Custom Two Stage Bottom Bracket - Is it Feasible?

Discussions related to motors other than hub motors.
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby Miles » Mon Mar 05, 2012 1:28 am

You could also use 15/16"x1-3/16"x5/8" drawn cup needle rollers....
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby Miles » Mon Mar 05, 2012 9:39 am

The SRAM 'Press Fit 30' BB "standard" is given in the attached:
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SRAM frame_fit_specs.pdf
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby Miles » Tue Mar 06, 2012 9:15 am

Miles wrote: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 .....
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby turbo1889 » Tue Mar 06, 2012 10:36 am

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.
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby Miles » Tue Mar 06, 2012 11:01 am

That seems doable. You can try it out on one of your old bikes.....
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby turbo1889 » Tue Mar 06, 2012 4:10 pm

Miles wrote:. . . 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. :shock:
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby turbo1889 » Sat Mar 10, 2012 6:48 pm

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.

Image
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby ls7corvete » Sat Mar 10, 2012 7:31 pm

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.
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby turbo1889 » Sat Mar 10, 2012 8:05 pm

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.
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby Miles » Sun Mar 11, 2012 2:44 am

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.
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby Samd » Tue Mar 13, 2012 6:59 pm

For a one way clutch solution you might be interested in the dimensions of the Aprilia's bottom bracket components?
Page 11 of this doc: http://myc5.nl/aprilia/manuals/part%20list.pdf

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http://ballaratebikes.com/

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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby MotoMel » Mon May 14, 2012 4:11 pm

The motor could use an upgrade, but here's a LHS-->RHS implementation that we have working after much toil and not a little travail: http://www.youtube.com/user/BikeMotive?feature=mhee. I'd be interested in your feedback as to whether this would work for some of you on your builds.
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby MotoMel » Tue May 15, 2012 5:54 pm

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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby turbo1889 » Mon Jun 11, 2012 4:36 pm

MotoMel, sorry I didn’t get back to you right away I’ve been pretty busy and haven’t checked this thread in a while. What you have there is exactly what I am talking about. Only yours is an actual working prototype as demonstrated on your uploaded videos, mine is still in my mind and in my CAD program.

The only thing I would mention on your build is that the motor you used mounted in the frame triangle above the bottom bracket seems to be rather noisy. I was figuring on using a direct drive hub-motor mounted in the rear frame triangle on a long-tail frame Stoker-Monkey style which I think would be quieter with only chain and freewheel noise and very little if any noise from the motor. If I'm going to do an electric build which will cost me more for less performance then a 4-stroke 25cc or 35cc Subaru/Robin mini-engine set-up from Staton-Inc (A set-up I already have and highly recommend as one of the best combustion engine set-up available) then I want it to be really nice and quiet almost like riding under pedal power only and such that unless they look closely and know what they are looking for most people won't even realize that it is an electric assist bike which is easily accomplished by cowling in the rear triangle where the hub-motor is mounted with a direct drive hub-motor that is nearly silent.

Also, what kind of bearing set-up are you using? The biggest design challenge I have encountered at least on the drawing board is figuring out how to put enough bearing support in-side the limited space of a standard size bottom bracket to ensure long term durability. Especially considering that I would have to pay to have a machinist custom make at least some of the critical components that I really don't want to wear out quickly considering their cost and difficulty in replacement.

My build is tentatively scheduled for this Winter season and for this Summer I’m basically in research, development, and design mode right now and I’m still making noise with a Staton-Inc rig (although the 4-stroke bad at all compared to a 2-stroke) on my daily 25+ mile work commute and still burning gas but several orders of magnitude less then a car (100+ mpg).
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Re: Custom Two Stage Bottom Bracket - Is it Feasible?

Postby exco » Tue Jan 22, 2013 5:42 pm

turbo1889 wrote: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.

Image


^^ love it. Well thought out. I think if I need more gears I will try to build your design and scratach mine ;-)
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