Double RH Freewheel hub design

[acuteaero]

So I went back and read hundreds of pages of ES threads about running double freewheels on the right hand side of hubs for "parallel" drive-

http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=12449
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=13532
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=12267

I understand the reasons that cutting splines inside the BMX freewheels and putting them on a freehub has been used and seems to be the de-facto solution- I have been thinking of an alternate option- making up a hub with stepped threads- a 1.375" thread for an ENO freewheel, likely the sick-bike-parts flanged unit, and a M30 thread for a <=15t BMX freewheel to use for the pedaling chain.

I understand that the splined freewheel on freehub solution works well- but it's always seemed a bit odd to me to put the double freewheels in parallel in series with the freewheel in the freehub--- I have never seen an explanation if this is a desirable feature- it seems to me that it is less than ideal-

Without further ado- here are the pictures I've made. The hub design is based strongly off the hub I removed from a 17" moped wheel I got from Stevil_Knevil. http://www.endless-sphere.com/forums/viewtopic.php?t=35066 . The design uses the same sized bearings and spoke flanges.

I realize that a fundamental issue is that the 28mm OD bearing won't fit through the M30 thread. Both bearings have to come in from the other side. This makes some kind of goofy compromises, and makes the assembly naturally not axially constrained. That's why I added the large retaining snap ring. I also assume the bearings would be press fit into the hub bore, or loctited in, either way. Other potential issues- the bearing on the threaded side has to be pretty far away from the dropout- that's why I enlarged the axle to the 15mm bearing ID size all the way to the dropout. With a cro-moly axle it'd probably be OK---. I also switched from external M10 threads on the end of the axle to internal M8 threads into a 10mm boss- this is a bit easier to machine than the external threads... One other odd aspect is that the M30 freewheel ends up threading against the removal dog flange on the white freewheel- I think there's just enough engagement there to prevent disaster, a thin steel washer could also be made.

Shown with a SBP Eno and crossfire 13t freewheel.

The chain-line to the flanged freewheel looks pretty good with a hookworm-wide tire on the wheel.

What do you think? If you don't persuade me it's a bad idea I'll make a couple up next weekend, or maybe the weekend after that.

-H

 

[amberwolf]

I understand that the splined freewheel on freehub solution works well- but it's always seemed a bit odd to me to put the double freewheels in parallel in series with the freewheel in the freehub--- I have never seen an explanation if this is a desirable feature- it seems to me that it is less than ideal-

I think it's just a side effect: these cassette-freehubs are the only thing you can just go out and buy that already has a long enough body sticking out to put both freewheels on.

The only other easy way to do it with off-the-shelf parts is to use a regular threaded hub, partially thread on one freewheel, and then use a BB cup threaded into the first freewheel's threads to "extend" the hub so the outer freewheel can be installed.


Custom-building a hub to just do dual freewheels could be simpler than the way you're describing, but it doesnt' allow for the smaller freewheels like yours will.

 

[Miles]

I understand that the splined freewheel on freehub solution works well- but it's always seemed a bit odd to me to put the double freewheels in parallel in series with the freewheel in the freehub--- I have never seen an explanation if this is a desirable feature- it seems to me that it is less than ideal-

The original freewheel is effectively redundant. You could say it's one more thing that could break. The splined freewheels solution is simply the least work to get parallel freewheels, for most existing wheels. The alternative is stacked standard thread freewheels on a standard threaded hub.

Anyway, I like your idea. Just wondering about the possibility of a roller bearing on the threaded side?

[Edit I must be a very slow typist ]

 

[acuteaero]

Custom-building a hub to just do dual freewheels could be simpler than the way you're describing, but it doesnt' allow for the smaller freewheels like yours will.

And, if you want to use the flanged ENO freewheel the threaded boss must taper down to about 30mm after about 1/2 inch- since the ID of the freewheel tapers down for the removal dogs... Sure, there are ways to attach large sprockets to other freewheels besides the flanged one, but it is pretty slick... Cutting two different threads will be only a small amount more work than just cutting the one- although the small thread creates the bearing fitment problem... I guess you could make it work either way- my design was based around using the flanged ENO freewheel---

 

[Tench]

I have been looking into a very similar design myself for my next build, i have not made my mind up yet whether to put the motor drive freewheel on the wheel or motor yet though, less torque but more rpm's at the motor so the freewheel gets an easier life but when coasting the chain will be circulating.

 

[Miles]

I think the ideal (most flexible) hub system would have spline fixing.

 

[acuteaero]

I understand that the splined freewheel on freehub solution works well- but it's always seemed a bit odd to me to put the double freewheels in parallel in series with the freewheel in the freehub--- I have never seen an explanation if this is a desirable feature- it seems to me that it is less than ideal-

The original freewheel is effectively redundant. You could say it's one more thing that could break. The splined freewheels solution is simply the least work to get parallel freewheels, for most existing wheels. The alternative is stacked standard thread freewheels on a standard threaded hub.

Anyway, I like your idea. Just wondering about the possibility of a roller bearing on the threaded side?

[Edit I must be a very slow typist ]

Thanks Miles--

Anything is possible when you're machining it yourself... I thought a bit about using a roller bearing- I presume you suggest it because they are generally of a thinner profile, so they could fit between the thread and the axle- I also though about putting in double or tripled thin section bearings (kinda like the 80100 motor does on the end bell side...)- When I looked at the model with that in mind the big ball bearing further inboard seemed still like the best idea- partially because it's right under the spoke flange, and somehow I like the idea of the force being supported in shear by that 15mm steel axle rather than by the threaded aluminum tubular protrusion on that side of the hub. Seems better to my gutfeel engineer.

Another adjacent topic of thought--- Is there any benefit to using taper roller bearings or angular contact bearings in the hub? I suppose I could make a threaded locking ring to capture and preload them from the brake flange side- though it would be a pretty dinky and insubstantial ring to be able to fit in there... The hub I copied some dimensions from has plain old 6902RS ball bearings in it.

 

[acuteaero]

I think the ideal (most flexible) hub system would have spline fixing.

I agree, and I read all through your modular hub thread- the persistant problem is that splines just always require a fair bit of tooling, at the minimum an indexer for cutting external splines- at the maximum some big custom broaches (but you know all that)...

And I've heard that freewheel threads, while they kinda suck from a serviceability and flexibility standpoint, rarely fail- (unless they're on hubmotor covers that are made of cheese)

 

[acuteaero]

I have been looking into a very similar design myself for my next build, i have not made my mind up yet whether to put the motor drive freewheel on the wheel or motor yet though, less torque but more rpm's at the motor so the freewheel gets an easier life but when coasting the chain will be circulating.

I get the idea that torque handling is not a weak area of the White freewheel... PaulD's bike has been set up in the past with the freewheel on the jackshaft- it makes a tiny bit of coasting drag, and quite a huge racket from the freewheel clicking at 3-4x wheel speed.

 

[Miles]

I think the ideal (most flexible) hub system would have spline fixing.

I agree, and I read all through your modular hub thread- the persistant problem is that splines just always require a fair bit of tooling, at the minimum an indexer for cutting external splines- at the maximum some big custom broaches (but you know all that)...

Now that we know that Mel had a batch of flanged Crossfire freewheels made, perhaps a splined version would also be possible?

For those that missed, it here's the modular hub thread:
http://www.endless-sphere.com/forums/viewtopic.php?f=28&t=30846

 

[liveforphysics]

I would buy splined freewheels! Way too much of a PITA to make them, and it's too handy of a part not to have available.

 

[Miles]

Another adjacent topic of thought--- Is there any benefit to using taper roller bearings or angular contact bearings in the hub?

I would think not.

I presume you suggest it because they are generally of a thinner profile, so they could fit between the thread and the axle- I also though about putting in double or tripled thin section bearings (kinda like the 80100 motor does on the end bell side...)- When I looked at the model with that in mind the big ball bearing further inboard seemed still like the best idea- partially because it's right under the spoke flange, and somehow I like the idea of the force being supported in shear by that 15mm steel axle rather than by the threaded aluminum tubular protrusion on that side of the hub. Seems better to my gutfeel engineer.

How about doubling up the 28mm bearing, on the drive side?

 

[acuteaero]

How about doubling up the 28mm bearing, on the drive side?

This would be trivial to do- I'm guessing the concern about adequate bearing support on the drive side is due to the force exerted on the axle by the drive chain? I haven't got this aspect of the dynamics entirely thought through. I am guessing that the hub I based my design off has a single bearing in each side, but I will press it apart when I get a chance and take a look.

Indeed, I would buy a set of splined freewheels if such a thing were manufactured- that would make it very easy to set this sort of a system up. Splined White inner rings would be great so that vairous outer rings could be applied- although maybe that same ability is present on the crossfire. Either way, these ideas have been talked up and down in different threads bunches of times, no need to do it again

I have been thinking about the most efficient order of operations to machine up this hub, I think it will be pretty straightforward. Looking forward to getting it set up, I think it will be pretty sweet.

 

[Miles]

One serious advantage of your system is the ability to use stock sub 15t freewheels... Looking forward to developments.

 

[Stevil_Knevil]

Interesting approach, Hank ..I like it!

Just FYI - if it works as expected - I have 5+ more of of those hubs (new take-offs from other rear wheels which received hub motors), so your efforts are not necessarily limited to a one-off design.

Best of luck 8)

 

[acuteaero]

Just out of curiosity I pressed one bearing and the bearing tube out of the existing hub- Just to verify the bearing arangement and make sure there were no surprises. No surprises:

Just to put it in perspective this hub was (likely custom made) for the Voloci electric motorbike- 55lbs total weight, NiMh, 30mph, no pedals. Not saying that the design necessarily reflects perfect engineering and should be used as a template for every other bike hub, but FWIW- this is the setup it ran.

I don't have a strong opinion about doubling up the bearings- I don't know what the effect of adding additional ball bearings is. I would guess that it increases the effective load capacity of the system, but I would also guess that alignment and consistent fits is critical. Anyone have any strong feelings about this matter? I'm curious to learn more about this.

One other thing I'm missing is the optimal spoke flange hole diameter and spoke flange thickness- I'm thinking that running good quality 14g spokes is my ideal setup here. Anyone got numbers they like for this? I'm sure I've run across them before but I have not taken them down...

 

[drewjet]

This is very cool. I used this same hub for the rear on my race bike. I am inputting around 28KW into it and it is holding up just fine. It would be nice to have a freewheel for the motor, right now I just use an adapter to a gokart sprocket and run it direct.

 

[Miles]

I don't have a strong opinion about doubling up the bearings- I don't know what the effect of adding additional ball bearings is. I would guess that it increases the effective load capacity of the system, but I would also guess that alignment and consistent fits is critical. Anyone have any strong feelings about this matter? I'm curious to learn more about this.

I'm not sure I do, either. I just thought I'd bring it up for discussion. I expect one bearing would suffice but two would increase their lifespan. Also, having two means that one can be directly under the flange and the other as far under the motor freewheel as possible. As for the effects of alignment under load, I'm not sure...

 

[acuteaero]

I asked a mechanical engineer friend of mine who works doing powertrain integration on vehicles- he said:

Double bearing is fine, and it can be seen in many applications, among other places on my beloved Nissan 240. Make sure that you are using 2 identical bearings, they are loaded on the centers of the bearing perimeter, and that they do not have any directional preferences. Just note that the max bearing loading isn't exactly double with 2 bearings. Its more like 1.75 times depending on the bearings and setup. Oh and if you go double bearing, go double bearing on both sides.

So maybe more bearings = more better. I can do that.

 

[spinningmagnets]

During the previous discussions of a parallel double-freewheel on thre right-side, I had thought it wouldn't be difficult to use a Nexus 3-7 speed IGH as a jackshaft just behind the BB. I beieve any of their models can be ordered with a trike shell, which gives you two sprockets from the factory..