The following is a tutorial on how to setup a motorized trim wheel using a Pololu hardware feedback interface board and ProsimA320. Alternative avionics software such as Jeehell FMGS does not have native Pololu compatibility and will require additional driver support, such as FSUIPCtoPololu from TNS-Systems. Hardware trim setup can be reviewed over here.
Wire up the feedback potentiometer to the Pololu (Jrk 21vs3 used in our setup) as follows:
Connect the power supply for the DC motor to VIN and GND. Wire up A and B to the motor output pins.
Install the Jrk configuration software. Connect the Mini-B USB to a USB port on the computer.
Run the configuration software. Go to the Feedback tab. Select ‘Analog voltage’. If your potentiometer is connected correctly the ‘Scaled Feedback’ numbers should change when you move your trim wheel. Click on the Learn button to set the limits of the trim wheel.
Next, go to the Motor tab. Click on ‘Detect Motor Direction’. Follow the dialog boxes and the software can determine the direction of the motor and if it needs to be inverted.
** PID tab ** ; it is a requirement to enter a value in the Proportional Coefficient to ensure motor function. Values depend on your type of DC motor and gears. Experiment with different numbers. For our setup a value 3.0 is used.
Go to the Input tab. Change the Input mode to ‘Serial’. Click on the ‘Automatically set target’ box. Now when you manually set a target the DC motor should move the trimwheel until it meets the target.
Experiment with different Proportional Coefficient values until your trimwheel is accurate in meeting the target values.
The speed of the trimwheel can be changed by going to the Motor tab and adjusting ‘Max Duty Cycle’. A value of 200 was used in our setup.
Setting up with ProsimA320
Open the ProsimA320 Systems application. In the configuration page go to Flight Control, Lever, Elevator Trim.
Select the Jrk feedback board and ‘Feedback Input’ for Analog input. For Motor output select ‘Motor output’.
Physically move your trim wheel to the different trim numbers (4 DN, 0, 4 UP, 8 UP, 13.5 UP) and click the appropriate boxes to set the values.
Move the slider to set a target. The trimwheel should now move until it meets the target value.
Thats it! No script writing is required with the Pololu hardware and it allows you to easily fine tune the motor function. The trimwheel should now automatically trim when the aircraft is in normal law. On landing the trim resets to zero.