Motion Drive 3.0 - User Guide

Sensor Configuration

Although the motion base in simulating an aircraft, it is not able to totally emulate one. A motion base has a fixed frame and limited amounts of movement. Therefore one of the most important aspects of the motion platform is its sensors. These feed information back to the controlling software, Motion Drive 3.0, telling the software where the platform is positioned and how close it is to the limit of movement in any one of its axes. The software can then modify the signals it is sending out to the platform so that, whilst remaining accurate and correct in the motion cues being given, the platform does not go beyond those limits of movement.

However large the range of movement you have decided to allow your platform for each of its axes, there is still a need for sensors to be feeding back positional information to the software. Motion Drive requires this information and will detect an error and stop running if the information is not in accordance with what is expected. So, we come to another of the aspects of the motion platform configuration that has to be fixed. We have designed a system of sensors that is both effective and inexpensive. This section will describe what kind of sensors should be used and how they should be set-up.

Sensor types and requirements

A sensor in this context is simply an electrical device which detects the required action and sends back information that a detection has occurred. There are many different kinds of sensors that are available from electrical suppliers, but the ones that you need must have a number of key features:-

• Accurate and repeatable triggering
• Staying in triggered state for movement beyond the trigger point
• Easy and cheap to obtain and install
• Not subject to mechanical wear or disturbance during use
• Simple switch type action, normally open

With these points in mind, the main candidates are magnetic reed switches and mercury tilt-type switches. Both are useful for different aspects of sensors. we would recommend mercury tilt-type switches for roll and pitch sensors, where the platfrom is tilted during movement. For the heave axis, where there is no tilting action, we recommend magnetic reed-type switches. Both types are cheap and easy to obtain from good electrical component suppliers and are also easy to install and calibrate. Having made that recommendation we shall now concentrate on how your platform sensors need to be installed and calibrated.

The Motion Drive Sensor System

The sensor system relies on there being at least one sensor triggered for each axis at all times. Thus the sensors are arranged to create zones of position for each axis. That way the platform knows where it is and gets new signals as it passes across the boundary between the zones. There are four sensors for each axis arranged to create five zones. This is best shown in the diagram for the Roll sensors:-

The actual sensors are shown in red - four mercury tilt switches for Roll Right Right, Roll Right, Roll Left and Roll Left Left. Between them they can make up five zones, as shown in black. The thin vertical lines show the boundaries between each of the zones. Where the boundaries are set is up to you - according to how much roll movement you want to have. The centre zone is formed by an overlap of the Right and Left sensors and its boundaries should be set up to be about +/- 2 degrees about the level point.

You will note that, being tilt-type switches they stay triggered once the movement goes past the trigger point - so the Roll Left sensor needs to be set up so that it triggers at 2 degrees of roll right and stays triggered through to the extreme of left roll. The extreme sensors should be set so that they trigger about 70% through the range of movement (about 11 degrees for a 15 degree of total movement) each side.

Having attached your sensors to the platform and wired them up to the correct pin on the correct Port of USB module #2, you will now want to calibrate them.

Sensor Settings Page

The sensor settings page is opened from the menu by clicking on Sensors - Test Sensors. When opened it looks like this:-

There is a bar for each sensor axis. When the requisite zone is triggered the bar shows up red, otherwise the mock LEDs show as being green.

You will see three buttons which operate the sensor testing part of the programme. Poll Once sends a one-time request to the sensors and returns with a graphic respresentation of the platforms overall position. Poll Continuous sends a stream of requests and, whilst running, updates the sensor readings if they change. Stop Poll stops the continuous polling.

Setting up Roll Sensors
Again, we will use the Roll sensors as the first example. First you need to set your platform level in Roll. Then you should Poll Once to see what readings you have from the Roll Sensors.

Now, disconnect the Roll Left sensor and move the platform so that it is tilted left by between 1 and 2 degrees (you will need a good quality spirit level which allows for measuring slope angles). Click on Poll Continous, and while it is running, adjust the Roll Right sensor so that it is just triggered at that angle. The Roll Left sensor should now be reconnected and the result should be that the platfom shows as being at Roll Centre.

Repeat the procedure for the Roll Left sensor whilst the platform is tilted at between 1 and 2 degrees to the right.

Now tilt the platform to the left until about the 70% of roll span position (say 11 degrees for a 15 degree span). Adjust the Roll Left Left sensor so that it is just triggered. Repeat for the Roll Right Right sensor. Tighten up all the holding bolts for the tilt-switches and click on Stop Poll. The Roll sensors are now set -up.

Setting up Pitch Sensors
Repeat the same procedure for the Pitch sensors, starting with setting the centre point and then the Pitch Back Back and Pitch Forward Forward sensors.

Heave Sensors

There are two choices for setting up heave sensors. Which you use depends on how much heave movement and detail you want. Some platforms will utilise this third axis but not be designed to allow for a great amount of heave travel. For some, a heave travel of +/-50mm will be enough, say. Others will want greater travel in heave. Motion Drive allows for these two situations. For the larger heave travel platfroms, you should use four heave sensors. For more modest heave travel, you can use a 2 sensor design.

In either case, we recommend that you use magnetic reed type switches for sensors in Heave. You will need to establish the triggering distances from the magnets and find a suitable location to place the set of sensors. As a tip, you should place the magnet on the moving part and the reed switches on the fixed part of your platform. Then the magnet moves past the arrangement of reed switches.

Once you have chosen your Heave sensor style, then you should go to the Platform Configuration page, and in the No Heave Sensors box enter 2 for two sensors and 4 for four sensor. Click on Save Current, then Apply Current.

Large Travel in Heave
By Large Travel, we mean distances in excess of 100mm either side of a Heave centre point. In these circumstances, you will almost certainly need to adopt the four sensor approach. Having arranged you switches on the platform, you can follow the same procedure as for Roll and Pitch sensor set-up.

Small Travel in Heave
By Small travel, we mean distances less than 100mm either side of centre point. In these cases a two sensor approach will be fine. Wire up the sensors as shown in the diagram below, using only the Heave UpUp and Heave DownDown sensors. They should be placed next to each other, straddling the heave centre point. Adjusting the sensors is then simply a matter of making sure that the sensors are triggered as the platform enters the zone of the two combined sensors. When the platform is wihtin that zone, it is said to be "Inside the OK zone" and heave travel will run normally. When no sensor is triggered, then it is "Outside the OK zone" and the platform will washout back until it is inside the zone again.

On the Heave sensor monitor on the Sensors page, "Inside the OK zone" will be shown as lighting up Heave Up and Heave Down and Heave Centre all at once. Heave positions outside the OK zone will show up by lighting up the Heave UpUp or Heave DownDown lights.

Error Messages

When you test the sensors, either using Poll Once or Poll Continuous, the system checks that the message coming back from the sensors is a sensible one. If it is not, then you will see an error message displayed on the page, showing which sensor set is faulty. This error message will stay until reset, which is done by the next Poll command. You should check the wiring and connections of your sensors, correct any faults and then Poll again.

© Active Simulation Limited 2007

Motion Drive 3.0 User Guide version 1.0