Re: Testing timing of Red Atom Modules

[oldfogeyuk]

That’s a pretty good summary of the issues Bill.

The one thing I’ve been struggling with is trying to accurately model the R2/R3|C1 behaviour. The ‘standard’ model for capacitive reactance works fine for sinusoids, but in this application the applied voltage is an inconsistent ramp, so calculating suitable values for R2 R3 & C1 beforehand was never going to be simple.

I resorted to experiment rather than planned design primarily because I wanted to explore the limits of capability of the ‘Atom’ design and whether it could be tailored to suit this engine.
The last lot of figures I got allowed me to work out dv/dt close to the switching point at each of the extremes, so I could feed that into a spreadsheet to come up with an idea of the parallel reactance of C1 and its effect, and it just confirmed what I found and what you’ve just explained: Contrary to the simple explanation in the patent, the ignition advance actually reduces with increasing speed.

I also had a go at making a ‘Red’ Module, but I can’t get the engine to run with it. I’m a bit worried about the newly acquired batch of TIP162s, they might be dodgy, as in not actually TIP162s at all. More work to follow. (UPDATE: they’re all fake, local supplier is replacing them from another source. A bit of dig on the web suggests there’s a massive flood of fake transistors from guess who? clue: the man in charge of the forty thieves.)

Most recently I tried out one of the Nova II modules for comparison. It provides 18 degrees advance at all speeds. Notably though, it has to be connected with reverse polarity to work. The terminal with the + on it needs to go to chassis. Given that we know the internals of the ‘Atom’ and which terminal is actually positive, the Nova II markings make no sense. I wonder if this is a fake too?

I also stripped down the magneto and flywheel on my engine and measured the angles w.r.t TDC. Guess what: The magneto armature is inclined perpendicular to 22 degrees BTDC, and the magnets in the flywheel are 23 degrees BTDC (This is a dual magnet, single armature type magneto). So, the earlier tests confirm that you can push the module advance right to the extreme point of changeover of the magnetic moment in the magneto.

Still no luck with a decent scope trace, all my photos show overlaid double traces, but I’ve made some progress. It seems my best chance is to shoot a movie of the trace on my ‘phone and then work through each frame to locate a good shot, this has worked on a couple of frames but they’re at the wrong timebase and voltage to provide decent measurements. Also I might need to do it at night to remove the reflection too.

More to come….