A 2-Stage Electronic Model Rocket (With 3-D Printed Parts!)

Hello Everyone! Have you ever wondered what the limits were to what a simple model rocket could do? Many moons ago I wondered the same thing and after some trial and error I believe that the limits and complexity you can add to your run of the mill model rocket can be rather simple and cheap with the right mindset!

Now it is fairly well known that model rocket engines come in all shapes and sizes, of which will get you only so high. So Estes and a few other model rocket producers decided to make engines that could ignite ones behind it. Technically, this makes it a "2-stage" model rocket, meaning when the lowest engine is burnt out it ignites one above it to provide more thrust and thus a higher final height (apogee). I have trifled with such multiple stage rockets and I felt the whole set-up was lacking the feel of a real rocket. So I opted to think of something better!

What I needed was a system that would bring out the rocket engineer in myself. After some thought and help from the internet I determined that an electronic control system would be the best way to achieve true inter-stage independence, not to mention it would be much more reliable then a fuse system or what Estes had done previously. Along with some handmade (can also be 3-D printed) parts and traditional model rocket parts it became possible to create a multiple stage rocket that could reach unprecedented heights!

The result was control system that uses a timer, two power supplies, a reed switch, and a MOSFET to ignite a quest low current rocket engine igniter. In the following Instructable I will explain the design and construction behind this exciting new way to launch model rockets!

(A SMALL DISCLAIMER) I have not yet had the chance to print out my 3-D printed parts, not to mention the weather in my hometown has been rainy and/or windy for the past few days, so in the next week or two I shall have a video of my rocket launching! Thanks for your patience!

Step 1: The Vision!

Back in high school, I had envisioned a model rocket that could soar to great heights, separate, and then blast off even higher, so I opted to try my first really challenging electronics project.

The first version was simple but also rather imprecise as the whole project ended in flames (literally). I started off with the idea that I wanted to use an Arduino micro-controller to act as a programmable timer to guide the 1st stage launcher and the eventual 2nd stage ignition. I settled on the use of a relay to activate a 9v power supply to an igniter. After testing the relay on a breadboard, I then jumped to making a perfboard for the relay and expanded upon it by adding a safety switch, an LED to indicate that the safety switch has been thrown, and a buzzer to led the 1st stage operator know when to fire off the 1st stage igniters.

The perfboard turned out alright, but when I went to build the rocket and went to fire it, the resulting vibrations from the 1st stage engines vibrated the relay past its tolerances and the small switch inside of the relay closed and proceeded to fire the second stage engines almost immediately. The result was a spectacular collision of stages and the lower part of the rocket caught on fire, so I resolved to a new way to build the rocket, and thus the second version was built.

Step 2: Supplies

Step 3: Nosecone Electronics

The electronics for this project are fairly simple, and I will break down my train of thought towards how I developed this particular system, and will thoroughly explain how and why I used each component.

In the simplest terms, it is a circuit that takes a reed switch signal and operates a timer that has a safety switch which, after a pre-programmed amount of time, opens up a path in the MOSFET to the capacitor which ignites the second stage engines.

In more elaborated terms!
(1) A reed switch is connected to a magnet on the rocket launching plate and sends input signals to the Arduino to indicate if the rocket has left the launch pad.
(2) The Arduino reads the input from the reed switch and will turn a small LED on or off on the board itself to indicate whether the magnet is indeed on the switch. This allows you to check the positioning of the rocket as it sits on the launch pad so that the lack of a good contact will not cause the engines to ignite in your face!
(3) A small safety switch activates the final program in which the removal of the magnet from the safety switch (which occurs when the 1st stage engines lift off) triggers a timer that sets off the second stage engines approx. 1.7 seconds after the 1st stage engines have fired and died out.

Disclaimer: One could also use a piezo element to sense the activation of the 1st stage engines in place of the reed switch. It would be easy to do but the program would have to be slightly more complex as it would have to take an initial reading of the vibrations coming from the rocket and would have to somehow keep the timer engaged for the duration (approx. two seconds) of flight before the second stage fires. Otherwise, the timer could reset in flight and the staging could end not so favorably.

Construction
The construction of the circuit perfboard is fairly straightforward and should only take a few hours at most.

(1) First, you are going to want to construct the MOSFET power control. The package it arrives in contains all the components you'll need and you simply need to solder the components to their respective via's.

(1.5) The Arduino should come ready as is when you receive it, so do not worry about doing anything to it (besides programming it of course!)

(2) The Arduino power supply is provided by two CR2032 button cell batteries. As long as they are fully charged then they should provide a stable power supply. However, as fate would have it, some of my space button cells are not all at 6 volts and I had to add an extra button cell to get the Arduino to work properly. Concerning the actual construction it's simple; the battery holders are soldered together with a wire in between the anode and cathode. BUT there is something to be aware of: if you buy the battery holders from Radioshack like I do, then the polarity marked on the holders is wrong (or at least it is for this project). This is because the batteries go in the holder but are not seated properly, making them prone to fall out at the slightest bump (and this will obviously not suit well for a vibration-plenty environment). Just pretend positive is negative and vice versa, and for further protection from vibration, I took some electrical tape and wrapped it tightly and individually around each holder.

(3) The reed switch assembly is just the reed switch soldered into a perfboard with one pole being wired red (representing that it goes to the +5V pin), and the other pole having a 10k resistor and green wire soldered to it (representing that the wire goes to digital pin 7). The open end of the resistor gets a black wire soldered to it (representing that it goes to the GND pin).

(4) The Arduino socket/perfboard is the hardest part but should be fairly simple. First, take the female headers and cut them to size, with two rows of 15 pins. Then, solder them to a perfboard with a width of 5 via's. Directly above the top of the socket, leave yourself maybe 3 via's distance. Solder the SPDT switch to the perfboard, then on one of the throws of the switch solder a 10k resistor to the board. THEN, above that, place the capacitor screw terminals and solder them as closely to the switch as possible. After those components have been placed, all that is left to solder is the wires, yay!

(5) Concerning the tangle of wires, just break it down by component subgroups and you should have an easy time managing it all. First, you are going to want to red wire the positive side of the button cell power supply to the VIN pin, followed by black wiring the negative side of the supply to the ground pin that is next to the VIN pin. Next up is the screw terminals for the CAP. The positive side is red wired to the MOSFET board on the terminal marked +, and then the negative side is black wired to the the ground pin on the Arduino. The MOSFET has its - terminal wired to the ground pin on the Arduino and the C terminal wired to digital pin 5. The switch has its pole wired to the +5V pin and the throw has the resistor and a wire going to the digital 8 pin, with the end of the resistor getting wired to the GND Pin.

That's it! The main board is done! Nice Job!

Step 4: Nosecone Structure

The nosecone is the section that contains all of the electronic control systems for the rocket. It has a 3-D printed mount for all of the various parts.

First off, you're going to want to crack open your Dremel tool case and take a drill bit to the little flange on the bottom of the cone. Drill out a little hole which you can use to anchor the upper line to the parachute. Otherwise, when the ejection charges go off, the nosecone (with all the delicate and expensive electronics) will go flying down to the ground, while the rest of the rocket floats safely down to the ground!

Next up is the opening for the electronics mount. It has to be about 4cm wide and 3cm tall in order for the mount to fit in. You don't have to cut it the exact way I did, but the way I did it works perfectly fine in any case. Just take a Dremel tool cutting attachment and carefully cut the sides while keeping the cutout intact. (If you're wondering why I didn't just cut the whole bottom off, it's that when reattaching it to the top of the rocket the cut sides cause the cylindrical shape of the bottom to cave in and not attach properly. In the event you manage to get the whole nosecone on it may be harder to pull off and you then run the risk of the parachute not deploying because the nosecone is stuck on!)

Once that is done, then the nosecone is ready to have the mount inserted into it. But first, the mount has a few things to be done to it. The aft end of the mount has a small circular tab on the top that is the same diameter as the hole in the middle of the cutout. Take the cutout and put a dab of hot glue on it and glue it to the mount. Next, take a small magnet and glue it to the bottom of the nosecone. The bottom of the mount is designed to have space for whatever size magnet you choose. So just fill the entire hole with hot glue and insert the magnet to the depth that puts the other end of the mount flush with the nosecone. The glue will then harden and the magnet will be stuck at the right depth, ensuring that the mount fits perfectly in the nosecone every time!

To prepare the electronics for gluing to the mount, bend the wires and shape the whole package as shown in the picture. Then glue the upper mount to the capacitor, followed by gluing the lower mount to the battery pack. Once that is done, then the whole assembly can be inserted into the nosecone.

Step 5: Body Structure (Lower)

The lower structure of the rocket is mostly 3-D printed with a standard BT-80 body tube. The main parts are the body, the engine mount, the backblast retaining ring, and the tube coupler.

After the parts have been printed out . . .
(1) Take the BT-80 body tube and cut it roughly in half.
(2) Take the tube coupler and push it into one of sides of the body. Push it in until only about 4mm of it is showing at the top. Secure it into place by gluing it in.
(3) Take the main engine mount and push it into the side without the coupler until it is flush with the body. Glue that in as well.
(4) The last part is the retaining ring. This part is secured to the engine mount after the engines have been inserted with the use of a long metal bolt and nut.

Let me explain myself here!
I figure I might as well explain the reasoning behind my design of the engine mount. I decided upon the fact that a multiple engine mount would be difficult to make and would also be light. So I decided to make a 3-D print of one. It's a simple mount that has slots for the engines that won't allow them to move forward, and has holes to direct the ejection charges. Then there is a retaining ring that has a slightly smaller diameter than the engines to hold the engines in when the ejection charges ignite.

Disclaimer: The metal bolt used for the retaining ring is something I found in my house; you may also have to improvise or maybe take a trip to Home Depot!

Step 6: Body Structure (Upper)

The upper body of the rocket is a little bit different than the bottom, being that the electronics follow down to the bottom of this stage to serve their purposes. There is a standard motor mount that has holes on either side to accommodate the reed switch and the igniter screw terminals.

(1) The motor mount is straightforward; just follow the instructions in the package and match it up to roughly what is shown in the pictures and it will be more then adequate. Just glue it in and then your motor won't go anywhere!
(2) Take a Dremel tool and drill two holes: one large one for the screw terminals, and a small one for the reed switch wires.
(3) Take the reed switch and feed its super long wires through the hole and to the other end of the rocket.
(4) Solder a red and a black wire to the terminals on the housing and angle it in the hole so that the screws are still accessible. This is important because it will connect the igniter to the MOSFET while allowing you to remove the spent igniter post-flight and then replace it with a new one.
(5) Glue the screw terminals in place.
(6) Take both wire groups and twist them to ensure they look clean and stay out of the way of the parachute.
(7) Glue ends of wire groups so that they do not move around the tube.
(8) PRESTO you are done. This rocket is starting to REALLY take shape!

Step 7: 1st Stage Launcher Electronics

The first stage launcher consists of several switches and indicators to ensure proper and timely ignition of the 1st stage engines.
First, there is a main power switch which provides power to the whole assembly. Then, there is a key switch which is basically a safety key for when you are ready to launch the rocket. Lastly, there is a missile switch cover to protect the final ignition switch which will ignite the four 1st stage engines.

This schematic is much easier to follow and I hope it helps in the wiring of the launcher!

Step 8: 1st Stage Launcher

This step is pretty simple as it only involves the structure of the launcher. What I ended up doing was taking a pair of scissors to an old Sparkfun electronics box and cutting out the appropriate holes for the switches that I wanted to add. The box opens up fairly easily so you can have easy access to all of the internals and batteries.

Step 9: The Code

The programming for this project is fairly standard, it consists of . . .

(1) Lines for initializing which pins we are using and what they will be called
(2) Setting up variables for the two inputs
(3) Designating what each pin is; either a input or output
(4) Starting the loop off with a IF ELSE statement which blinks an LED to tell us if our reed switch has a good magnetic contact
(5) Followed by a multiple condition IF ELSE statement that checks both the safety switch and if the rocket has left the launch pad, as done by if the reed switch state is LOW
(6) If both inputs are in the correct states, then the Arduino waits a few milliseconds and then activates the MOSFET which triggers second stage ignition.

Step 10: 3-D Printed Parts Files

Here lies all of the CAD models that I designed and used in this Instructable. I hope you find them helpful, and if anyone happens to print these before I do, PLEASE let me know how well they work. Thanks :)

Step 11: Final Preparations for Launch and the Launching Pad

This Instructable was written mostly to help in the construction of the electonic systems and corresponding modifications to the body tube of a model rocket. As such I digressed and did not mention anything about FINS or PARACHUTES because they are a fairly standard and easy finishing touch to a rocket and they don't require in depth explanation. That, and the fact that there are probably plenty of websites that can better describe how to perform such tasks.

Once said menial tasks are done, this rocket is ready to fly. The last thing you need to build is a launching pad, or retrofit an already existing one. As the whole timer sequence is triggered by the rocket being removed from the presence of a magnet near it, one has to place the magnet on the launcher by the reed switch in order for this to work.

After the pad is done, install the engines, put fresh igniters on, power up, and let her fly!

Disclaimer: That is not my rocket firing in the picture, I picked a generic picture placeholder until I get the chance to fire my own off!

Introduction: A 2-Stage Electronic Model Rocket (With 3-D Printed Parts!)