GeoCrawler 2 (Lego Autopilot) Instructions

Description: The main aim of this project is to both make the world's cheapest full-featured UAV and the first one designed to be within the reach of high school and below kids, as a platform for an aerial robotics contest. Like the Lego FIRST league, but in the air.

(There is another aim of this project, which is more about policy. At the moment the FAA regulations on UAVs are ambiguous (we believe that by staying below 400 feet and within line-of-sight we're within them). But there is a good deal of concern that as small and cheap UAVs become more common, the FAA will toughen the rules, making activities such as ours illegal without explicit approval. I hope this project will illustrate why that approach won't work.

By creating a UAV with Lego parts and built in part by kids, we haven't just created a "minimum UAV", we've created a reductio ad absurdum one. If children can make UAVs out of toys, the genie is out of the bottle. Clear use guidelines (such as staying below 400 feet and away from tall buildings) would be welcome, but blanket bans or requirements for explicit FAA approval for each launch will be too hard to enforce. The day when there was a limited "UAV industry" that could be regulated are gone.)

Features: In GPS mode, unlimited pre-programmed waypoints, with programmable options such as circle and hold. Ability to integrate other sensors, such as ultrasonic, compass, gyros, accelerometers, or barometric pressure (altitude). With optional bluetooth cellphone integration, control via text message, including dynamical-changed GPS waypoints, "come home" and "circle" commands, etc.

This is the most complete UAV, so I'll start the instructions here from the beginning:

1. Learn to fly R/C planes! These UAVs don't take off or land by themselves, so you've got be a competent pilot. If you've never flown before, I suggest starting with a Hobbyzone Firebird Phantom ($60). Once you've got the hang of that (you'll crash a lot when you start, but it's tough and can take it), upgrade to the Hobbyzone Aerobird Swift ($150), which has ailerons. Don't worry if you total this bird; we'll be able to use its radio system later.
2. Get the UAV airframe: a Hobbico Electristar (63" with radio and motor, $299). You're going to need to upgrade a few things from the basic kit. First, we need a six channel transmitter to handle autopilot functions (this one [$120]is fine; you'll use the spare bits sooner or later). Also, don't buy the recommended NiMH batteries. We'll need to save weight, so go for two of these Li-Ions instead ($80 each). You'll also need a Li-Ion charger ($130) and balancer ($30)
3. Autopilot: I'll assume you've already got Lego Mindstorms NXT. For the basic version of the UAV you'll also need a compass sensor. You can see how the whole thing works here (it's easy to build the mechanical assembly, which is quite simple. Just remember to screw the base pieces into the airplane's plywood servo floor so they don't move) Here's the Mindstorms code: Main, Subroutine (download both). Note: the the GPS version is still in development. You can see the pbLua code that integrates GPS abd Bluetooth integration with NXT, which was done by Ralph Hempel, here.
4. For stabilization, use the FMA Direct FS8 Co-Pilot, which uses infrared sensors ($115).
5. For video, use the Range Video Aerial Video System 2 (camera, rx and tx, $365; pick the "portable video" option, which gives you a rechargeable battery on the receiver). You'll get much better range and transmission quality if you use this directional antenna ($44) on the ground. It screws into a standard camera tripod and you can have someone keep it pointed at the plane in flight.
6. You can build a pan-tilt camera mount out of Lego and some spare servos, like this. Use the spare transmitter, receiver and battery pack from the Electristar to control the pan-tilt. Or, if you crashed the Aerobird Swift, its repurposed transmitter, receiver and servos will work fine--you can even use its motor power output to power the camera, turning it on and off with the throttle slider on the transmitter! I assembled the whole video downlink assembly on the back of the Electristar battery door, like this.
7. For recording and viewing the video, you'll want a video capture card for your laptop. Anything will work, but if you have an ExpressCard slot, I recommend the Avertv Express MCE.
8. It's hard to see laptop screens in daylight, so you might want to get one of these screen shades.
9. Later, we'll add the GPS and cellphone for real-time waypoint uploading via SMS.

Notes:

Many people have asked why the Lego autopilot moves the whole servo back and forth, rather than just controlling the servo arm the way a R/C receiver would. There are three answers to this: 1) we always want to have a manual override, so in this case you can manually control the rudder servo arm even as the autopilot is moving the whole assembly back and forth to control the rudder another way. 2) I know of no good way to communicate directly from the NXT brick to a R/C servo. 3) Even if I could control the servo directly from the NXT, it's difficult to transfer control from one system (R/C) to another (NXT) in mid-flight.