Introduction: Overkill Model Rocket Launch Pad!
A while ago I released an Instructables post about my ‘Overkill Model Rocket Launch Controller’ along with a YouTube video. I made it as part of a huge model rocket project where I am making everything as overkill as possible, in an attempt to learn as much as I possibly can about electronics, programming, 3D printing and other forms of making. The Instructables post was very popular and people seemed to like it, so I decided it was worth making one about my new overkill launch pad!
A typical model rocket launch pad consists of a rail which guides the rocket and a basic structure to hold it. But as I am trying to make things as overkill as possible, I knew I couldn’t just have a rail. After a lot of research I found a couple of model rocket launch pads that are similar to real launch pads, though they were made of wood and looked quite messy.
So I began brainstorming how I could make mine the most advanced and over complicated in the world. I decided that no idea was ‘too crazy’ or ‘impossible for a 16-year-old to achieve’, so any idea that was affordable was written down and created. I decided right from the start that I wanted to continue the badass theme that is seen on my rocket and controller, so a steel frame and aluminium plates was certainly the way to go.
But Eddy, what does the launch pad have and what does it do that makes it so different?
Well my model rocket isn't exactly a typical rocket with fin. Instead the rocket is filled with custom electronics and thrust vector control equipment. Thrust vector control, or TVC, involves moving the motor inside the rocket to direct its thrust and therefore steer the rocket to its appropriate trajectory. However this involves GPS guidance which is ILLEGAL! So my rocket uses TVC to keep the rocket super stable going upright with a gyroscope on the flight computer, no GPS equipment. Active stabilisation is legal, guidance is not!
After this long intro I still haven’t explained what the pad actually does and what its features are! The launch pad is not a simple rail, but instead a very complex system filled with mechanical parts, electronics and pneumatics. The goal was to make it similar to a real launch pad, which explains a lot of the features. The pad features a pneumatic piston to retract the strongback, 3D printed upper clamps and base clamps, wireless communication with the controller, lots of RGB lighting (of course!), a steel frame, aluminium checker plate covering the base, brushed aluminium sides, a flame trench and multiple custom computers to control everything.
I will be releasing a YouTube video about the launch pad very soon, as well as lots of other videos of stuff I’ve made in the lead up to the first launch in about 2 months. Another important thing to note it that this Instructables post will be less of a how-to and more of my process and some food for thought.
As I live in Australia my parts and links will likely be different to yours, I recommend doing your own research to find what’s right for your project.
Material to build the frame (wood, metal, acrylic etc)
Buttons and switches
Lots of M3 screws
You can use whatever tools you have, but here is what I mainly used:
Cigarette lighter (for heat shrink tubing)
Multimeter (this was a life saver for me!)
Step 1: Getting Started
What does the launch pad need to do? What does it need to look like? How can I make it do this? What is the budget? These are all super important questions to ask yourself before you start to tackle this task. So start by getting some paper, drawing some sketches and writing down ideas. Doing lots of research will also help you a lot, it might just give you that golden idea that makes it that much better!
Once you have thought of everything you want it to do, break it down into sections so that it’s not as overwhelming. My main 6 sections were metal work, base clamps, pneumatics, software, electronics and lighting. By breaking it down into sections, I was able to do things in an order and prioritise what needed to be done the soonest.
Ensure that you plan everything extremely well and make diagrams of every system so that you can understand how everything will work. Once you know what it needs to do and how your going to do it, it is time to start building it!
Step 2: Metal Work
I decided this launch pad would be a great opportunity to learn a bit about metal work, so that’s what I did. I started off by designing the steel structure and including all the dimensions. I went for a fairly basic frame, though I decided to cut the ends to 45 degrees wherever there was a 90-degree bend, just to learn a bit more and get some more experience. My final design was the basic frame, with the strongback mounted to it on a hinge. It would then have aluminium covering it and edging strips to make it a bit neater. It would also include a flame trench made from steel tubing that had some 45-degree cuts on the end, so that the flame comes out on a slight angle.
I began by cutting all the pieces of the frame and then welding them together. I ensured there was no welds on the outside, otherwise the aluminium plates wouldn’t sit flush against the frame. After a lot of clamping and magnets, I was able to get the frame welded straight. I then cut all the aluminium plates to size with some big metal shears and cut the edging strips with some tin snips. Once that was done everything was screwed into place, which proved harder than I expected it would be.
The strongback steel and aluminium edging was then painted black and the strongback was installed on its hinge. Lastly, some simple steel brackets were made for the piston, which allowed it to pull back the strongback and rotate at its pivot point.
Step 3: Base Clamps
With the main frame done and the pad starting to look like something, I decided I wanted to get it to hold the rocket as soon as possible. So the base clamps and upper clamps were next on the list.
The base clamps needed to be able to hold the rocket while its under thrust, and then release it at an exact time. With about 4.5Kg of thrust, the rocket would destroy the sg90 servo motors that are used on the base clamps. This meant I had to create a mechanical design which would take all the stress away from the servo and instead put it through a structural part. The servo then had to be able to easily retract the clamp so the rocket can lift off. I decided to take some inspiration from a useless box for this design.
The servos and mechanical parts also had to be completely covered so that they would not be in direct contact with the rockets exhaust, so side and top covers were made. The top cover had to move to close the ‘box’ when the clamp retracted, I simply used some rubber bands to pull it down. Although you could also use springs or another mechanical part to pull it. The base clamps then had to be mounted to the launch pad on an adjustable rail so that their position could be fine tuned, and they could potentially hold other rockets. Adaptability was important for the base clamps.
The base clamps were very challenging for me as I have no experience with mechanical parts, and everything needed to have 0.1mm tolerances to work smoothly. It took me 4 straight days from when I started the clamps to when I had the first fully working clamp as there was a lot of CAD and prototyping involved to get them to work smoothly. It was then another week of 3D printing, as each clamp has 8 parts to work.
Later when I had the pad computer installed, I realised I had only planned to use one Arduino pin to control the four servos. This ended up not working and I also had voltage regulator problems, so I made a ‘servo computer’ which is underneath the launch pad and controls the clamps. The regulators were then mounted onto the pads aluminium plates to be used as a large heat sink. The servo computer also turns on and off the power to the servos with MOSFETs, so they are not on under constant stress.
Step 4: Upper Clamps
After weeks of work on the base clamps and related electronics it was time to make more clamps! The upper clamps are a very simple design, though they are very weak and will certainly be upgraded in the future. They are just a simple bracket which screws onto the strongback and holds the servo motors. Mounted on these servo motors is the arms which have a servo horn glued into them with epoxy. Between these arms and the rocket is some small, curved pieces which rotate and mould themselves to the rockets shape.
These clamps have cables running down through the strongback and into the main pad computer which controls them. One thing to add is that it took a long time to fine tune their open and closed positions in the software as I was trying not to stall the servos, but still securely hold the rocket.
To design the clamps, I drew a 2D view of the top of the rocket and strongback, with the exact dimensions between them. I was then able to design the arms to the right length and the servos the right width apart to hold the rocket.
Step 5: Lighting
Most of the steps from here aren’t really in any order, I could basically do whatever I felt like on that day or week. However I still only focused on one section at a time. The launch pad has 8 RGB LED’s which are connected to three Arduino pins, meaning they are all the same colour and are not individually addressable. Powering and controlling this many RGB LEDs was a big task on it’s own as each LED needs it’s own resistor. The other problem was that they would pull too much current if they were on one Arduino pin per colour, so they needed an external voltage source, regulated to the correct voltage.
To do all this I made another computer called the ‘LED Board’. It is capable of powering up to 10 RGB LED’s which all have their own resistors. To power them all I used transistors to take power from the regulated voltage and turn on colours as I wanted. This allowed me to still use just three Arduino pins, but not pull too much current that it would fry the board.
All the LED’s are in custom 3D printed brackets which hold them in place. They also have custom made Dupont cables which plug into the LED Board and are neatly routed through the launch pad structure.
Step 6: Penumatics
I’ve always been interested in both pneumatics and hydraulics, though never fully understood how the systems worked. By buying a cheap piston and cheap fittings, I was able to learn about how pneumatics worked and apply them to my own system. The goal was to smoothly retract the strongback with the pneumatic piston.
The system would require an air compressor, flow restrictors, an air tank, valves, a pressure relief valve and an array of fittings. With some smart designing and a bunch of custom 3D printed brackets, I was able to barely fit all this inside of the pad.
The system I designed was fairly basic. An air compressor pump fills an air tank and a pressure gauge is used to view the pressure (30PSI target). A pressure relief valve would be used for adjusting the tanks pressure, safety and releasing the air when its not being used. When the strongback is ready to retract, a solenoid valve would be activated by the computer, letting air into the piston and pushing it back. Flow restrictors would be used as a way of slowing down this retract movement.
The air tank is currently not being used, as I do not have the required fittings for it yet. The tank is just an old, small fire extinguisher, and it uses a very unique fitting size. And yes that is a 2Kg dumbbell, if it wasn’t there the pad would tip when the strongback retracts.
Step 7: Electronics
The most important part, the main part and the part with endless problems. Everything is controlled electronically, but some simple but stupid PCB design and schematic mistakes caused nightmares. The wireless system is still unreliable, certain inputs are faulty, there is noise in the PWM lines, and a bunch of the features I had planned for don’t work. I will be remaking all the electronics in the future, but I am going to live with it for now as I am keen for the first launch. When you’re a fully self-taught 16-year-old with no qualifications and no experience, things are bound to go wrong and fail. But failure is how you learn, and as a result of my many mistakes I was able to learn a lot and further my skills and knowledge. I expected the electronics to take about two weeks, after 2.5 months it still barely works, that’s how badly I failed this one.
Away from all the problems, let’s talk about what does work and what it was/is meant to do. The computer was originally designed to serve many purposes. These include LED control, servo control, valve control, ignition control, wireless communication, mode switching with external inputs and the ability to switch between battery power and external power. A lot of this does not work or is faulty, though future versions of the Thrust PCB will improve this situation. I also 3D printed a cover for the computer to stop direct contact with the exhaust.
There was a huge amount of soldering involved throughout the process as I made two main computers, a servo computer, two LED Boards, lots of wiring and custom Dupont cables. Everything was also insulated appropriately with heat shrink tubing and electrical tape, though that did not stop shorts from still happening!
Step 8: Software
Software! The part that I talk about all the time but am reluctant to release at this stage. All the projects software will be released eventually, but I am holding onto it for now.
I had designed and produced very complicated and lengthy software to interface it with the controller perfectly. Though wireless hardware problems forced me to remake the software extremely basic. Now the pad turns on, it sets and the clamps to hold the rocket and it waits for one signal from the controller that tells it to begin the countdown. It then automatically goes through the countdown and launches without and follow up signals being received. This makes the E-stop button on the controller useless! You can press it but once the countdown is started, there is no stopping it!
It is my highest priority to fix the wireless system straight after the first launch. Though it will take about a month and a half of work (in theory) and hundreds of dollars, which is why I am not fixing it right now. It has almost been a year since I started the project and I am trying to get the rocket in the sky on or before the one-year anniversary (4th of October). This will force me to launch with partially incomplete ground systems, though the first launch is more focused on the rockets performance anyway.
I will be updating this section in the future to include the final software and a full explanation.
Step 9: Testing
Testing, testing, testing. NOTHING I make ever works perfectly first try, that’s how I learn! It’s at this stage that you start to see smoke, everything stops working or things snap. Its just a matter of being patient, finding the problem and figuring out how to fix it. Things will take longer then you expect and be more expensive then you thought, but if you want to build an overkill rocket with no experience, then you just have to accept that.
Once everything is working perfect and smoothly (unlike mine) you are ready to use it! In my case I will be launching my very overkill model rocket which is what the whole project is based around…
Step 10: Launch!
Anyone who remembers my last Instructables post will know that this is the point where I let you down. The rocket still hasn’t launched, as it is a huge project! I am currently targeting the 4th of October, though we will see if I meet that deadline. Before then I have a lot more stuff to make and a lot of testing to do, meaning there is more Instructables posts and YouTube videos on the way over the next two months!
But while you wait for that sweet launch footage, why not follow the progress and see where I am it with it all:
Twitter (daily updates): https://twitter.com/RAS_Space
Controller Instructables: https://www.instructables.com/id/Overkill-Launch-C...
My dodgy website: https://robinsonaerospace.wixsite.com/rocket
I am currently working on the launch pad video which will be on YouTube within a couple of weeks (hopefully)!
Step 11: One Step Further!?
Obviously I still have a long way to go until everything is working as I want it to, though I already have a list of future ideas of how I could make it better and more overkill! As well as some important upgrades.
- Stronger upper clamps
- Strongback dampening
- Wired backup (for when the wireless is being a pain)
- External power option
- Display mode
- Launch umbilical
- And of course, fix all the current problems
Speaking of current problems:
- Faulty wireless system
- MOSFET issues
- PWM noise
- 1 way strongback actuation
Thanks for reading my post, I hope you get some great inspiration from it!
Participated in the