Hi Richard!
The Extrawheel Project is far from dead, just resting at the moment.
Extrawheel kindly sent me two more replacement quick-release hitches, which I am in-process of testing now. They have much-improved tolerances and what appears to be a solid stop.
One problem I ran into using the Extrawheel on the extremely rough terrain where I have used it is a conflict between the attachment forks (standard and long) and my SKS P55 rear mudguard. When the Extrawheel bounced enthusiastically or the terrain was such the bike and trailer formed a \/, the trailer fork fouled the 'guard attachment bolts and broke the 'guard itself. I ordered a replacement set (USD$100 delivered...shipping costs ensured a damage-free delivery) from SJS Cycles and it is awaiting installation pending further testing. Still working on this issue; this would not be a problem if the Extrawheel was used in the same conditions on a bike with no rear mudguard.
As for the vane material, I've now concluded my basic materials testing using a number of flexible membranes including some made by Goodyear. The hot ticket for spoke vanes has so far proven to be urethane-backed lycra (same material commonly used in helmet covers), but it is very hard to obtain a regular supply. My regular fabrics supplier (The RainShed:
http://www.therainshed.com/ ) doesn't always carry it. Absent the urethane-backed stuff, regular lycra will do, though the 8.5oz/yd stuff has proven most durable for impermeable while retaining the other needed qualities.
The material is only half the battle; the shape is important in a static state and as a chord under wind-load...you want "scoopage" but not to excess. Catenary cuts help here, aided by the wedge shape of the spoke lacings. Sufficient "capture" of the wind is critical for efficiency.
The reason why vane shape is so important is the nature of the dynohub's higher initial starting torque. It requires a boost to start and once running does fine. It is self-starting if the wind is brisk or steady, but it can be an issue in very gentle breezes or if the wind waxes and wanes in the night. Wind direction can change, so the vanes also need to capture from either side. If you try this, do use caution in propping the inverted bike or trailer. Lateral wind-loads on the vaned wheels could cause the lot to turn turtle unless solidly braced with a Click-Stand, stick, or other means.
Just as important is the means for attachment. The large hooks from hook-and-eye sets proved idea for quick attachment and release from the spokes, but they (like all methods that are spoke-based and temporary or non-adhesive) allow creep toward the hub under load, so a tether 'round the tire is necessary as well. It is not as complicated or time-consuming as it sounds to attach the vanes; the lot can be done in about two minutes from start to finish. I'm refining the design so it will remain lightweight, pack small, and deploy or store quickly. Nearly there.
The project continues apace at DanneauxLabs.
A quick aside: do you know when the Extrawheel was last updated in respect to quality of build, fittings and paint?
Yes, as I recall, except for remaining old stock at vendors, all Extrawheel Voyager trailers sold new in 2012 have the new design. The key word to look for is "Voyager".
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After extensive testing, I can say having access to the equivalent of another bikes'worth of dynocharging capacity is a dream come true, especially so when it operates while I'm sleeping!
All the best,
Dan.