Who likes Crank-drives?

[trex]

I reckon the pressure on the teeth is responsible for the wear. Consequently, if presented with a choice between say gear No 5 or No6 on a 5% hill, I tend to choose No5 - the chain runs faster, but less pressure on the sprocket. I believe the choice results in less chain stretch and perhaps fewer shiftings

 

[flecc]

But as said Trex, the chain isn't running faster for a given road speed, assuming a single chainwheel as on the CD. It's just running on a larger rear sprocket which turns more slowly.

 

[John F]

I reckon the pressure on the teeth is responsible for the wear. Consequently, if presented with a choice between say gear No 5 or No6 on a 5% hill, I tend to choose No5 - the chain runs faster, but less pressure on the sprocket. I believe the choice results in less chain stretch and perhaps fewer shiftings

I think that's right because isn't the motor having an easier time and therefore not having to produce as much power?

 

[trex]

may be not but it feels like it does. Your TCM is very much like my BBS01, the faster the motor runs, the higher the yield up to about 75 RPM so the motor produces plenty of power up to that point then it starts to be less productive but somehow, because it sounds sweeter when it runs faster, it seems to have an easier time but if you look at the ground speed, it produces more power when it runs faster.

 

[flecc]

I think that's right because isn't the motor having an easier time and therefore not having to produce as much power?

Not really, for a given performance the power onto the road has to be the same, so the input has to be the same.

It's the power and torque difference again. The same speed chain runs on a larger rear sprocket so spreads the load over more teeth, so would seem to produce less wear.

But the torque in a lower gear is greater so the pressure on the teeth is increased, and because the larger sprocket is turning slower, the chain roller pressure on a tooth is for longer.

Ergo there is no gain in wear terms.
.

 

[trex]

I remember vaguely that the friction wear wasn't a linear function, because at some moment, you get to a catastrophic wear region where metal fatigue causes the metal lattice to disintegrate.
At first, the wear is caused by deformation at the point of contact. It increases with temperature and contact pressure. Running on more teeth reduces both the temperature of chain and cogs and the contact pressure.

 

[flecc]

Yes, it's a very complex area with a huge number of factors to consider Trex.

Most though are very minor, and I think for the reasons I've given that a given performance delivered though a chain running at a constant speed, the wear is roughly constant. Juggling the rear sprocket in use on a derailleur just produces opposing changes.

In essence it's no different than the tyre tread wear for that given performance, in that the same power is needed.

 

[RobF]

Chain wear is mostly due to the combined effects of dirt and lubrication, according to Sheldon Brown.

Makes sense, he gives the example of enclosed chains which last forever.

But Bosch crank drives are said to be hard on the drivetrain, so I remain confused.

Perhaps it's the changes under load, which can be very clonky on a Bosch derailleur bike.

I've learned to soft pedal changes on the AVE which helps a lot, as does trying to avoid changing gear when going uphill, especially on assistance.

http://sheldonbrown.com/brandt/chain-care.html

 

[flecc]

Chain wear is mostly due to the combined effects of dirt and lubrication, according to Sheldon Brown.

Makes sense, he gives the example of enclosed chains which last forever.

It's true. When I entered the trade in 1950 I was surprised at how many Sunbeam totally enclosed oilbath chaincase bikes were still in use on their original chains and sprockets since the 1920s and '30s. Some had been in use through the war as well. These ran the chain through a pool of oil at the bottom of the chainwheel.

If we combined those oilbath chaincases with modern metallurgy, chains and sprockets could last indefinitely.

But the problem is the derailleur, fundamentally incompatible with this type of enclosure. With a crank drive unit, an oilbath chaincase combined with the NuVinci hub is probably the perfect solution.

However, removing the rear wheel is a problem. With the steel frames of the day, we just used to expand the frame to change tyres and tubes. With alloy frames a removable frame section would be needed on the left dropout to pass through tyres and tubes.

 

[Arbol]

It's true. When I entered the trade in 1950 I was surprised at how many Sunbeam totally enclosed oilbath chaincase bikes were still in use on their original chains and sprockets since the 1920s and '30s. Some had been in use through the war as well. These ran the chain through a pool of oil at the bottom of the chainwheel.

If we combined those oilbath chaincases with modern metallurgy, chains and sprockets could last indefinitely.

But the problem is the derailleur, fundamentally incompatible with this type of enclosure. With a crank drive unit, an oilbath chaincase combined with the NuVinci hub is probably the perfect solution.

However, removing the rear wheel is a problem. With the steel frames of the day, we just used to expand the frame to change tyres and tubes. With alloy frames a removable frame section would be needed on the left dropout to pass through tyres and tubes.

Interesting, flecc.

How would you compare oilbath chaincases with belts, assuming a crank drive / IGH hub combination?

I see in both cases one needs to "break" the frame to remove the chain / belt.

Wouldn't then a belt be simpler (no need of oilbath, no case)? Or are there inconvenients for a belt, which make an oilbath chaincase better?

 

[flecc]

Yes, a belt would definitely be simpler, although, despite the manufacturer's claims, they are less efficient than chains and sprockets.

However, on an e-bike where there's motor assistance, a small loss of efficiency doesn't matter. And anyway, the NuVinci hub I suggested is not particularly efficient either, when compared to a derailleur, probably making worries about belt inefficiency irrelevant.

 

[Arbol]

Could a sprocket for a gates carbon belt be fitted in a say Xiongda singlespeed (or any other singlespeed hub, such as the Q100 singlespeed)?

I ask this because the IGH accepting belts are advertised as "special". So, I do not know if it would be possible to add the specific sprocket for belts in a motor, or if the motor should be build at initio with that specification in mind.

 

[Arbol]

Yes, a belt would definitely be simpler, although, despite the manufacturer's claims, they are less efficient than chains and sprockets.

However, on an e-bike where there's motor assistance, a small loss of efficiency doesn't matter. And anyway, the NuVinci hub I suggested is not particularly efficient either, when compared to a derailleur, probably making worries about belt inefficiency irrelevant.

By the way, an interesting (experimental) claim (but only at zero pre-load, so not interesting in practical terms):

Smith noticed that the slope of the two lines wasn't equal with respect to increasing applied load, though – in other words, the chain generates more friction than the belt with increasing applied load. Smith calculates that the crossover point falls at about 208 watts in terms of constant pedaling output, and the belt's advantages only increase from there.

http://www.bikeradar.com/road/news/article/chain-or-belt-drive-which-is-faster-36074/

So, an e-bike could take advantage of a belt in efficiency terms.

 

[flecc]

I'm not sure I understand the question, do you mean internally to replace the orbital gear set, or as an external belt sprocket to use the hub motor in a crank drive fashion?

 

[flecc]

By the way, an interesting (experimental) claim:

I frankly don't believe that claim.

 

[mike killay]

Could a sprocket for a gates carbon belt be fitted in a say Xiongda singlespeed (or any other singlespeed hub, such as the Q100 singlespeed)?

I ask this because the IGH accepting belts are advertised as "special". So, I do not know if it would be possible to add the specific sprocket for belts in a motor, or if the motor should be build at initio with that specification in mind.

This is the direction that development needs to go, improving things that are known weaknesses rather than yet another whizz-kid designer trying to push bizarre looking frames, smart phone technology etc.
It sounds to me that these designers live and work in well heated, closeted city offices, make assumptions such as that ALL people own mobile phones let alone smart ones, and the closest they get to dirty fingers is when they use the electronic pencil sharpener.
What we need, is engineers, mechanics, electricians who are out there in the muck and rain and actually ride electric bikes.

 

[Arbol]

English is not my mother language, so I may be committing a language mistake. What I mean is:

The sprocket of the rear wheel, such as in the image:

http://dirtragmag.com/review-gates-centertrack-carbon-belt-drive-system/

is a small wheel with teeth, which are interconnected to the belt.

Then, a hub motor has also sprockets, such as in post #3 of:

http://forums.mtbr.com/wheels-tires/clash-titans-hubs-844599.html

(which can be freewheel or cassette).

Then, there are hub motors which are singlespeed, ie they only have one sprocket (instead of 7spd for a standard freewheel or 9spd for a cassette).

My question is if for a singlespeed hub motor, one could take out the standard sprocket, and put instead a specific sprocket for a carbon gates belt, such as the one at:

http://dirtragmag.com/review-gates-centertrack-carbon-belt-drive-system/

Then one would have a singlespeed bike (but 2spd if using a Xiongda) with an electric motor and a belt, which would be cheaper than having a crank motor plus a Nuvinci plus a belt, and possibly usage would be roughly the same, even at steep hills. And one cable less from the handlebar.

 

[amigafan2003]

The best crank drive would be a silent one.

Until that day though.

My BB02 is pretty quiet - much quieter than the Tongxin/Cute Q100/Mac geared motors if have experience of.

 

[flecc]

This is the direction that development needs to go, improving things that are known weaknesses rather than yet another whizz-kid designer trying to push bizarre looking frames, smart phone technology etc.
It sounds to me that these designers live and work in well heated, closeted city offices, make assumptions such as that ALL people own mobile phones let alone smart ones, and the closest they get to dirty fingers is when they use the electronic pencil sharpener.
What we need, is engineers, mechanics, electricians who are out there in the muck and rain and actually ride electric bikes.

I'm afraid Britain is in the same consumer trap as America, commerce and designers desperately searching for something new to satisfy their consumers' insatiable demand for something new to shop for.
.

 

[flecc]

English is not my mother language, so I may be committing a language mistake. What I mean is:

The sprocket of the rear wheel, such as in the image:

Thanks for the explanation, your English is undoubtedly far better than my knowledge of your language, whatever that is!

I understand now. If the hub motor has a standard freewheel thread, and most have*, I think a toothed belt sprocket may be available to fit. Not certain though, most are used with hub gears. A belt sprocket could easily be adapted though.

*A very few hub motors have been produced with smaller BMX threads for single speed use. I doubt a belt sprocket would be available for those, but you are unlikely to encounter those.