I'm an undergrad EE student at Georgia Tech and this summer I'm working in an aerospace research lab at Penn Sate University, headed by Dr. Jack Langelaan. My project is to outfit a Zagi THL glider with an autopilot system. The reaserch is being funded by the NSF, and the aim is to work on developing open-source autopilot hardware and software, with a goal of having the drones do useful work, such as monitoring meteorological conditionsWe want our autopilot to be based around an IMU. We're using an IMU because we need a system that is more robust than the IR sensors that the ArduPilot is based around. This system will need to be able to stabilize the aircraft in heavy clouds, near mountains, and in other conditions that are likely to fool the IR sensors.We were initially planning on using the Sparkfun 6DOF V4, but due to the availability of the Vectornav VN100, we have decided to use that instead. Connecting either module to the ArduPilot presents a challenge because of the limited IO ports on the ATMega microcontroller. However, while the Sparkfun module only has a UART interface, the VN100 also has SPI, which should make it relatively easy to interface with.The VN100 implements an extended Kalman filter onboard, so we will get an attitude solution from the module, which we will use on the ArduPilot to stabilize the aircraft.Navigation will be accomplished using a GPS, in our case the u-blox 5 module from Sparkfun. This seems to be one of the best chipsets available today, and unlike NMEA, the ubx protocol provides vertical velocity data, which is useful for aircraft navigation.Our airframe is a Zagi THL glider. This is a flying wing, with elevons as the only control srufaces. This makes control of the aircraft slightly more difficult than with an Easystar, as it requires mixing of the control surfaces to execute a level turn. I've attached a photo below.I'll keep this post updated with my progress throughout the summer, and add more details about some of the pieces I'm working on.
Wondering if anyone might have experienced a problem that I'm having. My ArduPilot has been working fine, but yesterday, the servo outputs suddenly quit working. After doing some troubleshooting, I think I've narrowed the problem down the the multiplexer (74ACT157). It gets power, and gets a proper signal from the failsafe, and I found a 50 Hz signal on the inputs. However, the outputs are always low, at 0V.I've been using a 4-cell, 4.8V receiver battery to power my setup. When fully charged, it gets up to 5.3V, which should be safe for the multiplexer. Maybe I shorted out one of the outputs, or zapped it with static? Anyone else had a similar problem?
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I received my u-blox GPS receiver and connector from Sparkfun recently, and needed a PCB to hook it all together. I've put together a simple layout including a lithium backup battery and a 4-pin 0.1" header to connect it to my ArduPilot.I've attached the Eagle file for the layout. I case you don't have Eagle, you can get it free at www.cadsoft.de. I've also attached two PDFs, one with labels, the second with only the traces and pads, mirrored to use for toner transfer. This is such a tiny board that I didn't want to send it off to be made, so I used to toner transfer method to make a quick prototype. I didn't have the proper transfer film, and used inkjet photo paper, which didn't work great, but was good enough for a first prototype.The GPS connector is a bit tricky to solder on, but if you have some experience with surface mount soldering, it is not much different than a fine-pitch IC. You might want to order a couple of extra connectors in case they get damaged, they seem pretty delicate. I chose to not use to backup battery at this time, and connected a jumper wire from the positive pad for the battery to the 3.3V supply. The correct battery for the PCB is part P244-ND from Digikey. It was tabs attached to the battery to allow it to be soldered to the PCB.The GPS connector does not provide a good mechanical connection, so the breakout board must somehow be attached to the GPS receiver. I used double-sided tape for this.After connecting power to the board and hooking it up to the PC with a 3.3V FTDI adapter, I successfully connected to the receiver with the u-blox software, and got a GPS lock. Now on to getting it working with ArduPilot!Note: This is a single sided board - the GPS connector mounts on the top (copper) side, while the 0.1" connector and battery mount on the bottom. You must take care to ensure that the battery lead does not extend far enough to touch the receiver PCB (and possibly short something).UPDATE: I've temporarily removed the PCB files. The way I had the TX/RX pins on the board was swapped with respect to the ArduPilot, so I am fixing that, and will post new layout files soon.
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