What and where are free-wheel cranks found?

[swbluto]

Hello, I'm looking to make an RC drive that connects through the cranks but I don't know how to attack that problem in the best way. I was spinning my pedals and I noticed that it didn't freewheel, which could be a problem if I wanted to attach the motor there. So, I'm thinking I'll probably need "free-wheel" cranks or something.

Where do you find them? Also, what kind of options are there for driving the cranks on the left side and right side of the cranks? It seems like it might be less interfering if I had a sprocket on the left side of the cranks and that way I could use the entire gear range of the right, but I'm so unversed with the appropriate technology and wouldn't know what equipmenet I'd need and where to find it.

 

[Miles]

You can't isolate the pedals from the motor if you drive the left-hand side :wink:

http://www.endless-sphere.com/forums/viewtopic.php?p=165215#p165215

 

[jdcburg]

You can get crank freewheels kits from several places - SickBikeParts, Cyclone, Elation and Eclipse that I know of. I live in the US and had very good luck with SickBikeParts and Cyclone Taiwan for quick service, tech assistance and the ability to buy parts a la carte rather than a whole kit. I designed and built a dual freewheel front chainring setup that allows me to pedal without turning the motor as well as motor without turning the cranks and also provide pedal assist to the motor in any amount I choose. You can read about it at http://endless-sphere.com/forums/viewtopic.php?f=28&t=15529. I've been using it for a few months now and am very pleased. I've tweaked the setup a bit from the video one and added LiFePO4 power but the basics are the same.

 

[amberwolf]

You can't isolate the pedals from the motor if you drive the left-hand side :wink:

http://www.endless-sphere.com/forums/viewtopic.php?p=165215#p165215

Unless you do it like CrazyBike2 and have two bottom brackets (or a BB and a jackshaft, etc)....and the freewheels for motor and pedals are on the left side of the rear BB, with pedals on the front.

Depends on the space available on the bike.

 

[liveforphysics]

Dual broached freewheels.

Full drivetrain isolation at the rear wheel. Nothing matches that. Freewheeling cranks are a noisy band-aid.

 

[swbluto]

Dual broached freewheels.

That sounds like a code-phrase.

I looked at your post and saw a video, but I didn't see any pretty pictures of how this integrates with the bike. I think I saw a small <15tooth freewheel gear that looks like it'd go on the back hub, but 15 tooth doesn't sound like enough for a single stage reduction. (If I were to connect the motor directly to the hub, I'd use a single stage or "direct drive" propulsion, like something like a 90-150 tooth gear. Clearances look iffy on my bike, though.)

 

[amberwolf]

Dual broached freewheels.

Full drivetrain isolation at the rear wheel. Nothing matches that. Freewheeling cranks are a noisy band-aid.

Unless you're driving thru the cranks/regular drivetrain.

 

[liveforphysics]

I didn't see any pretty pictures of how this integrates with the bike. I think I saw a small <15tooth freewheel gear that looks like it'd go on the back hub, but 15 tooth doesn't sound like enough for a single stage reduction.

I think your above post is a good indicator that it's not for you.

Go for some noise high speed spinning bicycle chain/cranks contraption.

 

[swbluto]

I didn't see any pretty pictures of how this integrates with the bike. I think I saw a small <15tooth freewheel gear that looks like it'd go on the back hub, but 15 tooth doesn't sound like enough for a single stage reduction.

I think your above post is a good indicator that it's not for you.

Go for some noise high speed spinning bicycle chain/cranks contraption.

I don't really know if you're implying a lack of requisite understanding in utilizing the idea fully (Highly likely), or just incompatibility with my preferences. I realize the mechanical efficiency of driving through the cranks is probably comparable with other multistage systems, so I'm not totally against external multi-stages.

If the problem with cranks is just noise, I'm fine with that, as I'm sure the chain system and motor will be as noisy if not noisier. It just needs to be capable of passing through 3 kw of mechanical power at 30ish mph.

 

[jdcburg]

SWB - with that kind of power you probably wouldn't need/want to go through the front chainring/derailleur and I don't think the derailleur or its built-in freewheel would handle 3KW for very long. I haven't really looked into it but the broaching stickie at the top of the thread might be the best way for you to go. That will allow you to pedal independent of the motor and you wouldn't need a front crank freewheel - jd

 

[swbluto]

SWB - with that kind of power you probably wouldn't need/want to go through the front chainring/derailleur and I don't think the derailleur or its built-in freewheel would handle 3KW for very long.

Free-wheel cranks wouldn't handle 3 kW for long? The derailleur should be fine, as I don't plan on switching gears while engaging the motor (Or it won't be full engagement).

I have this fear of the drive system being inadequate, though, given how often the belt breaks on my scooter with more than a kW. My only real problem has been the drive system, so I solve that *right* the first time (Or maybe after a fix or two), and I should have no more problems.

 

[jdcburg]

I'm certainly no expert but 3KW is ~4 hp or (by definition) lifting 2200lbs 1 ft/sec. I'd say that's about 10x the force of a 220lb person pushing on the pedal crank at 60rpm. I think the bicycle chain is at risk. When I was first experimenting with my 350W motor I was at a dead stop and accidentally hit a switch to start the motor. It snapped the chain like it was a thread. Also remember there is a freewheel connecting the derailleur cassette to the wheel hub that is also not designed for that kind of loading. The torque curve of that motor may mean you don't really need to go through the shifting cassette but could get by with a simpler system. Don't mean to sound negative but there are lots of things to consider with that kind of power on a bicycle, where everything is designed for much lower power/strain levels - jd

 

[swbluto]

I was hoping I wouldn't be bumping against the torque levels of everyday components. With my belts breaking, I looked up the torque level rating of the belt and it's like 5 NM. DOH! So I turned down the current limit to reduce starting torque (I used my simulator for the calculations), and they haven't been breaking.

....

So, I might need to replace the regular back freewheel with a stronger freewheel. Eno, I'm guessing.

According to http://answers.yahoo.com/question/index?qid=20080821072112AA9BVD8, bicycle chains have a force capability of 1300 kg or around 12,000 newtons. If I keep the motor's torque to under 10 NM, than a 12t sprocket with a 2" radius( or .0508 M) should impart 10 NM/.0508 = 196 newtons on the chain. If I don't limit the motor current, then it looks like it could get upto 20 NM, and that'd be around 400 newtons.

If the "first stage to second stage" reduction is around 3, then it looks like the force on the drive sprocket would be three times that on the motor's chain. So maybe around 1200 newtons on the drive chain.

It looks like it should take it. I think. I'm guessing the "350 watt" motor snapping may have been related to alignment or tightness? Or maybe a worn out chain?

Now I just wonder about the freewheel cranks... hmmmm? I don't know if the freewheels on the cranks can be upgraded.

I'm looking at other's systems and it looks like they just simply went to a single gear in the front and said "forget the derailleur!". :lol: I'm thinking that's probably what I'll do since the derailleur is taking up precious space on that round clampable part of the swing arm. I also looked at my bike and reducing the back tire to 20" will cause the pedals to hit the ground. So I'm thinking I'll need to shorten my cranks by 2 or 3" and I'm not sure if that's possible.

 

[REdiculous]

When I was first experimenting with my 350W motor I was at a dead stop and accidentally hit a switch to start the motor. It snapped the chain like it was a thread.

Was there something wrong with your chain or..? I used to be able to push 350w for a decent amount of time and could probably peak a bit higher pedaling. My motor pushes nearly 500w through my chain from a stand-still and it's got an old rusty section pulled from a kid's 16" Huffy..seriously.

Just curious how you can do that w/ 350w when it should be designed for at least that much power.

 

[jdcburg]

I used to run with a relay and rocker switch. I'd hit the power after I was moving. I hit it accidentally it from a dead stop (no push off or anything) and it snapped the chain in an instant. I use that as an example. I think 9x that power would be stressing parts that aren't designed for that kind of load. ymmv - jd

 

[veloman]

I'm certainly no expert but 3KW is ~4 hp or (by definition) lifting 2200lbs 1 ft/sec. I'd say that's about 10x the force of a 220lb person pushing on the pedal crank at 60rpm. I think the bicycle chain is at risk. When I was first experimenting with my 350W motor I was at a dead stop and accidentally hit a switch to start the motor. It snapped the chain like it was a thread. Also remember there is a freewheel connecting the derailleur cassette to the wheel hub that is also not designed for that kind of loading. The torque curve of that motor may mean you don't really need to go through the shifting cassette but could get by with a simpler system. Don't mean to sound negative but there are lots of things to consider with that kind of power on a bicycle, where everything is designed for much lower power/strain levels - jd

A properly installed bike chain can easily handle 3kw, especially at the high rpms that these motors will be turning them.

Two days ago I put 1945 watts at 90rpm through my skinny 9 speed chain which has over 10,000 miles on it. Do the math on the torque, then compare it to 3kw at 2000+rpms.

 

[swbluto]

So... let me get this straight. If I get the ENO freewheel along with the crank that goes with it from sick bike parts, I can just "put that" in with my regular chainring set into the bottom bracket, connect the motor to the largest chainring and I'm done?

If I were to do that, that'd mean (Please check me), if motor runs, the pedals aren't "spun". When the wheel spins, the motor nor pedal isn't "spun". When I pedal, the motor is turned since it's directly connected to the chain rings. Is that right? I think I could take that. I mainly just don't want the pedals to chop my legs off when the motor's running, and the pedaling range I'll be left with will be the hill-climbing / starting gears / granny gear anyways. Plus, I'll need to get the motor to rotate while pedaling to start it up using a "pedal first" / sensorless controller. Not that I plan on using one, but it'd be nice to allow me to use a sensorless back-up in case the halls fail.

 

[jdcburg]

Hi SWB - You need a few more parts: their chainrings (sprockets), which are designed to fit the front freewheel, and you'll probably need a longer spindle as the freewheel takes up a little more space. If you have a cartridge BB you may need the BB replacement kit. But they may have a cartridge system now, which would include the longer spindle. Also the chainring hardware kit they sell for about $5 makes it easier to tie everything together. You are correct on the operation, with one caveat: because the motor is driving the rear wheel through the same rear sprocket as you are pedaling, it won't matter whether you are in lower or higher gears - the motor rpms will determine your crank cadence.

veloman wrote:
Two days ago I put 1945 watts at 90rpm through my skinny 9 speed chain which has over 10,000 miles on it. Do the math on the torque, then compare it to 3kw at 2000+rpms.

SWB is talking about potentially starting from near zero rpms with 54% more watts than you, which I think will stress the chain, especially over time. But the real weak link is the derailleur cassette freewheel. When I was thinking about marketing a kit I talked with one bicycle freewheel sprocket manufacturer about a freewheel for a motor driven sprocket and he said they wouldn't consider it - the loads are too great. I wouldn't go with anything less than the White ENO. I don't know if that can be adapted to a cassette - jd

 

[swbluto]

What if free-wheel cranks were put on the left side, and two chainrings were also put on the left side, and then one put a (For example) 56T on the disc brake using an adapter? Is that possible? And the motor would connect to the large chainring of the two, and the wheel's sprocket would connect to the smaller one. Let's say the chain rings were 56T on the large one and 24T on the small one.

I know that Miles responded to a similar question with a negative, but I think this question might be unique...

I think that should give a suitable gear ratio of (56/11)*(56/24) = 11.24. And as most of the us know... a higher gear ratio is better. (If I were to stick with the right side, it seems like my gear ratio would be constrained to 7.5 due to the cassette's tooth limit of 34T which puts more of a heat strain on my motor on hills according to my simulator, no matter the kV; If I get the gearing to 12, I can reasonably expect to keep motor heat under 350 watts while sustaining 35 mph speeds up hills. At a gearing ratio of 7, I can expect motor heat of 550 watts to attain similar performance... not good. )

If that's possible, would the pedals and motor be isolated? Motor wouldn't drive the pedals, but pedaling would drive the motor. But.. wait... the motor wouldn't freewheel with the wheel and coasting is kind of point of this freewheeling business. Oh, well, if that turns out to be the easiest and least unreliable route, I'm probably not going to complain about motor drag.

 

[boostjuice]

But the real weak link is the derailleur cassette freewheel. When I was thinking about marketing a kit I talked with one bicycle freewheel sprocket manufacturer about a freewheel for a motor driven sprocket and he said they wouldn't consider it - the loads are too great. I wouldn't go with anything less than the White ENO. I don't know if that can be adapted to a cassette - jd

It is true that some makes/models of freehubs are known to be susceptable to premature failure due to poor engineering. However quality wheel hubs have ratchets & pawls as beefy as an ENO. Particularly ones that dont use the standard Shimano style modular replaceable Freehubs. There is no reason for them not to be up to the task of traction breaking torque.

Take the Hope Pro II for example;

Compared to an ENO;

 

[Miles]

What if free-wheel cranks were put on the left side, and two chainrings were also put on the left side, and then one put a (For example) 56T on the disc brake using an adapter? Is that possible? And the motor would connect to the large chainring of the two, and the wheel's sprocket would connect to the smaller one. Let's say the chain rings were 56T on the large one and 24T on the small one.

In that case, you wouldn't really need a freewheel on the cranks... You could use a freewheel body for ease of mounting, but with the pawls removed.... Preferably not the ENO, for this, though....

 

[swbluto]

You could use a freewheel body for ease of mounting, but with the pawls removed.... Preferably not the ENO, for this, though....

???

Do you have a product link that personifies this "Freewheel body, but with pawls removed"? I'm thinking a freewheel when you say that, but than you say not the paragon of freewheels, so I'm a bit lost.

Also, I take it this "freewheel body" connects to the bottom bracket and interfaces with the cranks somehow? Or is that the part I have to invent?

 

[Miles]

Yes, I should have just said "a freewheel with the pawls removed". [Just woken up, need a coffee].

The ENO isn't best for running power through in freewheeling mode, because it only has a single sealed-bearing unit.

It would just be a convenient way of using the cranks as an idler shaft and wouldn't interfere with their functioning at all.

 

[swbluto]

It would just be a convenient way of using the cranks as an idler shaft and wouldn't interfere with their functioning at all.

I'm so lost. I'd ask for a excruciatingly painful detailed description of what you're talking about because I have a hard time imagining it, but that's a bit much to ask.

So... I'll try my best to describe what I'm thinking. So, you have the freewheel attached to the outside of the crank. Wait... how could that be? So, it's attached to the bracket in between the bracket and the crank. And then... I feel lost... the two chain rings bolt themselves to the freewheel because the free-wheel has the 5 bolt pattern. The freewheel thus doesn't interfere with pedaling, and the motor is isolated from the pedals AND the wheel. Is that right?

How would the freewheel secure itself to the bottom bracket?

 

[Miles]

You use a RH trials crank on the LH side.

Screwed onto this is a freewheel with the pawls removed - which means it just functions as a bearing.

The chain to the rear wheel would run on the freewheel teeth.

A chainring would be mounted to the freewheel to accept the chain from the motor.

You are just using the cranks as a jackshaft, so no interference.

Does this help?