Revision 1Revision 1 hardware was designed around a PIC 18F66j11 Microcontroller due to its very low cost. Unfortunately, this ended up being the revision 1 killer. The particular 18F66j11 was unable to reliably operate FreeRTOS due to random stack underflow / overflow issues. There seemed to be issues with Microchips support of this particular chip due to its lack of widespread use, and very low cost. The linker script seemed to be full of errors, leading to improper / unreliable ECCP module operation. Revision 2The revision 2 motor controller is designed to control the speed and acceleration of three brushed DC motors, and provide a combined continuous current of 17 amps off power supplies of up to 12 volts. It utilizes the ST-Micro STM32 Cortex-M3 ARM Microcontroller to perform all the required functionality (And handles this with ease).  Image of Revision 2A Motor Controller HardwareRevision 2A Features:
Hall Effect Propeller Speed SensorsHall effect sensors are transducers which operate by sensing a magnetic field. The hall effect sensor used in the TresCopter contain internal comparators which compare the sensed magnetic field to a preset threshold. When the magnetic field exceeds this threshold (i.e. the magnet is close enough to the sensor), a signal (falling edge in this case) is sent to the micro-controller (indicating a revolution). Magnets are attached to the output shaft of the motors, and hall effect sensors are placed near the motor shafts and connected to the RPM inputs on the Motor Controller Board. When a magnet nears the hall sensor, a signal is sent to the motor controller.  Image of US5881 Hall-Effect Sensor Image of Hall Sensor to Magnet ClearanceThe hall sensor must be mounted as close as possible to the magnet in order to avoid double triggering the sensor, and causing erroneous (extremely high!) readings. AssemblyThe PCB's are assembled by hand using a toaster oven reflow method for surface mount components. This method is similar to the skillet reflow method, and uses many of the same principles (such as solder paste). A great tutorial is available by Sparkfun Electronics. Through hole components (only the .1" headers / connectors) are currently soldered by hand. |