Could somone please explain the working of the pickup coil used in the VIC.

The things i want to undertand are
1. why is the pickup coil center taped and a constant 5V is applied to the center.
2. is it reasonable to assume the pick up coil being acting as a constant electromagnet?
3. what could be the polarity of the pickup coil electromagnet as the voltage is fed in the middle?
4. what could happen when the primary coil is pulsed, i.e what will be the strength of the electromagnet before and after pulsing

I'm obviously no expert on Op Amps, but I've learned a lot about them in the last month.  As far as I know the +5 volts is just a requirement for the inputs to the 918 Op Amp.  The coil is tapped in the center so that one half of the coil can go to the + and the other to the - of the Op Amp.  On the buggy only one side of the coil was used, and the - side of the Op Amp was shorted to +5V.

I don't believe it would act as much of an electromagnet because of the high impedance of the Op Amp's inputs.  If that is so, not much polarity of the electromagnet could be observed.

With no other connections to secondary, or choke coils, the pickup coil and Op Amp will just output the same square wave @ 12 Volts, that was input to the primary, sometimes with the phase shifted. 

Quote

1. why is the pickup coil center taped and a constant 5V is applied to the center.

I had a look at this and I'll have a go at answering.
When the primary is pulsing normally, you can use the response of the pickup coil to make logic gate responses from it's own current pulse. In other words, the pickup is directly in phase with the frequency of the primary. However, if you need to probe the core's magnetic field during V- or a gate period when the chokes become self resonant, the core is closed because of the current restricting by the chokes. The normal logic would be to probe the core with the primary and measure response in the pickup at set intervals during gating to establish when the primary phases back into the choke pulse train but he doesn't do that, he measures the core response by probing with 5v and then monitors the flyback response before he probes with the primary. I can see why he does this: If he probes with the primary all the time, there is a chance he will enter the core out of phase with the chokes when they have burned off their voltage with the cell. It is like an airport. You don't probe the runway with the front of a plane to see if you are clear for take off, you probe it with a radar then phase the plane into the runway in perfect time between other planes.

When he tries to establish a working condition for the primary in the core that is an impedance match to the rest of the network he can use two sequenced logic questions of yes and no, when the core is closed the pickup could use other logic gates too. So besides 'yes, no', he can use 'if, or, then and nor'
So the pickup probe asks 'core open yes or no' . 'if yes then X' .' If no then X'.
It can then phase lock the primary back into the chokes and cell so that he is just pushing a wheel with a slight push instead of allowing the wheel to stop and start again using more energy.