Id love to hear some experience with the Bafang, good or bad?
The Bafang motors are far and away the most-manufactured mid drives on the planet, with a 10-year production run scheduled to change in 2025 to CAN-bus, which is a whole other story) and millions of them sold worldwide over that decade span. You don't see those kinds of numbers in the USA but bear in mind the Far East has literally an order of magnitude more ebike sales than the rest of the world combined. Bafang literally is larger than the Bosch's and Shimano's of the world in terms of sheer production volume (For motors. Not bike components).
Despite the smaller footprint in the USA, they own the lion's share of the DIY market here. Get on Youtube and the internet and try to find some DIY advice on Bafang mid drive motors and you should see more than plenty of thorough, start-to-finish install and service vids. Reality is operating at your level you should never need to mess with it, and it is common to hear BBSHD or BBS02 lifetime mileage counts in the many thousands of miles. My main daily driver built in 2021 is pushing 5000 miles. My secondary one that is now getting the lion's share of errands and commutes is at about 2500 miles; I put it into service in Feb 2023.
You mentioned Tongsheng, which is primarily the TSDZ2, which has been on the market for quite some time, and now the TSDZ8. Tongsheng is essentially the Avis of the DIY motor market. They are number 2 but its a distant #2 in terms of installed volume. I don't know if I would say they have reliability issues. Sure the blue gear gives some people fits but I think overall they are largely reliable. But your available pool of aftermarket parts suppliers is tiny by comparison, as is volunteer and aftermarket support. Its there, but I would not want to be a beginning DIY biker and make this my first build.
You also mentioned the 'Proton' and you actually mean the Photon (the Proton is the bigger brother that was never released and may in fact be cancelled at this point). As in the Cyc Photon. You are correct it is a pricey little bugger at about US$1000 before you get to the battery. This is the one I would tag as having maintenance issues, which is something that Cyc has historically been challenged with on the X1 Pro, the Stealth and now the Photon. Long story, that and I'll skip the details. This is another product I would not make my introduction to ebike building with.
I work from home now, but I commuted on an ebike for many years. I know you have to have reliability, and for that I would do a Bafang. I would make it a BBSHD, which is probably more motor than you need, but also its a motor whose power you can dial back. A motor that idles or runs at 20% versus running flat out is going to last forever, trouble-free. Its more expensive, and heavier too. I'd still do the HD so I can have that reliability, aftermarket parts and community support.
---
And don't even think of a hub motor conversion, or trying to somehow spiff what you have. What has happened to you here is pretty common: you have run face-first into the reality of hub motors: They power from the axle. So they are single-speed. So they are out of their element in steep hills. In fact only YOU can utilize the drivetrain on a hub motor bike so whatever you get out of pedaling is what your muscles can grunt out. The motor will bog just like your legs do trying to grunt up a hill on a high gear. A mid on the other hand can take advantage of a downshift just like your legs do, and thus you already understand its inherent advantage. This is why hub motors are ideal for flat land or low rolling hills, and out of their element on steep hills. You can, btw, extend the efficacy of a hub motor into steeper territory with a smaller wheel, which gives a torque advantage and helps explain in part why so many 20" small-tire ebikes exist.
---
There are separate issues with cadence. As
@Smaug has noted, cadence sensing is a whole different animal when you dig into a mid drive, and the Bafang motors in particular can be configured easily to be ideal for cyclists... but the process is counterintuitive. Plus the cadence sensing that comes from the Bafang factory is... horrible. But you can change all that and its easy to do. Here's a tutorial on exactly what to do, written by Yours Truly.
https://talesontwowheels.com/2023/08/09/bbshd-settings-for-a-pedaling-cyclist-2023-edition/
Both the Tongsheng and Cyc motors have customizability in this regard as well. So do the ToSeven motors but they are new in the marketplace and I would let some other pioneer take the arrows in the back on them. Come back in two years and see if the bugs have been shaken out by then (its been 2 yrs with the Photon and they still aren't all gone).
There are other things to be aware of, and do smart versus internet-dumb (plenty of bad advice online whether you ask for it or not). Would not be a terrible idea to let us know what kind of bike you are thinking of converting, but you can also look at a ground-up tutorial on the subject that gets into frame choices. Just because it says 'from scratch' doesn't mean you can't use what you already have as your donor. The bike that is the subject of the series below was destined for scrap and given new life. Fork and frame came from 1999 and 2000.
https://talesontwowheels.com/2022/04/27/how-to-build-an-ebike-from-scratch/
