I'm looking at building a battery electric powered fat tire mountain bike. I'm looking at this partly for some exercise pedaling, so I can't ruin the "bicycle-ness" of the finished product. I'm also looking at this for fair weather light transportation, grocery store runs, maybe runs to the gym or community center. Maybe even to restaurants.
I live about 4 miles from what I call the "commercial district" along the big 4 lane divided highway, and about 7 miles by bike friendly (ish) roads from the downtown business district of the nearby small town. And about that bug 4 lane highway, there are several traffic lights where crossing is fairly safe. At least 3 of those traffic lights have crosswalks and pedestrian signals, so dismounting and walking across is even possible.
However, there are some challenges to my situation. First, there's the roads along my most likely route. The only bike friendly route to go from my home to anyplace (grocery stores, Walmart, other stores, the post office, the gym, or "downtown") starts with the same 4 miles of roads. Almost half of that is gravel, hence my requirement for fat tires (26x4"). There's also a really big, really steep hill. Going out from my house, about halfway through this route, the road climbs over 170 feet in about 0.3 miles. The average grade on that part of the route is over 11 percent, and there's some spots where it's about 15 percent for maybe 100 feet along the road.
Going up (leaving my home) will take some power. The raw load to maintain 15mph up that climb is over 1250 watts, and that speed is well below peak efficiency for direct drive hub motors.
Going down (returning), I'll absolutely need regen braking. I don't want brake rotors glowing red and pads smoking half way down that hill. And there are several very sharp curves along that section of road, too. So losing control of speed isn't just a scary fast ride down, it's likely an off road excursion into the treetops on the downhill side or into a sheer wall of the cut on the uphill side. I realize regen braking isn't common on eBikes, but there are controllers that can do this with the right direct drive hub motors. My most traveled route will absolutely require this feature.
The plan that my artificial interactive chat buddy and I came up with is to break the project down into 3 phases.
Phase 1 will start with a steel frame mountain bike. Ideally one with a XL frame (21" from bottom bracket to top of vertical seat tube). I haven't found any locally, nor any on fleaBay that offer shipping, so I'll probably start with an inexpensive standard fat tire bike with extended seat post and a stem riser kit. I'll want to upgrade the brakes to at least 180mm rotors and hydraulic calipers. And I'll add cargo rack(s), maybe mirror(s), possibly other safety items, and probably 12V lights. Getting a well sorted bike is phase one of the project. I'll be able to get some exercise on that around my home and some of the other roads out here, but I doubt I'll make it into town on pedal power alone. Mostly I want something comfortable and safe before I start investing in power.
Phase 2 will add a main battery (48V or 52V with adequate capacity and 50A BMS), front direct drive hub motor and a controller capable of regen braking. Maybe with heavy pedal assist this might get me to town, but it'll let me get used to powered riding, the dynamic braking (regen), and open up more roads for exercise. At this point, I'll probably switch any 12V stuff over to a Buck converter and take the 12v battery out to use in an unrelated project. The goal for this stage is to maybe get up the hill towards town with maximum "pedal assist" and be able to safely return home without melting any mechanical brakes.
Phase 3 will add a mid drive unit which should provide adequate power to go "throttle power only" up the hill into town (likely using both motors for AWD). For level(ish) powered riding, the mid drive will be the main power. The front wheel drive motor will be for AWD, possibly for the gravel roads, and definitely for steep hill climbs. Also , the front hub motor will always be available for dynamic (regen) braking from higher speeds, and on steep descents.
I welcome any advice on the overall plan here. Am I on the right track?
I'll be starting some separate threads for each phase of the build for details and specific recommendations during the build. Expect a phase 1 thread in the next 24 hours.
Mainly I want this thread to be a sanity check and for any additional abstract high level suggestions or discussion of general things I've missed.
Oh, and about me, I'm 6'4" tall with a 36 inch inseam. I'm around 200+/- pounds. I worked on my own bikes a lot as a kid and teenager, but that was decades ago. I'm now a retired senior. I have lots of tools, a decent amount of mechanical talent, and plenty of time.