cbr shadow said:
I posted a few weeks ago asking some initial questions about building an ebike for my commute. I've updated my expectations and thought I'd make a new post with more information.
I'd like to build a fast ebike for my commute.
My Commute:
https://www.strava.com/activities/2740310450
I can charge batteries at home and at work.
The bike I'm considering:
https://sfbay.craigslist.org/sfc/bik/d/san-francisco-surly-big-dummy-long-tail/6995711420.html
My performance hopes:
30 miles distance, 30-35mph on flat areas
Slower on hills
I'm a strong cyclist and would likely assist 200+ watts for the entire commute
I'd like the conversion to be as simple and reliable as possible.
Questions:
1) I see a lot of mid-drive setups (Bosch?) - is this better than a hub motor for my purposes?
2) I'd like a simple charging solution with "built in" BMS. These used to be called A123 Batteries, I believe. Are those still around? I previously used LiPo batteries which I'd like to avoid this time because I don't want to worry about exploding batteries and balancing correctly.
3) Are there downsides to using this specific bike that I'm considering?
Any suggestions/advice welcome!
That's quite a commute. 60 miles a day. 300 miles a week. 1200 miles a month. If you do the usual 5 day/week job. This would be in range for most commercial ebikes at 20 mph. At 30+ it needs a lot more of everything - energy, wear, motor heat, brakes, battery capacity. Your commute is about equal to my round trip commute in distance and climbing. On that I found that regular ebikes barely had the range and climbing capacity for the one way of my trip or half your trip. Eventually my commuting machine would do the whole round trip without charging and at your speed, so equivalent to your one way trip. You can read about that machine, the link is in my signature, the SuperCommuter. Not quite what you are contemplating, but this is a machine that will do what you are seeking to do, so this is what you need to compare to.
A few crumbs from the experience of building and commuting with a bunch of ebikes.
Mid drives put a lot of wear and tear on everything. Chain, cogs, brakes, tires, battery, motor. A lot of maintenance is involved with over 1,000 miles per month. Bosch is a closed system, they won't let it meet your requirements.
Flat tires are a problem. Changing tires on the way to work can be problematic if you are on a time schedule. I don't like to change tires on the road. So I went for tough tires. I found that the toughest bike tires were not that great. Moped tires however worked. They brought the flat rate down to once per year. And they are about half the cost of a good bike tire. But they are heavy and require moped rims.
Brakes wear fast on ebikes, especially those without regen used in hilly country. With good regen or elecric braking the brakes don't wear out.
Geared hubmotors also wear out clutches and gears when they are used a lot, and they don't let the heat out. They are very prone to failure if their limited power capacity is pushed.
Regular DD bike hubs are pretty good. In my case the gradients (to 15%) were too much and they were getting very hot. So I went to a larger DD hubmotor. QS motor type, 50mm wide magnets. Churns out a lot of torque and also very good at regen for electric braking.
This wide hubmotor did not leave room for many gears on my 135mm wide frame. A wider frame could solve this. In my case I used an ATS two speed crank with one chainring to a single speed freewheel, set up for about 12 and 25 mph, so I could pedal and help it at up to near full speed, or at slower climbing speeds. It worked out pretty well. If the motor was offline I could pedal it on the level in the low gear. I can kick in 600 watts for a short time when climbing, on the flats I can help if I reduce the throttle a bit, at full speed I'm pretty much spun out. I tended to treat it more like "wind sprints" so I got some nice exercise without sweating. Pedal hard for a short time during a startup or climb, then rest a few minutes. No shower needed.
Maintenance wise there was very little. Fix the occasional flat, replace the rear tire every 3000 miles or so, the front lasted 3x longer. The single speed freewheel needed replacement occasionally so I eventually just changed it with each rear tire replacement. With electric braking the friction brakes did not wear out. Chains and sprockets didn't wear out, eventually they would but not often.
The battery ended up 18S 32AH (75V charged). It happens to be lipo but could easily be 18650 with BMS since you are interested in that. It was enough for the round trip, though I generally charged it at what would be the halfway point for your commute. Depending on your hills and speed you might need a bit more capacity.
Dual 203mm hydraulic brakes did a good job in the front. In the rear there was no room for a disc so the electric braking was rigged to a linear magnetic sensor and switch in the rear brake lever. This operated the regen/electric braking in the controller which was very controllable and didn't heat up the front discs.
Best of luck on your challenging project.