Thursday, March 25, 2010

9DOF Board Has Arrived!

Alright, so a few updates since the last post:

The 9DOF IMU (Inertial Measurement Unit) has arrived today from SparkFun. At 1.95" x 1.10", the board is only slightly larger than the MaEvArM. Currently, the connections are set so that the board outputs all of the sensor data over the serial output (Tx and Rx pins), however we'll be looking into the other possible connectors on the board (look like SPI). If they are, we may be able to use the board to grab data from our barometric pressure unit, which also arrived today. This keeps the sensor data separated from our main processor (the Atmega32U4 on the MaEvArM) which will be doing the PID and motor control. More on this board will be posted soon.

9DOF Razor from Spark Fun

FTDI USB to Serial adapter from Spark Fun:

Barometer IC from Spark Fun:

MaEvArM Microcontroller with ATMega32u4:

The props have arrived. We've decided to get a couple variations to test which works best. (All our sets consist of two normal and two counter-rotating blades. This prevents us from having to tilt the motors in order to counteract the rotational inertia).
  • The first set are two-blade, 8x3.8 props. (8" diameter, 3.8 blade pitch). These are fairly large rotors and have decent specs when run on our motors (will post more detailed results later).

  • The second set are tri-blade, 7x3.5 props (7" diameter, 3.5 blade pitch). After some research, it was found that tri-blade props can be quieter than dual-blade when run at the same speed. We'll also post tests with these props once the motors come in (still on their way from Singapore!).

Lastly, we've been starting to program the MaEvArM's basic tasks to ensure that our specifications will be made. So far, two main tasks have been tested and working properly:
  • Four 16-bit PWM channels (0-65536 resolution) have been tested to control the four motor controller (Brushless ESCs). With the System Clock set to 8MHz, a 150Hz output signal was able to be generated with a resolution of 0-53333 (this will have to be tested with the ESCs since they normally take 50Hz Remote Control Standard servo controls).
  • Buffered Interrupt-controlled serial communication was successfully accomplished by modifying the AVR306 (Atmega UART) code to work with the Atmega32U4 registers. This will allow us to read the output from the 9DOF board without wasting CPU usage (allowing for our PID calculations, PWM Control, and Wireless Receive to run continuously). This code uses a Circular Buffer technique to get store data when the CPU is in use and read it when it has time to.

That's it for now, but we'll keep you updated with our progress!

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