TRIBUNAL

So I installed a Bafang 750w BBSO2b motor on a 2017 Surley Krampus 29"x3" Mountain bike and it's GREAT!
I weighed more in the beginning, figure 350lbs. Its been up the mountain trails in Colorado and California. When going up the steep hills I have to pedal and help the motor out.
I was able to fit a 28t chain ring which I was able to mount behind the chain ring adapter t bring my chain offset down a little bit. Long story short, the motor is slightly spaced out maybe a quarter of an inch and the chain is just offset too much on the two largest gears of the 11-42t cassette. This means I'm stuck using the second from the largest, a 32t gear as my biggest.
My biggest problem is heat, the motor is struggling with the weight and lack of gear.I'm thinking I could upgrade my cassette to an 11-52t. My thoughts are, with this setup it would put me on a 40t gear at the same gear location and that should help a lot.
I assume this may not be enough and heat is still going to be an issue.
I did write to Bafang about the heat issue and asked what they recommend, they actually responded by one of their tech guys and he gave me a lot of info and said it was normal considering the use, maybe they were being humerus when they advised me just not to use it up hill... lol helpful, but i see their point. shortly after I had a breakdown. I'm currently awaiting parts from china, a motor core, because I got an 08 H hall sensor error. The coils all look fine as best i can guess and it never shut down completely due to heat, it wasn't even that hot when it failed, but I guess its been pushed a little bit, only had maybe 100 miles of use on it. Internals all look perfect, I'm going to re-grease with mobile 28 as people recommend.
Now I'm thinking as my next move what about a second motor, a hub motor, perhaps something I can use with the same battery. I haven't done much research yet, I figured I would start here and see if anyone has any suggestions. It would be nice to have it for up hill climbs and just as a backup wouldn't hurt.
The alternative to this is to go with the 1,000w Bafang BBSHD motor, or perhaps another motor thats better? The cassette and 1000w motor upgrade might be enough to get the job done.. I do like the idea of a second motor though.... ahhh decisions decisions
If anyone has any other suggestions that might help it would be appreciated.

TRIBUNAL

2old

I've operated a BBS02 with three rear cassette gears, 11-17-28 in 8-speed spacing and this was adequate for off road rides in CA. The 8-speed components were inexpensive and strong and the three gears allowed a "straight" chainline. Perhaps you can do the same with individual, larger gears. Look at endless sphere for ideas about big rear hub systems, which are very heavy and use lots of battery, but necessary for steep hills. I have an inexpensive 1000w, diirect drive rear hub motor with a 30 amp controller and with a 52V battery (1500w depending how one calculates) that ascends moderate (probably 10%) hills well, but wouldn't be adequate for severe off road activity IMO.

andychrist

Along the lines of what 2old wrote, perhaps you could rebuild your cassette placing the 42 cog further outward. That would spare you the expense of purchasing a pricey new 50T cassette and wasting the largest cog anyway.

Just built a dual 500W Bafang hub drive recumbent cargo bike with a 50/39 chainrings and 11-28 cassette. I myself weigh around 180lbs in winter clothes; unloaded but with two 21Ah batteries, panniers and trailer attached the bike itself tips the scale around 120lbs. Adding the hundred pounds or so of supplies I schlepp home the total approximates 400lbs, and the bike still makes it up some really steep grades at 10.6mph with assist level set from 2 to 4 (out of 9). Wattage displayed on the 500C and P850C rarely exceeds 265, has only briefly ever flashed over 400 (probably when shifting gears and relaxing pressure on the pedals.) Have you noted the output on your Bafang display, TRIBUNAL?

Am for the most part only riding paved, so my use case is not exactly comparable to yours, and again agree with 2old that off-roading will demand greater power. If your suspension fork supports it, perhaps an extra front hub motor would be all you’d need. And of course having two wheel drive is a definite plus when attempting to surmount obstacles or even just riding over slippery/loose surfaces. Dunno though whether the single battery pack you’ve got now would have the discharge rate to power two drives simultaneously, I’d ask the good people at Bafang what they’d recommend.

2old

Good points above. A few years ago I rode a BH bike with dual motors up a fairly steep off road trail (eight miles, 3,000' elevation gain) easily, but the ascent was gradual. In fact, the bike had a "jammed" torque sensor and I could slow it down only with the brakes which cut off the motor, so it flew. However the descent on the hardtail wasn't pleasant with two fairly heavy wheels and no rear suspension. The company had fashioned some kind of "splitter" so only one battery and controller ran both motors. AR, either could be operated individually. You have a rigid fork, so a front hub system (with torque arm) is feasible, but you'd probably need an additional battery and controller (or hook up an external controller and "splitter" so you could use one battery).

TRIBUNAL

Wow thanks for the help guys. Im really new to biking so I know almost nothing. I was wondering if I can use a smaller cassette and space it out from the inside so that the largest gear is more straight. I was thinking its probably not possible, but sounds like maybe it is? I don't really understand what you were saying entirely 2old but ill have to look into this. I only really want a few gears to use, my main use is almost all uphill, even two or three gears would be sufficient, but I need one really big one. I saw a 52t 11 speed cassette for $60. Im going to look into that site endless sphere.

I would definitely consider the front hub motor, but I am planning to install a fork with suspension because the downhill is brutal and the further i go uphill the more i begin to wonder if i can handle the trip down, on the bright side my arms and shoulders are feeling really strong lol. I see the fork on the new Surly Krampus is going for 379 which isn't terrible. Is a hub motor not compatible with a suspension fork? Getting another battery is fine, Im probably going to drain too much amperage with two motors and who knows might have battey temp problems if I tried. I wouldn't need a big battery like I got for the mid drive, just something for that up hill boost, theyre not that terrible in prices.

andychrist

Your Surely is equipped with 29” x3” wheels, haven’t seen that particular size in any hub motors, only either 2” or 4”. So might be a problem trying to find a compatible unit.

A single 1000-1500W mid drive would likely be more energy efficient over all anyway. But would be even more taxing on the drive train and spokes of the rear wheel than your current setup. What I like about my own dual hub drive system is that it actually reduces load/wear on the drive train and eases shifting to boot. But what with the dual 21Ah battery packs it did add about 50lbs to an already fairly heavy bike. But then I required 100mi range, which you most likely do not so could get away with a much lighter power supply.

Recently saw a YouTube on an attempt to run two hub drives from a single controller. Was not successful, but perhaps there are programming workarounds that Bafang could advise upon. But then motor controllers don’t weigh much, only problem is finding the extra room on a bike frame. Probably not such a big deal for you, TRIBUNAL, as your mid drive’s controller is built-in so not hogging space the way my own bike’s two external units do.

andychrist

Good question whether a hub motor would be compatible with the suspension fork you’re looking at, TRIBUNAL. There are a some dual drive, pre-built e-bikes with front suspension but those forks might have been specially designed to handle motorized hubs, have no idea. OTOH the non-suspended fork on my recumbent has an extremely slack steerer angle to which the addition of a hub motor must add considerable stress, yet at the time of this writing the headset hasn’t imploded so am keeping my fingers crossed.

As 2old mentioned you’d likely need torque arms to support hub motors; they generally fasten on with hose clamps but if your fork has fender eyelets the Grin Tech TorqArm V3 can utilize those instead.

I wasn’t taking any chances with the aluminum fork on my recumbent so installed TorqArms V3 on both left and right dropouts.



Just this one in the rear so far, have a second TorqArm V4 on order for the drive side and no more are currently available in the US.

Again, moot point if you’re limited to 3” wide wheels and have only the choice of 2” or 4” motorized hubs.

Pop N Wood

Lots of posts claiming a BBSHD handles heat significantly better than a BBS02. I would go that route over trying to synchronize multiple simultaneous motors.

Karl is a Bafang mid drive guru, this article has statements that ought to really hit home to you

https://electricbike-blog.com/2016/0...hopping-guide/

Maybe a different chain ring while you are at it. This one appears to offset more toward the granny ring than the one in your picture, hard to tell.

https://electricbike-blog.com/2016/0...irsty-monster/

TRIBUNAL

Its all a lot to consider. Now I think I may have found a solution on karls post, the cyclone seems to be exactly what i need, torque! "With a 48v battery (2000W) this drive system does not even get very warm running continuously at full throttle."
"The BBSHD does not even really get that warm when running it on full throttle for extended periods, as long as there are no hills." But I want the hills so...
I saw a cyclone kit on Luna, but why is it so cheap? Shouldn't it be more expensive? https://lunacycle.com/cyclone-mid-dr...planetary-kit/ $350. I paid a lot more for the Bafang BBSO2.

That chainring I looked at but its for the HD it says and I think mine sets the teeth back further as the rear of the chain ring nearly hits the housing. My chainring is also 28t im pretty sure

2old

If you're considering the Cyclone, there is a long thread in endless sphere (maybe more than one). Just remember the extra strong motor will be a lot harder on your drivetrain.

TRIBUNAL

Yea I was doing some reading last night, looks like ill definitely need to make sure the chain's straight with that setup, I also saw the controllers about 100+ more so its more like 500. I wish I bought that motor to begin with, maybe ill sell or just keep my bbs02 for another project. It would be nice to have a second bike for a friend to use. ill check out that post on the cyclone.
Also turns out the chainring i have is 30 not 28

2old

I had a Cyclone (from Sick Bike Parts) and it came stock with a 40 amp controller. I sold it because the BBS02 is perfect for my use. I haven't seen them in Luna's or "Sick's" site recently, but some individuals are ordering directly. ebikesca has the only front motor that IMO is safe with suspension forks, the GMAC. This could be a consideration.

Doc_Wui

I would expect the cyclone to be plenty strong, but also pretty raw. Noisy for sure. The exposed gears/chain are going to eat something someday too. Gotta keep any middrive spinning briskly, or they heat up.

TRIBUNAL

Yea I don't like the noise thing, but I can deal with it i guess. I could try to get the bbso2 spinning faster with a larger gear, and I will still do that either way it will be helpful, Just need to figure out how to do that exactly. Yea Id just go with the 40amp, my battery is only rated for 40amp output i read, also less power should help the temp a little.