Trigger wheel phasing

[Aaron Silidker]

So I made my trigger wheel. a 30-2 worked out quite nicely to have the teeth just a tad wider than the sensor tip and to have the gap similar in width to the teeth (a quarter of a degree wider). For reference this is going on a 400cc 4 stroke single.

Here is a photo. I had it wire EDM'd at school for free.


Anyhow, I am getting conflicting info on how to time the wheel to the flywheel. One friend who works for bosch motorsport says to put the leading edge of the gap about 70 degrees btdc so there is less room for error because the computer will synch to the gap and then fire the spark soon afterward (max advance is around 50, so 70 is safe).

But for startup on a single I assume I want trigger return since RPM is all over the place...which means I want the gap 12 degrees BTDC or so. This presents an issue however because spark might occur in the gap correct? And I will have nearly a full 360 degrees of revolution of the wheel sometimes before firing spark after the gap which leaves a lot of room for synch error I assume.

Let me know your thoughts so I can get the ring pressed on and try to get the bike all wired up.

[Matt Cramer]

While the code lets you put the missing tooth anywhere, it's less accurate if the spark is near the missing tooth. So you would put the gap ahead of your maximum expected advance, like maybe 90 degrees BTDC. However, the code picks the tooth to trigger off of based on the amount of advance. See here for how it works:

http://www.megamanual.com/ms2/wheel.htm

[Aaron Silidker]

While the code lets you put the missing tooth anywhere, it's less accurate if the spark is near the missing tooth. So you would put the gap ahead of your maximum expected advance, like maybe 90 degrees BTDC. However, the code picks the tooth to trigger off of based on the amount of advance. See here for how it works:

http://www.megamanual.com/ms2/wheel.htm

Right I understand that, but for starting I think I have to use trigger return since my engine speed is all over the place while cranking. If I use trigger return the gap has to be where I want spark to be while cranking correct?

Will a 400 single 4 stroke with high compression work with calculated start spark...I think synch will be a major issue.

[Matt Cramer]

"Trigger return" mode only works with very specific Hall effect sensor setups and I don't believe it works with multitooth wheels at all. Instead, it uses an every-tooth decoder, which is kind of the equivalent of trigger return for multitooth wheels.

[Aaron Silidker]

"Trigger return" mode only works with very specific Hall effect sensor setups and I don't believe it works with multitooth wheels at all. Instead, it uses an every-tooth decoder, which is kind of the equivalent of trigger return for multitooth wheels.

Cool, I guess I am a bit confused by the documentation I will have to do some more reading and try to understand it better.

How does that trigger wheel look by the way? The EDM is a badass machine!

[Aaron Silidker]

Ok, so trigger rise is what I meant. If I do trigger rise my gap would have to be 12 degrees BTDC correct? If I set trigger offset at 7 teeth can I somehow use that with trigger rise?

What is my best option for starting this bike with a 30-2 wheel? Trigger rise or calculated. High compression big bore big stroke engine...single cylinder. I can phase the wheel however I would like very accurately.

Thank you again!

[Aaron Silidker]

Any more advice?

[Matt Cramer]

If using trigger rise, the MicroSquirt fires the coil on specific teeth on the trigger wheel, determined by the delay teeth (and skip teeth if you have more than one ignition event per revolution). So the only phasing requirement when using trigger rise mode is that you have a real tooth located at a point where you can fire the ignition during cranking and have it start. With a 30-2 wheel, about the only phasing I can see that couldn't work with trigger return mode is if you put the 2 missing teeth right in the best location for cranking timing, since with a tooth every 12 degrees you're almost certain to have one in the area needed for starting. Wheels with lower tooth counts might have to use calculated timing - for example, if you had a 6-1 wheel with the missing tooth location at TDC, trigger rise mode could only fire the coil 60 degrees BTDC or 60 degrees ATDC.

[Aaron Silidker]

COOL! Still a bit confused I apologize.

If trigger rise fires spark on the tach signal, then won't that be TDC since I place the tach signal at TDC? Or does trigger rise let you specify how many teeth past the gap you want spark on startup...and then also lets me specify what tooth corresponds to TDC?

Also, what edge of the tooth does microsquirt see as the tach signal...or is it the middle of the tooth? Also with the gap...is the end of the tooth at the back of the gap the 0 point or the front of the tooth at the back of the gap the 0 point...or is it the middle of the tooth? Sorry for the million likely dumb questions, the documentation is all over the place and confusing at best to me and I would really like to configure this correct right off the bat so I have little debugging to do.

[SQLGUY]

Trigger rise will still apply the trigger offset (if you've set one), so the tooth doesn't have to be right at TDC.

If you use calculated, then cranking will use your timing table. If you don't have too much advance in the upper left corner, then this is probably OK as well.

MS triggers on signal edges, which are pretty close to tooth edges. Which edge depends on your pickup polarity and also on whether you've configured your base ignition settings to Rising Edge or Falling Edge. Generally, Falling Edge with a non-inverted pickup (so that the falling edge does correspond to the trailing edge of the tooth) is the most accurate setup.

If I were you, I'd just install it with the missing tooth somewhere far away (timing-wise) from any place you'll be firing spark, then play around with trigger offset, rising/falling edge, pickup polarity, and a timing light, to get it set up the way you want.