Trim Devices

Usage

The elevator, aileron and rudder are nominally controlled by the yoke (elevator and aileron) and the pedals (rudder). The fine adjustment of these controls will be performed by dedicated trim devices, one for each control, i.e. elevator, aileron and rudder. Each of these trim devices are implemented by one rotation encoder and one servo. The functionality is as follows:

Elevator Trim Device

The conceptual and the final design of the rudder trim device is shown in the right picture. The trim device is made out of rigid white FOREX foam (2 mm and 5 mm thick) and PLA parts, made by a 3D printer. All visible parts are finally sprayed with black dull and bright paint. The implemented design required a servo gear train (1:1), turning the trim indicator, which is on the same axis as the rotation encoder.

The trim indicator will be illuminated during dawn-dusk and night flights by a 5 mm white LED. The elevator can be set by the trim wheel within a range of -15 to +15 degrees, which is shown on a small scale within the elevator trim case.

Printing the 3D parts is straight forward. However for the trim wheel three dedicated parts were necessary, as shown below. These were properly sanded to achieve a smooth surface and then glued together. In a last step the wheel was sprayed with black paint.

Rudder Trim Device

The rudder trim device is made out of rigid white FOREX foam (2 mm and 4 mm thick) and PLA parts, printed by a 3D printer. All visible parts are finally sprayed with black dull and bright paint. The trim indicator will be illuminated during night and dawn-dusk flights by a 5 mm white LED, which is located in a dedicated small 3D printed housing. The conceptual design of this trim device has been taken from www.simvim.com/b58.

The rudder trim device has 3 electrical connections:

The encoder will issue a positive or negative signal, depending on the turn direction of the encoder, and hence the trim wheel, which will be processed within the micro-controller to issue an event to FSX. The rotation encoder is connected to the Flight Control-Controller by the following ports:

The servo is connected to the Servo Slave-Controller at port PD7, Servo 2, RUDDER TRIM.

The actual trim position will be transmitted from FSX by the “RUDDER TRIM PCT” variable, which has a range from -1.0 to +1.0. The most left position is -1.0 and the most right position is +1.0. To indicate to FSX, that the rudder trim shall be increased or decreased, the following Events are used:

Aileron Trim Device

The aileron trim device is made out of rigid white FOREX foam (2 mm and 5 mm thick) and PLA parts, made by a 3D printer. All visible parts are finally sprayed by black dull and bright paint. The trim indicator will be illuminated during dawn-dusk and night flights by a 5 mm white LED.

As for the other trim devices, it consists of a rotation encoder, a servo and a gear train with 40 and 20 teeth. The labels are printed on glossy photo paper and were finally glued to the correct position on the fixed trim scale and the turning one.

All three trim devices are mounted onto the left and front side of the pedestal.

The trim devices are controlled by the Flight-Control controller, as shown below in the schematics, which is built up around an ATmega32 micro-processor. The cables of the trim devices are connected to the connectors SV1 and SV2 (only pin 4).

However it shall be noted, that the pulse signals for the three servos are generated by a dedicated servo slave controller, which is built up by an ATmega8 micro-processor. This separation was necessary because generating the servo pulses will take a lot of computation time (including delay loops) and would significantly affect the performance of the communication throughput with FSX. The interface to this slave controller is realised by the connector SV7 - Bank 2a and is based on a handshake procedure.

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