Servo Wiring - rotorflight/rotorflight GitHub Wiki

For smaller builds you will probably choose to use a flight controller designed for quadcopters. These offer a great deal of features, and due to the popularity of drone racing, they are usually lightweight and very low cost. This makes them ideal for use in helicopters, with the exception that wiring them up can be fiddly. The most difficult part is usually wiring up the servo bus, as you will want to create something that accepts your existing servo connectors while also being wired to different control outputs AND power.

Servo Numbering

Below is a quick reference to how different swashplate types are numbered. This is useful when wiring and plugging in your servos. Care should be taken to understand which servo output is identified as what Servo. This information can be learned from the Target Builder used in the upcoming steps to configure your flight controller.

120deg / 135deg / 140deg 3-servo CP swash

120deg_swash_plate_3_servo_config.png

90deg 3-servo CP swash

90deg_swash_plate_3_servo_config.png

90deg 4-servo CP swash

90deg_swash_plate_4_servo_config.png

90deg 2-servo FP swash

90deg_swash_plate_2_servo_config.png

Wiring Loom

The most straightforward option using on-hand materials is to create a wiring loom:

To create this you will need some sockets that can accept the connectors for your servos. For small helicopters these will be "PicoBlade" and for larger helicopters they will be 2.54mm pin headers, sometimes called "Futaba" or "DuPont" connectors.

If you do not have any connectors, you can remove them from your outgoing flight controller. To do this, plug a servo into the connector you want to remove. This will prevent the connector housing becoming soft and deforming. Underneath the board, apply enough solder so that you have drenched all three pins. First, press on the pins evenly from the bottom of the board with your soldering iron. Finally pull on the servo plug to remove the connector. Be careful: If you just try to pull on the plug without pushing the pins first, you will likely leave a pin behind on the board.

Next, using some hookup wire, solder wires to each of the control pins, as well as the power and ground pins. Connect all the power wires and solder into a single wire, then do the same for ground. Lastly you can connect your control wires to the servo outputs on your flight controller.

You may wish to use a cable tie to secure the loom together, alternatively you can carefully use CA to glue the connectors together and create a block.

Rotorflight PCB's

Adapter board and Top hat PCB's make for a very tidy install. There are many PCB fabrication workshops throughout the world (an example is https://jlcpcb.com). The following designs are provided in Greber file format which generally can be loaded to the manufacturers website, viewed and purchased.

"Top Hat" PCB

A neater way of accepting servo inputs is to use a "top hat" PCB designed for your application. There are a number available to be fabricated in different sizes. Please refer to the instructions in the linked repositories:

Adapter boards

The following boards can all be found https://github.com/pkaig/rotorflight-boards.

16x16mm -

This is a very compact board that has:

  • 5x 3pin headers for the motor/servos
  • 4 pin header for a receiver with telemetry
  • 2 pin header for BEC
  • Vbatt for flight pack voltage

20x20mm - Simple version

  • 5x 3pin headers for the motor/servos
  • 4 pin header for a receiver with telemetry
  • 2 pin header for BEC
  • Vbatt for flight pack voltage
  • 2x 3pin headers for Aux signals such as Openlarger

20x20mm -

  • 5x 3pin headers for the motor/servos
  • 4 pin header for a receiver with telemetry
  • 2 pin header for BEC
  • Vbatt for flight pack voltage
  • 2x 3pin headers for Aux signals such as Openlarger
  • 2x extra signals as required. Maybe GPS in future?

30x30mm -

  • 4x 3pin headers for the motor/servos
  • M1 4 pin header with telemetry
  • 4 pin header for a receiver with telemetry
  • 2 hole header for XT30 for BEC.
  • Vbatt for flight pack voltage
  • 2x 4pin headers for full UARTS as required
  • 2x 3pin headers

Atomic Skull's breakout board with built-in 5V regulator

The main purpose of having a regulator on the PCB is to run a 2S~6S or 3S~6S FC reliably off a 5.5v~8.4v ESC BEC or a receiver pack on an IC powered helicopter without risk of a brownout from low voltage. Basically it replaces the 5V switching regulator on the FC with a 1A ultra low dropout linear regulator that feeds the 5V line on the FC which in turn powers the 3.3v regulators that feed the gyro and MCU. On paper it's also less noisy than a switching regulator too.

Here's a zip file with the gerbers and a comprehensive readme.