Bike.1 has an intermittent problem with the motor, and I'm still waiting for a new controller to help diagnose it.
Bike.2 - the motor makes a grinding noise, and I need to open up the motor to see what's wrong. It sounds really bad.
Bike.3 is working fine. I've just added a voltmeter to is, and a centerstand. But it's sensorless, which means that the motor doesn't work until I'm moving forward slightly. That wouldn't be a problem for cruising, but when geocaching, it's all stops and starts.
Bike.4 is the Synergie, 20 inch wheels. It's OK for caching, but not great.
Bike.5 is the Downtube; the motor overheats when I use it for several hours.
I've decided to replace the motor on bike.2, and I've ordered a 48 volt motor frmo Germanladen. From what I can fathom, this is a warehouse in Portsmouth with a hyperspace link to China. Maybe not hyperspace, maybe they just stuff loads of stuff into a container and ship it. They sell such a huge variety of stuff, I doubt if they have any ebike expertise. But I don't think I need that.
The kit includes a 26 inch wheel, with inner tube and tire. I'll be taking off their tube and tire, and putting on my own very heavy-duty inner tube, line and tire, so protect against punctures. It includes a controller (but I might use my own, because I like the way the Infineon works). Plus a disc brake, ebrakes, a thumb throttle, pedelec sensor (which I don't use) and a few miscellaneous bits.
The toughest decision was whether to go for 36 volts or 48. All my existing bikes are 24 volts, but the modular way I use batteries means that I can cope with 36 or 48 volts. I read some web pages on whether 36 or 48 is better, but most of them seem to think that 48 volts gives you more torque, which is obviously wrong. On the same wheel, 48 volts will give you more torque than 36, but if the wheel is designed for 36 volts, that can have as much torque as a wheel designed for 48.
I suspect, though, that Germanladen are selling the same motor as either 36 or 48, and the difference is in the controller; maybe even in software in the controller.
There is one clear advantage, and one clear disadvantage. This is more obvious if you compare 24 and 48 volts. If you're running 250 watts of power, then 24 volts needs 10 amps, whereas 48 volts needs only 5. So you get less losses in the wiring (but the losses are very low anyway). The disadvantage of 48 volts, is that if you put your fingers on the terminals of a 24 volt battery, you won't feel anything; with 48 volts, you'll feel a tingle at least. Maybe more, it depends on the individual, because some people are more conductive than others. But 48 volts isn't actually dangerous; the fact that it's DC (not AC) helps. And I've made a spark suppressor, so that when I plug the battery in, there isn't a big blue spark.
So I decided to go for 48 volts, although I will also try it out at 36. For 36 volts, I'll use 10 cells in series (two 4s and a 2s), giving 37 volts nominal, 42 volts freshly charged. For 48 volts, I'll use 14 cells in series (three 4s and a 2s), giving 52 volts nominal, 59 volts freshly charged.
The kit cost me £179, which is a very good price if it works as advertised. It's even good value if I only use the wheel, and not the other stuff. And because it comes from Portsmouth, the shipping is free and I won't have to pay import duty or VAT.