Maths Channels

Sooner or later, you are going to want to use a maths channel in your data logging, so now is as good a time as any to learn how to do it.

You can use a maths channel to record what gearing your were using on a particular day and show it either as a gear ratio or as miles per hour per 1000rpm. You can calculate braking force  by calculating longitudinal g force and, once you have got the hang of things, you can even create a maths channel to measure understeer or oversteer. The possibilities are pretty well endless.

To create a maths channel you need to be in the Math Channel dialogue box. You get there through the menu system (Modify ¦ Math Channel) or by pressing the  Alt and F8 keys. The box looks something like this. (Click on to the image below for a better view.)

The stages that you have to go through are

·        Open the dialogue box

·        When you click on the Insert button the words “new channel” appears in the box on the left.

·        Select this name (using a mouse click)

·        Click on to the button that contains the three dots to the left of the word Name under channel parameters and you can then put in whatever name you choose.

·        In this case we can use mph per 1000rpm so type it in.

At this point we have a new channel that doesn’t do anything. To make it work, we need to put a formula into the Formula box in the bottom left hand corner. You do this by typing in what you want. For mph per 1000rpm we need to divide speed by rpm. Don’t forget that you are using a computer program that is very picky about giving precise names for everything, so in the case  shown in the picture, speed is called Speed­_1 and rpm are recorded using the AIM conventional name of Engine. The formula needs to be

Speed_1/Engine

So long as you use the exact names (the correct capital letters are important) and leave no spaces you will have calculated mph per rpm. This gives a pretty big number, so it is conventional to convert the answer to ‘per thousand rpm’ by dividing rpm by 1000. This means that you are doing two calculations in your formula so it is better to separate them by using brackets. Otherwise you can end up with not quite the answer that you were expecting. It would look like this.

Speed/(Engine/1000).

Click on the Test channel button to check that your formula works. If it does, the channel will now appear in your list of channels but probably not in your charts. The likely reason for this is that the AIM default scale is for some reason, -1 to zero. For this sort of gearing calculation, the answer is likely to be in the range zero to 30 miles per hour per 1000 rpm. You can scale your channel using the buttons in the dialogue box.