BFF CL Software - Short User Guide


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Appendix A. Configuring the CL system for "Potentiometer-less" operation.

IMPORTANT - "Pot-less" mode is now the default mode for the system and all BLDRV-12/24 cards and newer CL_SPU + BLDRV2-24 cards are supplied preset for this mode.

In its original configuration the CL system used game-controller joystick card potentiometers to report control axis position (see the standard system wiring diagram). This potentiometer data was required for the power-up calibration of the BLDRV-12/24 driver cards, and also as control position input to the flight simulator software.

For systems using BLDRV-12/24 driver cards with firmware dsPIC v35 and 20X v28 (or later) the system can now be operated by default WITHOUT potentiometer position data on the main control axes. This allows the control mechanisms to be built without position reporting potentiometers - a significant simplification of the build. Instead control axis position is derived from the motor encoder position and is sent directly to FS by the BFF CL Software v1.1 (or later) via the FSUIPC control input offsets.

The "potentiometer-less" system wiring configuration is shown here.

Although this produces a simpler system, it does mean that control input to FS is only available when the CL system cards are powered-up and calibrated and the BFF CL Software is running. When the CL system is inactive there will be no control input to FS from the FFB flight controls. A separate simple joystick configured as a standard game-controller input to FS might prove useful for controlling FS in circumstances when the CL system is inactive. So long as the output from this joystick is clean (no jitter) FS will ignore it whilst it is not in use.

To configure the CL system for pot-less operation the driver cards must be pre-set, and then a configuration change made to the CL software background process settings. Note all BLDRV-12/24 cards now supplied are by default configured for pot-less mode operation.

"Potentiometer-less" operation configuration steps

  • If required - Pre-set the driver cards for "potentiometer-less" calibration. This is a once-only procedure carried out using the BFF Driver Test App v28+. Once set, the cards will be able to complete their power-up calibration without the presence of live game-controller joystick position data. Not required for new cards - they are already pre-set for this mode.

    See section 10 of the BFF Driver Test App user guide for details of the procedure; it is a simple procedure carried out on each card individually.
  • Set the BFF CL Software for pot-less operation. This will tell the CL software to read control position data from the driver cards and write it to FS via FSUIPC. The position data is written directly to the FS control offsets WITHOUT additional calibration, as a result the control input to FS is linearly proportional to the drive motor rotational position. Usually (depending on the flight control mechanics) this also means the control input is linearly proportional to stick position.

    To make the settings run the Configuration Manager and select Tab 5 Item 1 "Use Motor Encoder Positions". Click the Apply button.

    Then set Tab5 Item 25 = 1 (Fixed x10 resolution enable).

    Save the settings to file.

In operation the CL software will then check the driver cards for valid firmware and if confirmed will proceed to read control position from the cards (encoders) and write to FS via FSUIPC. A healthy background process loop rate (50 Hz or ideally higher) is required to minimise lag in the FS control movement. If necessary in the Configuration Manager Tab 6 Item 13 Force loop delay parameter can be reduced to increase the processing rate - but keep it below 100Hz.

The changes made to these settings apply whenever the CL software runs and so to all aircraft configurations used by the CL Software thereafter.

IMPORTANT If you are swapping an existing system over to "pot-less" operation remember to remove the unused joystick axis assignments in FS. If FS "sees" additional joystick control inputs at the same time as receiving CL position instructions the FS controls will jitter.

Although pot-less operation removes the need for potentiometers on the main control axes, a joystick card will still be required for the trim inputs to the CL system. These can be by pot or by button - see the section 7.

FS control input calibration in "pot-less" mode

When operating in "pot-less" mode the FS control positions are written directly to FS (via FSUIPC) by the CL software - this prevents calibration of the FS control response using the usual gamecontroller or FSUIPC calibration methods. With the BFF_CL_Background process v1.25 or later this calibration can be done within the CL software.

Please use the Configuration Manager - use Tab 5 Items 6, 7 & 8 to set "sensitivity" factors for each of the control axes as required. These factors adjust the movement response of the FS controls to the movement of the real controls - read the displayed help tips for more details.

The settings can be used to either slow or speed-up the movement of the FS controls with respect to that of the real controls when operating around the mid-point region. 

Inhibiting Flight Control position writes to FSX when in "pot-less" mode

If the system is set for pot-less mode the control position writes made to FSX via FSUIPC by the CL system can be disabled. This allows users to provide their own position feedback to the flight sim without changing the operating mode of the driver cards.

To disable the position writes from the CL system go to Configuration Manager Tab 5 Item 27 and set it =1.


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