This page is to help with setting up the Primary Trigger option
Specifically for the VAG 60-2 wheel, but it will contain general information
MegaTune is an easy way to setup the trigger values, but you need to know what you are changing.
current decimal values
| Primary Trigger | GRM setup | Mcel | ||
| Edge | Rising | Rising | ||
| Type | Multitooth | Multitooth | ||
| Filtering | Disabled | Disabled | ||
| Tooth Relation (Usually Disabled) | Disabled | Disabled | ||
| Trigger Settings | ||||
| TDC after trigger (degrees) | 60.0 | 60.0 | VAG wheel on ABA block is 90d off TDC at the center of the missing teeth via calibrated eyeball | |
| Number of teeth on wheel | 58 | 58 | actual nubs | |
| Trigger Tooth | 3 | 15 | The third nub after the space actually the missing ones are counted, 3= the first after the space | VAG ABA wheel appears to have the center of the missing teeth @ 90d off TDC, would this make this value 2 |
| Next Trigger Tooth | 15 (V8)/20 4clyn | 15 | Manual states NextTrigTooth= imaginary teeth * 2 / cylinders (60 *2 / 4 = 30) | |
| Crank minimum period (usec) | 1280 | 1280 | ||
| Tooth Width | ||||
| Engine Phase, when reset | 240 | 240 | determines toothwidth unit; (equivalent to 720 crankdegrees = 2 crankrot= 120 teeth) | |
| Angular width of tooth | 2 | 2 | 120 teeth is 240, so 1 tooth width is 2 | |
| Angular width of missing tooth | 6 | 6 | 3 times the above (2 missing teeth) |
| This part needs to be made either transparent to the end user or extremely well explained with a shortcut on howto do it. | ||
| Tooth Relation to Normal (usually 181) | 181 | 181 |
| Tooth Relation to Missing (usually 118) | 118 | 118 |
These are all you settings, but these are not normally how motorheads describe thier motors or triggers.
Typical Descriptions
- TDC -- Regular meaning when #1 cylinder is at top of rotation
- Number of actual teeth on wheel
- Number of missing teeth on blank spot on wheel if there were teeth there
- Relation of blank spot to TDC this would be in degrees
- Leading edge angle from TDC
- Trailing edge angle from TDC
So using these values how do we get the other ones.
Suggestion
Do the number trunkation etc in the make mtt portion. Most NON - EE/CompEE/CS engineers will not get the howto about converting decimals to an arbitrary (seemingly) number less than 255 ( 8-bit micro unsigned issue)...
So basically a good picture and straightforward equation, IF it is not automagically done for the config. If they don't care, they should copy a working example and not mess with the numbers they don't know.
Min Crank Period (review this statement)
This definately needs to be calculated somewhere else.. I thought it was for "cranking" aka starting the car. but it is directly related to Rev limiter.. you could call this the OVERREV point or something. I'm guessing its an early variable.
Angular width, etc.. This should all be auto-calculated.
since an 8bit number only can goto 255 (8-bit unsigned) so the whole point of this is scaling.
Example 60-2 wheel
- 1 its a ratio..
- 720d / 255 = 120teeth/ x ; x = 8bit approximation of degrees / tooth but this has to be rounded down so that it is a nice root ie. divisible and integer like.
- 2 Given the number of teeth in a 720d rotation what is the new number in this ratio
- 120teeth/ rounddown(x)= 720d / y
- y is the new normalied max value (y <= real angle per tooth )
- (y)(number of teeth) = engine Phase
- Engine phase refers to the new number y * number of teeth that represents 720d
- The proper name would be scaled 720d value
- 3 Scaled Tooth angle is y
- 4 Scaled missing tooth angle is y * # of missing teeth
Proposed table
| Variable names | 1-10 | 1-12 | 1-16 | 1-36 | 2-60 | ||
| internal | Total Teeth | 10 | 12 | 16 | 36 | 60 | |
| Number of teeth missing | missing teeth | 1 | 1 | 1 | 1 | 2 | |
| Number of teeth on wheel | Teeth Present | 9 | 11 | 15 | 35 | 58 | |
| internal | Crank Rotations per complete clycle | 2 | 2 | 2 | 2 | 2 | (2 for 4cycle 1 for 2 cycle) |
| internal | Degrees per complete cycle* | 720 | 720 | 720 | 720 | 720 | |
| 720 / Total Teeth = Angle Per tooth (degrees) | 36.0 | 30.0 | 22.5 | 10.0 | 6.0 | ||
| Total Degrees scaled to 8 bit unsigned: 255/total teeth | 12.8 | 10.6 | 8.0 | 3.5 | 2.1 | ||
| Truncate for integer math | 12 | 10 | 7 | 3 | 2 | ||
| EnginePhase when reset | Scaled degrees per cycle | 240 | 240 | 224 | 216 | 240 | |
| Angular width of tooth | Scaled degrees per tooth | 12 | 10 | 7 | 3 | 2 | |
| Angular width of missing tooth | Scaled degree of missing teeth we count spaces so add 1tooth | 24 | 20 | 14 | 6 | 6 |