Destroyed! A warning to those using freewheel cranks....
- Thread starter boostjuice
- Start date
John in CR
100 TW
Miles said:
So I guess that kind of BB drive just can't work without another FW or bearing. Motor from the rear seems like it should help. Does that mean the FW should be mounted between the 2 sprockets, not on the outside? Mine came 2nd hand but unused with no instructions, so I was curious about how to mount the thing.
I have a few of the cheapie bolt on FW's. If they can be opened then I should remove the pawls and use it as a bearing to support the other side. Am I on the right track?
This particular problem is specific to the ENO with its single sealed radial bearing unit. Most of the freewheels with integral bearings have 2 opposing sets. With an additional outboard bearing, an ENO would be better than anything else...
These would only add 8mm to the crank offset: http://simplybearings.co.uk/shop/p170104/160052RS+Budget+Rubber+Sealed+Deep+Groove+Ball+Bearing+25x47x8mm/product_info.html
These would only add 8mm to the crank offset: http://simplybearings.co.uk/shop/p170104/160052RS+Budget+Rubber+Sealed+Deep+Groove+Ball+Bearing+25x47x8mm/product_info.html
John in CR
100 TW
Miles said:
I think I got, but do any of the FWs have wide enough spaced sets of bearings, or is the single FW layout just a fail without an additional set of support bearings? I'd like to save my bolt-on ENO for a better use than my cranks, so my choices are:
1. Dual bearing Dicta BMX FW that is 16mm wide- Is that wide enough and Boost was just a special case?
2. Dual cheapie bolt on FWs, one on each sprocket mounted outside of the pair of sprockets for maximum width of my bearing support.
Which would you recommend? I appreciate that the ENO plus a bearing is the better way, but it's better for me to test cheap and acceptable, because I want solutions for the common people here, and that can't include an $80 FW,
magudaman
10 kW
Ive been curious about one way bearings and their ability to handle the torques of electric motors. I was thinking about adding a one way bearing into my drive on that motoped for true coast ability and easy pedaling. There are a bunch on amazon that actually have keyways already broached into both the outer and inner races. Maybe its time to start pressing these babies into some of these freewheel mechanism.
boostjuice
10 kW
Miles said:
Yes, they look like ideal bearing dimensions given the available space within the structural constraints for the required adapter rings. Thanks Miles.
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John and others, your misinterpreting - to different extents - the issues unique to certain freewheels being integrated into different designs, with differing constraints. Generalisations cannot be so easily made.
Think about the planes of force created by two independent chains connected to adjacent/side-by-side chainrings mounted on the crankshaft/BB spindle via a freewheel (In my case both chainrings are of equal tooth count). When the driving (motor) sprocket and driven (rear cassette cluster) sized sprockets - from the perspective of the chainrings mounted on a common shaft - are of variable but most importantly different size (variable/differing gear ratios) then the force on driving and driven chains is not equal. This applies a pulling/pushing force on the chain-rings which translates into a lateral twisting force on the bearing/s supporting the twin adjacent chainrings. Twin opposing angular contact bearings - as used by cheapie freewheels - will tolerate loading on all axis. A single deep-groove radial bearing - like in an ENO - is only designed to cope with radial loading - but will take a small amount of force from other axis, but not too much or it will fail quickly. For its intended design, this is fine as it will support angular loading in a locked state - the only time it should be seeing significant load.
-The Dicta I used failed from torque overload - bearings coped fine. Failure was a result of some combination of; $#!T metallurgy, too few synchronous engaging pawls, and loading beyond mechanical ability of the structural design - despite the choice/quality of steel used. The same freewheel used at the rear wheel - where they are supposed to be mounted - where torque is usually significantly less than at the cranks (gearing down the torque/upping the speed), it would likely have handled the reduced torque loading fine.
-The ENO i used failed from inappropriate axis of bearing loading when in an overrunning/freewheeling condition. The problem was exacerbated through the central plane of the single bearing within the freewheel not aligning with the centre distance between the force planes of the two equal tooth count chain-rings adapted to it. If chain-rings of differing size were used, then the best compromise mounting offsets of the two chain-rings would be different as it would affect the force relationship of the two independent chains.
In summary;
-Failure issues with ENOs and other single bearing freewheels should only be a problem in SERIAL DRIVEN CHAIN-RING scenarios utilising freewheel cranks.
- For PARALLEL DRIVEN scenarios utilising freewheel cranks - such as Miles' Moulton and Matt Shumaker's PK ripper- an ENO or equivalent should work fine as it is not subjected to significant bearing loading in an over-running/freewheeling state.
- The centreline of the single bearing within an ENO is NOT the centre of the freewheel, it is about one quarter the distance of the freewheel thickness from the lockring side. below shows why.
John in CR
100 TW
Thanks Boostjuice,
I understand that serial is the problem, and Bobb was stuffing FWs in a serial alignment too in the earlier thread. I get it that there are forces on the 2 rigidly joined sprockets, and they net to an angular force trying to push/pull those sprockets onto a different plane.
I was messing around with the BMX freewheel today, which has 2 sets of bearings, but is designed for a force in the same plane as the freewheel and centered between the 2 sets of bearings. There's enough play in the FW that it takes very little angular force for the outer ring to be pushed to a slightly non-parallel plane. While it's freewheeling, the bearings can probably handle it, but I can easily imagine problems when the pawls are forcefully engaged while the FW is freewheeling off center.
With the exception of multi-cog FWs, none are designed for the angular forces resulting from a serial crank FW rig. If a dual bearing FW survives, I suspect that placement of the FW is key, ie between the 2 sprockets to give the bearings their best chance to act as dual support. I think the bearings are too closely spaced for proper 2 bearing support though, and the extra bearing that you guys have come up with is needed.
My question is, whether a 2nd cheapie FW is good enough to provide that additional bearing support. One FW on the BB side of the sprocket pair, and the other on the crank side puts the outermost bearings well outside the planes of the 2 sprockets, so it seems like good enough bearing support to me.
John
I understand that serial is the problem, and Bobb was stuffing FWs in a serial alignment too in the earlier thread. I get it that there are forces on the 2 rigidly joined sprockets, and they net to an angular force trying to push/pull those sprockets onto a different plane.
I was messing around with the BMX freewheel today, which has 2 sets of bearings, but is designed for a force in the same plane as the freewheel and centered between the 2 sets of bearings. There's enough play in the FW that it takes very little angular force for the outer ring to be pushed to a slightly non-parallel plane. While it's freewheeling, the bearings can probably handle it, but I can easily imagine problems when the pawls are forcefully engaged while the FW is freewheeling off center.
With the exception of multi-cog FWs, none are designed for the angular forces resulting from a serial crank FW rig. If a dual bearing FW survives, I suspect that placement of the FW is key, ie between the 2 sprockets to give the bearings their best chance to act as dual support. I think the bearings are too closely spaced for proper 2 bearing support though, and the extra bearing that you guys have come up with is needed.
My question is, whether a 2nd cheapie FW is good enough to provide that additional bearing support. One FW on the BB side of the sprocket pair, and the other on the crank side puts the outermost bearings well outside the planes of the 2 sprockets, so it seems like good enough bearing support to me.
John
If you look at boostjuice's photos at the beginning of this thread you can see that, as he said, the bearings are, in effect, an angular contact pair without preload. So, they should be able to withstand angular loading. It would be wise to find a freewheel without too much play, though....... The lockring needs to be bonded in place as it will tend to unscrew with the freewheel running in the opposite direction to that which it's normally running when at the rear wheel. For this reason, trials freewheels designed for use on the cranks sometimes have the lockring on the opposite side.John in CR said:
Lock them together with a bottom bracket cup, you mean?John in CR said:
Elation use a CSK35 on their crank freewheel. It remains to be seen how reliable these chinese sprag clutch bearings are, though... I had a PM from someone who had 2 failures in 6 months. Their specifications are reliant on them being housed with a press fit (particularly the outside housing, I should imagine).magudaman said:
TylerDurden
100 GW
Supporting the ENO is not a failsafe...
MitchJi
10 MW
Hi,
An installation with support bearings on both sides of the pawls should work. Which side does the ENO bearing support? The side without the pawls? Does the Miles solution (either the cad drawing or the stock bearing) put the additional support on the opposite side of the pawls from the factory bearing?
But a properly supported ENO would be the strongest FW available?TylerDurden said:
Miles said:
An installation with support bearings on both sides of the pawls should work. Which side does the ENO bearing support? The side without the pawls? Does the Miles solution (either the cad drawing or the stock bearing) put the additional support on the opposite side of the pawls from the factory bearing?
The ratchet is on the outside (closest to the crank), so would not be between the inboard bearing and the outboard support bearing.
It might be possible to get a support bearing on the other side, it depends on the cranks used...
It might be possible to get a support bearing on the other side, it depends on the cranks used...
MitchJi
10 MW
Hi,
How hard would it be to support the chainrings with a bearing rather than the FW?
Thanks Miles!Miles said:
How hard would it be to support the chainrings with a bearing rather than the FW?
mdd0127
100 kW
- Joined
- Sep 30, 2008
- Messages
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I think he means something like using an outer reinforcement plate/s that bolt to the outside of the chain rings and rotate on the crank with bearings, effectively triangulating and bracing the chain rings so they can't twist the freewheel. Kind of complicated but it would work fine. I'd draw one in paint but I'm computered out. You could even incorporate it into a bash guard. 
You could do that. It would mean fixing the freewheel directly to the BB shaft, though, and if you're doing that, you might as well implement briangv99's twin freewheel solution: http://www.endless-sphere.com/forums/viewtopic.php?p=356222#p356222
Maybe I'm missing something but the only gain I see is better bearing separation. If that's what you're after, you might consider something like this:
Maybe I'm missing something but the only gain I see is better bearing separation. If that's what you're after, you might consider something like this:
MitchJi
10 MW
Hi Miles,
I am wondering what's the simplest solution that puts a support bearing on both sides (one on each side) of the FW ratchet.
I am wondering what's the simplest solution that puts a support bearing on both sides (one on each side) of the FW ratchet.
mdd0127
100 kW
- Joined
- Sep 30, 2008
- Messages
- 1,084
It's the outer part of the freewheel, the part with the sprocket teeth or bolt flange that needs to be supported....or the chain rings themselves. In a proper design incorporating two chain rings on one freewheel, there should be a bearing centered under each chain line. The current bike design is a compromise but works because there's only one sprocket. The crank doesn't spin very fast so you could do either plate/s that bolt to the chain ring with a bearing that rotates on the crankshaft like my terrible paint rendering or something like a pinch setup where two wheels pinch the chain ring/s, reducing the twisting forces. Either way, custom machining will be necessary.
It would be pretty easy to make a CSK40PP to 1.37 x24 tpi adaptor and a bolt flange housing to press it into. They're heavy though. The CSK35PP is 1.378 ID so it would have to go on a 30mm hub and that's even pushing it???
It would be pretty easy to make a CSK40PP to 1.37 x24 tpi adaptor and a bolt flange housing to press it into. They're heavy though. The CSK35PP is 1.378 ID so it would have to go on a 30mm hub and that's even pushing it???
MitchJi
10 MW
Hi,
And got this response:
My reply (hopefully not a mistake!):
His reply:
If nobody beats me to it I'll start a new topic (maybe a poll) later tonight.
mdd0127 said:
Sent this to Jim at Sickbikes:Miles said:
Mitch said:
And got this response:
sickbikeparts.com said:
My reply (hopefully not a mistake!):
Mitch said:
His reply:
sickbikeparts.com said:
If nobody beats me to it I'll start a new topic (maybe a poll) later tonight.
