Bafang Ultra Fatbike build

[Daxxie]

How does the Ultra do bottom bracket size?. I realize no bottom bracket per se, but I want the big Q factor to go around a fat bike tire. Really just the chainring from center as far as possible.

There are 2 versions of the Ultra's spider. One specifically for Fatbikes.

[TOLM]

Amazing build. So clean. As good as a fat e bike can be

[AZguy]

Wouldn't worry about C but L and R would be very telling...

[ncmired]

Really just the chain ring from center as far as possible.

I thought that maybe they could accommodate a pretty wide range of chain lines using different depth spline chain ring carriers, out to a hard limit set by the drive side crank spindle distance. But I've not seen other chain ring carriers available, or even if the Max chain ring carriers would fit on the Ultra.

[JPLabs]

I guess coil resistance and inductance (capacitance, help me here....) might be a good indicator? If either are significantly different, then motor winding design must have changed? Resistance actually might match, if thicker but fewer windings were used, so we need more than that, right?

[AZguy]

I was thinking the same.... Just off the top it should be easy to confirm same poles and coils but who knows about the windings....

Enquiring minds want to know =]

[JPLabs]

Is it known/confirmed it's the same KV? Windings are easy to change, maybe they optimized for lower revs?
Or, quite possibly kept it the same for more top speed, as you said...

Just curious, since I never saw KV specs for either.

[xcnick]

How does the Ultra do bottom bracket size?. I realize no bottom bracket per se, but I want the big Q factor to go around a fat bike tire. Really just the chainring from center as far as possible.

[AZguy]

Very close to 22:1

When I took mine apart I made notes:

8 poles
12 coils
9t (motor shaft)
32t - 11t (nylon gear and shaft)
68t (secondary reduction final)

9:32 * 11:68 = ~21:97979...:1

[ncmired]

Apologies for my bad reference info - what's the BBS02/BBSHD reduction ratio(s)?

[AZguy]

That's *less* than the BBS - I'd have thought they'd gone with a higher reduction (higher motor speeds)... It's believable - it appears from the photos each reduction is not very great. Perhaps same motor core with same KV and lower reduction will give a higher top speed for a given battery if same KV motor.... dunno...

[Daxxie]

+1

Do you know the reduction ratio(s)?

The Bafang Ultra has a Reduction ratio of 1:18.26

9t Motor shaft > 23t
25t > 66t
17t > 46t

9/23 * 25/66 * 17/46 = ~ 18,25569 : 1

[ncmired]

Do you know the reduction ratio(s)?

Eric (with Josh) said 25:1 during the Luna Ultra teardown video (2:38 point): https://www.youtube.com/watch?v=1lki_sGQfJ0

This motor, along with the Max and some other Bafang "integrated" motors, might have more chainline correction possibilities via the splined chain ring spider. I would like to see wider market acceptance for this motor series.

[AZguy]

+1

Very awesome. That is very mechanically different than the BBSHD and from the photos looks well-engineered and manufactured particularly given it's chinese.

Three sets of reduction gears vs. two in the BBS. Do you know the reduction ratio(s)?

[JPLabs]

Awesome info in this thread!! Thanks.