3-rotor engine with the 36-2-2-2 wheel?

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Reverant
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3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

I just installed an MS3 on a RX-8 with a 3-rotor engine with a Renesis front plate and Renesis 36-2-2-2 wheel and VR sensor.

Unfortunately I got the message that this combination is not supported.

Digging into the code confirms this:

/* ---------------------- 36-2-2-2 ------------------------ */
- snip-
/* only 2 rotor or 4-cyl or 6-cyl supported */
conf_err = 1;

How hard would it be to add support for 3-rotor engines on the 36-2-2-2 wheel?

Thank you!
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Reverant
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

I got this to work by modifying the code in ms3_ign_wheel for the 36-2-2-2 wheel:

trigger_teeth[0] = 6;
trigger_teeth[1] = 17;
trigger_teeth[2] = 26;

trig_angs[0] = -150 + tmp_offset;
trig_angs[1] = -150 + tmp_offset;
trig_angs[2] = -150 + tmp_offset;

However the RPM gauge is somewhat erratic; it's bouncing up and down by 7-26rpm at 1000rpm (stim RPM). When I set the engine configuration back to 2 rotors, the RPM gauge is dead on solid at 1000rpm and literally doesn't move.

Is the RPM calculation based on specific trigger teeth or on ignition events? The tachout teeth on the scope don't seem to coincide with any ignition events.
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by jsmcortina »

Reverant wrote:Is the RPM calculation based on specific trigger teeth or on ignition events?
It is based on the trigger teeth.

James
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Reverant
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

Well I add an additional trigger (num_triggers = 3) and change the trigger angles, nothing else. The trigger teeth (number of teeth and duration of every tooth) remain unchanged, what could be wrong here?
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by racingmini_mtl »

Reverant wrote:trigger_teeth[0] = 6;
trigger_teeth[1] = 17;
trigger_teeth[2] = 26;
That's not 120 degrees between each trigger.
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Reverant
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

I trimmed each trigger tooth angle afterwards. Then I measured the period between ign A, ign B, ign C on the scope. At 833rpm, the engine cycle is 72ms and the period between each ignition event and the next one is exactly 24ms - verified on the scope. The engine actually runs now.
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

Yellow is trigger, green is ign A, blue is ign B, pink is ign C.

Engine period is 72ms:

Image

Ign A to ign B is 24ms:

Image

Ign B to ign C is 24ms:

Image

Ign C to ign A is again 24ms:

Image

The engine starts up faster than the stock RX-8 13B engine and runs well, so I'm a bit confused why the tacho reading is so erratic, even on the bench with a perfect signal.

This is what a 833rpm signal (the yellow signal in the pics above is at 833rpm) looks like in the logs when set to 3 rotors:

Image

The RPM values in the log are 810rpm, 820rpm, 828rpm, 837rpm, 845rpm, 855rpm.

When set to 2 rotors, it's literally a straight line showing a constant 833rpm.

What have I done wrong?
The man behind MS Labs
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by jsmcortina »

This is one case where the "Trigger logger" is actually useful - wheel decoder development. It shows you the times between each decoded trigger that are then used for the RPM calculation.

James
I can repair or upgrade Megasquirts in UK. http://www.jamesmurrayengineering.co.uk

My Success story: http://www.msextra.com/forums/viewtopic ... 04&t=34277
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by racingmini_mtl »

Reverant wrote:I trimmed each trigger tooth angle afterwards.
But the teeth are the trigger events that determine RPM. And your trigger teeth are not 120 degrees apart hence the varying RPM. The 2 rotor code has trigger teeth 180 degrees apart which is why the RPM is correct and stable. (Note that the 6 cylinder code also has the trigger teeth 120 degrees apart).

Jean
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

I was under the impression that the code decoded every tooth on the trigger wheel and calculated the RPM from each tooth as it passed by. Now I see where the problem is.
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

Fixed with the proper tooth selection. Thank you Jean for the explanation!
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by ekam99 »

racingmini_mtl wrote:
Reverant wrote:I trimmed each trigger tooth angle afterwards.
But the teeth are the trigger events that determine RPM. And your trigger teeth are not 120 degrees apart hence the varying RPM. The 2 rotor code has trigger teeth 180 degrees apart which is why the RPM is correct and stable. (Note that the 6 cylinder code also has the trigger teeth 120 degrees apart).

Jean
Jean, am I getting this right?! The decoder in the code uses all the teeth to determine the crank angle, but only one tooth per cycle (or how you call them 'trigger' teeth) to determine RPM?
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by Reverant »

It only uses the same number of teeth as is the number of ignition events. In this particular case, it uses 3 teeth of the 36-2-2-2 wheel, not the whole 30 teeth. This makes sense - the engine RPM won't change substantially between these events - at least not for generic RPM usage (ie fuel/ign table lookup, etc). If this was an 8 cylinder on 60-2 wheel, it would "only" use 8 teeth of the wheel for RPM calculation.
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by ekam99 »

Reverant wrote:It only uses the same number of teeth as is the number of ignition events. In this particular case, it uses 3 teeth of the 36-2-2-2 wheel, not the whole 30 teeth. This makes sense - the engine RPM won't change substantially between these events - at least not for generic RPM usage (ie fuel/ign table lookup, etc). If this was an 8 cylinder on 60-2 wheel, it would "only" use 8 teeth of the wheel for RPM calculation.
Well, although I totally agree with your statement, I'd like to remind that successful start of an engine is about 2 ignition events. First kicks the crank from 200-300 to ~800 rpm, and the 2nd - to 1400-1500 rpm. At the same time, fastest tach output is each ignition event in most if not all oem setups.
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by racingmini_mtl »

ekam99 wrote:... At the same time, fastest tach output is each ignition event in most if not all oem setups.
And that's what you get here too as I and Reverant said. There is one trigger tooth per ignition event. That's what the trigger is: it triggers an ignition event (not quite but close enough for this discussion).

Jean
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Re: 3-rotor engine with the 36-2-2-2 wheel?

Post by ekam99 »

Yep, thanks for clarification
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