My IRL rocket command centre

[Agent86]

I've been learning electronics for a bit on an arduino kit. I wanted to make something a bit more practical, so I've been working on a safe electric launch system for model rockets. Excuse any circuit diagram errors or what have you.

Here is the whole setup:

The big white box is the launch controller, the little white box is the launchpad control box, exiting it is a couple of alligator clips connected to an igniter. The blue cable is just a standard network cable. I used standard RJ45 sockets for two reasons, one, I had them lying around, and two, with a crimping tool, you can make a cable any length you want. I also made sure to only use pins 3, 4, 5, and 6 on the sockets so that a digital telephone cable can be substituted for the CAT5 network cable, using socket reducers. The cable shown is just for show, when using the rig I use a 6m cable that I made up for extra safety.

These images shows the control panel, with the two green test LED's lit up. Basically, the first LED tells you if the cable is plugged into the launchpad correctly, the second LED tells you if the igniter is functioning. The idea of these extra circuits is that you can do a little troubleshooting before launch, and after a failed ignition attempt. There's nothing more dangerous than pressing the GO button, seeing nothing happen, then walking over to the rocket and dicking around with it to see what the problem is. This can tell you if your igniter hasn't gone off, or if it did go off and just didn't light the rocket, or of there is a cabling issue.

Shown here is a used igniter attached to the pad control box. It is just a pair of twisted solid core copper wires from a CAT5 cable, attached to a 10 Ohm resistor.

Here is the MS paint schematic I drew up for the box. My end design was slightly different, I think I used two 10 kOhm resistors instead of one 100K resistor, and I have toggle switches instead of momentary switches because I bought the wrong ones. The voltage to the LEDs is a guestimation, but since they neither blow the globe nor fire the igniter prematurely, I haven't needed to change them. It uses two 9V batteries in series to give 18V. When the go button is pushed, 18v passes through the 10 Ohm resistor in the igniter, causing it to glow red and then self destruct after about 3 seconds.

I've used it to reliably fire off about 10 small R-candy ignition charges, but yet to launch a rocket with it, as I live in an apartment and my upstairs neighbors would be upset if I poked a hole through their floor. I'm sharing this mostly to show off what I've learned, but also to share a bit of knowledge with anyone else who might be interested in amateur rocketry (as if there would be someone like that on the KSP forums...)

[indroth]

The voltage to the LEDs is a guestimation

What really matters for an LED is the current. LEDs need a minimum forward voltage and current to light up, but once they do the voltage drop across the LED remains roughly constant. This voltage is usually documented as the forward voltage drop in the LED data sheet. The data sheet will also tell you how much current should pass through the LED for normal operation. Given the forward voltage drop and current requirement, you can calculate what resistance you need quite easily.

R = (V_power - V_forward)/I

R : Resistance

V_power : Power supply voltage (batteries or whatever)

V_forward : Forward voltage drop across diode

I : Current through circuit

So for example assuming 2V forward voltage drop, 10mA current, 18V power, we have R = (18V - 2V)/10mA = 1.6 kOhms

[linkxsc]

Very well made, good job sir. I especially like the continuity feedback loops. Save many a "why didn't it fire, were the leads hooked up right" problems.

I also like the usage of RJ-45 as your cabling (using stuff thats readily available to get the job done) I might be worried in the future about the wiring surviving the 1.8amps for the couple seconds while the igniter runs however. RJ45 isn't the highest amperage rated cabling there is. You might consider doubling or tripling the gnd/18V lines. You've currently got 1gnd, 1-18V, and 2 signal LEDs, that should live 4 extra wires in the cable doing nothing. Add 2 of those to the 18V circuit, and 2 to the gnd to spread the amperage. Less risk of damage if you find later on that its having problems putting that much power down 1 tiny wire.

Advice on straighter hole drilling. My suggestion to you in the future if you continue down the path is to get a nail and a hammer and tap a little dot for the tip of the drill to rest in while starting the holes. Less drill walking around, and your holes end up straighter and more even. That or a center punch, can probably pick 1 up at your local hardware store. But hey, not hating on you or anything, I have about 80 project boxes with holes all over the place for LEDs and crap myself (took till about my 40th electrical wingding before I stopped using tupperware boxes/altoids tins and actually buying project enclosures that have the lines on the inside to help line up where you want things)

I'm not one heavy into the rocketry myself (I've stuck to RC planes because the local police don't get so upset about them) though I've got more than 1 RC plane capable of firing 2-4 rockets that it can carry. If you plan to go a little farther down the electrical path (maybe make a rocket that keeps itself vertical as long as possible via onboard electronics, or tries to hold an angled trajectory... or even more, the skys the limit) I can give you tips on a lot of that stuff if you need it.

[Agent86]

R = (V_power - V_forward)/I

Oh, that's really helpful. I didn't properly calculate the resistance requirements, I just used trial and error on a breadboard to come up with something that gave the results I was after. I've never really understood the correct way to apply that formula to my circuit until now. I'll use that method to calculate the correct requirements for my next box.

Very well made, good job sir. I especially like the continuity feedback loops. Save many a "why didn't it fire, were the leads hooked up right" problems.

I also like the usage of RJ-45 as your cabling (using stuff thats readily available to get the job done) I might be worried in the future about the wiring surviving the 1.8amps for the couple seconds while the igniter runs however. RJ45 isn't the highest amperage rated cabling there is. You might consider doubling or tripling the gnd/18V lines. You've currently got 1gnd, 1-18V, and 2 signal LEDs, that should live 4 extra wires in the cable doing nothing. Add 2 of those to the 18V circuit, and 2 to the gnd to spread the amperage. Less risk of damage if you find later on that its having problems putting that much power down 1 tiny wire.

Advice on straighter hole drilling. My suggestion to you in the future if you continue down the path is to get a nail and a hammer and tap a little dot for the tip of the drill to rest in while starting the holes. Less drill walking around, and your holes end up straighter and more even. That or a center punch, can probably pick 1 up at your local hardware store. But hey, not hating on you or anything, I have about 80 project boxes with holes all over the place for LEDs and crap myself (took till about my 40th electrical wingding before I stopped using tupperware boxes/altoids tins and actually buying project enclosures that have the lines on the inside to help line up where you want things)

I'm not one heavy into the rocketry myself (I've stuck to RC planes because the local police don't get so upset about them) though I've got more than 1 RC plane capable of firing 2-4 rockets that it can carry. If you plan to go a little farther down the electrical path (maybe make a rocket that keeps itself vertical as long as possible via onboard electronics, or tries to hold an angled trajectory... or even more, the skys the limit) I can give you tips on a lot of that stuff if you need it.

Thanks man, that's all really good advice. I'm really only using 18V because my 12V battery pack didn't fit into the enclosure. As for running 12V down the CAT5, I've used that cabling for 12V power supply to CCTV cameras, running 12V on a pair to cameras at about an amp each, so I was pretty confident it would handle my circuit. I wanted to use as few wires as possible, because I plan to add additional circuits to a later iteration using those spare pairs. I've got a few mini LED flashlights that I'll modify and attach to the launchpad I build, to light up the rocket on the pad like little spotlights, and I'll run them off a 12V power pack from the control box. The red LED on the control box is meant to be a low voltage warning light, but I haven't wired that up as I need some transistors, and I'd like to add a blinking red light on the pad control box to warn when the launch controller is connected, so that you'll know to use caution when approaching.

Once I'm happy with all of that, my next project is to turn my arduino into a flight computer to record altitude and deploy chutes, but that's a long way down the track.

[linkxsc]

I've got a few mini LED flashlights that I'll modify and attach to the launchpad I build, to light up the rocket on the pad like little spotlights, and I'll run them off a 12V power pack from the control box. The red LED on the control box is meant to be a low voltage warning light, but I haven't wired that up as I need some transistors, and I'd like to add a blinking red light on the pad control box to warn when the launch controller is connected, so that you'll know to use caution when approaching.

Cool

Once I'm happy with all of that, my next project is to turn my arduino into a flight computer to record altitude and deploy chutes, but that's a long way down the track.

Don't worry they're super easy to use, and it has one of the most helpful support forums I've been on. And on the note of altitude you can get a barometer board the size of a quarter for ~$10 and they're a dozen guides on setting them up. And at least going off the 1 that runs on my drone. It uses GPS/compass for its main positional info, but keeps accelerometer/gyro/barometer to keep a second "where it think's it is" without GPS. (you know, encase a cloud comes by jsut right and loses signal, it'll be smart enough to fly itself back to where I launched it from, pop out a chute and land without crashing)

The barometers are pretty accurate too. 1 I use is within .4m in altitude after calibrating it on the ground, though the drone never gets above about 100m (don't even think I'm supposed to have it that high) the barometer is rated to ~9000m. Don't think you'll be having any rockets hitting that altitude anytime soon. (if you do tell us, and film it, I'm sure we'd all enjoy)

[indroth]

Oh, that's really helpful. I didn't properly calculate the resistance requirements, I just used trial and error on a breadboard to come up with something that gave the results I was after. I've never really understood the correct way to apply that formula to my circuit until now. I'll use that method to calculate the correct requirements for my next box.

Just make sure you keep in mind that this just works for a simple circuit with a resistance and diode in series. For anything more complicated, I would suggest a review of Kirchoff's Laws and Ohm's Law.

Once I'm happy with all of that, my next project is to turn my arduino into a flight computer to record altitude and deploy chutes, but that's a long way down the track.

That's cool. Maybe you can try to trigger a Soyuz style soft-landing rocket if you get the altitude thing working well.

Don't worry they're super easy to use, and it has one of the most helpful support forums I've been on. And on the note of altitude you can get a barometer board the size of a quarter for ~$10 and they're a dozen guides on setting them up. And at least going off the 1 that runs on my drone. It uses GPS/compass for its main positional info, but keeps accelerometer/gyro/barometer to keep a second "where it think's it is" without GPS. (you know, encase a cloud comes by jsut right and loses signal, it'll be smart enough to fly itself back to where I launched it from, pop out a chute and land without crashing)

As an added bonus, you can get higher precision position data by combining sensor and GPS data.

[spaceman1999]

Is that "MAKE IT SO" a star trek refrence?

[linkxsc]

As an added bonus, you can get higher precision position data by combining sensor and GPS data.

Actually in all truth, the GPS chip has accuracy within a 35ft diameter sphere (I coulda bought a better 1, didn't was cheap) And as it compares notes between the 2 altitude values. If the barometer shows up within the vertical error of the GPS chip, it uses the barometer value. If it shows that its outside of the GPS altitude on the barometer, it sends me a little alarm to tell me that somethings may be wrong (hasn't happened ever though except right at startup while its still using the stored values of its last flight for calibration, then it runs calibration and it goes away.) Mainly its there encase we get a notable pressure change that would be throwing the barometer readings off from what their current altitude settings are.

Have been having thoughts of building some kind of laser rangefinder into it so it could have a 3rd setpoint for altitude since of checks, since well, the ground is the most dangerous to the health of the craft.

SO its been a couple days though, hows the box working, got any vids of launching?

[Agent86]

SO its been a couple days though, hows the box working, got any vids of launching?

I'm a pretty busy person, and it took me a week of nights to design and build the box, but I've tested a few igniters. No videos of them. I have one completed rocket, but I'm a little hesitant to static test it, because I'm fairly sure it's illegal to do so where I am. The pursuit of science must go on, though! I need to find a farm or secluded place to conduct a test firing, and when I do, I'll certainly record it and put it up.

I plan on doing a round of static tests to determine the ideal fuel ratio and nozzle structure to use, and hopefully can conduct a real launch with by the end of September. I probably won't add complex flight computers to my first launches until I can determine that science payload recovery can be done safely under chutes.

[K^2]

Is that "MAKE IT SO" a star trek refrence?

.

[Agent86]

SO its been a couple days though, hows the box working, got any vids of launching?

Just for you. And anyone else that cares to see. Not a launch, just an ignition test and showing off my motor.

https://vimeo.com/104169387