I was reading the SDS EFI web site and notice they  don't offer rotary
ignition support.

This  is just an idea at this stage.

A simple ignition system  using RX8 coils with a 2.5 ms
dwell time has a  problem.

7000 RPM is   116.7 rev per  second or 42,000 degrees per
second  or one  e-shaft degree in .02 ms.

1 ms is 1/1000 of a  second.

So the ignition will be retarded 42,000 / 2.500  or
16.8 degrees. What is needed is advance at high  RPM.

In the old days that was done by a distributor with  mechanical and
vac advance.

That is for a  real simple system that fires when the
CAS sends a trigger to  the coil. A computer can fix this
but there may be a simpler  way.


Hall Effect sensors are cheap and several can be  used.
Lets say we have 4. The first one is used for 0 to 2000  RPM.
A small magnet would be mounted on the e-shaft  pulley.

#1 0 to 2000 RPM 0 advance for good  starting.
#2 2000 to 4000  14 degrees
#3  4000 to 6000  22 degrees
#4 6000 to 8000. 33  degrees

There is a device called called a data  selector.
It is just a black box that can select one of  these
HE sensors depending on RPM. Or the pilot can select  one.

The black box can be controlled by a computer or  an
analog to digital converter chip.

These  charts are for cars but we have used a fixed advance
22  degrees BTC with good results.
If you set it at a greater  number to compensate for the
coil 2.5 ms dwell that means you  would have 16.8 +_22 which
might cause starting  problems.

Just thinking out loud here.

Paul Lamar

Paul,  This  would be a backup for a Hall  effect sensor failure where the
pilot could select one of the other  timing points. Might need a toggle
switch to bypass the variable  timing system and read only one at 22
degrees.
george grimes

Yes built in back up.

Paul Lamar

Paul,
I have mentioned before that Kawasaki used a hall  effect sensor to advance
the timing on their 2 cycles by running a  permanent magnet stator with a
projection and gapping the hall effect  sensor as wide as you could get it
to trigger. They got a thyristor that  triggered at at about 50% of max
voltage and the increase in the sine wave  amplitude with rpm would trigger
the ignition sooner. Very effective and no  moving parts.
Bill Jepson


Yes I remember that. Only a few  degrees.
We are talking 10 and 20 degree difference here.


Paul  Lamar

On the other hand, 20 degrees of advance at the pulley is 60 degrees at the
rotor. It is not some sort of magic that 20 degrees is plenty for up to
9,000 RPM. Smokey would have loved the dwell time of the rotary. There  is
plenty of time to get the burn done and you can use some crap 87 octane pump
fuel. No starting problems up to 27 degrees of advance fixed.

Lynn E. Hanover

"On the other hand, 20 degrees of advance at the pulley is 60 degrees at the  rotor."  True but that is rather academic.
The ignition timing is always referenced to the e-shaft angle and not the rotor angle.

The word "dwell" is reserved for the time the coil is on and the current flow is charging the coil.

I think you mean the length of time any given "stroke" is consuming rather than dwell time. http://www.rotaryeng.net/how-wank-works.html


Interesting about the 27 degrees. I guess in the back of my mind I was thinking of hand propping.

Paul Lamar