Input-Input!

Introduction

We’ve been hard at work to research the very best simulator control options. Our selection criteria was based on a balance of the following attributes:

• the best accuracy
• the easiest installation and setup
• low cost

There are just such a plethora of options available that it became important to understand what the benefits of each are and work from there. The control options were categorised along the following lines:

• Inputs – the sensors providing information to the control devices
• Control Devices – the controller hardware which receives the Input information
• Control Software – the software that is required for the Control Devices in order to interpret the Inputs and provides the simulator with information it can understand.

As indicated in various previous posts, there is no need to read information from the simulator to control external monitors, gauges and the like. Given that our simulator is built around VR interaction, our controls only need to provide a one direction feed to the simulator. In other words, we are creating a giant joystick interface.

The following is a summary of our findings on means of input. We will post separately on the control devices and control software.

For inputs we differentiate between Digital (as in switching) and Analog.

Digital Inputs

The Digital inputs can be:

• Physical –
  • Toggle switches (Lever and Rocker),
  • Pushbuttons (momentary, latching and interlocked latched) and finally
  • Rotary switches.
  • In our design we use both Toggle switches and Pushbuttons but not Rotary.
• Hall Effect – This is switched by the proximity of a magnet. They can be:
  • Latching (switch stays in position even when the magnet is removed, and can be either
    • pole sensitive where you need say a South Pole to activate and deactivate the switch, or
    • Non-pole sensitive, where any pole will do.)
  • Non-latching (switch flips as soon as the magnet is removed). Again, these can be:
    • Pole sensitive – examples are the Allegro A1101/2/3/4/6, which switch on South Pole only
    • Non-pole sensitive – example the UTC UH8104
  • In our design we use exclusively the UTC UH8104 non-latching, non-pole sensitive switches for the proximity sensing of the following:
    • switch cover is open or closed
    • fuel cut-off position
    • gunsight dimmer slider position
    • chassis control lever position
    • (the incorporation of these are currently undergoing redesign)
  • Finally it should be noted that Hall Effect Sensors come with through-the-hole (SIP3) wiring or as SMD (Surface Mounted). The latter makes it a pain to connect so we have stuck with units that are available in through-the-hole.
• Encoders – These send on/off signals or pulses through two channels. The signals between the two channels are offset in a certain pattern depending on which way the encoder is being turned. It is then up to a controller to determine the direction and speed and provide that information to the simulator. It really provides multiple button or key presses and they are ideal for controls where there is no set number of rotations. An example would be setting a clock or altimeter. We have settled on a Bourns PEC11R which has a 12mm threaded through panel mount. They provide between 12 to 24 pulses per 360 degrees.

Analog Inputs

The Analog inputs serve axes of movement, such as trim, rudder, elevator, throttle etc. They can be linear, i.e. slide forward and backward, or rotary/angle sensors, measuring number of degrees turned. Most often the role for these were fulfilled by mechanical potentiometers, which slid across a resistive material thereby providing an indication of its position. These are being largely replaced by solid state Hall Effect sensors.

The advantage of Hall Effect sensors is that they provide a very steady, accurate signal, whereas potentiometers very often provide a bit of a quivering signal. A potential problem with Hall Effect sensors is that they send data in serial bitstream, which adds complexity and increases the real-time processing requirement to interpret these signals.

In the last few years however these have become more and more friendly, some providing an analog output based on a variation in voltage, typically from 2,5V to 5V.  These can then be simply used as straight-up replacements for potentiometers.

So for our design we have decided to keep it simple yet very accurate by replacing all rotary potentiometers with the Melexis Tri-Axis MLX90371 (Gen III). These are tri-axis – they provide linear and rotary on-axis or off-axis. They also come in SIP3 Through Hole and provide an analog output. It should be noted that they measure 360 degrees, so for instance for the elevator trim where 4 turns are required end to end, we will be designing printed gears.

There are a few applications where a linear Hall Effect sensor will be used, eg. the brake lever. Replacing the original design, which had a very expensive Bourns 3046 linear pot, has simplified matters greatly through the use of an Allegro A1324 linear Hall Effect Sensor, again with analog output.