For Christmas I'm making a model rocket launch pad for my nephew. I already have the pad printed out and it works great, but now I'm working on the controller.
Here's how it will work:
A key lock will turn on the power to the system. A physical key is inserted and turned.
The system is then armed with a big red switch.
Holding down a button starts a 10 second countdown on a 7 seg display, after which the fuse will be ignited.
Using a Nano to run the whole system, mainly for the 7seg display and the buzzer for various noises. It could probably be better done with discreet components, and not use a microcontroller, but I already have the nano, and I want to use it :P.
A few questions, as I'm newer to arduino and electronics in general:
I'm going to be powering the system with a 9v battery. Can I connect the battery directly to Nano, or should I build a voltage regulator?
The ignitors use resistance to fire off (I believe), but is it possible to send a low enough current through the ignitor to see if the curcuit is patent or not without triggering the ignitor? I would like this to be an indicator light on the control. I'll do some R&D (read Trial and Error) on this, but I won't bother if it's not even possible.
The ignitor will be directly connected to the 9v battery, I would like to use a transistor to trigger that circuit, if so, which one? Or should I use a relay (Rather not, seems like over kill to me, but I don't want to fry anything I don't want letting the magic blue smoke out)
Should never appear in the same sentence. If you have to ask the questions that you have then by definition you do not know how to build and program the rocket launcher safely.
Any and all suggestions are appreciated.
Buy or make him something that can cause less damage if/when it goes wrong.
Wouldn't you expect the hobby store to sell the product the OP wants to make ? It sounds like a "must -have product for the NOOB ROCKET ENTHUSIAST (now there's a title that should strike fear in your heart)
Yes, normally you can pass enough current through an igniter to light a LED, but not heat the match.
If you put the current limiting resistor and LED in series with the match, then the LED will light if the circuit is complete, then a switch across both the resistor and LED will allow ignition.
Growing up, I had a very large kit of model rockets, so these are not new to me (or my brother, who will be be in close supervision of the whole project with his son).
I have built my own launchers in the past, and am very comfortable with those mechanics/electronics. I had one the could launch 6 rockets at a time. Each was fired by it's own pushbutton. The basic circuit is no more than a battery, light bulb, a switch, ignitor, and a button in parallel.
What I am looking for is help integrating a Nano and other electronics for cosmetic purposes. The standard safety measures will be in place, plus some extras (the current passing across the ignitor for instance, allows for the user to discern if the misfire is a broken circuit or a slowburning motor. Increases range safety).
As to the thread title, It was meant to raise of bit of humor. I spent too many years in EMS to put anybody in danger through negligence, hence why I'm asking questions to solve my problems.
Wouldn't you expect the hobby store to sell the product the OP wants to make ? It sounds like a "must -have product for the NOOB ROCKET ENTHUSIAST (now there's a title that should strike fear in your heart)
That's not the point of the project. As I posted above, I have years of experience (albeit some time ago) with these, and have made launchers before.
The point is an elegantly 3d printed box (which I'm working on now), printed modular Launch Pad (already printed), and some nice electronics to make it a good looking package.
My roommate almost shot down a small private plane with one. He went to Sepulveda Reservoir in the
San Fernando Valley , which a public park like Vasona Lake in L.G., CA. Anyway, because we live close to
Van Nuys airport we have become accustomed to tuning the sound of aircraft on approach. Eventually,
you don't even realize that you are tuning it out (mainly because 'tuning it out " means not thinking about it). What he forgot to take into account , was that the park was directly in the approach path for small
aircraft (cesnas etc). He was so engrossed in setting up his launcher that when he did his final countdown
and pushed the button, we watched the rocket shoot straight up. As he followed it up , he saw , to his
horror , that it was on a collision path with a small private plane. The ironic part was that it was heading
directly for the wing fueltank and the pilot reacted like a vietnam fighter pilot, experienced in dodging
RPGs. He tipped dipped his left wing sharply and the rocket went straight up where his right wing would have been without hitting the wing. He then leveled off and I presume proceeded to radio the tower that
there were hostile VC just outside the airstrip. My friend paniced and grabbed everything and ran to his
car , threw it in the trunk and got the hell out of Dodge and probably had to change his shorts when he
got home. We laughed about it but we realized how close he came to disaster.
That is kind of the point about a real countdown. You don't just shout "tennineeightseven" but there are specific things to be done or checked at each point of the countdown.
Ask NASA about the recent Orion launch that was delayed because of a private boat in the missile range area. There are specific points in the countdown where you ask the range officer "Is the range clear?"
Pilots call these 'checklists'. Turning the fuel switch on is one item that must be done before takeoff, not after.
Addressing the original question: how do you stop a countdown in progress? This needs to be really obvious on the box so that anyone can shut it off after they ask "What does this button do?" while your back is turned.
raschemmel:
My roommate almost shot down a small private plane with one. He went to Sepulveda Reservoir in the
San Fernando Valley , which a public park like Vasona Lake in L.G., CA. Anyway, because we live close to
Van Nuys airport we have become accustomed to tuning the sound of aircraft on approach. Eventually,
you don't even realize that you are tuning it out (mainly because 'tuning it out " means not thinking about it). What he forgot to take into account , was that the park was directly in the approach path for small
aircraft (cesnas etc). He was so engrossed in setting up his launcher that when he did his final countdown
and pushed the button, we watched the rocket shoot straight up. As he followed it up , he saw , to his
horror , that it was on a collision path with a small private plane. The ironic part was that it was heading
directly for the wing fueltank and the pilot reacted like a vietnam fighter pilot, experienced in dodging
RPGs. He tipped dipped his left wing sharply and the rocket went straight up where his right wing would have been without hitting the wing. He then leveled off and I presume proceeded to radio the tower that
there were hostile VC just outside the airstrip. My friend paniced and grabbed everything and ran to his
car , threw it in the trunk and got the hell out of Dodge and probably had to change his shorts when he
got home. We laughed about it but we realized how close he came to disaster.
That's the type of negligence I was referring to. There is a set of checklists you must go through to ensure safety, and making sure the range is clear is one of them.
the igniter should be a piece of nichrome wire or some very thin wire.
you should be able to put in a few ma without any heating at all. test the resistance with your multi meter.
if you use a 10k resistor and connect the other wire to an ADC pin on the arduino, you will get some sort of reading.
you can then use that to light an LED.
a 10k resistor will limit the current to less than a ma, so, unless the wire is very thin, there should be no possibility of heating.
if you pulse out the value from a digital output you can drop the available power at the wire to something very insignificant.
Well, as the entire lot of Nano's I bought were DOA (Sainsmart knockoffs), it'll have to be the old standard launcher design, but with the same nice custom box though. I'll post up some pics when I'm done.
Well, as the entire lot of Nano's I bought were DOA (Sainsmart knockoffs)
Are you sure ? I've bought lot's of their stuff and never had a problem. How did you test them ?
I reread this thread and could find no statement from you that you have ever used a Nano before. Do you
have experience with arduinos , specifically Nano ?If so, what experience, and with what uCs ? Why are you
so quick to assume they are DOA. Sainsmart doesn't have a reputation of shipping dead product.
Marmotjr:
Well, as the entire lot of Nano's I bought were DOA (Sainsmart knockoffs), it'll have to be the old standard launcher design, but with the same nice custom box though. I'll post up some pics when I'm done.
I don't buy from Saindumb any more. I received a bunch of parts stuck in white packing foam, held in with packing tape. Not an antistatic bag or foam in sight. An emailed conversation with someone there who doesn't even know what ESD is, then the fact that everything I bought from them is damaged, I will not buy from them again.
Hobbyking is pretty good. I'm lucky enough to have a distribution point 5 miles from where I work, if they have it in the warehouse I can go pick up my order in a day or two.
My rocket launcher was a pin inserted to connect the circuit, four AA cells, an incandescent lamp, and a pushbutton that shorted the lamp. The lamp cut the current low enough not to heat the nichrome wire.
Were I building this, I'd wire it so the countdown timer only proceeds if you continue to hold the launch button. So that is your safety. That, and something like the pin on my original launcher, which was on a string around my neck.