Kickstart engine
Big single cylinder four stroke bike engines that are kick started needs very exact ignition timing during startup. They normally rotate only 2 revolutions when kick started, this generally means that the engine only barely reach TDC when you kickstart it. The engine is normally positioned just after TDC on the power stroke before you kickstart it.
We normally get two trigger pulses during this time, one for the charge cycle and one for the compression cycle. The RPM is however fairly unpredictable and the engine needs very exact ignition timing to start.
The only sensible solution is to place the trigger sensor where you want your ignition to occur during the starting procedure. Usually around 10deg BTDC.
We can expect the rpm to be in the 20-120rpm range, this equals a rotational speed of approximately 8.33-1.38ms/degree. This means that we don't need to care much about dwell even if an inductive ignition system is used. If we start to charge the coil for 2-3ms after the trigger and then let it go the ignition will only be max 3deg to late. This is acceptable.
At high rpm the engine is timed from the single pulse of the crank trigger with a "tdc_after_trigger" of around 360-380 degrees.
As an alternative a long tooth can be used together with a hall sensor, this allow us to start on one edge of the sensor pulse train and to time the engine from the other side of the pulse train if the rpm is high enough. This would be the best solution.
What we need
Starting:
We need the firmware to charge and fire the coil as soon as a configurable edge is seen in the trigger signal. There could be a benefit in letting this continue even when the ignition is timed from the previous tooth (below).
Running:
Above a configurable rpm the engine is timed from the last rising of falling edge (configurable). "tdc_after_trigger" can be well over 360degrees.
This allow the engine to be run with a hall sensor that reads a single narrow tooth that is used for starting and running the engine or with a wide tooth, where one edge is used for timing the engine and the other edge is used for starting the engine.
Jörgen Karlsson
Gothenburg, Sweden.