OEM Boeing 737 Stick Shaker - Interfacing and Operation — Flaps 2 Approach

OEM 737 stick shaker installed to Captain-side column. The lower section of device is what vibrates

The stick shaker is standard on all Boeing series aircraft; the Next Generation having two units (Captain and First Officer) and the earlier classic series having one unit. The stick shaker is mounted directly to the control column and is designed to vibrate if air speed degrades to stall speed. The Stick shaker I am using is manufactured by a company in New York. It is powered by 28 Volts (27.5 Volts to be exact).

Configuration

Configuration of the stick shaker is a relatively easy task. The electrical cable from the device is connected to 28 Volts, or if this is not available 12 Volts; 12 Volts still produces enough power for the shaker to vibrate, although the intensity is not as great as if the unit was connected to 28 Volts.

To allow Flight Simulator to connect to the stick shaker, a relay card is required such as a Phidget 0/4/4 relay card. A USB cable then connects from the card to the computer. The stick shaker will vibrate when variables that relate to low air speed are met. The variables are determined by the flight avionics software (ProSim737 or Sim Avionics).

Phidget 0/0/4 relay card showing the main positive wire (red wire) cut with each end inserted into the correct terminals of the relay card

Interfacing and Wiring

The Phidget 0/0/4 relay card is mounted in-line between the 28 Volt power supply and the stick shaker. Either of the two wires (+-) from the power supply can be cut to install the in-line relay; however, only one wire is cut; the other remaining unbroken from the power supply to the stick shaker.

The 0/0/4 relay card has four relays of which one is required. Each relay has three terminals: normally open (NO), common (C) and normally closed (NC). For the stick shaker the common and normally open terminals are used.

Carefully cut one of the two wires leading from the 28 Volt power supply. Insert the wire coming directly from the power supply into the terminal marked common (1C, 2C, 3C or 4C). The other end of the cut wire, which comes from the stick shaker is inserted into the terminal marked NO (normally open) of the same terminal.

If the wires have been inserted into the correct terminal of the relay card, the circuit will be complete only when the parameters established within the flight avionics software are valid. At all other times the relay will break the circuit by not allowing the power to reach the stick shaker. If you have made a mistake, the stick shaker will vibrate continuously.

Protection

When connecting the stick shaker, it is a good idea to include a diode to protect your computer from any magnetic return signal should the relay fail. A return signal to the computer may cause problems with the computer, and in it worse instance allow 28 volts to surge into the computer destroying your mother board.

Positive and negative wires from the stick shaker enter the terminal block on the right. A diode is placed on the corresponding end of the terminal block prior to the two wires running to the relay (not shown)

A high-end relay, such as a Phidget 0/0/4 relay should not fail, and if it does it should fail in the closed position. However, if 'Murphy' or 'Sod' is your First Officer then it is better to be safe than sorry, so best install a diode.

A diode is an inexpensive and very simple device that behaves in a similar way to a black hole (astronomy). In a black hole all matter is sucked into the hole and no matter, including light leaves the hole; it is one way trap. A diode behaves in exactly the same way. If a failure of the relay occurs, any power that is being transmitted through the wire from the stick shaker (28 volts) will enter the diode and be trapped. No current will leave the diode.

Three 6 cm diodes. The silver spirals indicate the positive side (red tape) while the opposite end is the negative (white tape). Diodes come in an array of differing shapes, sizes and trapping capacities

The heavy duty diode should be placed in parallel between the stick shaker and the relay card. It is best to try and place the diode as close to the stick shaker as possible. Place the positive side of the diode (usually appropriately marked) on the positive side. The other end of the diode place on the negative side. If you use a terminal block it is very easy to connect a diode into the circuit (see photograph).

Incorrect Wiring

Do not become concerned if you have connected the wire to the wrong terminal - the stick shaker will not be destroyed. It will be obvious if you have inserted the wires incorrectly, as the stick shaker will operate continuously as it has unbroken power.

I was debating to re-paint the stick shaker, however, decided to keep it as it is. I like the used look rather than the pristine 'never been there' look.

Although the stick shaker is not essential, it’s often the smaller things and attention to detail which help bring the simulator to the next level. I am using OEM control columns and adding a stick shaker enhances the immersion.

OEM and Reproduction

When an OEM stick shaker vibrates, especially when you are not expecting it, the vibrations startle you . The yoke vibrates and the noise of the vibrations is quite loud. In contrast, reproduction stick shakers generate lower vibrations and noise.

Acronyms