The Flying Gator

More on the ardupiolt Mega and the Transterpreter. When we started the Transterpreter did not support Arduino Mega boards… this was a problem as we are using the Mega to fly our plane. Currently Matt, Drew, and Radu are working on getting us Mega support and are doing an awesome job. We should have it soon. Due to not having the Mega support right away we have been using a Freeduino to do all of our testing on so far.

It has worked great so far, but for the GPS we need 2 serial ports to see whats going on and we only have one. We did however emulate a running GPS and from that wrote a simple GPS string parser. Once we get the mega we may refine our parser, but as of now it works pretty good!

One more hurdle we have tripped over is that floating point numbers are not fully supported in the Transterpreter. We can use them but we can not print them to our screen and see whats going on so. We hope to have floating point printing soon. It has not hampered us to much though.

More to come a post on how we interpreted the output of our sensors.

Yesterday we received a package from Hobby King. This is our new battery charger. It charges and discharges up to 6-cell Li-Po battery packs as well as NiMH and NiCD battery packs. It also has a built in Li-Po cell balancer.

These are our batteries so we can use our charger… and power the plane! They are 4 cell 3000mAh Li-Po batteries and they have a 20c discharge rate. This means we can continuously pull 60 amps from each battery. We will only use one at a time though.

This is the speed controller we got for the motor. Its a 60 amp controller with cell protection which protects the battery from being over discharged.

This is our motor. It will spin a 12 in. propeller at about 8000rpm!

More updates to come on the sensors that we have been using and some of the programing we have been up to.

The fuselage, like the wing, was built using both pink insulation foam, and the foam core poster board.

First the two side panels were cut out of the pink insulation foam.  A bottom plate of white posterboard was cut out andthe two side panels were glued to the bottom plate.

Formers were glued into the fuselage to support the two side panels and help them keep their shape.

A wooden plate was glued to the bottom of the fuselage to allow the attachment of the landing gear. A plate was also glued to the inside of the fuselage to prevent the nuts from pulling through the foam. The landing gear was then bolted in place.

A balsa wood box was built to allow the front nose wheel to be held in place. Plastic bushings were glued into the wood to make sure that the nose wheel turns smoothly.

A wooden box was crafted to allow attachment of the motor. The design of the rear of the fuselage was changed slightly as the motor was larger than expected.

The tail was built using 3/8 inch square hardwood rods, and carbon fiber strips glued to the top to reduce flex.  The horizontal member of the tail was cut from pink insulation foam  and the vertical members are white posterboard.  Both horizontal and vertical stabilizers have carbon reinforcement.  The tail was made removable with four bolts and plastic wingnuts.  Wooden plates were glued inside and on the bottom surface of the wing to make the foam sturdy enough to handle the stress from the tail.  In the next post we will show the next batch of goodies that arrived in the mail.

To catch everyone up on some of the details of the Flying Gator build I will walk through some of the construction steps (with pictures) that were involved.  The motor, batteries, speed control, and charger should be here from Hobby King in a couple days, and the Razor IMU unit should show up later today so there will be more updates when those arrive.

The first day that we officially started working for the summer, I jumped right into the construction of the wing.  I had originally intended to just make a modified wing for the slow stick, but couldn’t resist doing more.  The wing and fuselage were constructed using both 3/8″ pink insulation foam from Home Depot, as well as white foam core poster board that is available at the Dollar Tree (thats right a dollar a sheet!).

Wing Construction

Aircraft wings have three main structural components: Ribs, Spars, and Sheeting.  The ribs form the profile of the wing, and many are used from the root to the tip of the wing.  The airfoil shape that was used in the construction of our UAV is the Clark-Y.  This airfoil has very nice flying characteristics and allows for a very stable wing. Spars run from length of the wing to provide support, and a place to connect the wings together at the root.  Our spars are fifty cent Home Depot yard sticks that have lightening holes drilled in them.  The sheeting is the “covering” of the wing.  There is sheeting both on the top of the wing as well as the bottom.  In typical construction the bottom sheeting is foundation of the wing, and the ribs and spars are build on top.  Once the ribs and spars are completed the top sheeting is formed over the airfoil to give us a nice aerodynamic shape.

Each wing panel was built separately so that the wings could be connected at the correct angle. The wing spar was glued directly to the bottom wing sheeting and then left to dry. The adhesive used was gorilla glue, which is great for use on foam due to the expanding action. Gorilla glue also sands very nicely which makes it easy to shape.

The ribs were then cut out of the pink insulation foam using a template obtained through the airfoil generation software, Profili 2.0. The ribs are 12 inches in length

The ribs were cut in half and the trailing edge pieces were glued into place. Ribs were spaced at five inches except for at the tip, the root, and where the tail booms are to be attached.

The front half of the rib was then glued into place.

Once both wing panels were built (making sure not to build two right wing panels!) they were connected with a small amount of dihedral. Dihedral is the V shape that the wing has which gives the plane a very stable flying character.

More sheeting added

In the next post I will include details on the fuselage construction as well as information on the removable tail that we built.

The goodies

The red Sparkfun box we had been waiting for arrived early last week.  Everything that was ordered came in… Here is a look at what we bought.

1) ArduPilot Mega

This board is the bigger brother to the very popular Arduino Based ArduPilot.  The ArduPilot Mega was designed by Chris Anderson and Jordi Munoz at DiyDrones.  The Mega utilizes the Atmega 1280 microprocessor which has 16 MHz of processing power, as well as the Atmega 328 as a hardware failsafe in the case of a program crash.  The pilot has the ability to reroute servo control back to the Radio control transmitter and turn the autopilot off through the 328 processor in the case of a software problem on the main processor.  The ArduPilot Mega has can be used with up to 8 channels from the Radio Control system.

ArduPilot Mega control board

2) Venus GPS Receiver and external antenna

The Venus GPS receiver boasts better than 2.5 meter accuracy which gave this chip the heads up over the other GPS chips available.  It allows tracking of 14 seperate satellites (even though its only possible to see a maximum of 12 at once!), as well as a refresh rate that can be increased up to 10Hz! The Venus ouputs standard NMEA data and has both a UART serial interface as well as SPI connectivity.  At just under $50 for the Chip and another $12 for the antenna, it is a very attractive choice for this level GPS.

Venus GPS Receiver and External Antenna

3) Razor 6 Degree of Freedom Inertial Measurment Unit

The Razor IMU contains one LPR530AL two axis gyro (pitch and roll), one LY530ALH single axis gyro (yaw) , and a ADXL335 three axis accelerometer. This is a very compact chipset that should give us a good idea of what attitude we are at in 3D space.  The chip we received initially from Sparkfun had a few surface mount components that were missing or not where they were supposed to be, but Sparkfun quickly remedied the situation and dispatched a new board right away.  Thanks to the folks at Sparkfun for great customer service!

Razor 6DOF IMU

Coming Soon: Building the Flying Gator!

Thats all for now!

A very stable aircraft is important in UAV design and construction.  Originally we had proposed purchasing and building the very popular GWS Slow Stick that has helped many beginners start their journey into the world of Radio Control airplanes.  Being basically a stick this airplane would lend itself well to attaching sensors and other cool “stuff”. But…

After researching, it seems as though the Slow Stick is not the greatest platform since it only utilizes a three channel control system.  Each radio control channel gives you proportional control over one aspect of the aircraft while in flight; in the case of the slow stick throttle, rudder, and elevator are the three controls available.  Throttle controls the speed of the airplane, elevator controls the pitch of the nose, and the rudder on the Slow Stick (due to the large amount of dihedral) has both an effect on the roll and yaw of the airplane.  We decided that we would like to have individual and finer control over the roll and yaw axes of the airplane in flight.  This would require at least a custom wing, or a different platform…

The Flying Gator

Wingspan: 62″

Wing Chord (front to back): 12″

Sneak Peek of the Flying Gator

Here is a quick look at a picture of the wing seated on the fuselage.  The wing is all foam construction with a full length wood spar, and carbon fiber/ wood leading edge.  More construction details will follow with pictures!