Motion Drive 3.0 - User Guide

Simulation Configuration

Now the platform is ready to begin running in Auto Operation mode. But there are still some settings that need to be established. This section covers those that are set according to the flight simulation programme that is running.

Upon opening the Game Settings page you are shown this page.

The settings here are established for each flight simulation, not just for the platform. This is because different simulations will have different characteristics and require different settings to make the motion of your platform realistic. For example, a combat flight simulator will need different settings from a commercial airliner based simulation. Motion Drive also looks to the future. Although the simulations configured are from the Microsoft family, we want to add other simulations in the future and they may well have different flight models etc.

There are three settings to establish for each flight simulation:- Adaption, CutOff and Washout Threshold. The Adaption and CutOff settings are needed for each axis.

Setting all of these will be a matter of adjustment over time and over several runs of that simulation before you find what feels right. And that is the essence of the settings from now on. It will be ones that feel right when you are flying that you are looking for. There will be few if any hard and fast rules to finding the correct values. What we shall do here is to discuss what each setting does, how it affects the performance of the motion base during running and give guidance on some initial values that you might like to try. The values we suggest are based on our 3 Axis, 3 Motor platform, using the particular kinds of motor drives we use, and of course the payload we have tested with. Your platform will be different but, with some experimental runs you will quickly home in on the right values for you.

Axis Adaption

One of the major themes in establishing settings from now on is to find the balance between allowing the platfrom to be free to move wherever the simulation sends it, and retaining control over it so that it doesn't keep running into the physical end-stops of travel.

The axis adaption setting is one of the major controls in keeping the platform within its limits. Here's how it works:-

Taking a simple Roll as an example. If the platform is in Roll Left position (the platform - not the plane), and a command comes to roll further to the left, then the adaption setting is used to reduce the strength of that drive signal. If the command comes to roll back to the right, then no adaption is implemented. Also, the effect of the adaption increases as the platform stays longer in that Roll Left zone. If the Platform moves further to the left and enters the Roll LeftLeft zone, then further movement to the left is prevented completely. That way, motion cues are still transmitted to the platform and the pilot, but the platform is kept within its limits of movement.

Choosing an adaption figure that is too low will mean that the platfrom moves very quickly and freely, but will often hit the physical end-stops. Choosing an adaption figure that is too high will mean that the platform will feel inactive and dead. The neutral figure is 100. Value above 100 apply attentuation to the signals as described in the previous paragraph. Values less than 100 will give the opposite effect and will tend to make the platform move wildly.

We advise that you do not use values less than 100. They are available in case of future need. For now you should choose a value that applies adaption in the intended way. Our trials have shown that a starting figure of between 110 and 115 will be suitable. You may wish to be more cautious in your approach, however and start with a higher figure and work downwards.

The three axes of Roll, Pitch and Heave feel different. So you will need to experiment with flying and adjust each one seperately. They will almost certainly end up with differing values.

Axis CutOffs

The simulation will, from time to time output some very high acceleration figures. Most often these figures are rogue numbers, in the sense that they are the result of a glitch in the simulation itself. Two examples are:- you will get a very high heave figure when you first start a simulation, as the plane apparently jumps from 0 to simulation run altitude within a few milliseconds; you will get a very high roll figure as your plane rolls "over the top" as the output goes from a roll position of +180 degrees (full roll left) to -180 degrees (full roll right) within a fraction of a second.

If these figures were transmitted to the platform, it would jump or roll at full power for an instant, which would be unfaithful and possibly dangerous. So, Motion Drive has a filter called the axis CutOffs, which tell the software to ignore such rogue values.

The setting is specified in terms of the 0 to 255 8bit binary word scale. The values you are trying to filter out are much higher than 255, several times higher. The level of CutOff will also be different for each axis too. Roll movements tend to be faster than Pitch or Heave movements, especially in combat aircraft. So the Roll CutOff needs to be higher (ie allow through higher roll accelerations) than Pitch or Heave.

The symptoms you are looking for are these. If the CutOff is set too low (filtering too many accelerations), then you will see the platform miss some plane movements. If it set too high (not filtering enough) then you will see apparently random and strong movements when rogue events occur (such as at the start of a flight, or plane crash).

We suggest, based on our trials, that reasonable starting figures are:-
Roll CutOff = 1600
Pitch CutOff = 600
Heave CutOff =500

Being cautious, you may wish to start with lower figures and work them up until you reach a satisfactory point.

Washout Threshold

You set up two of the three washout settings when you completed the Platform Settings sheet earlier. Now it is time for the last one. As the name suggests, this value is the threshold at which the platform starts to washout back towards centre level position. To understand this setting we need to go into a bit of background.

As you already understand, the platform and it software are designed to transmit motion cues to the pilot as he flies the simulation. And that these motion cues are in terms of accelerations. There is a level of acceleration below which we cannot feel the force being applied on us. The force is said to be subliminal. Now, given that the platform has limited movement when compared to the real plane, we need to take every opportunity to keep the platform at or around its centre level position so that its available range of travel is always maximised.

So, when the required accelerations are zero (straight level flight for example) or would be subliminal if the platform did apply them, we take the chance to not send driving signals, and use the time to do a bit of washout. The Washout Threshold is the value of acceleration at which the software decides whether to send driving signals, or to send washout signals.

The value is set in terms of the 8 bit binary word scale. What the value should be will depend on your platform - the power of your motors/drives, the position of the actuators and some other things as well. So you will need to find the right value for the simulation you are running.

Again, we can suggest a starting value based on our experience. This might be between 40 and 50. Pointers to look for are:-
- If the value is too low then the platform will find it hard to keep within its movement envelope as there will be insufficient proportion of time spent doing washout. The platform will also feel as though there are times when it is doing nothing as it is transmitting subliminal driving signals which you cant feel (though you will see them from outside)
- if the value is too high the the platform will be spending too much time trying to washout back to level and too little time doing active driving. Some possibly significant manouvres will be missed in favour of washout.

This will come from experience, and is very much a "seat of the pants" setting.

Entering and Saving your Game Settings

To enter you settings for a particular game, first highlight the game from the list of games shown, then click on Select. To confirm that you selection has been made, it will be shown as selected. Upon making the selection, the saved default settings will be displayed for that game.

Make changes as you wish to to the various settings. As with all the settings sheets, you can apply the new settings to the next run, save them as the new default settings, restore the old defaults or cancel and change nothing.

Time to look at establishing settings for your aircraft.

© Active Simulation Limited 2007

Motion Drive 3.0 User Guide version 1.0