Custom Two Stage Bottom Bracket - Is it Feasible?

[liveforphysics]

Curiously, someone's misunderstanding WRT left-hand driven bottom bracket drives was the subject for my first posts on the Sphere http://www.endless-sphere.com/forums/vi ... ?f=2&t=536

We are all extremely glad that happened my friend. You are such a fantastic asset here, and I still don't know that I've seen another build that matches the elegance and commuting perfection of your beautiful machine my friend.

[Neovin]

I just found something that could be useful on ebay,

http://www.ebay.co.uk/itm/CPI-Formula-5 ... 1271wt_942

it looks like it could work well for me, its the same chain size and ready built, I have seen others for cars and larger bikes i think i'm on to something here

[Miles]

That looks promising. Easily adaptable, too....

[Neovin]

i'm thinking if we could use the smaller bearing looking type to seperate the main drive from the pedals and the starter clutch to seperate the motor from the main drive, a left hand motor driven crank may be done. Ooh think of the gears

i wish i had a mountain bike so i could do some measuring up, could you guys give me the internal diameter, thread size and width of a standard bottom bracket.

How wide do you think we could comfortably go on the pedals.

[Miles]

could you guys give me the internal diameter, thread size and width of a standard bottom bracket.

1.37" x 24 tpi. Most common shell width is 68mm.

How wide do you think we could comfortably go on the pedals.

You need cranks with minimal offset to compensate for the extra axle length.

http://www.spadout.com/a/q-factor-the-s ... -our-feet/

[turbo1889]

Thank you for all the comments and the two links posted to previous threads along these lines (apparently the search function is pretty worthless since I had not seen them before).

I’m not rejecting the use of one-way needle bearing clutch assemblies but it appears that they require rather large sizes to handle the peak torque loads produced by pedaling and do not exist as ready built components built specifically and “ready to use” for bicycle applications.

Where on the other hand freewheel assemblies that can be used on the crank side are available in both right and left hand assemblies. Right hand side being the most commonly known (Sick and Cyclone parts plus others) but there are left hand side units available for Staton-Inc that would serve well on the left hand side of a double stage bottom bracket assembly for motor input:

http://www.staton-inc.com/store/products/5_Hole_Flange_LEFT_HAND_thread_freewheel_sprag_clutch-967-0.html
http://www.staton-inc.com/store/products/65_Tooth_25_1_4_x_1_8_LEFT_Hand_threads_Freewheel_Sprocket-695-0.html
http://www.staton-inc.com/store/products/72_Tooth_35_3_8_x_3_16_LEFT_Hand_threads_Freewheel_Sprocket-756-0.html
http://www.staton-inc.com/store/products/25_80_Tooth_LEFT_Hand_threads_Freewheel_Sprocket-687-0.html
http://www.staton-inc.com/store/products/60_Tooth_35_LEFT_Hand_threads_Freewheel_Sprocket-679-0.html

Granted most of them use other chain sizes then common bicycle chain sizes but there is no reason not to use a different chain size on the left hand side motor chain loop. It may even be an advantage allowing greater choices of industrial type sprockets to put on the motor output shaft and also allows a simple sprocket on the motor since the freewheel is built into the left side crank sprocket. All the sprockets in question are intended for use on the left side of the rear wheel hub for use in Staton-Inc gas motor kits but they should work just as well on the left side of a double stage bottom bracket assembly especially since some of the more powerful motors used in the Staton-Inc kits are putting slightly over 2 horsepower through them so they should be more then strong enough for all but the most over-powered e-bike builds.

The information Miles has provided with his thread (nice 3D solids drawing by the way) has been very helpful. Especially on one key point. That being that there is really no need for a second inner bearing race between the inner and outer shafts and only a tight slip fit is needed. This is due to the fact that there is only significant stress loads on the inner spindle shaft when the rider is pedaling and when they are doing so the inner and outer spindle shafts are rotating together and the bearings on the other spindle shaft carry the load. Unless of course the rider is doing light slow “fake” pedaling which isn’t putting in any power into the drive system and just letting the motor do the work while making it look like they are pedaling in which case there isn’t very much load on the spindle anyway. About the only time there would be significant load on the inner spindle while it was stationary and the outer spindle was rotating around it under load from the motor is if the rider where not pedaling and was standing up on the pedals instead of sitting down on the seat.

So one can simplify the assembly significantly by just making the inner spindle shaft a tight slip fit with a little grease in the inside of the outer spindle shaft. Yes it would wear over time more then if it had an inner race of needle bearings but that wear would be reduced according to how much the operator pedaled and standing up on the pedals while the motor was running would be a “don’t do that” item. In other words, allowing the pedals to freewheel instead of being constantly driven by the motor like the stocker-monkey set-up would be mainly a safety and convenience feature and the operator would still be encouraged to pedal to reduce the wear over time on the custom double stage bottom bracket assembly. Not a bad trade off for the simplification in the design it allows especially for the conventional smaller size bottom bracket sizes.

I did actually dig through my pile of old bike frames and components stash along with taking some measurements off of my up and running bikes and not all bottom brackets are as small as diameter as the somewhat standardized 1.37x24tpi cartridge assemblies. My bike full suspension mountain bike has a much larger bottom bracket diameter that is using a heavy 30mm diameter spindle. I didn’t pull it apart to get internal bearing race diameters but there is definitely a lot more room inside its bottom bracket and it appears to use press in industrial type sealed ball bearing race assemblies one on each side instead of screw in cartridge cups. In addition the frames designed to use the old single piece Ashtabula type cranks have bottom brackets that are larger and more roomy then the standard 1.37x24tpi cartridge bottom brackets as well so there are certainly larger size bottom brackets out there that would make things even easier.

My ultimate goal would be to put this kind of custom double stage bottom bracket assembly into a Yuba Mundo long-tail cargo bike using a sprocket drilled with six holes to match the disk brake mounting pattern on the left side of a hub motor mounted in the rear triangle to provide electric assist power through the bottom bracket just like a stoker-monkey only without having driven pedals. Now that I know it is possible I guess the next step is to save up and buy the Yuba and then pull apart its bottom bracket assembly and figure out what type it uses and take exact measurements and then go from there.

Here is an updated diagram (same color coding):

[Miles]

This is what we need.....

[Miles]

If you could persuade these guys to make one of their frames with a BB30 Standard bottom bracket.....
http://www.designlogicbikes.com/

Ref: viewtopic.php?f=31&t=36596

[Miles]

Something that I considered using for the outer shaft bearings was the needle bearing/end cap units from the Shimano XTR M950 bottom bracket.

[turbo1889]

I have taken a look at the option of using of the various 25mm diameter spindle screw in external bearing cups that use 6805-2RS size ball bearing (25x37x7) with a 25mm outside diameter hollow outer spindle that has a 4mm wall thickness with a 17mm solid square taper end inner spindle running inside of it but thought that was less then ideal due to the expansion of the tread width of the pedals (Q-factor) by the thickness of the external bearing cups which is already going to be expanded by the space on the left side for the left hand thread freewheel chain ring on that side and the custom spider assembly on the right side so thought it would be best not to aggravate that issue further if possible through the use of an external bearing assembly.

Is the spindle diameter for the Shimano Octalink bottom bracket cartridges which as you mention do use internal needle bearings also 25mm?

[Miles]

Is the spindle diameter for the Shimano Octalink bottom bracket cartridges which as you mention do use internal needle bearings also 25mm?

24mm, I think. I'll check that.

[turbo1889]

I did some online research and some people say the Shimano Octalink spindle diameter is 22mm and others say it is 22.2mm (either way that sounds like 22mm put sounds like it is not exactly 22mm). ISIS is consistently listed at 22mm for the spindle diameter. That is from gleaning info from the startpage search engine across multiple web-sites with trial and error search queries.

So far the largest outside diameter for bearings inside 1.37"x24tpi screw in cups I have found listed for any bottom bracket that puts the bearings inside the cups is 30mm which are used on a couple custom and high-end bottom bracket assemblies including the ISIS standard SKF bottom brackets which appear to be among the very best and come with 10-year full warranties including the bearings and cost $$$. And looking through SmallParts.com it looks like the two most common sizes of needle bearings that could work are 25x29 for open cage bearings (no inner our outer race just the bearings in a cage) in various widths and brand names and 22x28 for drawn cup outer race bearings (no inner race) in various widths and brand names. And if I really wanted too use inner bearings as well 15x18 open cage bearings are a common size which could work if the inner square drive spindle was turned down 2mm in diameter from the common 17mm diameter standard for square drive spindles (which is possible I think considering some are 5/8"-SAE diameter which is smaller then the common 17mm metric designation and is closer to 15mm then 17mm.

Possibly the best option would be to have someone custom machine a right and left side 1.37"x24tpi cup with an inner diameter of 29mm out of stainless and then heat treat so that the cup is the outer bearing race for the 25x29 open cage bearings and then run a 25mm spindle inside them. Using non-hardened cups with 28mm inside diameter and using the drawn cup needle bearings would be cheaper for machining costs and would not have any wear on the custom machined screw in cups due to using drawn cup needle bearings but would mean a smaller 22mm outer spindle instead of a 25mm one.

I really wish I could find a good source of 25x30x14 drawn cup needle bearings since Staton-Inc already sells a cup set designed to to use doubled up (four bearings two in each cup) 17x30x7 sealed ball bearings and they could be easily modified to use a single 25x30x14 drawn cup needle bearing one in each cup instead.

[amberwolf]

I have what I think is a Shimano Octalink spindle and cranks in a box here. FC-M950 is the p/n on one of the cranks, though there is none on the spindle itself. Might have more markings under the bad rattle-can black paintjob but I can't tell.

I haven't taken it apart yet, but it is missing the bearing and thread-in cap on one side (the right, I think) but still has it on the other. Looks like whoever took it off the bike it came from didn't have the right tools and did a vair amount of banging it up, but I should still be able to measure the diameter of the spindle for you, if I can borrow someone's electronic calipers (or find my old manual ones, assuming they will go large enough).

It is just under 22mm with a ruler at the outer diameter of the splines; appears to be maybe 1/4mm more on the spindle's shaft surfaces itself.

[Miles]

I really wish I could find a good source of 25x30x14 drawn cup needle bearings since Staton-Inc already sells a cup set designed to to use doubled up (four bearings two in each cup) 17x30x7 sealed ball bearings and they could be easily modified to use a single 25x30x14 drawn cup needle bearing one in each cup instead.

You could sleeve the BB shell and press in a pair of 24x31x20 drawn cups?

[Miles]

I did some online research and some people say the Shimano Octalink spindle diameter is 22mm and others say it is 22.2mm (either way that sounds like 22mm put sounds like it is not exactly 22mm). ISIS is consistently listed at 22mm for the spindle diameter. That is from gleaning info from the startpage search engine across multiple web-sites with trial and error search queries..

Yes, 22mm. Sorry, I misremembered.

[Miles]

You could also use 15/16"x1-3/16"x5/8" drawn cup needle rollers....

[Miles]

The SRAM 'Press Fit 30' BB "standard" is given in the attached:

[Miles]

You could sleeve the BB shell and press in a pair of 24x31x20 drawn cups?

31mm OD seems to be a common bearing size for bottom brackets. If one could find some reasonably deep 31mm ID caps .....

[turbo1889]

Eureka !!!

Woke up in the middle of the night last night realizing the solution was right in front of me. Again and again it has become clear that this would be so much easier with one of the larger size press in bearing type bottom brackets. Yet the bike I would like to do this on does not use one of the 30mm spindle standard bottom brackets with press in bearings but rather uses a 1.37”x24tpi screw in bottom bracket cartridge set-up.

Now let’s take for example, a threaded hole in a small eyelet jutting out from the top of the rear drop out of a hard tail bike frame threaded to fit an 8mm diameter bolt that supports a rear cargo rack mounted over the top of the rear wheel. Let’s say you are careless and booger-up those threads. The eyelet is too small to drill out and thread to a larger bolt size without compromising its strength. What do you do? Simple, you take an 8mm drill bit and drill out the threads and then use a slightly longer bolt with a nut on the other side. Not quite as convenient since you now need two wrenches instead of one but it works just fine because when you drill out the 8mm internal threads in the eyelet to a smooth 8mm with a drill bit that the 8mm bolt will pass through you loose very, very little if any wall thickness on the eyelet and it is 99% as strong as it was before.

What if the same logic is extended to the threads in a 1.37”x24tpi threaded bottom bracket. Those are 1-3/8” internal threads, is it not possible to use a 1-3/8” diameter reamer to cut out the threads and leave a smooth surface instead without thinning the bottom bracket tube walls by anything that would be significant and thus now have a press in bearing bottom bracket that uses bearings that are 1-3/8” outer diameter? Taking things a step further 1-3/8” = 34.925mm. Thus not only is there the possibility of easily converting a 1.37”x24tpi standard bottom bracket to accept 1-3/8” outside diameter bearings in a press in configuration but for just the thickness of a couple hairs more material removed it could also be a 35mm outside diameter press in bearing bottom bracket.

And if you pull the bearing sizes available you can get 1-3/8” outside diameter size bearings with a variety of inside diameters ranging from 5/8” to 1-1/8” depending on the bearing type and you can get 35mm outside diameter size bearings with a variety of inside diameter ranging from 17mm to 28mm. Long story short press in bearing 1-3/8” or 35mm bottom bracket made by simply reaming out the threads to form a smooth inside lip to press the bearings into could accept any spindle size from the small diameter 5/8” or 17mm tapered square end standard, up to the 7/8” or 22mm Octalink/ISIS splines, up to the 24mm and 25mm hollow core spindles, and custom 1-1/8” or 28mm diameter spindles which are only slightly smaller then the big 30mm spindles and plenty big enough to build a custom double stage bottom bracket set-up inside.

Heck, it kind of surprised me that I couldn’t find any mention of 1-3/8” or 35mm press in bearing bottom brackets with a couple google searches. I would think it would have been a logical progression from the 1.37”x24tpi threaded cup bottom bracket just for machining and quality control cost reasons alone before they went to using even bigger sizes.

[Miles]

That seems doable. You can try it out on one of your old bikes.....

[turbo1889]

. . . You can try it out on one of your old bikes.....

Absolutely !!! I will definitely use an old "donor" frame with the same width of 1.37"x24tpi bottom bracket (not sure if its 68mm or 73mm) and will do the entire build on the "donor" frame and then once I got the bugs worked out and done my goof ups on the old frame then I will transfer it over to a Yuba frame.

You'r not going to catch me taking a reamer to the bottom bracket threads of a $500 bare frame only cost level bike until I've already proved that it works on a junk frame first !!! That's for sure.

[turbo1889]

Continuing evolution of the design based on further improvements that Miles has put forth in his thread on the same subject:

As drawn:
----- 1.37"-24tpi x 73mm bottom bracket reamed on each side to accept press in bearings of 35mm outside diameter.
----- Primary bearings are 28mm x 35mm x 20mm (ID x OD x W) directly pressed into bottom bracket from each side.
----- Outer spindle shaft is 28mm outside diameter and screws together in the center via. M24-2.0 LH thread 30mm long.
----- Secondary bearings are 17mm x 21mm x 13mm (ID x OD x W) pressed into the two ends of the outer spindle shaft.
----- Inner spindle shaft is 17mm outside diameter solid with tapered square end.
----- Axial containment and sealing of the primary bearings is provided by simple brass washers taking up the slack between each side of the bottom bracket shell and the outer spindle.
----- Both sides of the outer spindle use standard 1.37"x24tpi RH threaded freewheel threads to accept White Industries Heavy Duty crank freewheel unit.

[ls7corvete]

Interesting, are these all off the shelf parts? Do you have a parts list and price list? I know that some of this was answered already but most of this is over my head, lol.

[turbo1889]

At least some custom parts will have to be made to accomplish this know matter what you do from what I can tell. Obviously, for cost reasons the number of custom parts should be kept to a minimum if at all possible.

----- A large variety of bearing sizes and style are available "off the shelf" from SmallParts.com
----- ----- The bearing sizes I list in my most recent drawing are all available through them for a reasonable price
----- Crank arms that are threaded for a freewheel on the right side crank arm are available "off the shelf"
----- ----- The cheapest and most available set to have shipped to my location is sold by SickBikeParts.com
----- RH Freewheel crank chain ring units are available from a couple different suppliers "off the shelf"
----- ----- The best quality, cheapest, and most available such unit to have shipped to my location is the White Industries Heavy Duty unit sold by SickBikeParts.com
----- LH Freewheel units are available from a couple different suppliers "off the shelf"
----- ----- The only source I know of that has them made to fit large, high tooth count chain rings is Staton-Inc.com
----- ----- Staton-Inc.com also currently lists a 6" long tapered square end spindle that is a solid 17mm diameter bar which could work excellently as the inner spindle

Long story short, if one plays their cards well enough on the design you could conceivably get away with the outer spindle (including the right hand chain ring spider interface that must be either an integral part of the outer spindle or attach to it somehow with a torque bearing junction) being the only custom part(s) that you would have to have a machinists make up for you custom and everything else would be either "off the shelf" parts or stuff you could make yourself with simple tools.

[Miles]

Looking good, turbo.

The only snag, that I can see, relates to the apparent eccentricity between the freewheel threads and the tapered axle mount on most of the RH trials cranks. If that does turn out to be a problem in practice, you could either miss out the RH inner bearing or have some sort of floating connection between the crank freewheel and the chainwheel assembly.