Autopilot maneuver demonstration

While I work on the flight hardware including the carbon fiber structure and molded polystyrene aero shell, here's an old video of the early HAPP prototype that shows testing of maneuvers controlled by the autopilot - in this case, a series of 90-degree turns. Previously I posted a video that showed the stabilization function, but here you can see the potential to run programs that pan around for interesting video shots. Enjoy!

The flight hardware is coming along and I hope to have some photos in the next few weeks.

Altitude chamber: Redux

So I blew up the first altitude chamber. Well, actually I destroyed it with a violent implosion. This is unacceptable as I need to measure the performance of the 3D printed jet nozzles in near-vacuum conditions, similar to those the HAPP will experience at 30Km altitude. What's a mad scientist to do? Solution:

(1) Take a steel drum like the one used for the altitude / vacuum chamber version 1...

(2) Then let Steve at LeForge's Pipe and Fab work on it for a while...

(3) And then you have a steel vacuum chamber reinforced with a welded steel exoskeleton. THAT oughta do it!

(4) While you're at it, have Steve cut open the crushed drum v1 so you can remove some bits of the test rig that you'd like to re-use for altitude chamber v2:

Bada bing, got your test rig bits right here:

And for the next round of vacuum test firing, I promise to set up the GoPro at 240 FPS. Just in case anything interesting (and violent) happens again.

Onward!

Altitude chamber: Violent implosions

Shizznit's gettin' real yo. Today I got lucky and avoided injury when I had a violent implosion of a 55-gallon steel drum in my basement lab. Kids, don't try this at home!

There's a reader quiz at the end so stay with me...

Let me back up a few steps. While waiting for delivery of some additional components for the HAPP structure, I continued working on a vacuum chamber to simulate high altitude conditions. The idea is to test fire the 3D-printed jet nozzles in low atmospheric pressure and measure the resulting jet force, which will be different than the force produced at low altitudes. The controls software needs to know the jet force as a function of altitude so it can accurately control the HAPP's rotation at any point during the flight.

Previously I found the most accurate way to measure jet force was using a rotating platform with a well-known moment of inertia. This means the altitude chamber must be large enough to hold the rotating test apparatus. So my thought was to use a standard 55-gallon (208 liter) steel drum, hang the test apparatus inside, and run live fire tests after pumping out as much air as I can before the drum implodes. Why, you ask, would a steel drum implode? Answer: Because the sides of the drum get squeezed with over 38,200 pounds (17,300 Kg) of force once the air is pumped out!

Air at sea level is at 14.7 pounds per square inch (PSI), which means the net pressure on an empty drum is 14.7 PSI. That may not sound like much compared with your car tires, for example, but the problem is not the P. The problem is the SI. The sides of a standard steel drum have a total surface area of approximately 2600 square inches. So 14.7 x 2600 = 38,200 pounds of force on the sides of the drum. Anyway, I figured I could run tests at various "altitudes" and go as far as possible before the drum started making strange sounds, at which point I would back off.

Of course I needed a transparent, removable cover to insert the test apparatus and make observations during the tests. After doing some math I decided a 1.25" thick sheet of cast acrylic plexiglass would suffice.

This cover also needed an airtight gasket of some sort, which I custom-fabricated to match the steel drum's rim. This was easier said then done. After lots of tinkering I finally came up with the idea to use a router to cut a circular channel in the face of the plexiglass, then fill it with liquid silicone that vulcanizes at room temperature. Voilà, instant gasket.

Clockwise from top left:
Router and protractor on plexiglass slab;
Pouring RTV silicon into the trough;
Peeling away protective masking;
Attaching hangar for monofilament;
New compact test apparatus;
Steel drum;
Apparatus hanging from plexiglass cover.

The other issue was how to control the test apparatus once it's inside the vacuum chamber. Data is logged to the onboard micro-SD card, but I needed some way to give commands, especially the commands to start test runs and then null out any rotations between tests. My solution was to enable WiFi-based control of the Arduino on the apparatus and "drive it" from my smartphone. I found a great app called Arduino Manager from a guy named Fabrizio Boco that greatly accelerated this process (thanks Fab!). After downloading the app I had the following control panel up and running on my iPhone in literally half an hour. You can read the labels on this screen shot and get an idea of the various functions I created.

iPhone controller made using Arduino Manager

I rigged up a standard vacuum pump and I was ready to rock. Being the (mostly!) sensible type I ran a series of tests at different simulated altitudes, starting with sea level and gradually evacuating air from the drum in steps of 2.5 inches of mercury (the units used by my pressure gauge; about 1.2 PSI). The rig was performing flawlessly and the iPhone controller was working great.

I was wearing safety glasses but I kept my ears exposed despite the noisy vacuum pump; I wanted to listen for any hint of complaints from the steel drum so I could back off the vacuum if needed. I assumed I would hear something as I approached the failure limit. 1500 meters altitude... check. 3300 meters... roger. 5500... five-by-five. 8400 meters... good to go. 10,300 meters... all systems nominal. Then BANG! No warning, no creaking metal, just a violent implosion and a 50-pound plexiglass sheet airborne in my lab. Duck! The carbon fiber air tank charged at 4500 PSI was chipped and is now unsafe to use, but fortunately it didn't rupture. All kidding aside, that could have been catastrophic.

Below is what's left of about two weeks of work. I don't mind rebuilding, but I'm really pissed I did not capture the implosion with a GoPro at 240 frames per second. You, dear reader, could have had great fun measuring my reaction time as I jumped back liked a scared cat. Sorry to deprive you!

From clockwise at top left:
Imploded steel drum;
Contents barfed out of the drum;
Pressure fitting sheared off;
Bits and pieces of the apparatus & nozzles.
Glad those red LiPo cells didn't go nuclear!

READER QUIZ: Calculate the crush force on the steel drum given the simulated altitude of 10,500 meters at the instant of crush. First correct answer posted to the comments below wins... well, probably something cool. Someday.

What doesn't kill us makes us stronger. I shall return to this phase of the project, and it will be bigger, faster, and stronger than before. We can rebuild him. We have the technology...

Would this man quit after a minor disaster? No!

Flight hardware kickoff

To this point the HAPP prototypes have been constructed mostly from plywood, cardboard, tie straps, and hot glue. Plus a few household items you'd find in anyone's well-stocked pantry, such as a 4500 PSI carbon fiber air tank, a couple of Arduinos with inertial navigation chipsets , a pressure transducer, and custom-designed controls software. You know, the absolute basics of the simple life.

Now that we've figured out propulsion and stabilization, it's time to build the flight hardware and finalize all the performance data, especially the inertia tensor and jet force (as a function of gas pressure and altitude). Even after that's accomplished, there's plenty to do - still haven't fully designed the GPS system, satellite downlink for data transfer, or parachute & pyrotechnics - but I want to get the basic structure finished first.

Over the next few posts I'll put up pics and information about the flight hardware build. To whet your appetite, here's a partial list of some of the more adventurous items:

• Carbon fiber internal structure.
• Molded plastic aero shell - which I will attempt to vacuum-mold myself. Which means I'm building a vacuum-molding machine in the "lab" (a.k.a. basement).

Also, I joked in an earlier post about borrowing an altitude chamber for testing the jets in near-vacuum conditions. I've concluded that I actually need to do this. But as this is a 100% roll-your-own adventure, I'm also in the midst of building a vacuum chamber that can hold the old test rig for live fire testing. This is probably the most dangerous part of the project so far (not counting solder iron burns :-) because structural failure of the chamber means violent implosion. We'll see if I get the math right!

It's going to be a fun month. Feel free to ask any questions using the comment section below. In the meantime, here are a few pics to kick off the flight hardware build phase. Enjoy...

Final design for jet nozzles (v8).
Optimized for high altitude and lookin' like a BOSS.
Being 3D printed right now.

First flight hardware arrives.
Plenty o' techie goodness in those boxes!