quite easily in a customized manner for use by small children.

There are plans for a low-cost six-volt system on the NAR website. This simple system could be 'jazzed' with more buzzers, buttons and LEDs.

I created a 12-volt system with plans found on the Internet. A 12-volt lantern battery, extension cords, a 35-mm film canister with a push-button and installed. The safety interlock is an extension cord socket about 3-feet from the launch controller (film canister). To safe the system, I unplug the launch controller and take it with me to the launch pad. To disconnect power, I can unplug another extension cord socket.

Some people will argue the modified extension cords are unsafe in the home. Locking the system in a small toolbox would increase safety for homes with small children.

I look forward to reading more suggestions regarding an efficient relay based launch controller system.

Respectfully submitted.

Mike

 

[paparoof]

Thanks Mike. That helps.

A relay system is not necessarily small or easy to build (or use?)

Well, the circuit design I showed above does work and is easy. Bob's diagram looks far safer, but I need help understanding it before I can even decide if I will implement some of those features.

I don't want to squelch the suggestions, KEEP 'EM COMING. Just please explain them in a bit more detail.

I still need to know if the voltage flowing through the LED in my diagram is something to worry about or not.

I'd also like a true continuity check in my system, but I need help understanding how you figure out how much voltage you can send through the igniter (to prove continuity) without actually firing the igniter.

This seems like a very wide ranging subject with a LOT of opinion. Am I trying to ask too many questions at the same time?

 

[Bullpup]

I built a box about 8 years ago from plans I found on the net. They no longer seem to be around and I don't have a copy unless I reverse engineer what I built. It used two relays in the pad box. One relay for continuity and one for launch. It used a buzzer inline with each relay so that if a relay welded shut it would not stop buzzing.

 

[eastvolt]

I still need to know if the voltage flowing through the LED in my diagram is something to worry about or not.

LEDs are not voltage devices. They are current devices and require an electrical current to operate. LEDs can be powered from a 1,000,000 volts without any damage whatsoever, as long as you have the appropriate limiting resistor.

An LED is a diode. Think of it as a device that only conducts electricity in one direction. Now when current flows through the LED, it causes a voltage drop to occur across the LED. This is known as the forward voltage of the LED. For a red LED, this is typically about 2.0 volts. Now, most LEDs will work with any current from about 5mA to 15mA. 15mA will keep it adequately bright especially in sunlit conditions.

Now if you have a 12V battery and 2V across the LED (Vfwd = 2V), then you have 10V to drop across the limiting resistor. So you want to size the resistor to allow 15mA of current to flow with 10V.

Using Ohm's Law: V=R*I or rewritten as R = V/I

R = 10V / 0.015A = 666 ohms. So any resistor around there will be fine. Standard 5% resistor value would be 680 ohms.

To properly connect the LED, the cathode needs to go to GND. This is typically the "shorter" lead on the LED. Basically, hook it up. If it doesn't work, its probably installed backwards. Also, installing backwards won't damage the LED.

I'd also like a true continuity check in my system, but I need help understanding how you figure out how much voltage you can send through the igniter (to prove continuity) without actually firing the igniter.

Again, this comes down to voltage and current and ohm's law. Now, first of all, I'd use an LED here, not an old fashioned bulb. Again, you have the LED and resistor in series. You know your source voltage (12V), your LED forward voltage (2V) and the amount of current you need to illuminate the LED 15mA.

Now, you solve the same way. Again, you get about 680 ohms for 15mA. And that 15mA will never ignite an igniter.

Of course, you'll need to investigate what the actual resistances are for the igniters you plan on using.

Hope this helps.

 

[paparoof]

EastVolt: thanks for going through that detail - that WILL help eventually. But I don't understand voltage and amperage as well as I need to to make proper use of your efforts.

I need to go read a book. I know volts and amps are not the same thing. I know when I stick my finger in the light socket it's not the volts that kill me, it's the amps. It's been a LONG time since I've had someone run me through an analogy on this - am I going too far back into electricity 101 to ask you to explain this part? Even a link to the right article at howstuffworks.com would be acceptable. I don't mean to make YOU teach me everything, but I need a little 101 before I can go beyond my simple diagram above. At least I know I'm smart enough to understand if I can find the right learning resource.

That said.... let me flail away at this anyway (and again I apologize for the day-1 questions here):
R=V/I (resistance = volts divided by... impedance? is that the right word?)

the hand controller will contain a 9v battery. the blinking LED I bought says it wants 3v.

so sticking those numbers into your equation, is this correct?

9v minus 3v means I need to drop the voltage by 6v. 6v divided by .015a = 400. So I need a 400-ohm resistor to correctly power the LED from a 9v battery?

 

[mike_bar]

I need to go read a book. I know volts and amps are not the same thing. [Snip]

am I going too far back into electricity 101 to ask you to explain this part?

This documents contains some "Electronics 101" and it actually applies to your project!

I hope this helps.


Model Rocket Launch Systems Guide
Contains a wealth of information. Photographs and clearly drawn schematics make it easily understood. The electrical theory of launch systems is explained and a number of special study problems are included. (18 pages)... EST 2811


Download documents here:
Estes Educator - Publications


Source website:
Estes Educator
https://www.esteseducator.com/

 

[paparoof]

OH DOOD.

That looks like something I will be able to understand and at first glance it appears to explain exactly what I'm getting stuck on. I see analogies and everything!

I am going to run away now, read that whole thing, then come back and re-read everyone's responses.

Thank you thank you thank you.