After a long self-taught (and frequently confused) journey involving assembling this rocket, and building the electronics bay, I just needed to track down some black powder, set up my ground station, and conduct a bit of testing. Basically, the idea here is that the e-bay (roughly in the middle of this rocket) has a flight computer on the inside and a black powder charge on the outside, and I can remotely detonate it, causing a small but controlled explosion that will separate the rocket and deploy the parachute.
The black powder was surprisingly difficult to find. The Seattle metro area certainly has no shortage of gun shops, but virtually none of them actually sell black powder. I called more than a dozen shops at increasingly far distances from the city limits in all directions, but it seemed like nobody sold it. Everyone pointed me to other shops.
Finally, I located a place about an hour’s drive away, and after they confirmed they had some in stock, I made the trip. The specific type of black powder I was looking for was FFFF.
all systems go
Like Jason in ancient Greek mythology returning with the golden fleece, I completed the epic journey, explosives in hand.
When it comes to the rocket separation charges, you want to use an amount of black powder that is sufficient to separate the rocket with some real verve, but also not so much you damage or destroy the rocket. Based on an online calculator, I started with 0.5g or approximately 1/8 teaspoon of black powder. This was the lower end of the estimated range (roughly between 0.5g and 1.0g) but it’s generally a good idea to start with less, test, and work your way up.
ready!
How do you actually pack the black powder after measuring it out? It goes into the appropriate container attached to the outside of your e-bay (on mine, a small PVC pipe end cap. But the real explosive force happens when the powder is packed tightly and confined to a small, totally sealed area.
This requires adding some “wadding” in the PVC end cap, and then covering the opening completely with tape. Any kind of tape will do the job – masking, electrical, etc. Again, the idea is to ensure the black powder is tightly packed and stays that way, and remains sealed off.
Having prepared this, I readied the rocket by putting the e-bay inside and then activating or arming the flight computer. I also have a “ground station” that can communicate with (and control) the flight computer remotely, consisting of a small handheld Yagi Arrow antenna, a TeleBT (dongle that connects to the antenna), and laptop using Altus Metrum software.
Using the software on the laptop, I armed the flight computer’s pyro charge and the countdown began. 3… 2… 1… fire!
post separation charge
The ground test worked and the rocket separated perfectly. My conclusions? I’m going to do more testing and will increase the amount of powder – gradually – to the high end of the range to see what works best.
I also need a sturdier structure to hold the rocket in place. I’m just using some makeshift wood supports I quickly threw together.
But the exciting thing is that it worked – with the push of a button on a laptop, I remotely activated the separation charge. The rocket separated, and the parachute deployed.
This shed-to-workshop project is coming along well. So far, I’ve cleaned it out, added two new windows, replaced the old plywood doors with a nice new door (with a glass panel for even more natural light), and given a fresh coat of paint to the door frame and exterior shed walls. Not bad.
The next step is a less dramatic transformation, perhaps, but arguably one of the most important things for a future workshop: a proper work bench.
One of the main reasons I needed some sort of workshop in the first place was just for the additional space and work surface. Sure, it’d be great to have some simple power tools (table saw and vacuum for sawdust, drills, and so on) and other equipment, and a place to efficiently store all those tools. But my single biggest need is just for some extra space – a large work bench for projects, primarily building rockets.
butcher block work bench
I decided to go big with a butcher block countertop from Home Depot. In fact, they offer a few different sizes, and I went with the largest one they had, a full 96 inches (8 feet) in length. I found out two things about butcher block: it’s extremely heavy, and it’s expensive. But worth it!
After doing some initial research and arriving at a decision, I made the mistake of running up to the store myself and trying to purchase this alone. I could write a lengthy article just about the epic struggle of getting this thing off the shelf and hauling it to the front of the store, and loading it awkwardly into my small car (sticking partly out of an open trunk). I blocked many increasingly annoyed contractors in the store’s loading zone. I eventually managed to transport this thing home successfully, but at great cost to my pride, and my lower back.
The butcher block was unfinished wood, and this meant applying some sort of stain and/or seal to the wood, in order to protect it long-term. On a separate trip to the store, I picked up some simple clear wood stain, and also some clear polyurethane water based sealant, along with a couple of brushes.
As a side note, polyurethane can be either water based or oil based, and the difference is how they look after finishing the wood: water based is completely clear, while oil based will give the wood a soft amber look. It’s a purely aesthetic distinction and totally based on your own preference.
wood stain
The staining and sealing process was nearly as epic as the journey from store to shed, though I didn’t realize this would be the case at first. Following the instructions provided on the can, at least two coats of the wood stain were necessary (to both the top and bottom of the butcher block, as well as all 4 sides), allowing ample time between coats to dry.
The polyurethane was even more demanding, requiring a minimum of three coats per surface. The fact that it took at least several hours for each coat to dry, and the sheer weight involved in trying to rotate this board, meant a multi-stage staining and sealing process that ultimately took more than a week.
This was also mid-winter and while Seattle winters are relatively mild, it was still cold enough to numb my hands halfway into the application of each new coat of stain and sealant. Several of those trips were done with light snow blowing into the shed, potentially ruining my otherwise perfect work.
polyurethane seal
Eventually, I finished preparing and protecting the board and mounted it along one wall inside the shed, centered under a window that provides plenty of natural light. Mission complete!
The only other major feature that a true workshop needs is electricity. And while digging a massive trench and running conduit and wire from my house out to the shed is an awful lot of work, it should also make a decent story, and a couple of good blog posts.
I added a new step to my project that wasn’t in the original plan: painting. Gotta improvise sometimes.
before
With the old plywood doors removed and the new door and frame installed, the shed was looking much classier. But that part of the project required framing the new door properly, filling in new gaps with plywood, and caulking between the plywood sheets to seal it up. Basically, this left a bit of a mess, as you can see above.
In addition, the new door frame was just bare wood, without any paint or stain to cover and protect it. This would need to be painted not just for cosmetic reasons, but for longer term protection.
after – newly painted
As for the rest of the shed, a new coat of paint will always clean things up. Besides, it had been a few years and was probably due for a new coat anyway. With nearly constant rainfall in the Seattle area all year round, exterior surfaces really take a beating from the weather.
The most difficult part of this phase wasn’t the painting at all – that was simple enough, and fun. It was trying to come as close as possible to matching the exact shade of blue here. To be fair, it didn’t need to match precisely, especially if I were going to re-paint the entire shed anyway. But our house was painted with the same color blue as well, and ideally the shed should continue to match the house.
pre-paint job
So after half a dozen trips back and forth to Home Depot and a ridiculous number of paint chips, I was finally able to match the color. Much to my surprise, it’s not blue at all, but actually called “Sheffield Gray,” at least according to the paint’s official label.
The white paint for the door frame/ trim was a lot easier, and it didn’t matter quite as much whether it matched. I’m actually still torn about this color even after painting the frame because the house uses more of a gray color for the trim around all of the doors and windows. But hey, white looks nice too.
post paint job
As mentioned above, the painting work itself is straightforward and actually fairly enjoyable. The exterior of the shed is not a particularly large surface area, and it’s not difficult to reach any area, so I didn’t even need a ladder or any tools other than a simple brush (and a screwdriver to pry open the paint can lid, and a hammer to shut it again).
If only the entire shed-to-workshop transformation project were this easy.
I was originally going to create a series of articles dedicated to this topic: building an electronics bay for a rocket. Having never done this before, and having no idea what I was doing when I began, it took me quite a while to figure everything out and to actually build this thing.
In the end I decided nobody cares how long it took me to do this, and everyone is better off with a summary, even if it’s a slightly lengthy one. Quick table of contents based on the section titles below:
Why am I here?
What you’ll need
More about the flight computer
Step 1: Decisions and planning
Step 2: Attaching the components
Step 3: Dual deployment capabilities (optional)
Final thoughts
Why am I here?
So to get started: I’ve covered in a few previous posts what an electronics bay (or “e-bay”) is, and why you might want to build one. Just to recap here, an e-bay is not strictly necessary to launch a rocket, but it lets you do a variety of cool things. For example, with the right electronics, you can measure and record exactly how high your rocket goes; fire charges to deploy one (or two!) parachutes with more precision during the flight; track its location after it disappears from sight and inexplicably lands far away; and much more.
flight computer
But assuming you already know what an e-bay is and some of the cool things you can do with one, the next step is building it.
What you’ll need
There are a lot of different ways to go about doing this. A simple e-bay can have minimal components. For example:
an altimeter to measure the rocket’s maximum height (it actually measures barometric pressure and uses that info to deduce the height);
a battery; and
an on/off switch.
That’s it, for the main components. In addition, you’ll need:
copper wire to physically connect things together (if your switch doesn’t already come with wires); and
some way to secure everything in place during flight (e.g. screws, or glue, etc.).
This last bullet can include nylon screws and washers (which I used for the flight computer), or just a lot of glue, or rubber bands or zip ties… you can get creative.
This simple e-bay wouldn’t have any ability to communicate wirelessly with things outside of the rocket, but it doesn’t need to. As long as you can locate your rocket post-flight and remove the e-bay and altimeter, it will provide you with useful data.
You can also go toward the other end of the spectrum and make the electronics as complicated as you want. But the basic concept is the same. You have at least one circuit board or flight computer, powered by at least one battery and connected to an on/off switch.
More about the flight computer
I chose to start with the TeleMetrum, which is a flight computer from Altus Metrum. It combines the functions of an altimeter with a few other abilities, including firing two separate pyro charges (for dual parachute deployment), GPS tracking, and a radio transmitter – hence the long antenna.
Physically, the TeleMetrum is just 1 inch wide by 2 3/4 inches long. It’s amazing how much cool tech can be crammed into such a small board. The antenna is 7 inches long, and ideally for this particular board you’d want an e-bay with at least 10 inches of interior length to accommodate the board and antenna. My e-bay was less than 8 inches, though, so I needed to extend the antenna somewhat outside of the actual e-bay. The antenna is flexible wire, but it’s best to keep it as straight as possible.
e-bay mid-construction
I’ve also previously posted about building the e-bay minus any of the electronics, so I’ll just skip ahead here, assuming you have already constructed an empty e-bay based on my spectacular instructions and are ready to add all of the fancy gadgets and components.
Step 1: Decisions and planning
As noted above, you’ll need to first decide exactly what you want in your e-bay. Do you just want a simple altimeter to measure height? Do you need to fire pyro charges to be able to do dual deployment? Do you want GPS tracking and radio communication with your rocket?
For my purposes, I wanted all of the above, which is why I selected the TeleMetrum after carefully reviewing the options.
I also got a rechargeable 900 mAh LiPo battery from Altus Metrum. It’s really small and lightweight. Finally, I got an unnecessarily large push-button on/off switch, and some 20 awg copper wire from Home Depot. As a side note, “awg” technically stands for American wire gauge, but this would typically be referred to as “twenty gauge wire.” Somewhat counter-intuitively, the larger the gauge number, the smaller or thinner the wire diameter. The one I bought, 20 awg, is sometimes called “bell wire” because it’s used for common household purposes that require small amounts of current, like doorbells or buzzers.
e-bay nearly complete
You can see from the pictures above how I placed the components in my e-bay. Simple, right? To be honest, I’d say at least 95 percent of this is just planning and understanding what you’re doing – making sure you have all the right parts, you understand how everything works together, and where exactly it will be placed. Once the planning is done, the rest is a piece of cake.
Step 2: Attaching the components
To attach the flight computer, which has pre-drilled holes right in the circuit board, I drilled 4 holes in the e-bay wooden “sled” and used 4 nylon screws. I also added a dab of epoxy to hold them in place, just in case. I’ve actually heard that nylon screws work really well for this purpose, because they will shear. If the rocket suffers a catastrophic failure or really rough landing, the impact may shear the nylon screws (which absorb most or all of the force), but preserve the flight computer intact. I don’t plan to test this out, but it can’t hurt.
The push-button switch I simply glued in place with epoxy. It’s important to note that you’ll also need to drill a small hole through the external wall of the e-bay, and that hole should line up with the switch. You should be able to push the button – and therefore arm or disarm your rocket’s flight computer and electronics – from outside the rocket by simply inserting a pencil, screwdriver, or other small thin object through the hole to push the button. Make sure the hole lines up with the switch!
Finally, to help secure both the switch and the battery in place, I cut a few very small pieces of wood and secured them using wood glue. This isn’t strictly necessary, but it helps give extra security to the switch, and keeps the battery from moving around. I also used a zip tie with the battery, which I can cut if I needed to remove or replace the battery – though that isn’t likely.
e-bay view of one end cap
Depending on what kind of electronics you’ve chosen and/or what you want to do with your flight computer, you might be done at this point. If you just have a simple altimeter, or you aren’t interested in dual deployment (yet), you now have a finished e-bay. Congrats!
However, if you are interested in dual deployment, or you just enjoy exposing yourself to dangerous materials and explosions, read on.
Step 3: Dual deployment capabilities (optional)
For dual deployment, you’ll need – in addition to the above list – the following things:
two small (1 inch) PVC pipe end caps;
some small screws and matching washers;
black powder (recommend FFFF); and
electronic matches (“e-matches”) or electronic igniter, such as the MJG Firewire Initiator.
In addition, while not strictly necessary, you may find it helpful to also have:
two 2-way barrier strips; and
at least one 4-circuit male connector and one 4-circuit female connector.
the underside
You can see a white PVC pipe end cap and white two-way barrier strip in the photos above. One of each is attached on the outside of the e-bay, on each end, and they’re secured by drilling a hole, using a screw and washer, and also adding a few dabs of epoxy for good measure to hold everything in place.
The PVC pipe end cap will hold a small quantity of black powder, which will give you your explosive charge, separating the two parts of your rocket at the appropriate time and deploying your parachute. The black powder is ignited with the e-match, which is wired up to the flight computer (which tells it when to activate).
The reason for the barrier strip is to connect the e-match to the flight computer without having to disassemble everything every single time – it’s just more efficient to have permanent wires running from the flight computer to the barrier strip (which, again, is located on the outside of the e-bay for convenience), and to just be able to swap out the e-match more easily each time.
Similarly, the reason for the 4-circuit male and female connectors is just to more easily be able to pull your e-bay out and access things inside. With the connectors, you can simply disconnect the wire and pull things apart much more easily, and you can also use a shorter amount of total wire which takes up less space and doesn’t clutter up the inside as much.
finished e-bay!
Final thoughts
In this last picture, you can see the overall build of my e-bay. It’s nothing special to look at, but hey – it’s my first one. I also thought it was important to leave as much additional space as possible in case I want to add more electronics later, either for redundancy or to provide new capabilities for the rocket (GoPro camera anyone?). But your layout is up to you.
If all goes well, this whole setup will allow me to do much more in high power rocketry and accomplish a variety of goals I’ve set for myself in 2020.
A few final thoughts and some helpful tips:
Plan. As mentioned above, most of the work here is just planning and understanding what you’re trying to do, and ensuring you have the right parts. Once you’ve solved for all of that, building is the easy part.
Glue. When in doubt, use more wood glue or epoxy, not less. You can secure the components many different ways and have a lot of options.
Layout. Leave room for additional future components (if you have the space for it). If not, no worries.
Get creative. My antenna didn’t quite fit within the e-bay so I drilled a small hole to let it poke outside. And since it’s kind of close to explosive black powder, I shielded it with part of a plastic straw.
Label everything. It’s good to sketch out what you’re trying to do ahead of time, and it’s also helpful to label parts as you go. You can see, for example, I wrote “TOP” with an arrow on the outside of the e-bay to make sure it’s inserted into the rocket body the right way. Once the e-bay is completely sealed up, it’s not always easy to remember which way is up!
Next up, I have some ground testing to do – before sending this thing thousands of feet into the air.
Defenestration (n). The act of throwing someone or something out of a window.
a classic and memorable defenestration
In particular, the Defenestration of Prague in 1618 involved some angry folks tossing several government officials out of a window from Prague Castle. Generally, when you have unwanted guests and you’d like them to leave, the preferred approach is to drop subtle hints that you need to wake up early the next morning, or start cleaning up. Maybe turn on a vacuum if they don’t get the hint. A forcible ejection through the window can have the immediate desired effect but may ultimately lead to a long and terrible war (in that case, the Thirty Years’ War).
Speaking of forcible ejections through the window, many things can go wrong when building or using a workshop, and I named each phase of my shed-to-workshop project after a small sample of them. In this “defenestration” phase, I’ll add windows to the shed.
taking this shed to the next level
First, I had to plan a bit: how many windows? And how large should they be? Of course, I want to maximize light, and my initial answers were more windows and bigger windows, respectively. But more windows cost more money and are significantly more work to install. And most importantly, there’s only so much room inside to actually use or store tools and equipment, and windows eat up some otherwise useful wall space.
Two windows seemed sufficient to really open up the space and provide ample natural light. I thought one on the side and one on the back wall made the most sense.
A shed would typically have pretty small windows, too, something like 12×24 inches or maybe 12×36. Larger would always be better, but then again, I didn’t want the windows to look ridiculously oversized on such a small structure. I ended up going with two windows that are each 24×48 inches.
The walls here are just simple plywood, so after the initial planning was done, this project required:
measuring and cutting away the plywood rectangles where windows would go;
cutting some wood and framing the window; and
installing the window itself, along with some flashing.
Overall nothing too crazy, but a decent amount of work. I did have someone help me with this project; I’m ambitious but only mildly handy, and certainly not an expert.
let there be light!
And this is the finished product! It’s amazing how much a window or two can transform a room. It looks like a completely different space, flooded with light. It even feels bigger, and is the type of place I wouldn’t mind spending an afternoon working on a rocket build or some other project, especially in the spring and summer once the weather gets nicer.
On to the next step: replacing the plywood shed doors with a real door. Something to help class it up, maybe with some glass to add even more natural light. And a handle, ideally, to open and close this door. Maybe I’m going too far? One can always dream.
I recently had a chance to visit the Museum of Flight in Seattle for the first time – long overdue, in fact, since we moved out to the area more than 18 months ago. It was an impressive place with some great exhibits. In particular, we spent most of the time in the Charles Simonyi Space Gallery, although there was much more to see.
One highlight was an actual module from a Soyuz spacecraft. Soyuz was the human spaceflight program in the Soviet Union (and continues today in Russia), and the Soyuz rocket and spacecraft were integral parts of this program. Interestingly, the Soyuz rocket is the most reliable launch vehicle, as well as the most frequently used launch vehicle, in the world. The first Soyuz manned capsule was used in 1967, and Soyuz flights have taken place more than 1,700 times since then, in both manned and unmanned missions.
The Hubble telescope
The exhibit also had some life-size models of things like the Hubble telescope and even a life-size space shuttle that you can climb aboard. Pictures (such as the Hubble, above) obviously don’t do the size of these things justice, although the relatively small floating astronaut next to the telescope helps provide a sense of scale.
The Hubble telescope is of course extremely well known. It was launched into low earth orbit in 1990 and remains in operation today – 30 years later! – and it’s produced countless amazing images of the cosmos.
One thing that I didn’t know was that the Hubble is expected to last until 2030, or perhaps as late as 2040, and that its successor is the James Webb Space Telescope, scheduled to be launched in 2021 – from an Ariane 5 rocket. What a time to be alive!
Rocket Science 101
The space gallery also had a variety of other exhibits, including some interesting info about how rockets work, differences between solid and liquid fuel rockets, and displays related to the world’s largest rockets and orbits. I’m no expert on any of this, and I really enjoyed this “Rocket Science 101.”
I only included a handful of pictures here, but for more, you can check out my Instagram.
The Museum of Flight really has a lot of other exhibits to see as well; in fact, it’s primarily dedicated to aviation and airplanes (e.g. from the early days of flight and the World War I and II era), with only a smaller space dedicated to spacecraft and rocketry. But it’s absolutely worth a visit, whether you live in Seattle or next time you’re visiting.
The rocket construction is complete, but there’s one minor issue I still need to address. The rocket has a 54mm motor mount tube, meaning I need a 54mm diameter motor to fit inside. But I couldn’t find any H or I level motors (note: for the level 1 certification flight, the motor must be an H or I) that are 54mm. I could only find 38mm motors.
ENTER: THE MOTOR ADAPTER.
adequate adapter
The motor adapter is exactly what it sounds like. It allows you to adapt a motor of a given size to a differently sized rocket.
You can always use a smaller diameter motor in a larger rocket as long as you get an appropriate adapter; in my case, I just need a 38 to 54mm adapter. It’s like using a booster seat at a table if you’re too small for the seat. (Important corollary: if your motor’s diameter is too large for your rocket, you’re simply out of luck, and at that point you just need to build a bigger rocket.)
The rocket is made from durable and reinforced cardboard, so I figured a cardboard motor adapter would be sufficient. And it probably would be, but I wasn’t satisfied.
indestructible adapter
The cardboard adapter was extremely durable and fit perfectly. I had no doubt it would keep the motor properly centered. The only issue was retaining the motor – i.e., keeping it from falling out the bottom of the rocket. And not just falling, but forcibly ejecting out the bottom after the motor has burned through all its propellant and the explosive ejection charge happens at the other end.
I’ve explained this before but just to recap the serious danger: ideally the motor stays put, and the hot explosive gas at apogee forces the rocket sections apart (deploying a parachute). But if the motor isn’t properly secured, what can happen instead is the motor itself ejects and falls out the bottom. That’s bad. Even worse is the fact that the rocket didn’t separate as a result, and the parachute didn’t deploy, meaning now the entire rocket will come crashing down.
Retaining the motor is a big deal.
I did try attaching some small metal retaining clips, but I wasn’t confident they would hold under extreme conditions.
In light of this concern, I upgraded to a machined aluminum adapter. It’s more expensive, but the primary advantage here is that it looks fancier. Also, this adapter has its own retainer, so there’s no worrying about the motor ejecting out the bottom at apogee. Things will work as intended!
The business end of a rocket
One other nice feature is that the 38mm adapter and its retainer fit perfectly inside the larger 54mm retainer. This allows both to be used at the same time for smaller motors, or alternatively, the adapter can easily be removed and the 54mm retainer can be used solo for larger motors.
I think I’ve exhausted this topic. In summary, metal > cardboard, and retainer > no retainer.
As I get more into building larger rockets, I’ve been increasingly aware of the limitations of my work area. Specifically, I don’t have one. We have a fairly small house and there’s no dedicated space for gluing or drilling or doing anything with large parts. I’ve had to temporarily co-opt our dining table.
We do, however, have a mundane shed in the backyard. It’s in good shape, but it’s dark and dirty, with no windows or any natural light, no electricity, and is generally just full of old junk that came with the house. But it has potential.
Run of the mill shed
I decided one of my goals for 2020 is to convert this shed into a useful workshop, primarily for rocket-related projects. This is just the first of a series of posts documenting the process of transformation and the resulting workshop.
This is kind of a big project, so I’m breaking it down into a few major concepts or steps:
Remove junk & clean.
Install windows.
Replace door.
Install new countertop work surface.
Add electrical wiring for light fixtures and outlets.
This isn’t necessarily a comprehensive list, but I think that once I complete each of these parts of the project, it’ll go a long way towards making this a practical (and really cool) workshop. And then I’ll give it a name to class it up, like the Rocketshop.
I’m getting all the parts together to build an electronics bay for my first high power rocket. Totally winging it here.
An electronics bay in a rocket, capable of dual deployment of parachutes, requires a couple of things: a flight computer or some similar electronic chip; a battery to power the chip; an electric match or igniter; and some explosive black powder. And, of course, some additional cords and pieces needed to wire everything together properly.
The basic idea is that the flight computer activates a “pyro charge” at the appropriate time. This electrically ignites the match, which in turn creates a spark inside some very tightly packed black powder. Which explodes – with some real verve.
It’s not as crazy as it sounds. The explosion and resulting expansion of hot gases causes the rocket body to separate at a pre-planned location, and a parachute deploys, assuming all goes well.
red end goes bang
This is a “firewire initiator” from MJG Technologies. In other words, it’s an electric match.
Apparently the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives (“ATF“) generally regulates electric matches and igniters, but this is the only non-regulated version on the market. It’s made specifically for rocketry.
I previously uploaded a quick video of me testing one of these, but the real fun will be combining it with the compressed black powder, for one of your more vigorous explosions. Stay tuned for more ground testing.
Improbable Ventures 