Ultimate Telemetry Platform

I have been working for the past 4 years, off and on, on building the ultimate telemetry platform for rockets and balloons. I started originally with a set of stackable Arduino shields - GPS, SD card, etc. Over the years my understanding has grown and the technology has shrunk quite a bit, to the point where I've designed what I think to be the ultimate platform.

Ultimate Telemetry Platform

The ultimate platform consists of:

1. Arduino Mega
2. Mega proto shield
3. Adafruit "Ultimate GPS" breakout
4. Adafruit microSD breakout
5. Adafruit 10 DOF IMU
6. 2m amateur "radio on a chip"
7. 3.3v power supply

I liked the Mega because of the extra size. My vision is that my local Scout troop will start a NOVA team and that the kids will throw additional experiments onto the telemetry platform, and the Mega gives me plenty of pins!

Thanks to my employer, Caliber Security Partners, I was able to stock up on supplies for the project:

Arduino Uno, Mega, and the breakout boards.

My original design focused on ballooning, but I ran into an opportunity to launch the telemetry platform via a rocket. My buddy and amateur radio "Elmer" has a high-power rocket with a payload. Perfect for the Mega!

Here's a shot of the Mega proto shield with the breakout boards:

Mega proto shield with the GPS and IMU. Radio chip and power supply will go in the empty spot on the left.

With the radio chip and power supply, there's not enough acreage for the microSD card, so I put it on the bottom!

This tangle of wires is the 3 sensors on a breadboard, tied to an Uno

Life Is Full of Opportunity

I ran into a number of issues building my platform:

• My buddy had to back out - no motor, his high power license expired, and he's out of time.
• The radio and power supply haven't arrived
• The microSD card draws too much power to use without an external power supply
• ...

So now I have an opportunity! My launch is scheduled for 11/15, and it's 11/11 today. I have to build a solution practically overnight.

Options

Launch Platform

I have an old Estes "Maxi Force" 3-motor cluster rocket that I can launch with. It wasn't made for payloads, so I'm taking a bit of a risk here but at this point I am going to go for it. The nose cone is just exactly wide enough to fit an Arduino Uno:

It's this, or we launch with a kite (and the kite's not all that exciting, especially since we're launching rockets the boys built as part of Space Exploration merit badge).

Telemetry Package

I have a few options on the telemetry side:

• Powered Arduino sd shield, with is big and bulky
• Strip out the GPS and send up the microSD shield and the IMU on an Uno
• Do the same, but use a PC board and solder on a nano

The next few hours will be telling, as I hook the Nano up to the breadboard to see if it can handle everything. I have a number of 3.3v batteries from various cell phones, so I think I can actually use them to power the microSD card. If the nano idea pans out, I just need to find enough power to bring up the Nano and the sensors.

Repairs Complete

A day later and the repairs are finished. The tail section isn't perfect, but it should fly without complaints. Much like 2x4's, it appears balsa thicknesses have changed over time, so I had to putty the seem where I replaced the broken leading fin. You can totally see the seam.

If it's less than straight in flight, replacing the tail fins with laser-cut plastic, and assembling with a custom fin jig will be the next step. We will see--this guy launches in less than a month!

Rocket Repairs

I was hanging on with my Elmer Chuck (WB6YOK) the other day and the conversation turned from radios to radios in balloons. We have been "working on" a balloon project for what, five years now? We started in with Arduino several years ago and, while we haven't launched anything yet, we've got solid plans and a lot of functioning code for various sensors. As we were talking about the balloon project, I mentioned that I am interested in starting a BSA Nova program (BSA's new STEM initiative, to encourage youth to study science, technology, engineering and math). I told him that we are doing space exploration merit badge in Novemeber and mentioned that I would like to launch a rocket at October's Jamboree on the Air campout, to start to generate some interest.

Well, as it always does, the conversation quickly devolved into some wild fantasizing about having a rocket that was large enough to carry the balloon payload, so we could test it. As we were discussing that, Chuck said "Hang on, wait a minute..." and left the room. He returned with an enormous 3-peice rocket (base, payload bay, and nose cone). "This ought to do what you want," he said. Turns out, Chuck is high-powered certified. This is the rocket he certified with--it's powered by a single "H" motor and should go as high as 8,000 feet or more. 

As we talked further, I got more excited about the possibilities. That rocket could carry an Arduino, a Pi with a camera--pretty much anything! Suddenly Chuck left again and returned with this rocket:

An Estes Maxi-Force 3-engine cluster 50" tall rocket. These were a short-lived rocket built by Estes in the early 80's. Chuck said "It's yours if you want to fix the fins." Well, gosh... How difficult could that be? I took it before he could change his mind! 

Two out of three fins needed repair. The first had several cracks lengthwise, and the second had lost its leading edge. Today's project was to swing by Hobby Lobby after my trail run, to grab a few motors and some balsa wood, and then to fix the fins.

These are the cracks on the first fin (above).

And this is the broken leading fin. 

The fins are made of several peices: the main or base fin, a leading fin above it, and some edging which appears to be made of tougher material to withstand the bumps of landing.

My first plan was to just rip all three fins off and replace them with laser cut plastic fins (another buddy has a laser cutter). The more I thought about that, though, the more I realized it was more work than it's worth. As I looked over the fins again, I realized they were totally fixable. I needed to trace one of the leading fins to make a pattern to cut a new one from balsa, and I needed to glue the cracks together on the other. 

So today I dropped by the store and picked up balsa. After a few chores, I started in. First I opened up all the cracks in the fin, as shown below:

Then with a toothpick, I started to slip Gorilla Glue into all of the cracks. It's not as precise as I would like to be, but it worked. Here is the fin, drying, with a little pressure supplied by a couple rubber bands:

Next I traced an intact leading fin, cut some balsa, and dry-fitted a new leading fin. First I had to carve away the remainder of the leading fin--it isn't perfect, the surface of the rocket body was a bit wavy when I finished but the glue will help with that. Balsa is a really forgiving medium, and the dry-fit went quickly.

Knowing that it would be a challenge to have the new leading fin attach at every point and stay aligned, I opted to only glue where it touches the base fin and where it contacts the rocket body nearby. Once it's dried, I will glue up the rest. It's that easy...

I had to laugh--I spent more time thinking up a variety of ways to replace the fins than I actually spent repairing them. In fact, I've spent more time writing up this blog entry! With only an hour's effort, everything is glued except the front of the leading fin.

My next steps are to sand out the excess Gorilla Glue, then using a light putty I will fill in gaps and holes. Once the fins are smooth and straight, I think I'll paint the base again--probably black, just to put my own touch on the rocket.

The Scouts don't know about this rocket, but this is the one we will launch at JOTA, in an effort to pique their interest. I think it'll get their attention!

If I had unlimited time and funds, I would put together a tiny XBee unit, with an XBee 2 transceiver and a GPS. Then I would find a way to slip that into the nose cone so we could stream telemetry while flying the Maxi-Force. But I decided to keep my focus on building a package for the November launch, instead.