Thanks for all the suggestions,
We were given a pneumatic ram and solenoid valves as a possible means of completing this problem, however it was a common solution, and our current set up is no bigger/ heavier than those valves and also the weight/danger of a pressurised gas on board the car.
Our motor will consume approx 300W for a single shift operation, however even the use of a simple solenoid actuator such as this one is 320W, and the pneumatic valves to handle the pressure required also consume power in a similar order of magnitude.
We are now aware that this project has been over-engineered, however our academic project supervisors cannot know that we have put in 3 months of work for nothing, so our final solution must be a system actuated with a stepper motor, and weigh less than 5kg.
(of course we now know that it is possible to do the whole thing with a solenoid in 1.5kg but we can't redesign with 2 weeks left!)
Push Button Electronic Gearchange, Electric Shifter, Quickshifter, Flatshifter, Disabled Bike Adaptations build a neat custom solenoid to perform our exact function.
It is also the existance of systems such as this which led us down our somewhat 'experimental' route...as at least we have proved that a motor is not a viable option.
After trying to design a capacitor bank boost system today, it turns out that that would be either too expensive or too slow (Series combinations of super caps lead to high ESR which increases time constant etc)
We have ordered parts to build a bigger conductor which will not saturate in our switch mode booster, however this will be too heavy when included with the rest of the circuitry required.
So our 'final' plan is to use this SLA battery in series with the car's high capacity battery (which has an alternator running also):
Yuasa | Batteries | Batteries and Chargers | Lead Acid Batteries | Yuasa NP Range |NP1.2-12RS
In series with the car's battery system this will give approx 26V. It's low Ah capacity (chosen to minimise weight) means its voltage will drop to approx 11V under the 13A load. After a shift has been completed, we will use a MOSFET switching circuit to recharge this 12V SLA accross the battery and alternator.
the SLA is 0.65kg, and our motor is 3.95kg
Our coupling mechanism has been built from aluminium and weighs approx 100g
This leaves 300g for the remainder of our electronics!
Could anyone recommend a better battery technology? I think only a SLA will give us the 13A 200ms pulse we require, but if anyone knows of a lighter and capable technology it would be great to hear from you?
Thanks, Paul