"half-rpm" indication from Lightspeed

[Rotary10-RV]

Originally Posted by Paul Eastham

Thanks for everyone who chimed in with ideas. To follow up (and hopefully close this thread forever : ), Klaus sent me a loaner controller box. After about 4 hours, 3 flights, and at least 8 starts, the problem has not returned. Fingers crossed!

Paul,
I truly hope the box was your problem. I though I might offer a FYI for everyone. Most automotive stores carry or can get brass feeler guages to do magnet to coil distance setting. Perhaps everyone here knows this already, as I have a 20-year-old set in my tool box. I got them from Snap-on but only because they were there that day. I did motorcycle ignitions back then. Many types of hall effect sensors. moving magnet, coil and magnet with a reluctor, they all have to have the gap set. I even got a brass wire guage set by special order. FWIW
Bill Jepson

[AlexPeterson]

Bill, there is no access at all to the gap when the ring gear is in place - that is why the clay is the best route. Clay is put on the sensor, the ring gear is very carefully put in place (with the crank forward or aft, depending on which measurement you are after). Then it is removed, and the clay measured with a digital caliper or equivalent.

[Rotary10-RV]

Originally Posted by AlexPeterson

Bill, there is no access at all to the gap when the ring gear is in place - that is why the clay is the best route. Clay is put on the sensor, the ring gear is very carefully put in place (with the crank forward or aft, depending on which measurement you are after). Then it is removed, and the clay measured with a digital caliper or equivalent.

Sorry to say, but YUK, what a deficient design. Needs a "windowed" ring gear.
Perhaps that isn't practical though. Too bad.
Bill

[AlexPeterson]

Originally Posted by Rotary10-RV

Sorry to say, but YUK, what a deficient design. Needs a "windowed" ring gear.
Perhaps that isn't practical though. Too bad.
Bill

Yes, it is a bit of a hassle. I would like to see more margin on the upper clearance as well. I'm sure that there are classic trade-offs involved.

[Rotary10-RV]

Originally Posted by AlexPeterson

Yes, it is a bit of a hassle. I would like to see more margin on the upper clearance as well. I'm sure that there are classic trade-offs involved.

Alex, This is the reason most of the auto and motorcycle ignitions went to a small reluctor wheel with a radially spaced hall-effect pick up. Most went to a fixed permenent magnet mounted behind the coil and a reluctor. Just a toothed wheel to cut the flux lines. Much easer than mounting the moving magnets. It must cost more or everybody would be using it!
Fly safe,
Bill Jepson

[AlexPeterson]

Originally Posted by Rotary10-RV

Alex, This is the reason most of the auto and motorcycle ignitions went to a small reluctor wheel with a radially spaced hall-effect pick up. Most went to a fixed permenent magnet mounted behind the coil and a reluctor. Just a toothed wheel to cut the flux lines. Much easer than mounting the moving magnets. It must cost more or everybody would be using it!
Fly safe,
Bill Jepson

Bill, I believe that what you described is exactly what is inside the mag hole mounted version of Lightspeed, called "Hall effect" to erroneously differentiate it from the direct crank pickup (which is also hall effect). As with everything, there is a tradeoff - gears, moving parts, etc.