Hackszine.com: Flying Things Archives

Archive: Flying Things

May 5, 2008

Cornell University's student microcontroller projects - Spring08

Another semester's worth of cool microcontroller projects has come to a close at Cornell University and Bruce Land sent us the results for the Spring 2008 ECE 4760 course:

Students in ECE 4760 at Cornell University were given the responsibility of choosing, designing and building a project using Atmel Mega32 microcontrollers. Over 30 projects this year include a trumpet MIDI contoller, a motorized guitar tuner, a eyeblink/head-motion computer controller, Biometric Authentication system, and a rocket inertial guidance system.

There are a number of projects worth commenting on, but I really thought the rocket guidance system that one of the teams created was a particularly smart idea. It's a bit of a misnomer - it's not the rocket that's guided during flight, but the post-flight payload. The microcontroller, an accelerometer and two stepper motors are employed to steer a simplified parafoil-style parachute on the descent, ideally delivering the payload to a specified location, such as the launch point.

It sounds like this particular project had some launch-day engine malfunctions, but the idea is great. Something like this could someday be used to help direct food payloads and other cargo drops to a specific, controlled destination.

I think this marks 10 years worth of great work that's been documented online for this course. As always, these projects are incredibly well documented, both on the hardware and software side.

Cornell University ECE 4760 Student Microcontroller Projects
Rocket Inertial Navigation System

January 23, 2008

Accelerometer motion analysis

There's an article over on the WiiLi Wiki that goes into great detail describing how to translate 3D accelerometer measurements into an estimation of the position, rotation, and velocity of a device like the Wiimote. By making a few assumptions—people's arms have a limited range of motion, most Wii play doesn't take place in moving vehicles, etc.—it's quite surprising what you can get away with with just the accelerometer data.

The amusingly named (but rarely used) term for the rate of change of acceleration is jerk. The jerk term for the remote shows up in the time derivative of the force recorded by the sensor, along with the rotation term that contains the angular velocity of the remote. We can extract both rotation and linear acceleration if we assume a few things:
We know the "up" direction before the motion starts.

Throughout the motion, the jerk on the remote perpendicular to the current direction of gravity is small.

Then we can assume the time derivative of the force component which is perpendicular to our current estimate of the up direction is caused by the user rotating the controller only. This allows us to update our estimate of the up direction for the next time step. In each time step, we can also get the linear acceleration of the remote by subtracting our estimate of from the current force sensor report. In effect we are integrating up a coupled set of ordinary differential equations. (Note, need to review the math here. Beware.)

The main problem with this technique is error accumulation in our estimate of "up." Since it is unlikely the user can keep the controller in constant linear motion without injuring themselves, the TV, or their opponent, we can look for times when the total reported force is close to g = 1.0 to recenter . You have to be careful when doing this because it is possible and probably common for the Wiimote to report an acceleration close to g = 1.0 while it is accelerating. When this happens your acceleration vector does not actually point "up" and you will recenter to an incorrect R. This can happen anytime you are accelerating both downward and in the horizontal plane.

I keep thinking that there should be some class of flying vehicle that, when operated under fairly restrained conditions, might be able to get by with just accelerometer measurements to obtain reasonably accurate state information. You could integrate the acceleration data through very limited motions that are within some margin of error, recalibrate, and repeat. This is probably a pipe dream, but I really want a solution for a $50 6DOF IMU. :/

Accelerometer motion analysis - Link

January 13, 2008

Arducopter: Arduino helicopter control

A recent Arduino -vs- Basic Stamp discussion over on the DIY Drones site really caught my eye. Jordi makes a nice argument for the Arduino, showing off the current state of his Arducopter, which you can see in the video above. Built using a low cost electric heli, an Arduino board, and the guts from a Wii Nunchuck, his system can currently auto stabilize roll and pitch. More detail and source code are posted at the link below. It's a really great start.

I've also been working on an autonomous helicopter project. While I've been able to build a general game-plan and test a few things with my BS2 controller, I know it's going to be insufficient for the device's needs.

I can say this with a bit of certainty, because I've built a GPS-guided RC car in the past using the BS2. Even with heavy optimization, I used just about all the available memory on the Basic Stamp. There's not much room to read additional accelerometer data and manage the control outputs of even a little 4 channel heli. Long story short, I've got a Boarduino in the mail.

Can a Basic Stamp manage reading and processing accelerometer, compass, and GPS data at the same time? If so, I'd love to hear it, but I'm thinking it'd be difficult to impossible. Don't get me wrong—I love my BS2. It's great for prototyping and quickly building smaller projects. Objectively, though, the Arduino is a little faster, has more ram, and costs much less.

Arducopter - Link
DIY Drones discussion on Arduino versus Basic Stamp for UAVs - Link

December 21, 2007

Essential hacker stocking stuffers

Like most of us, you've probably got some last-minute shopping to take care of. Or maybe there's a special someone in your life who keeps asking you for gift ideas and you need to start dropping hints to avoid another button down and a neck tie. Whatever the reason, here's a quick and dirty hacker gift guide with a variety of gift ideas that should put a smile on someone's face.

Make sure to add your own favorites to the list in the comments area and pass it along. I'm focusing primarily on smaller items that are available in local stores, but feel free to toss in whatever you think is important and shouldn't be missed.

Reading Material:

Make: The Best Of - a killer collection of the best 75 projects from our favorite magazine.
The Dangerous Book For Boys - this is a great book for sharing with your kids. Chock-full of essential information like how to tie knots, play poker, use a compass, build a tree house, and relate to girls.
Knoppix Hacks, 2nd Edition - the swiss army knife for your computer.
Illustrated Guide To Astronomical Wonders - ideal for anyone who's interested in knowing their way around the universe.
Also check out other books from the O'Reilly Hacks Series - Link

Gadgets:

Asus Eee PC - this ultra-tiny Linux laptop is just starting to appear in stores - Hacks
Linksys WRT54GL Router - the L in the GL stands for Linux. It's a $60 router that can be customized to do more than it's thousand dollar big-brothers - Hacks
Western Digital MyBook World Edition External Hard Drive - any extra storage is really nice to have, but this network-available drive contains mirrored RAID storage and a mini Linux computer that can run a web and database server - Hacks
iPhone or iPod Touch - did I really put that here? - Hacks
Broadband Mobile Card from Verizon or Sprint - they are getting super
popular, and heck, they are cheaper than an iPhone.
Nokia N95-3 - the winner of our most hackable mobile phone survey - Hacks

Toys:

Air Hogs Havoc Heli Laser Battle - remember the Picco-Zs and their clones from last year? Here's two of them in a single package, enhanced with a trigger that let's you zap your friend's heli down.
E-Sky Lama V4 Helicopter- Yeah, I'm crazy for helicopters right now. The counter-rotating models like this one are about $100, ready (and easy) to fly, and very hackable.
WowWee RoboSapien V2 - fun for the kids. More fun with a soldering iron - Hacks

Gear:

2GB or larger micro SD card, plus various SD and USB adapters - perfect for scooting files around, the size of a finger nail, and you can put a full Linux distro, anti virus software, or a Puppy Linux virtual machine on it - Hacks
Mini Multimeter - always handy.
Bike Multitool - a good one will pack allen and hex wrenches, screw drivers, and a knife into a pretty small package. Perfect for voiding warrantees in a pinch. Oh, and there's a chain tool, too - Link, Link
Soldering Tools - whether it's a new Weller or just a pair of helping hands, it'll be welcome in any stocking - Link, Link

What have we missed here? Add your wishes to the comments. Then find a completely non-tacky way to get this list into the hands of someone who wants you to be a happy hacker.

November 11, 2007

Lego Autopilot

Chris Anderson came up with a kid-hackable UAV, the GeoCrawler 2, using an RC aircraft and a Lego NXT:

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.

Instructions for the GeoCrawler 2 project are available at Chris' DIY Drones site, a growing social network for folks interested in building unmanned arial vehicles.

This is really an underexplored area of amateur robotics, primarily because it's been so cost prohibitive until very recently. I'm excited to see what people come up with over the next year or two. I expect it will be mind-blowing.

GeoCrawler 2 (Lego Autopilot) Instructions - Link
DIY Drones - Link