Sounds awesome, can’t wait to see the finished product.Yes, I do mean to outfit the Sonni with an A12 and Gates. My sense is from the Rohloff side, it won't be too much of a problem. There's the T-bone brake mount brace to deal with and sprocket/chainring alignment, but these should be surmountable.
OTOH, the Gates belt drive part of the solution will be more challenging. While the Sonni has an elevated chainstay swingarm, the space between the main mondo pivot and the chainring looks a bit tight for a belt (Voima doesn't have this constraint as the main pivots are smaller). Moreover, however, is the belt tensioner issue. It would have to mounted on the motor rather than the frame (like with the Pinion), which is why I think the Sonni open-motor design is advantageous here. Nicolai Bikes appears to have Gates tensioner setup mounted to a Bosch motor, so I'm going to chase that angle down.
Then there's chain-growth of the bike to consider, and the smaller it is the better, because there has to be enough tensioner articulation room for the target belt size used (unlike chains, whose length can be set with link precision, there are only so many belt sizes to choose from to set slack. This could be compensated if the bike had horizontal dropouts like with many city bikes, but of course these bikes aren't of the city ilk ). I have a query out with Pole on chain-growth and they still need to get back.
The E14 electronic shifting addition would be icing on the cake, but not a dealbreaker. If I could get the above to work, I would have a Pole bike with a bulletproof, time-tested sealed geared transmission working with the best big-player e-bike motor on the market linked by a belt in a all-weather, near zero-maintenance solution.
