Single-pickup ignition options...

[ScramblerXLE]

Hey guys,

I have some questions for you folks… Please bear with me as I’m not much of an electrician, but I’m a good mechanic with a good mind for high performance engine theory and such and I’m trying hard to learn haha!

I’m looking to EFI a Yamaha YFZ450, which is a carbureted ATV. My hope is to be able to come up with a completely plug-and-play harness so that I can swap the EFI on and off quickly, and so that any parts that fail can be swapped out quickly without needing to do any cutting and splicing with the OEM parts.

So with that in mind, I’d like to use the stock, single-tooth flywheel if possible. My though (or rather a friend of mine’s thought if I’m honest) was to use the dual spark option on the microsquirt to have one input seeing the pickup to give you a reference, and the other counting stator pulses to give you speed.

The stator has 12 coils and 2 wires, which I think makes it 2-phase? If so, I’m guessing you would see 6 pulses on each wire per revolution, or does that depend on the number of magnets? If it is just 6 pulses, is that enough? If not, I imagine I could tap both wires, put a diode on each to keep them from shorting, and then tie them together to get the full 12 pulses. The trouble with that is, the bottom of the wave is gone. Can the Microsquirt deal with that? I also considered using a solid-state relay if I could find one that would switch fast enough, and I’m thinking I could get a good square-wave out of that?

Essentially, I’m trying to do this without needing a signal wheel.

One final note: This quad is one of my practice ones, but it sees race action from time to time. The races I do are typically dead-engine start races, so the machine will be off, then must be started once the flag is thrown. To this end, I want the minimum number of pulses to be ignored, as my carbureted bikes can typically start the first time they hit the power-stroke, so basically 1-2 revolutions. Just another point to consider, and that’s also why I’m not sure 6 would be enough… But then, somehow the stock CDI can calculate ignition advance using only that single pickup, so I guess I wonder why the megasquirt couldn’t do the same?

Thanks for any info!

-Walt

[dontz125]

I don't know if you could use the stator pulses, but I don't see any reason why you couldn't use the stock wheel. The stock ignition box seems to deal with it fairly well!

[mfro]

But then, somehow the stock CDI can calculate ignition advance using only that single pickup, so I guess I wonder why the megasquirt couldn’t do the same?

Actually, the Microsquirt does work with a single tooth if you set it up carefully.

There's nothing a CDI can (or does) "calculate" an advance curve from. At least the simple "moped" designs I know just have two settings they switch back and forth based on VR input voltage (which is a function of RPM): one "idle setting" where the trigger gets delayed for ease of starting and idle and one "full advance setting" for everything else.

The same can be done with the Microsquirt with the same limitations: you actually can't have more advance than the trigger point on the flywheel dictates (plus the small delay the Micosquirt needs for its calculations). At least not reliably - the calculation would need to be based on the status of the previous revolution which probably wouldn't be accurate enough. I didn't try this, actually. You'd also need two full revolutions for an initial spark which would probably rule out kickstarting.

In my opinion, the fine-grained resolution of the trigger wheel which allows a very precise setup of ignition timing is one of the great advantages of the Microsquirt and I wouldn't easily sacrifice that.

The idea of using generator pulses/phase changes to trigger the Microsquirt is an interesting one. I guess it won't work out of the box, but if you manage to create a simulated "N-0 wheel + cam trigger signal" out of it with whatever electronics is needed for that, I see no reason why it shouldn't be possible to make it work.