Purchase advice please - Bafang Ultra M620 vs BBSHD

[zoumerela]

Hello lovely people,
I found the Ultra M620 being sold as a standalone part on Aliexpress, and since it is a newer model than the BBSHD and has a torque sensor (I will be mostly riding offroad on hills and forest trails, some quite steep), I was wondering if it is a better option, but then I read that it requires a special frame and I am kind of unsure. Anyone purchased a M620 to install it on their regular bike and doing a self-made conversion?
Also, if I went for the BBSHD, do I need a special controller to plug it to my PC per USB, or is it doable with the standard Bafang ones offered with the motor? And how far is it customisable to compensate for lack of torque sensor?
Thank you all for your help!

 

[amberwolf]

Anyone purchased a M620 to install it on their regular bike and doing a self-made conversion?

This would require cutting up your bike frame to take the entire bottom bracket (pedals) area off the bike, and welding in an M6xx-specific mounting bracket in the right way to ensure it works and lines up on your bike with the original pedal chainline, etc.

If you have an aluminum frame, you have to use an aluminum bracket, and you then should heat treat the frame to recover it back to something closer to it's original strength (since the BB area is highly stressed, it's probably safer to heat treat than leave it alone).

If you have a steel frame, then you have to use a steel bracket (I'm not sure if they make one?), and heat treating is not required, but you may have to be careful with the welding to avoid warping the bracket (same with the aluminum one above).

That said, somewhere around here there is at least one build on the forum that custom-built their own bike around this bracket; I dont' recall if they modified a frame or made it from scratch. (and I don't rmemgber if they made their own bracket or bought one).

And how far is it customisable to compensate for lack of torque sensor?

What do you need it to do, specifically, and in what way? Meaning, how do you need it to respond to your pedal input in various situations?

A torque sensor response will be different than a cadence response; exactly how a particular system reads and responds to a torque sensor determines how different.

For example, it is *possible* to have a system respond instantly to any level of torque input on the cranks with whatever programmed level of power is desired. But that's not how all systems work. For instance, a Cycle Analyst v3 used to monitor torque/pas will not do this, because it requires input from the cadence sensor as well, as a safety feature to prevent runaway accidental operation...but it isn't optional, it is just how it works, and your'e stuck with that. I don't know how the Ultra systems respond, and given Bafang's history I doubt that all firmware versions of even the same hardware operate the same way, and different versions of the drive probably also operate differently. So they may require you to already be moving (spinning cranks) before torque is reacted to, or they may react to it without any crank movement (like from a complete stop).


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[zoumerela]

Thank you for the infos, I appreciate your help.

 

[spinningmagnets]

Here is a build where the ebiker wanted to cut his frame and weld-in a proprietary build. This will give you an idea of what that would entail...(The steel in this alignment jig is easily removable after welding)

https://www.electricbike.com/adding-bafang-ultra-frame/

 

[tomjasz]

M620 support and parts chain are not unlike our experiences with the early BBSxx series. Abysmal. I suggest anyone doing their own repairs and maintenance stay with the BBSHD.