ZF 48v Ebike System

[saneagle]

 

[peterjd]

Manufacturer information

 

[Benjahmin]

Wow, what agreat development. However I don't think I'll be seeing it any time soon 'cos it also looks very very expensive.
As presented, it looks more aimed at professional sports riders. The over run sounds truely scary, and the thought of a steep hill start...... well! It would have to be toned down a lot for general street use.
Not for me i think as, once again, it is a step away from simple garden shed maintenance and repair. I mean, algorithms' never go wrong or need updating/debugging do they?

 

[Az.]

It won't fit in my BB

 

[Ghost1951]

Interesting.

Picked up on two interesting innovations -

Strain Wave Gearing

High frequency sampling of crank speed

I don't really understand that gearing idea in detail. I looked at the wikipedia diagram, and see how the graphic seems to operate, but don't really see how it turns anything..... I think I would need one in my hands to grasp it.

Also - feeling a bit sceptical about how long a drive system depending on constantly flexing, annular gear is going to last. Is it made of nylon? If not, how does it flex like that? Wondering how many are going to fail here...

Explained here: also credit Jabor for the gif diagram.

https://en.wikipedia.org/wiki/Strain_wave_gearing

The slotted ABS type sensor wheel at the back surely improves speed measurement. I notice on my BBS01 that it takes a very detectable amount of time to display speed when I lift the back wheel and operate the motor. And if I kill the back wheel movement, the speed on the screen doesn't register the stop instantly.

There is also a delay in power cutoff as the speed limit is reached. I can see power on my screen as it reduces but then it may take about a second to completely cut off after I reach the set maximum speed.

The reverse is also true. As the bike loses speed, say down to 14, power remains off for about a second or more before coming back in gently. Maybe the micro controller in the motor is just overwhelmed and takes that long to deal with the calculation of what to do next. I'm not sure how much it is that, and how much it is the once a wheel revolution speed information.

One thing for sure - this ZF unit and bike will be very expensive.

 

[Woosh]

One thing for sure - this ZF unit and bike will be very expensive.

ZF made a similar motor for Bofeili years ago.
The Bofeili was only marginally more expensive than Bafang BBS01.

 

[saneagle]

Interesting.

Picked up on two interesting innovations -

Strain Wave Gearing

High frequency sampling of crank speed

I don't really understand that gearing idea in detail. I looked at the wikipedia diagram, and see how the graphic seems to operate, but don't really see how it turns anything..... I think I would need one in my hands to grasp it.

Also - feeling a bit sceptical about how long a drive system depending on constantly flexing, annular gear is going to last. Is it made of nylon? If not, how does it flex like that? Wondering how many are going to fail here...

Explained here: also credit Jabor for the gif diagram.

https://en.wikipedia.org/wiki/Strain_wave_gearing

The slotted ABS type sensor wheel at the back surely improves speed measurement. I notice on my BBS01 that it takes a very detectable amount of time to display speed when I lift the back wheel and operate the motor. And if I kill the back wheel movement, the speed on the screen doesn't register the stop instantly.

There is also a delay in power cutoff as the speed limit is reached. I can see power on my screen as it reduces but then it may take about a second to completely cut off after I reach the set maximum speed.

The reverse is also true. As the bike loses speed, say down to 14, power remains off for about a second or more before coming back in gently. Maybe the micro controller in the motor is just overwhelmed and takes that long to deal with the calculation of what to do next. I'm not sure how much it is that, and how much it is the once a wheel revolution speed information.

One thing for sure - this ZF unit and bike will be very expensive.

That gear system is similar to other systems that have been around for a very long time, which have been used in a few ebike motors before, and like the recliner mechanism of your car seats. It's often used when you want zero backlash.

The gear ratio comes from the difference in the number of teeth between the inner and outer gears compared with the number of teeth on the inner gear. All you need is a shaft with the right eccentricity to walk the inner around the outer while holding the two gears in contact. The outer must be held stationary.For each rotation of the shaft, the inner rotates backwards the amount equivalent to the difference in the number of teeth.

If the outer has 41T and the inner has 40T, the difference is one and the ratio will be 1/40. If the outer had 42T, the ratio would be 2/40.

If you can find something, like a dish with a stepped edge or anything flat with a hole in it, you can drop a 2p in, put your finger in the middle of the 2p and push it around the dish. Don't press too hard. You'll see the 2p rotating backwards. The closer the diameter of the hole is to the diameter of the 2p, the slower the 2p will rotate under your finger (if you let it).

In the car seat recliner mechanism, the eccentric shaft is tapered and spring-loaded along its axis, so it effectively gets larger as the gears wear. That's how they get zero backlash. If you had any free-play in the mechanism, the back of your seat would rattle about when driving your car, so it's a critical characteristic. That ZF system must also use a tapered shaft or something similar to have no backlash.

This ZF system uses that same principle. There's also "wobble gears" that use this principle. It's only a question of how you walk the one gear around the other. The strain wave gearing uses a flexible inner gear and a double eccentric so that there are two parts of the inner gear in contact with the outer. I'd love to know what material last an ebike lifetime for that, if that's what they use.

There are loads on Aliexpress if you find that your gearing is a bit too high:

https://vi.aliexpress.com/w/wholesale-Harmonic-drive.html?spm=a2g0o.detail.search.0

 

[saneagle]

There's a better explanation here, where a guy makes his own:

 

[Ghost1951]

That gear system is similar to other systems that have been around for a very long time, which have been used in a few ebike motors before, and like the recliner mechanism of your car seats. It's often used when you want zero backlash.

The gear ratio comes from the difference in the number of teeth between the inner and outer gears compared with the number of teeth on the inner gear. All you need is a shaft with the right eccentricity to walk the inner around the outer while holding the two gears in contact. The outer must be held stationary.For each rotation of the shaft, the inner rotates backwards the amount equivalent to the difference in the number of teeth.

If the outer has 41T and the inner has 40T, the difference is one and the ratio will be 1/40. If the outer had 42T, the ratio would be 2/40.

If you can find something, like a dish with a stepped edge or anything flat with a hole in it, you can drop a 2p in, put your finger in the middle of the 2p and push it around the dish. Don't press too hard. You'll see the 2p rotating backwards. The closer the diameter of the hole is to the diameter of the 2p, the slower the 2p will rotate under your finger (if you let it).

In the car seat recliner mechanism, the eccentric shaft is tapered and spring-loaded along its axis, so it effectively gets larger as the gears wear. That's how they get zero backlash. If you had any free-play in the mechanism, the back of your seat would rattle about when driving your car, so it's a critical characteristic. That ZF system must also use a tapered shaft or something similar to have no backlash.

This ZF system uses that same principle. There's also "wobble gears" that use this principle. It's only a question of how you walk the one gear around the other. The strain wave gearing uses a flexible inner gear and a double eccentric so that there are two parts of the inner gear in contact with the outer. I'd love to know what material last an ebike lifetime for that, if that's what they use.

There are loads on Aliexpress if you find that your gearing is a bit too high:

https://vi.aliexpress.com/w/wholesale-Harmonic-drive.html?spm=a2g0o.detail.search.0

That's a very detailed and thorough explanation. Thanks for taking the time to explain it. I'll have another look at the graphic now, and see what I can make of it with your description in mind.

Still wondering what material the flexible gear is made of, to last a sensible life in this application.

The other thing I was thinking about was why they apply such a lot of torque so rapidly when setting off. The presenter seemed mighty pleased that he was falling off the back of the bike, every time he set off. Personally, I wouldn't consider that an advantage, but it takes all sorts, as we see here regularly.

 

[saneagle]

Still wondering what material the flexible gear is made of, to last a sensible life in this application.

probably similar to what they make toothed belts out of. My question is how easy is it to service? One thing's for sure. You're not going to be able to get a replacement from Amazon or Ebay!

 

[Ghost1951]

There's a better explanation here, where a guy makes his own:

That really makes it clear and I'm just surprised that I never came across this concept before now.

Here is another example made in metal by another young experimenter and this one shows exactly how the idea works in a proper robust engineering material and in practical real life applications. Well worth a look, I'd say.