Fabricating Flaps Controller

I shared the design concept for my custom flaps controller a few weeks ago, and I got some great feedback from other pilots & builders. I’ve taken that feedback and made a revision 1 of the hardware, to include:

  • Stand-alone operation (no additional parts needed, connects directly to the flaps motor/position sensor)
  • Programmable flaps positions for each of the switch positions
  • Backlit labels
  • Legends and position indicators dimmable via external input
  • Customizable lighting options (e.g. “dark mode”)
  • Dual voltage compatibility – works with 14V or 28VDC
  • Standard 9-pin D-sub connector, for commonality with other avionics
  • Serial RS232 input, for interface to a Garmin G3X to allow for optional, programmable airspeed lockouts

While I took some time to incorporate these features, I also concentrated on incorporating robustness into the design. I selected automotive-grade components for majority of the circuitry, because they are rated for a wide temperature range (at least -40°C to +85°C) and vibration resistance compared to cheaper commercial-grade components. The circuitry is protected against reverse voltage (i.e. connecting the battery backwards). The flaps motor is driven by an electronic motor IC which features both thermal and over-current protection to protect against short circuits and other wiring problems. All of the components are surface mount devices (SMDs) so the entire circuit board fits into a tiny package (roughly 70x40mm). Between the use of SMDs and composite materials, the controller is very light – right around 120g (4 oz.) presently.

I designed this controller to use a non-contacting position sensor for the switch mechanism to isolate the switch from vibration and/or mechanical failure. The original design used a magnetic position sensor that was very precise (~1°), but added unnecessary cost. I changed the design to use optical sensors, which are just as robust for this kind of application but much less expensive.

Basic programming can be accomplished directly though the front panel via a pushbutton behind a pin-hole. For advanced setup, such as airspeed lockouts and customizing the backlighting, there is a micro-USB connector on the top edge to connect to a laptop.

I have started making a small prototype run to verify and test the design. The main circuit board is currently out for fabrication and should be back sometime this week. Meanwhile, I began the process of making the custom mechanical parts. The fascia is made from semi-transparent acrylic sheet. I use a CNC router to mill away the shape from blanks. Next, I paint the panel black, and then used a laser to etch the labels on the front side. This allows the labels to be backlit for visibility at night.

Milling operation for the fascia panel
Drilling and milling complete
Ready for paint

I have a few copies of a rev 0 board that I made to test out the lighting features in a mock-up. I populated the board and programmed the controller with a simple test program to evaluate the lighting produced by the LEDs. I wanted to be sure the LEDs are bright enough to be visible during the day, while still being dimmable to a low level for night flight operations. I took some video and will post to YouTube shortly.

Rev 0 circuit card assembly
Main circuit card and the fascia panel

I just got in the smaller PCB for the optical sensors, here’s what that board looks like:

The optical sensor circuit card
Mechanical components made of lightweight composite materials
Mockup assembled and lit up

For those that are interested in buying this Flaps Control Module, here is a preliminary drawing with dimension information. This module is designed to be mounted behind a 0.063″ instrument panel with a 60x50mm cutout, held in place with four 6-32 UNC screws (pretty standard for avionics). With a 0.063″ thick panel, the front flat face of this controller will be flush with the panel, resulting in a clean appearance.

I will be selling this module and other custom parts via my new business portal, Sparnas LLC. Stay tuned for more details!

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