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Old 09-13-2011, 01:03 PM   #21
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Anybody here at the Virginia MegaMeet where Bruce demonstrated the wheel decoder - with a circular saw and one tooth cut off the blade?
Awesome.
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Old 09-13-2011, 01:44 PM   #22
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It's a work in progress; the scatter shield is going to happen pretty soon. It's one of our off the shelf trigger wheels; they're designed to be dynamically balance as is; the welds may not be perfectly balanced though.
It'd still scare the crap outta me. Brave Sir Robin wouldn't even be in the same fiefdom as that thing while it was spinning.

Just as an FYI, I'm not sure if they're made by the same shop, but the 4" wheel I bought from you guys in '08 (the one with the triangular teeth which actually looks like a saw blade) wasn't quite round. More specifically, the teeth weren't all the same height. It was a very small error, but easily detectable with feeler gauges. This caused me quite a bit of electronic grief until I finally figured out what was causing the resultant (and only very occasionally) misfires. Ultimately, I put the wheel into a lathe and trimmed down the teeth a bit, flattening them out and making them all the same height relative to the center of the wheel.
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Old 09-14-2011, 10:28 AM   #23
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They are made in the same shop - we may revise the 4" trigger wheel tooth profile, as the laser can sometimes burn the tips of the sawtooth corners. The larger wheels don't have this issue as the edges of the teeth are arcs and not corners. Thanks for the notes on it.
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Old 09-14-2011, 11:21 AM   #24
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Yeah, merely flattening (roudening, technically) the tips of the teeth down to 2 or 3mm will improve the performance. After I trimmed mine, I got much stronger signal out of the VR sensor. Makes sense- flattening the teeth put a larger mass of metal nearer to the sensor.

Any reason why that wheel had triangular teeth in the first place as opposed to the more conventional tooth design on the other wheels?

Last edited by Joe Perez; 09-14-2011 at 11:51 AM.
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Old 09-14-2011, 12:39 PM   #25
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It'd still scare the crap outta me. Brave Sir Robin wouldn't even be in the same fiefdom as that thing while it was spinning.
It was quite perilous.
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Old 09-14-2011, 02:16 PM   #26
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Yeah, merely flattening (roudening, technically) the tips of the teeth down to 2 or 3mm will improve the performance. After I trimmed mine, I got much stronger signal out of the VR sensor. Makes sense- flattening the teeth put a larger mass of metal nearer to the sensor.

Any reason why that wheel had triangular teeth in the first place as opposed to the more conventional tooth design on the other wheels?
Concerns that the sensor needed a minimum gap width to trigger effectively.
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Old 09-14-2011, 06:47 PM   #27
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Jerry is a nut. I'm glad he is still in one piece. I can't decide if the best part was watching the RPM gauge wrap around twice or his statement at the end "It's got some pretty good range"
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Old 09-15-2011, 02:28 AM   #28
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Concerns that the sensor needed a minimum gap width to trigger effectively.
Ah, gotcha.

Here's a shot of what the signal coming off my 4" wheel looked like prior to lathing it:



As you can see, there's significant variation in the amplitude of one pulse to the next, and that first tooth after the gap barely made a zero crossing. The squarewave at the bottom is an LM1815 struggling to deal with the signal, and failing. It missed a pulse because the amplitude of it was so much lower than the previous one.

The MAX9924 did a much better job of decoding this signal, but it would still misfire maybe once or twice a day.

After I lathed the wheel and flattened the teeth a bit, the signal became much more uniform, and the amplitude of the signal increased as well, so much so that I was able to run a significantly wider gap and still have zero misfires.
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Old 09-15-2011, 09:29 AM   #29
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As you can see...[the] first tooth after the gap barely made a zero crossing.
That's an interesting phenomenon that occurs when using a VR sensor and a missing tooth wheel at the first tooth after the gap. Below is an example of the same thing using an OEM BMW 60-2 wheel and VR sensor. Blue trace is raw sensor, red is post conditioner (MAX9926).

It sums up why I prefer to use a hall sensor as possible.
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Over 19,000 RPM on a bench test...-1.jpg  
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Old 09-15-2011, 04:27 PM   #30
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I find that rather interesting.

This is the "after" shot of my setup, with the flattened teeth, doesn't show any problems at all on the first tooth after the gap. You couldn't draw a more ideal waveform with a pencil. Same sensor and wheel as the earlier image, just with the tips of the teeth ground down to have a 2-3mm flat section:



Note the scale on trace 1: that sucker is putting out more than 5v p-p, and this is merely idling. A

lso, the decoded trace is now being supplied by a 9924, whereas in the first image I posted, I was testing the LM1815.
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Old 04-05-2017, 09:28 AM   #31
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Old thread, image hosting has eaten the images of failing LM1815 :( Does anyone still have a copy of these images by any chance?
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