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Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects 9.2.3 Transmitter/Receiver Selection As mentioned in the previous section, the transmitter and receiver must be capable of supporting six channels; four control channels and two switches. In addition, the transmitter needs to be lightweight as it is included in the total weight score at competition. Also to meet requirement 0.PRJ.7 the transmitter must have a fail-safe mode that is automatically selected during loss of transmit signal. During fail-safe the aircraft receiver must select throttle closed, full up elevator, and full right or left aileron. After in-depth research the team has selected a transmitter and receiver that will fulfill all the necessary requirements. The transmitter selected is the Spectrum DX 6i with the BR6000 receiver [30] , both shown in Figure 86. Together these components have an overall weight of 2.0 pounds and operate on a frequency of 2.4GHz. Figure 86: Transmitter and Receiver With the appropriate transmitter and receiver selected, it is important to understand how all of the components will be connected to ensure functionally of the communication system. The rudder, throttle, aileron, and elevator commands are controlled by the main four channels. For extra control over the elevators, the second elevator servo is linked through the fifth channel, the flaps channel. The microcontroller arming switch is controlled through the final channel, the gear channel. The overview of the wiring can be seen in Figure 85. To save on complexity of the wiring inside the aircraft, all Y-harnessing is done through the circuit board. 9.2.4 Servo Selection The servos for the control surfaces and releasable payloads must provide adequate torque and be lightweight as the overall weight of the aircraft is an important design factor. The servo selection was divided into two groups: aircraft control servos and external store servos. All servos were selected based off the torque they can produce using 6 volts, which is the voltage 108
Project Final Report – CUDBF April 30 th , 2009 ASEN 4028: Aerospace Senior Projects provided by the receiver. The selected servos are from Hitec ® RCD [31] ; Hitec was selected over other manufacturers due to superior servo selection and performance. The required torque for the controls surfaces were found for the worst case scenario, cruise speed and maximum deflection of 25 degrees. The servos selected for each control surface is displayed in Table 23. For the nose gear, a servo was selected that would provide adequate torque to allow the nose gear to steer the aircraft while on the ground. Table 23: Servo Selection for Control Surfaces Control Surface Required Torque (oz-in) Selected Servo Servo Torque (oz-in) Aileron (2) 38.4 HS-125MG 48.6 Elevator (2) 47.8 HS-225MG 66.65 Rudder (2) 22.2 HS-82MG 47.22 Nose Gear 31 HS-82MG 47.22 The required torques for the external stores were found for the minimum needed to release the stores. Table 24: Servo Selection for External Stores and Nose Gear Required Torque (oz-in) Selected Servo Servo Torque (oz-in) Wing Stores 30 HS-125MG 48.6 Centerline Store 60 HS-77MG 76.3 9.2.5 Eagle Tree Telemetry Capabilities An overview of what the data recorder is capable of measuring during flight is shown in Figure 87. This data recorder will be vital to the testing and verification plan for next semester. 109
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