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Here's how to use Blimpduino:

First thing, needless to say: inflate the envelope. For that you'll need helium. You can get it in a party balloon kit that you can find at most Targets or Wal-Marts or any party supply store. You can also buy it from Amazon, or rent a tank from a local welding supply store.

You shouldn't need to fill the whole envelope with helium. Just tape the BlimpDuino board (with battery and RC receiver) temporarily to the envelope and add helium until it floats upwards pretty strongly with that weight. The envelope will still look pretty saggy, so get a straw and fill the rest with air so it looks full. You can then ballast the blimp by taping on coins until it's neutrally bouyant. The envelope will slowly leak over a week or two, so if you have a little extra buoyancy, you can just take off ballast from day to day as it loses a little lift.

Note that the envelope in the kit comes with some foam cutouts, which can be taped on to the envelope as fins. They looks cool and can add directional stability, but are not necessary. I usually don't bother with them.

Make sure the board is configured as per the photo above, with the switch side facing forward and the props pushing the air backwards, which you can check in RC mode. (click on the photo for a bigger version). Tape or velcro the board to the bottom of your blimp, with all the components facing down.

Note: The Blimpduino code sends lots of useful status and debug information that you can see if you leave your FTDI cable plugged in and open the serial window in the Arduino IDE (circled in red below):

1. It's best to start in RC mode. Plug RC receiver channels 1 and 2 into the first two (furthest from the reset switch) 3-pin connectors on the BlimpDuino board (see diagram below). Plug the vectoring servo straight into channel 3 (throttle) of the RC receiver. Turn on the transmitter, and then power on BlimpDuino. The code should auto-detect the RC signal, and after the green LEDs flash in a circle they'll flash back and forth and do another funky jig. That means you're in RC mode.

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3. Controlling a blimp is a little different than flying an airplane. The "aileron" stick controls the differential thrust of the motors to turn. The "elevator" stick controls the thrust to go forward: the further you push it up, the faster it goes. The "throttle" stick controls the pitch of the vectoring servo, which determines the tilt of the thrust. If the blimp is neutrally ballasted, you can often leave it in the middle position, but if the blimp tends to go up or down under power, you'll move that stick to control the vertical direction of the thrust. It's a little bit like an elevator with a plane, but with the added dimension of changing thrust.
4. Now is the right time to test that the motor are plugged in the right way. When you move the "aileron" stick, the motor on the opposite side should spin, blowing air backwards. If the motor doesn't turn in the right direction (blowing air backwards), just reverse their plug on the board. Pushing the "elevator" stick forwards should increase the speed of both motors, again blowing backwards. If that actually turns the props in the other direction, so they're blowing air forwards, despite them working correctly with "aileron" stick, you may need to reverse the direction of this channel with your transmitter.
5. If one green LED just blinks rapidly and the servos don't go through their startup moves, your battery is too low. Recharge it and try again. (If you find that this happens too soon or often, go the the definitions portion of the first tab of the code and change "#define low_battery_limit 6000" to a lower number)
6. Now you should be able to fly around. You'll note that it turns one way better than other due to motor torque effects. We're looking for a reverse-pitch prop so we can have the motors counter-rotate and avoid this. But for now it shouldn't be too bad.

If that all works, it's time to try...

1. Unplug the RC receiver channels from BlimpDuino, and plug the vectoring servo into the third 3-pin connector (closest to the reset switch).

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3. Plug the beacon into a 5-9v power source.
4. Make sure that there aren't any cables obscuring the ultrasonic sensor or blocking the IR sensors.
5. Hold the blimp at shoulder height over a hard floor (not over carpet).
6. Power it on and wait until the LEDs flash in a circle. That means it's measuring its altitude and is ready to hold it.The servo will turn the motors all the way up, down and back to the middle to show that it passed its self-test.
7. If one green LED just blinks rapidly and the servos don't go through their startup moves, your battery is too low. Recharge it and try again. (If you find that this happens too soon or often, go the the definitions portion of the first tab of the code and change "#define low_battery_limit 6000" to a lower number)
8. Before you let it go, make sure it can see the beacon and is responding correctly. The green LED should light up on the side of the beacon, and the motor should turn on the opposite side (at least when the beacon is on the left and right side). You can hold the beacon in your hand and test this.
9. If that works, let the blimp go and put the beacon on a chair in the middle of the room.

When the blimp can "see" the beacon, it's will go into navigation mode and the vectoring servo will move proportionally as the blimp steers towards the beacon (if you're holding the beacon and walking around, it should follow you). If the the blimp can't see the beacon, it goes into altitude hold-only mode, where the vectoring servo is pointed all the way up or down and it just holds altitude in one place.

Enjoy the show!

You'll soon be able to buy ArduPilot already made, but for those of you who would rather build their own, here are the necessary parts:

You can buy the boards here.

Eagle (PCB and schematic) files are here.

A pdf of the schematic is here.

Once you've made the board, instructions on setting the fuses and loading the bootloader are here.

A few notes on building the board: Aside from all the surface-mount components below, the only through-hole components you need to solder on are a 5-pin breakaway connector for the FTDI port (first five pins next to the GPS connector), the two 2x3 ICSP connectors, two 3-pin connectors for channel 1 & 2 output, one 3-pin connector for the power select and three pigtails (female-to-female servo connectors cut in half) for CTRL and channel 1 & 2 in. The other two channels (3&4) are not currently used. IMPORTANT: the power selector pins must have a jumper cap placed on two of the pins. Use the two closest to the servo-out ports if you're going to power the board from the RC receiver via the RC-in cables (that's what I've done in the picture above), or use the other two if you want to power the board with a separate regulated 5v power source. If you don't put the jumper cap on these pins, the board will have no power!

Components: ICs:

• 1x ATMEGA168: ATMEGA168-20AU-ND
• 1x ATTINY85: ATTINY85V-10SU-ND
• 1x Multiplexer (74LS157D): 296-14884-1-ND

• 8x 0.1uF: 399-3026-1-ND
• 1x 10uF: 511-1430-1-ND

• 2x Diode: BAS16WXTPMSCT-ND
• 2x Red LED: 350-2029-1-ND
• 1x Green LED: 350-2036-1-ND
• 1x Yellow LED: 160-1184-1-ND
• 1x Blue LED: 160-1646-1-ND

• 5x 1K: P1.00KLCT-ND
• 3x 10K: P10KJCT-ND

• 1x 16MHz resonator: 490-1198-1-ND
• 1x Reset switch (Sparkfun): COM-08720
• 1x Strip of breakaway connectors
• 1x EM406 GPS connector (Sparkfun): GPS-00579
• 1x EM406 GPS module (Sparkfun): GPS-00465
• 2x Female-to-female cables (cut each in half to make 3 pigtails to go to RC receiver): cables

• AVR ISP programmer and AVR Studio software
• FTDI cable
• FMA Co-Pilot
• Arduino IDE
• Latest ArduPilot (for the Atmega168) and MUX/Failsafe (for the Attiny) code. Check the ArduPilot home page for the latest versions.

Here are the instructions to build your own BlimpDuino platform. All the parts, with links and prices, are at the bottom:

Step 1: If you're buying a pre-made BlimpDuino board (not available yet), you're done! If you're doing it yourself, order the parts and assemble a BlimpDuino board. You'll need to also download the Eagle files from that post to see which components go where. Don't forget to check the polarity of the two big capacitors and the LEDs when soldering. Use the female machine pin connectors for the two motor outputs, and the male machine pin connectors for the 7-pin ultrasonic sensor connector. Once you've got the board assembled, set the fuses and load the firmware as per these instructions. Then you can load the BlimpDuino code with the Arduino IDE (remember to select "Arduino Pro" as the board. The latest code can always be found on the BlimpDuino home page.

Step 2: Cut out the gondola platform from the 1/16th plywood. Here are the dimensions:

• BlimpDuino board and components ($94.56)
• Servo ($8.00)
• Thin plywood (1/16th inch) (use any thin plywood or plastic you have around the house)
• 2x N20 motors (for much more power in RC mode, you can use these motors, but note that they will require changes in the code to lower the power to the motors in autonomous mode to remain controllable. They will also decrease battery life. ($8.00)
• 2x props ($4.50)
• LiPo battery ($12.99) (you'll also need a balancing charger and power supply if you don't already have an appropriate charger)
• Ground beacon ($14.95)
• 9v battery connector ($0.51)
• Envelope ($12.99)
• Helium (also available at your local Target in smaller but still sufficient size for about $29.00)

Lego parts: (All but the last can be found by going to Lego's "Pick a Brick" store and entering in the name in search box)

• 4x "Cross Axle 8M" ($0.64)
• 2x "Angle Element, 180 Degrees" ($0.32)
• 1x "Cross Axle, Extension, 2M" ($0.06)
• 1x "Double Conical Wheel Z12 1M" ($0.22)
• 4x "Technic Lever 3M" ($0.52)
• 4x "Technic Brick 1X2, Ø4.9" ($0.16)
• 1x large gear (only available from this third-party store right now; I'm working to get it in the Lego store) ($0.29)

Total: $158.32 (without helium)