Freewheel crank resources

I have a Cyclone 1000W setup, which uses a separate chain drive for the motor, using a 2nd chainring and a crank-mounted freewheel. This works fine, but because this setup uses standard #40 1/2" chain, it is noisy as all getout. Part of this might be because the freewheel used is of questionable quality. So far it has held together, though. Anyway the setup works well, and it is great being able to take advantage of the extra gearing provided by the Nexus 3-speed hub. This configuration runs on a 48V/13.8Ah 16s6p a123-based pack, and a 55A controller. It peaks out at about 2650W. Because of the extra gearing, this configuration has more low-end torque than the 72V/60A 5303 setup it replaced, with the same top-end speed. It is a lot less weight as well.

An RC-based setup would weigh even less, which is why I'm standing in line for a couple of Matt's new "eDrives", but rather than messing around with the cranks, like Mitch I plan on doing the "series drive" option. With two freewheels on the output shaft, one for the sprocket driven from the crankset, and one for the motor side, you can still pedal without any extra drag, I think.

-- Gary
 
I agree with Miles, for the most part. Pick your side-affect and minimize the looses that you can live with and go with it.

I have a bit of drag on my bike. But, it was calculated and it is within my desired limits. I cannot feel it at all. But, I do notice the bike does not coast quite as far as it did without the drive system.

No biggie, but it is measurable.

Matt

:EDIT:

Gary,

Yup, I know what you are saying.

Ultimately, every setup and every intended use is a touch different. That is what I love about this hobby!
 
John in CR said:
Why, as long as it's all an integral part of the gearing stages of the motor? The few % loss of the final stage being the bike chain should definitely be worth it to obtain variable gearing, and isn't only a loss if you aren't pedaling, or am I looking at it wrong and the loss is variable, not a fixed loss?
Click to expand...


I thought we were comparing the pros/cons of combining drives at the crank or at a jack-shaft? To combine at the crank requires an extra 3 or 4 to 1 reduction from motor speed (which probably means an extra gearing stage), which is then inverted. As I said, it's all about compromises....
 
Miles said:
John in CR said:
Why, as long as it's all an integral part of the gearing stages of the motor? The few % loss of the final stage being the bike chain should definitely be worth it to obtain variable gearing, and isn't only a loss if you aren't pedaling, or am I looking at it wrong and the loss is variable, not a fixed loss?
Click to expand...


I thought we were comparing the pros/cons of combining drives at the crank or at a jack-shaft. To combine at the crank requires an extra 3 or 4 to 1 reduction from motor speed (which probably means an extra gearing stage), which is then inverted. As I said, it's all about compromises....
Click to expand...

Now I got it, we'd be gearing all the way down to pedal crank speed, then back up to tire rpm. duh. :oops:
 
As long as we're not talking about an extra stage, how much loss are we talking about for the motor drive, less than 1% or something significant? My guess would be less real world difference than a perfectly maintained chain verses a typical one that most of us ignore, or a cool day verses a hot one. I like the cleanliness aspect, though I can only dream of a clean looking install like that belt drive rig you posted. That's a sharp one. Does the power of the motor do it justice?

John
 
Hi,
Miles said:
MitchJi said:
Serial drive the pedals and motor turn the same shaft. If there is a FW on the motor end of the shaft I think the only extra drag when pedaling would be (if I'm missing something let me know):

  • 1. the longer shaft
    2. the friction of the FW
    3. possibly a crooked chain line

I don't think 1 and 2 are significant. Marcus (who did a lot of testing) told me 3 isn't very much.
Click to expand...

Mitch,

Yes, the losses from chain mis-alignment would be minimal.
Click to expand...
I might have used the incorrect technical term (or you might have understood exactly what I meant and I'm missing it). I didn't mean alignment sideways (along the shaft). I meant that on most bikes you can't place the GB output shaft at the same height and between the Hub and Crank. On my Haro the shaft might be higher than the top of the rear swingarm. So the chain from the crank would go up to the the top of the swing arm and the second chain would go down to the rear hub.

If you're comparing this system with others, you haven't taken into account the fact that the pedal drive uses a second chain run....
Click to expand...

Correct! I didn't think about that.

To combine at the crank requires an extra 3 or 4 to 1 reduction from motor speed (which probably means an extra gearing stage), which is then inverted. As I said, it's all about compromises....
Click to expand...

As compared to a serial shaft its about an extra 2:1 reduction. You want roughly 180 rpm at the shaft if you want to pedal with it. Higher than a normal cadence because the crank is bigger than the rear sprocket.

With the crank you want the speed to match cadence but you have an extra stage built in to get it. With a serial drive the output shaft needs to be at the correct speed. Because you are not driving it directly the final shaft going to the crank doesn't need to match so you can use a much smaller sprocket on the shaft than on the crank (of course it gets bumped up again between the crank and rear wheel).

I don't see pedaling efficiency as a big issue. With the motor off and:

  • 1. A left hand drive you are pushing the chain between the hub and the GB.
    2. Crank style you are pushing the chain between the crank and motor (I think).
    3. Serial the power is being transmitted using a second chain at probably at least 97% efficiency.

With the size motors most of us plan to use I don't think drive efficiency is an issue comparing Crank and Serial. Who cares about 5% with a 3kw motor?

I think it comes down to which is the easiest to install which will vary by the bike and personal preference. I prefer serial so I bought a FS Frame with no chain growth. If I had a strong preference (like Deecanio) to frame mount I would choose Crank (no chain growth between frame and Crank). If I wanted to mount the motor on the front of the downtube I would probably choose Crank. Aside from any efficiency issues it would be hard for me to live with aesthetically (one chain going forward from Crank, the second chain going from in front of the crank to the read hub).
 
John in CR said:
My guess would be less real world difference than a perfectly maintained chain verses a typical one that most of us ignore..............
That's a sharp one. Does the power of the motor do it justice?
Click to expand...

Yes, so that's about 3 or 4%, then :mrgreen:

The motor is not particularly powerful, using the present voltage/gearing (the bottleneck is the controller), up to about 850 Watts. Version 2, using an RC motor and an extra reduction step, will be both lighter and much more powerful.
 
Mitch,

You're right, I misunderstood you. Jackshaft vertical displacement shouldn't affect efficiency. In what way do you think it might?

The exact ratios used will depend on a lot of factors. I was assuming that the jackshaft would be at nominal wheel rpm.

3 or 4% loss per chain would be a reasonable rule of thumb - depends on throughput, though.

If you only use the motor occasionally (for hills etc.) pedal drive efficiency is important.

5% extra loss on the motor's drivetrain is less important than 5% loss in the motor itself, but it's still 5% less battery...
 
3-4% for an extra stage makes sense, but if well executed it's not an additional stage, just bigger gearing ratios, so wouldn't that get you down into the 1% difference range? Also, I thought it was derailleur systems that are in the 3-4% loss range, so a stage with a properly aligned, lubed and sized chain, should be less shouldn't it?

John
 
Sure, if you can achieve the reduction to crank rpm in the same number of steps that you would otherwise use to get to wheel rpm, then the losses would be less great - smaller chain sprockets (below 13t) start to become significantly less efficient, though.

What factors in a derailleur system, are you thinking of, that might make it less efficient than a single speed?

I think you need to come up with a more specific proposal and then compare that - this is getting a bit vaporous... :)
 
On a derailleur the chain snakes around two extra rollers and always has some angle.

I'm getting one of Matt's 2 stage gearboxes, and I'd like to input it to the crank instead of a jackshaft by using a freewheel on the sprocket from the gearbox input, and a freewheel for the pedal input. I thought that's what this thread was about. Maybe what I want requires a hollow shaft for mounting the sprockets from the motor and going to the wheel, then the crankshaft would need one-way bearings as the freewheel for the pedals.

John
 
John in CR said:
On a derailleur the chain snakes around two extra rollers and always has some angle.
Click to expand...
Yes, but it's not under load, at that point - so, the losses due to that are very small.

John in CR said:
Maybe what I want requires a hollow shaft for mounting the sprockets from the motor and going to the wheel, then the crankshaft would need one-way bearings as the freewheel for the pedals.
Click to expand...
I'm not sure I understand this bit, John?
 
Anyway, to get this thread back on track....

Let's discuss the factors relating to a chainring adaptor for freewheeling cranks.

104mm BCD (mtb standard) or 130mm (better for larger chainrings)?

Specific to ENO 22t or generic 18t?

What things to consider for crank-driven set-ups?
 
The biggest hurdle for a crank driven setup would be getting enough reduction to run typical rear cogs. A double stage reduction is absolutely necessary if running an RC setup to get the chain speed down enough.

My mountain bike will probably be the first freewheeling crank, shiftable bike I build. I plan on using the smallest freewheel (11 tooth?) on the output shaft of the reduction unit. I am also worried about breaking the chain with that much power geared down so far to run to the small 13 tooth cog on my cassette. Odds are I will find 3rd or 4th cog to be the minimum I can run the motor on without worrying about chain breakage.

Hmm, I wonder about getting a cassette that has larger cogs to reduce chain stress?

Miles, any ideas?

Matt
 
Hi Matt,

im having the freewheeling crank also with a dual reduction - i know that if you have a rear cassette rather than freewheel cluster all the cogs are interchangeable, however i think the largest is 34?
Im going to cyclone my kona with dual reduction and an 11 tooth on the output shaft - if thats connected to a say 34t chainring giving me another 3-1 reduction there so i was hoping that if i had 2 x 34 chainrings the normal gears would be fine? if not you could always reduce the size of the chainring to the gears as we'd have to "adapt" it to fit the crank free wheel anyway?


Cheers,

D
 
Miles said:
3 or 4% loss per chain would be a reasonable rule of thumb - depends on throughput, though.
Click to expand...
I've heard that a clean chain can expect 2% losses.

So a dirty chain (worst case scenerio) would be 3% or 4% or above.

Also... about chain cleanliness... they've done studies and found that the solid lubrications (the wax type) actually do their work by preventing dirt from sticking to the chain. The friction (which is the efficiency loss) is caused by the dirt and nothing else. So metal on metal chain sprocket to chain is not as bad as a really gummy chain clogged with too much grim.

So what you want is a clean chain with a very thin amount of lube.

...people tend to make the mistake of thinking:

"Oh, I've got to lube my chain all the time to make it run better."

...and that tends to build up too much dirt and grim and makes the chain gummy and not work well. So the answer is to every once and a while remove the chain and completely soak it in something like paint thinner (do not use gasoline or you could cause a serious fire) and use a toothbrush and really scrub the chain down to the bare metal. In a "perfect world" (when I used to work at a bike shop) you could use the high powered air to blow the crap out. That's the ideal... air compressors rule when it comes to chains because you can do it on the bike.

Anyway... prevent the "gummy chain" and you will be in the 2% range.

Okay... back to whatever you guys are talking about... :)
 
I've been researching everything related to electric bikes for 5 years, now...... :)

How many gears do you need? Maybe consider 3, wide ratio, with the strongest BMX chain? Otherwise, you'll be eating chains at an alarming rate, I think.....
 
an interesting point Miles, i know opti does get wear on the sprockets and chain and that motor is pathetic in comparison to the monsters we're putting in.
5 years eh? maybe i shouldnt beat mself up too badly not understanding it all after two weeks then ? :roll:
Hope it can be done :?
 
Miles said:
I've been researching everything related to electric bikes for 5 years, now...... :)

How many gears do you need? Maybe consider 3, wide ratio, with the strongest BMX chain? Otherwise, you'll be eating chains at an alarming rate, I think.....
Click to expand...

Agreed. Remember, 5kw will only be the occasional output. For the most part, it will be pulling 1.5kw.

Can you run shifting cogs with a BMX chain? That chain is alot wider than a derailer chain.

Matt
 
I'm sure you'll get it to work :wink:

All chains were 1/8", at one time...

For 3 gears the spacing isn't so important because you can use the end stops on the mech.

Anyway, we need to try these things out... :)

Try looking for Wippermann BMX 1R8 chain
http://www.velimpex.com/2008promo/bmx-chains.htm
 
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