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Old Dec 28, 2013, 09:55 AM
Complete RC Idiot Savant
The Netherlands
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Quote:
Originally Posted by Chophop View Post
Since I really don't know what your circuit is, here is a cheap idea to work from. 14,000 rpm is 234 hz, this one can easily do that with a smaller sensor.
Looks like what you may already be working with.

http://www.ebay.com/itm/ws/eBayISAPI...ectorid=229466
What I am working with, is at least theoretically better since it provides a logic 0 or 1 as output, just as the RcExl unit requires....
It just doesn't give them off the way I want it....
But I have a scope now.....
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Old Dec 28, 2013, 08:28 PM
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Would be neat to use the spark plug as a sensor.
http://en.wikipedia.org/wiki/Saab_Direct_Ignition
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Old Dec 29, 2013, 04:16 AM
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yeah, that would be really neat....

In the mean time, the project has hit a snag:

I have done everything I could, even verified pulse shape on an oscilloscope (it is OK, regular, sharp timing, vertical rise and fall, timing is constant in relation to crankangle), pulse voltage (4.8V even under "load" of the ignition system), I have an absolute positive crank pin position detection, and STILL, the ignitionsystem refuses to fire the mixture, while on the Hall Sensor it fires without any problem, and the engine goes like it should.

The crankpin detection works. No doubt about that, I have verified this several ways. It works at standstill, and it works at higher RPMs.

The ignition system Sparks if the detector is triggered, that has been verified several ways too.

But as soon as I try to start the engine.... Nothing....
Only thing I have not yet verified is if the ignition keeps sparking at RPM (spark plug slightly difficult accessible). But.... IF that would not be the case, I am really clueless as to why it would stop sparking at higher RPMs because with the Hall Sensor it can easily follow up to 16000 RPM

I am really puzzled....

Brgds, Bert
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Old Dec 29, 2013, 06:52 AM
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Old Jan 02, 2014, 03:41 PM
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It took a while, but I have a running engine.
Not just stuttering, not poorly, but a regular 2-stroking run.
Have not yet been able to go to full RPM (it was 22:00 over here when I got it to run first time) but I have seen close to 8000 RPM and that is promising enough to continue....

But to be honest, I had almost given up....

Most likely the interference fields around the HV lead did influence the IC or the other electronics too much, because it looks like the decisive change was relocating the PCB....

Oh en Cees: Omdat je op mijn negeerlijst staat, KAN ik je bericht niet zien, WIL ik je bericht niet zien, en HOEF ik je bericht niet te zien: ik heb jou en je non-informatieve schijtzooi niet nodig...

Brgds, Bert
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Old Jan 02, 2014, 07:15 PM
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I would never trust a flying machine to a system that allows interference from nearby components to cause failure. Too delicate for me. Needs more analysis.
Congratulations on the run success though, every win inspires me in innovate.
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Old Jan 03, 2014, 03:06 AM
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Quote:
Originally Posted by Chophop View Post
I would never trust a flying machine to a system that allows interference from nearby components to cause failure. Too delicate for me. Needs more analysis.
Congratulations on the run success though, every win inspires me in innovate.
Why? Airlines have flown for years, trusting the passengers to shut down their cellphones...
Anybody knows you should not put your receiver close to the HV leads, to mention just a thing.....

I just did not expect this circuit to be so sensitive to that, but once it is known, a shielded box should be sufficient. Lots of electronics is placed in shielded boxes in lots of applications....

Don't forget that the circuitry was in the previous (and failing) tests actually just hanging on its leads next to the helicopter, it was about 2~3" from the plug, NOT in its intended position....
Once fitted where I intended it, even shielding most likely would not be necessary.
But I just have to figure out how sensitive it is, and what locations are suitable, because other people have helicopters with different designs: they should be able to determine their own location for the detector + circuitry based on what I see and observe...
Brgds, Bert
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Old Jan 05, 2014, 04:32 AM
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So now I have made a more definitive backplate, which improves detection.
I have changed the normal senstivity adjustment potmeter for a Multi-turn potmeter, which greatly enhances adjustability, as well as stability of the adjustment.

I have now proper detection, and as expected in the first post, timing is adjustable through the potmeter, rather fine actually and over a range of approx 15 degrees.

All fine and dandy, now the next "problem" presents itself:
There seems to be a small temperature drift in the IC. When I power up the ignition and set the timing, the first at least 5 minutes the timing slowly retards by some estimated 10 degrees...
It gets stable after some time, and it gets more or less stable at the same point, but waiting 5 minutes after powering up the ignition is not very convenient....
A first solution is to set timing when the electronics have ""warmed up", but I'd like to get that out of the way. No ideas yet, because I have no idea if that sensitivity drift originates from the IC warming up or from the resistors warming up.
The IC is said to have an operating temperature range from -50 till +150 deg C....

Brgds, Bert
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Old Jan 10, 2014, 04:52 PM
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Okidoki.... the inductive crankpin detection has definitvely stranded.
Could not get it to work, and the problems seem to be of electronic nature (interference).
I had the engine running ONCE on that set-up, so it is definitively viable, but I never managed to get a repeatable result.

BUT.... I found an alternative, which is LOTS cheaper, LOTS easier (no additional electronic circuitry), and gave me almost instant results, while still working with crankpin detection through the backplate.
Posted this in the engine section as well, but I am not sure if everybody here, is also reading over there, so here is my set-up, with which the engine seems to run absolutely good ("benchtest" was OK, hope to do flighttests this weekend).

For info, feel free to send a PM.

Brgds, Bert
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Old Jan 11, 2014, 09:28 AM
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This is the engine running with that sensor:

SkyFox, CDI and alternative timing trigger (0 min 37 sec)


And flying (still not 100% correctly adjusted):

Test SkyFox with RcExl CDI and backplate timing sensor (1 min 22 sec)


I feel confident to offer it for sale the way it is now (with the POM backplate), even if I want to do some more tests to see if I can make it work with the Original backplate....

Brgds, Bert
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Old Jan 16, 2014, 12:25 PM
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Update

I have found magnets suitable for crankpin detection through the Original backplate, so the plastic backplate is obsolete now...

Brgds, Bert
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Old Jan 21, 2014, 10:13 AM
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Just have been flying with an on-board tach (just a simple one I could read while hoovering, nothing fancy) and found that the sensor, set at a passing distance of max 2 mm from the crankpin, easily handles 14500 RPM, peaking at 15000 without misfiring, which I consider absolutely sufficient for any application....

The slight burbling that can be heard in the previous flying video, is due slightly rich mixture, NOT due the ignition missing a beat.... It went away after careful readjustment of the carb....

Brgds, Bert
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Old Jan 21, 2014, 10:37 AM
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Thanks for the mixture tip. I didn't see the newest sensor solution ? If you want to keep that a secret, I can understand, sometimes I blab too much. But I have been curious.
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Old Jan 21, 2014, 11:14 AM
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Oh, sorry.... no secrets here: I am using a magnet of 3 mm diameter, by 10 mm length, telescopic in a plastic tube for height adjustment. Magnet is tipped by Hall sensor MLX90217.
Sensor is glued to magnet, by common (Industrial strenght) CA glue.
Max passing distance between crankpin and sensor-tip seems to be 2 mm, so adjust backplate thickness accordingly (I use typical approx 1.5 mm)

See attached pics.

As for the mixture: leaning out the mixture will NOT give the same effect as with Glow Ignition.
You will hear the burbling in the exhaust get less and less, and a very slight increase in output, but you will NOT hear what you would hear when leaning out a glow engine....
It takes a bit of getting used to....
Basically, as long as it burbles it is above stoichiometric, and I believe it (this burbling) to be occasional after-ignition in the exhaust of the unburnt fuel, because I do not see ANY movement in the heli when it does that.

When the engine starts misfiring it is really too rich, and one can observe it by the tail getting twitchy.
Even though Methanol has a really wide burnable range, optimal mixture is pretty sensitive.
Too lean will present itself very easy recognizable: the engine quits when the throttle is opened, AS IF the ignition is switched off, and picks up again immediately when the throttle is closed.... This happens allready as little as "two clicks closed from peak RPM"....

As long as the engine is firing consistent, the mixture is OK, and lubrication can ONLY be influenced by oil content. Do not go richer for lubrication purposes; in that case just add more oil.
Just lift your backplate regularly, to get a good impression on how poor or well lubricated the engine is.
It seems, that for our stype of flying, 15% synthetic is adequate (the engines allready last at least one year on it....)....

Brgds, Bert
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Old Apr 04, 2014, 04:16 PM
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Sake's T rex600N met vonkendoos (0 min 33 sec)


Believe it or not, but it is a T-rex 600N with electronic ignition, and the sensor as shown in the earlier posts. And it runs like a charm.

The guy that built it, made a small window in the circumference of the fan cowling on the portside, with two marks (TDC, and 35 deg before TDC) and a different colour on the edge of one of the vanes of the fan. Very convenient for initial adjustment and every now and then a timing check-up.

He used to get approx 10 minutes out of a tankfull on 10% Coolpower, I am very curious how much he will get out of a tank full of 2% of our low-budget-mix, but it is expected, that the fuel cost per minute of flight will be lower than the replacement costs of LiPo's for an electric 600 for the same amount of flight time....

Brgds, Bert
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