I've managed to get some adapter pins made up, that attach the roller (actually a skateboard wheel) to the generator unit (a motor sold as a replacement spare for a child's electric scooter). These were the only bit I couldn't fabricate myself, and that's only due to lack of lathe... ;-)
The prototype generator, minus bike - note simplicity of construction, the base is a piece of 18mmm shuttering ply, hinged on to the stand using two pieces of angled steel, bolted on, as is the scooter motor - no welding required. All other equipment seen in this and the nest picture is a temporary addition, putting the amp on the bike for a compact setup - normal generators will only have the motor and a tiny box of tricks including a diode (to stop current flowing back into the motor), possible a cheap ammeter, and an output socket.
(For the record - equipment mounted is a voltage limiter (stops output rising above approx 14v, to prevent damage to capacitor & amp, would also provide correct charging voltage for battery charging), smoothing capacitor that also acts as a power store. This is far bigger than required just to smooth the output of the generator, but also acts a power store for clean bass etc some parts of the music requiring more power than can be immediately supplied by the source. I'll be trying much smaller sizes for different applications). The capacitor is then connected to a smallish car audio amp that gives me around 50W rms into the speakers.
Whilst this is a temporary experimental system used for the event yesterday, it may be useful to have at least some generator units with built in capacitor & regulator, so they can be plugged directly into equipment rather than via a central regulator/power unit that will be part of the main PA system.
(having said all this only the regulator is really visible, the capacitor & amp are on the underside of the plywood).
With bike - wheel is held against wheel using bungee cord - low tech, and easily replaceable.
A long held ambition - to have a bike powered sound system I can get to an event by bike - and here we are. Speakers are under the covers on the front pannier, turbo trainer on top and everything else in the panniers. This was for Kingston Green Fair on the 26th of May, running sound (mainly a CD backing track, and also a mic) for the children's stage, for Pete Wintercrane of Big Top Mania.
And in use - one speaker mounted on the back pannier, the other is the other side of the stage. The bike mounts are deliberately off-square so give space for the feet when pedalling - these speakers are also designed to be useable on either side of the bike while in motion, running the amp from a battery. This gives a completely portable sound system for cycle demos - critical mass and the naked bike ride. ;-)
