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# M1 math channel output in RPM, Possible?

### Tech Articles

Discussion and questions related to the course MoTeC M1 Software Tutorial

Hey guys, I am attempting to do a calculated clutch slip math channel.

I need to create a couple channels to then divide as you know to get the slip ratio (calculated input shaft speed and engine speed). However for some reason I can't find how to set the quantity (output) of the channel the RPM. I figured it would be under speed (like engine speed), but no such luck.

The example of my equation for Wheel speed in rpm using MPH as the unit.

100mph x Inches per minute 1056in / tire circumference 88in

(100x1056)/88= 1200 wheel RPM

I am sure I am missing something simple here......

Zack

You're probably looking for the channel "Engine Speed", with RPM is a units. If the base units of Engine Speed is Hz (Cycles per Second), then you need to multiply be 60 sec/min to get RPM (Revolutions per Minutes). This is how you would do this internally within M1 Build.

Now if you're doing this math in I2, you can specify the units you want a channel to be converted to like 'Engine Speed [RPM]' to get it in RPM.

OK, I just looked in M1 Build, and the base units for Engine Speed (which is a rotational speed) is degrees / sec. So to convert deg/sec to RPM, you divide by 360 to get rev/sec and multiply by 60 to get Rev/minute. Since 60/360 = 1/6, you just divide the base Engine Speed by 6 to get Engine Speed in RPM.

Thanks for the input. I will see if I can get this up and running. I am just trying to get the data displayed correctly I2, I should have specified that. I think I can still do it with the same math above, but "rpm" doesn't appear to be a selectable parameter for some reason.

Thanks!

Zack

In I2, you would change the channel properties for the channel "Engine Speed" to be "rev/min (rpm)" if that's what you want to display / work with. In a Maths expression you write this as 'Engine Speed' [rpm], or example, rate of change could be calculated as: derivative('Engine Speed' [rpm], .25)

I am unsure why, but engine speed as a channel property or revolution per minute both are not selectable outputs for my math channels in the I2 drop downs. It seem to me that rpm is a measure speed or rotation as you said. Under speed however I only get mph/kph etc.

I need to get the output of each of these compounded channels to RPM for the data to make any sense.

Still unsure what I am missing.

It will probably something simple as usual, but selecting the output units of an equation as RPM seems like it should be relatively basic.

Zack

So let's start at the beginning. What version of Windows are you running on your computer? What version of I2 Pro are you using? What device created the logged data file?

To me it sounds like the channel properties are different than are found from recent MoTeC devices. So clue us in.

Note many of these questions could be answered if you just posted the logged data file (i.e. xxx.ld) that has these channels.

RPM is under Angular Speed in the drop down.

Attached is the basic formula you would be wanting for a simple engine speed - calculated input shaft speed formula.

If you wanted to do any slip ratios or slip rates, you would need to remove the engine speed component and make this an input shaft speed channel to then do calculations on.

Formula is using metric for calculation, so adjust wheel speed to hub rpm as neccessary.

Also to note, if you logged channel is in a certain unit that isn't ideal for a calculation, you don't need to convert the unit (in most cases), you just need to change the unit representation in the formula. Ie:

'Wheel Speed RL' [km/h] is the logged wheel speed.

removing 'km/h' out of the brackets will bring a popup of the support units that can be used for the calculation such as km/h, mph, m/s, mm/s, in/s ft/s

We usually reply within 12hrs (often sooner)

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