I alluded to the fact in the last two posts that there are some laws and regulations applicable to electrical work.
Among other things, your city or state will require you to obtain a permit (and pay a fee) before you can even begin the work. In Washington state, this is the Department of Labor & Industries. The work needs to be done in accordance with certain requirements, and then an inspection is required once it’s complete. At that point, you notify the Department and schedule a date, and an electrical inspector will come on site to review all of the work.
It’s not uncommon to fail an inspection and for remedial action to be required. An inspector can fail you no matter how small the violation, relative to the overall work done.
Judge not, lest ye be judged – amirite? Unfortunately, it’s literally the inspector’s job to judge – and he or she has significant power and discretion.
What are the requirements governing electrical work? There are several, and they are no joke. I had to bring myself up to speed quickly.
The NEC is “national” but is not technically a federal law. However, it has been adopted in all 50 states, which can also modify it as they see fit – so the rules can and do slightly vary from one region to another.
So what are these rules, exactly? There are far too many for a comprehensive list, but here are a few examples:
Conduit minimum depth underground. Copper wire must generally be enclosed inside conduit (metal/rigid or PVC) and, if horizontal and running across the ground, must be buried so the top of the conduit is at least 18″ underground.
Securing conduit. Conduit that is vertical and runs along walls (indoor or outdoor) must be secured with straps (plastic or metal) at no greater than 36″ intervals.
Conduit bends. You can physically bend conduit – with heat, if it’s PVC, for example – or you can attach 90 degree (or 45 degree) PVC “elbows” for turns. But the total turns cannot exceed 360 degrees. That means, for example, you could have a maximum of four 90 degree “elbows” or PVC pipe bends.
Panel clearance. Installation of a new electrical panel or sub-panel must have a certain minimum amount of clearance in front of it. Specifically, a minimum width of 30″, depth of 36″, and height of 60″. Visualize a telephone booth-like invisible box in front of the panel that must be completely unobstructed to ensure access to the panel.
Tamper-proof outlets. Electrical outlets (or “receptacles”) inside a dwelling unit (e.g. a house) must be tamper-proof. Inside a shed, which is not a dwelling unit, they don’t need to be – until the 2020 version of the NEC takes effect this summer, at which point even the shed would need all outlets to be tamper-proof.
GFCI outlets. For safety reasons, a ground fault circuit interrupter (“GFCI”) is required. Either the electrical panel needs to have a GFCI circuit breaker, or at least one outlet needs to be a GFCI outlet.
Ground rods. The new electrical panel for the shed requires at least one copper ground rod, and depending on the soil quality (specifically, its electrical resistance), possibly requires two. A ground rod comes in a standard length of 8 feet and has to be driven completely down into the ground. A bare copper wire (not insulated or inside conduit) connects the ground rod to the electrical panel. This is again for safety reasons, to redirect excess current.
The NEC and its state and local variations of the electrical code have many more rules that must be followed. The above list is just a small fraction of things I learned during the course of this project – all from my friend Darrin, noted electrical expert and lifelong student of the electrical code, among other titles.
Again, the reasons for these rules are often pretty self-explanatory. Clearance in front of a panel is important so that a person has unobstructed access to the panel. Copper wire should be inside conduit when buried, in order to protect it from future damage – and that conduit should be buried pretty deep, for the same reason. The rules are mostly about safety and common sense.
As soon as we completed all the work, I scheduled the inspection. This was on a Sunday afternoon, incidentally, and the inspector showed up first thing Monday morning – record response time.
The inspector was friendly, and he seemed quite impressed with all the work and how thoroughly it was done. He agreed it met all the applicable requirements in the code, with just a couple of very minor issues to address. These were promptly fixed, and the project officially passed inspection.
All I need to do now is a bit of final cleanup work – fill in that huge trench; clean up the mess everywhere from sawing, drilling; get the landscaping back in order with about a hundred wheelbarrows of mulch; and so on.
I think at this point, the backyard garden shed can officially and rightfully be called a workshop.
In order to run electrical wire and conduit from the main electrical panel in the house out to the shed, the electrical code requires (more on this later) that the conduit be buried a minimum of 18 inches underground.
This requirement is totally understandable, given the nature of electricity and the danger of someone accidentally digging into it. It is also burdensome. It fact, is much more burdensome than it seems. This is partly because 18 inches is deeper than it initially sounds, and the difficulty increases exponentially as you get further down. If you’ve ever done any digging in your yard, even just to replant a small plant or bush, I’m sure this will resonate with you.
The minimum depth applies to the top of the PVC conduit, and you need to err on the side of too deep rather than too shallow if you want to make sure it’s up to code and will pass an inspection, so the trench really needs to be about 20 inches deep.
But the most difficult problem you immediately run into – if you’re me – is the soil quality. This is soil that nobody has touched in many decades. It’s dense and compressed, like clay, and also rocky. I mean extraordinarily rocky. There were points during which I achieved maximum rock, i.e., there was no soil at all and just pure rock.
I had nothing other than a simple garden shovel. I went out on a limb and halfway through the project bought something that is specifically made for digging trenches, which looks just like the shovel except it’s somewhat narrower. This was helpful, but the digging was still brutal.
I’d estimate digging this trench by hand took about 50 percent of the total time for this electrical project, with the other half being everything from drilling and cutting and bending conduit to actually running the copper wire inside it and installing outlets and light fixtures (for which, as mentioned in the last post, my friend Darrin was invaluable and did all the heavy lifting, literally and figuratively). In retrospect, maybe I should have brought in some kind of heavy machinery to dig this trench.
Did I mention the sheer quantity of rock?
Anyway, the trench was simple enough, conceptually. And from the main electrical panel in the house to the shed, only about half had to be underground. The other half is above ground and runs along the outside of the house.
Below is a picture of the trench mid-project, when I was busy naively underestimating the 20 inch depth requirement. It’s getting there, but by no means complete yet. You can see where the conduit comes up out of the trench, above ground, in between the door and the gutter downspout. We also installed a new junction box with electrical outlets and weatherproof cover there, just because we could.
Below is the view underneath the front of the shed, where the 1″ diameter conduit goes up inside the shed to a sub-panel. The smaller 1/2″ conduit on the left here contains copper wire, running from the shed’s sub-panel to the copper ground rod that you can see here.
As an interesting aside: with any electrical panel, you need to have at least one copper ground rod, and this comes in a standard length of 8 feet. The metal rod must be buried underground and attached via copper wire to the panel. In other words, you have to drive the rod straight down into the ground.
If the soil quality is good and its resistance is low enough, you may be able to get away with just a single 8′ ground rod. In our case, the soil was abysmal, and we needed to drive two separate 8′ copper rods into the ground. You’ll never be required to use more than two rods.
Here are two final pictures of the trench once it was dug further down to the required minimum depth, and we laid the conduit inside.
As this project went on, we needed to leap across increasingly wide and deep trenches, countless times. Particularly awkward was the trench needed to pass directly in front of the shed door, which required Olympic-level gymnastics to vault across the ditch but also simultaneously duck your head to avoid hitting the top of the door frame.
Eventually we realized it would just be easier to throw together a few wooden bridges made from lumber (2x4s or 2x6s). This prevented more injuries and also was a good idea for the inspector who still needed to come on-site after all the work was complete.
If you look closely (and maybe squint), you can also see in a few of these pictures that we came across some unexpected pipes and drain tiles. We called 811 before digging – required by law – and the various utility companies came out to ensure there was nothing buried underground in this area.
But there were drain tiles, which are not part of any utility but are just part of the property. These were loosely connected and immersed entirely in tons of rock, to facilitate water drainage from the house, and we hit them in two separate locations as they cut across the trench. We also encountered some other pipe (about the same size as the drain tiles, roughly 4 inches in diameter) whose origin and purpose were unclear. We just dug around and beneath it, without disturbing it, and continued on our way. That pipe remains shrouded in mystery.
The conclusion here is simple and painfully obvious: digging sucks. But it was a necessary step to bury the copper wire and conduit in order to comply with the electrical code. This was the most backbreaking part of the project but also allowed for the more fun electrical wiring to be completed in the shed (covered in the last post).
It’s taken a while to provide an update on the workshop because… this step was a significant amount of work.
I enlisted some serious help from my friend Darrin, who has a background in electrical engineering, prior experience doing electrical installations, and an immense collection of power tools and equipment.
The short version is this: we ran some electrical wiring from the house’s main electrical panel to the shed, burying it underground, and put a new panel inside the shed. From there, we installed a bunch of junction boxes with outlets, two light switches, and even an exterior light (just for fun), all connected to the shed’s panel. It’s done, and the shed has indoor and outdoor lights, and a ton of working outlets (soon to be put to good use).
The long version, if you care to read it, is below.
First, a few preliminary thoughts (from someone who has no background in electrical work) and the basics.
Conceptually, this project required a couple of steps:
adding a few new circuit breakers to the house’s main electrical panel;
running copper wires inside conduit along the outside of the house and then underground;
digging a trench;
installing a smaller sub-panel inside the shed, and adding circuit breakers to it;
connecting the wire/ conduit to the sub-panel inside the shed;
installing copper wire inside conduit, inside the shed;
installing metal junction boxes and electrical outlets in various places; and
adding an outside light fixture and wiring it up.
Here’s a list of the major supplies we used:
roughly 80 feet of pvc conduit (1 inch diameter), connecting house main electrical panel to shed’s sub-panel; along with a few 90 degree “elbows”;
roughly 20 feet of metal conduit;
roughly 20 feet of metal clad (“MC”) cable;
plastic and metal straps to secure the conduit to the house wall or shed wall;
metal junction boxes;
electrical panel for the shed;
circuit breakers for main house panel;
copper wire (black, white, red, and green), to connect everything inside shed as well as connecting shed to main house panel;
outlets or “receptacles” for the junction boxes (3 GFCI outlets, plus other regular outlets);
two copper grounding rods (each 8 ft in length) and acorn nuts;
roughly 20 feet of bare copper wire to connect both grounding rods to shed’s panel; and
external light fixture and mounting hardware,
I am very possibly forgetting a few things. As I mentioned above, this was a big project.
It also required a lot of different tools, some of which I didn’t know existed. We used basic tools like drills and circular saws, screwdrivers and mallets, measuring tape and a level, etc., of course. There were also giant drills with giant drill bits to punch huge holes through concrete or cinderblock; and a giant hammer attachment for this drill to drive an 8 foot long metal rod straight down into very rocky soil. We also used tools to cut (and to bend) metal conduit, and to cut (and bend) PVC conduit. As with every part of this project, I have to give full credit to Darrin. My role was participatory at best.
I’m going to create a completely separate post for the outside work – i.e., digging the trench and laying the conduit running from the house. But below are some pictures of the work inside the shed. First, the electrical panel, light switch, and conduit during the installation:
And after completion:
Likewise, here’s a bit of a closer view of the panel and light switch, during and after the install:
The side wall now has 4 junction boxes with outlets (2 above the bench and 2 below), with a 5th box on the ceiling for light fixtures. Below are pictures of the side wall during and after this work was completed.
As mentioned above, I’ll create at least one separate post about the work done outside – digging the trench, and connecting the shed to the house panel with conduit – and probably several separate articles. What I learned about the local electrical code and its many requirements, for example, could easily fill volumes (though it would likely interest nobody). In any event, this post is long enough as it is, and I’ll wrap it up for now. Stay tuned!
As mentioned in my last post, we recently got away for a week in Hawaii. What a trip!
This is a bit of a break from rocket activity, but it’s not totally unrelated – I did finish reading an excellent biography of Wernher von Braun during the flight, and I plan to write a couple of posts about that in the near future as well. And if nothing else, I needed an excuse to post a few pictures.
The Pacific Northwest is beautiful, but it can be pretty gloomy in the winter months – lots of darkness and clouds, with very little sun. This winter was particularly cloudy. Imagine day after day, week after week, with full cloud coverage, and virtually no sun. Relentless!
Luckily, Hawaii is not terribly far from Seattle: it’s just about a five hour flight. We’d never been to any of the islands before, and we decided on Maui.
The trip was a welcome relief from the despair of Seattle’s winter, and also a respite from the endless news coverage about the coronavirus throughout the country, particularly in Washington state. (See previous post.)
Below is a summary of our week’s activities in Maui, and of course, a couple of pictures.
Sunday – flight from Seattle to Maui
Monday – beach day at Kaanapali beach, dinner at Star Noodle in Lahaina
Sunday – lunch at the Fish Market Maui (fish tacos!) in Lahaina, and flight home to Seattle
We stayed at an airbnb in Lahaina, which was amazing. And of course, the trip was definitely punctuated by multiple trips to Costco (the only one on the island) to stock up on food and supplies, and for filling the gas tank.
Note: prices are even higher in Hawaii than they are in Seattle, and that’s saying something. But as you can see from the itinerary above, we really packed in a full week of adventure and also relaxation.
Below are a few final pictures (and, as always, check out my instagram if you want to see more).
Sometimes you have to take a break from building and launching rockets, if only to rest and recharge, and then get back at it!
You can’t go anywhere without hearing people talk about the coronavirus (COVID-19) lately. I mean, anywhere. Go for a jog or walk outside, and as you pass other people who are talking, more often than not their conversation is about coronavirus. Same with fellow diners in a restaurant, or co-workers in the office – if you’re still going into the office, that is, and not yet working remotely.
Airlines are reassuring passengers that they are taking appropriate safety measures to ensure that travelers are safe. The stock market is tanking, in part because of the economic harm caused by the virus (or by concern or panic about the virus).
I live in the Seattle area, and closer to home, the situation is a bit surreal. I read a recent New York Times article that prompted me to write something about this. Sure, this is generally a blog about building and launching rockets, but even that is impacted by the coronavirus epidemic and news coverage.
As the New York Times article notes, Seattle is something like the epicenter for this virus in the United States. The first death from COVID-19 in the US was in Washington state, in King County (which is Seattle and some neighboring areas). As of today – March 10 – the Washington Department of Health is reporting a total of 267 COVID-19 cases and 25 deaths across the state. Alaska Airlines, based out of Seattle, is one of many airlines offering no change or cancellation fees for flights scheduled through certain dates. Amazon and Microsoft, whose headquarters are in the Seattle area, have recommended their employees in the area work from home. Facebook (which has a large Seattle office) has said the same thing.
State and local governments in Washington have also advised people to avoid large public crowded spaces or events. In fact, the governor of Washington has declared a state of emergency, as have several other states across the country, and is banning crowds of 250 or more people.
With respect to rocketry and related activities, some local rocketry clubs have either cancelled launches or warned that people not attend. Similarly, the Lake Washington Ham Radio Club, where I got my amateur license a couple months ago, cancelled its monthly meeting due to the outbreak.
What can be done in this situation except escape Seattle for the remote beaches of Hawaii? That’s exactly what we did last week, and in another post I’ll share just a quick overview of what we did (and, of course, some pictures)!
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.
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.
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!
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.
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.
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.
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.
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.
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.
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.
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)
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.
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.
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.
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.
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:
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.
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.
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.