As I have been unable to get my machine to rotate as desired using frame based Guide Wheels I have now changed to an internal non driven wheel with the axle fixed to the frame.
The Guide Wheels are fitted around this Spoke Wheel, and held firmly against the Rotor. At startup the Spoke Wheel and Rotor will rotate as a complete assembly. At a suitable speed the Guide Wheels will retract. As there is there no speed  difference between the Spoke Wheel and Rotor, the retraction should be smooth. This will require electronic control of the Guide Wheels by wireless data in both directions
For initial testing I have built the Spoke Wheel, but it is fixed to the Rotor. This is installed, and runs quite smoothly up to 4MPS as of 12 Jan 2017.

The Spoke Wheel being installed in the machine. The outer rim is made from 27mm black steel tube with 2mm wall thickness. It has been pressure tested, and has 1 litre of ethylene glycol added as a balancing fluid. The spokes are 5mm zp steel threaded rod. The spoke attachment points  have been extended for mounting of the retracting mechanisms for the Guide Wheels. The weight is 21Kg.

The wheel is built on a bicycle front wheel hub and axle. 3mm alum plates have been pop riveted to the hub. 9 bracing tubes have been added. The spokes are attached via standard M8 connector nuts  .

The Spoke Wheel installed in the machine. Total weight of the rotating assembly is about 50Kg. The electronic Direct Drive system appears to be working perfectly. The internal space is now greatly diminished. This Spoke Wheel system would work on a much bigger machine with a central floor holding the Spoke Wheel . About 12 meters diameter minimum. I have designed a Slew Ring type of bearing which could be used instead of a Spoke Wheel, on a machine of similar size to the one I am building.

Six more 4 part coil sets have now been fitted to the drive system, and the Rotor assembly can now reach 7 MPS. (Feb 2017) These use Low Side only switching.