DIY 3-speed transmission

spinningmagnets

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The builder speaks French
http://www.instructables.com/id/transparent-gearbox-on-a-homemade-bicycle/?ALLSTEPS

The power input, sliding single-dog, and gear selection is on the top shaft. The bottom shaft is the output, and the only reason (that I can see) for the 4th chain (the gray one) is to add more gear-up inside the housing, so that the chainring on the outside can be smaller.

All the four sprockets on the bottom shaft are fixed to that shaft.

All four sprockets on the top shaft individually sit in their own tube-adapter that allow each of them to float on the input shaft. There is a longitudinal groove in the input shaft, and a square cross-sectioned rod slides back-and-forth in the groove. On one end of this sliding shaft is the brass shifting-fork adapter, and the other end (which we can't see) has a finger sticking out, to slide into a notch on the ID of the desired gear.

If he had extended the top shaft out both sides of the housing, and then connected the BB to the input shaft by a chain and a freewheel, he could've had an E-bike where both the motor and BB had three gears. I think this trans would've worked great with 2-gears that are widely spread, 30-MPH top speed, and 15-MPH for off-road so the motor was using high-RPMs on a slow uphill. Much better than using half-throttle and half-RPMs on a steep uphill.

The tooth-count on the lower shaft sprockets is 13T/15T/17T, The lowest gear is a 23T:13T reduction, high gear is an overdrive 13T:17T, cant see second gear.

If you don't have the tooling to make the proper groove in the drive-shaft, you could cut a slice lengthwise out of a thick-walled tube and DP-420 it onto a solid shaft.

F5GY0DFHAUNMD22.LARGE.jpg


FZ2PCPBHAUNMF9M.LARGE.jpg


FN4Z1UJHAQ3806N.LARGE.jpg
 
A typical example of an answer to a question no one has ever asked given that the ubiquitous derailleur systems has been around and proven for decades.
 
SamTexas said:
A typical example of an answer to a question no one has ever asked given that the ubiquitous derailleur systems has been around and proven for decades.
Did you forget to plug yourself in? You appear to be stuck in corrupted cliche mode :)

Seems, to me, like something which was done for the sheer pleasure of the exercise.
 
Here's one of Thuds 2-speeds (for those who are new to Endless-Sphere). Of course, Thud used axial dogs instead of radial. I don't need one, but this is a lot of fun for me.

SAM_0156_zpse52bd9e1.jpg
 
There have been 3-speed Internally-Geared-Hubs (IGH), like Nexus, Sturmey, etc...and they have broken from being used with motors. Whether a DIY transmission has two gears or three, their construction lends itself to higher power levels. Thud has made a pretty convincing argument for using #35 chain, and the axial-dog style is as about as compact as it is physically possible to make it.

#415H chain is rated for very high power levels and is very similar to bicycle chain in several of its dimensions. The sprockets are thicker and the thickness of the links is fatter, plus the quality of metal in the chain is stronger.

Thud has made several copies of his two-speed gearbox, and so far the customers sound satisfied with the results. Thud himself raced one of these, and...although he probably only used first gear at the starting line, sometimes getting a 6-foot lead on the pack at the beginning...makes all the difference in the world at the end.

And if it was fun to make, and fun to use...that alone makes me happy to know.

PA210010.jpg


file.php
 
i actually posted on here about this a while ago here:
http://endless-sphere.com/forums/viewtopic.php?f=1&t=46520&p=680065&hilit=gearbox#p680065

but its definitely an interesting gearbox. only thing i would question is using the lexan as the gearbox casing if motor power would be put through it, or would it be suffice? but it does look pretty darn cool!
 
I've been thinking it over for a week or more ever since I first saw this thread about this kind of transmission set-up. There is a way to make this kind of transmission fully automatic, automatic transmissions have been tried on bikes before and most were too weak, too heavy, and/or too complex. but using a set-up like this along with simple centrifugal force and the basics of a pawl freewheeling assembly this could be made to work and work well.

All that needs done is to make a freewheel assembly to put in the center of the sprockets that only locks up once a given RPM is reached otherwise it freewheels in both directions. Once it locks up it still freewheels but only in one direction and the centrifugal locking mechanism needs to be set-up so that it won't unlock under load if the RPM's drop back down below the threshold so it doesn't suddenly automatically shift down in the middle of a pedal stroke and dump you out which can injure a rider who is pedaling hard when it happens (another problem with previous attempts at automatic transmissions on bicycles).

I think I've come up with a simple but effective mechanism that would do all that:

8630943730_6fabf93a98_z.jpg


On the left it is shown when the center shaft RPM's are high enough for the weight of the two large heavy pawls to overcome the spring force and move out and engage so that it will only freewheel in one direction. It should also be noted that the pawls are tapered in so that once engaged under steady load it will NOT disengage until the load does. Long story short, when you need to shift down you have to back off on pedaling and/or the throttle for a second to allow the freewheeling mechanism to disengage and if they are the means of automatic shifting allow a down-shift to occur.

On the right it is shown when the center shaft RPM's are not high enough for the weight of the large heavy pawls to over come the spring force and move out and thus at this lower RPM the sprocket freewheels in both directions. The threshold RPM for engagement can be varied by using different strengths of springs.

Lets' say you set-up a two shaft, six sprocket, three chain transmission like those pictured to provide three speeds with automatic shifting using these kind of centrifugally engaged freewheels to perform the two up-shifts using two strengths of springs. For example lets say low gear was a 16t sprocket driving a 24t sprocket (regular bicycle chain), middle gear was a 20t sprocket driving a 20t sprocket, and high gear was a 24t sprocket driving a 16t sprocket. If you mounted all the input sprockets solid on the input shaft and on the output sprockets you used a regular normal freewheel for the low gear, and the centrifugal engagement freewheel with the lighter spring for the mid gear, and the centrifugal engagement freewheel with the heavier spring for the high gear. Starting out from a dead stop only the freewheel for the low gear would engage, once you spooled up on the pedals with or without motor assistance (just gear the motor to one side of the input shaft and the pedals to the other with freewheels on each for either-or drive) to get the output shaft spinning fast enough to engage the mid gear centrifugal freewheel it shifts up and the slower moving low gear sprocket just freewheels, then you accelerate further until the high gear centrifugal freewheel engages which shifts you up to high gear with both the low and mid gear sprockets still moving but at slower RPM's then the inner shaft so they both just freewheel. As soon as you let off the input power engagement of the mid and high gear is no longer "load locked" and the transmission will thus downshift if necessary.

Riding a bike with such a transmission would give you a 225% gear range which is wider then your average three speed hub and about the same as a bike with only one front chain-ring and just a rear derailer only for gears. Up-shifts would be automatic and adjusted by swapping out spring strengths in the transmission. Downshifts would be induced by backing off on the pedaling and/or throttle for a moment. Put the low gear with the regular freewheel in the middle of the triple with the mid and high gears out the two outside edges with the springs outboard to allow easy adjustment and I think it could work like a dandy especially for an electric motor assisted bicycle.
 
turbo1889 said:
I've been thinking it over for a week or more ever since I first saw this thread about this kind of transmission set-up. There is a way to make this kind of transmission fully automatic, automatic transmissions have been tried on bikes before and most were too weak, too heavy, and/or too complex. but using a set-up like this along with simple centrifugal force and the basics of a pawl freewheeling assembly this could be made to work and work well.

All that needs done is to make a freewheel assembly to put in the center of the sprockets that only locks up once a given RPM is reached otherwise it freewheels in both directions. Once it locks up it still freewheels but only in one direction and the centrifugal locking mechanism needs to be set-up so that it won't unlock under load if the RPM's drop back down below the threshold so it doesn't suddenly automatically shift down in the middle of a pedal stroke and dump you out which can injure a rider who is pedaling hard when it happens (another problem with previous attempts at automatic transmissions on bicycles).

I think I've come up with a simple but effective mechanism that would do all that:

8630943730_6fabf93a98_z.jpg


On the left it is shown when the center shaft RPM's are high enough for the weight of the two large heavy pawls to overcome the spring force and move out and engage so that it will only freewheel in one direction. It should also be noted that the pawls are tapered in so that once engaged under steady load it will NOT disengage until the load does. Long story short, when you need to shift down you have to back off on pedaling and/or the throttle for a second to allow the freewheeling mechanism to disengage and if they are the means of automatic shifting allow a down-shift to occur.

On the right it is shown when the center shaft RPM's are not high enough for the weight of the large heavy pawls to over come the spring force and move out and thus at this lower RPM the sprocket freewheels in both directions. The threshold RPM for engagement can be varied by using different strengths of springs.

Lets' say you set-up a two shaft, six sprocket, three chain transmission like those pictured to provide three speeds with automatic shifting using these kind of centrifugally engaged freewheels to perform the two up-shifts using two strengths of springs. For example lets say low gear was a 16t sprocket driving a 24t sprocket (regular bicycle chain), middle gear was a 20t sprocket driving a 20t sprocket, and high gear was a 24t sprocket driving a 16t sprocket. If you mounted all the input sprockets solid on the input shaft and on the output sprockets you used a regular normal freewheel for the low gear, and the centrifugal engagement freewheel with the lighter spring for the mid gear, and the centrifugal engagement freewheel with the heavier spring for the high gear. Starting out from a dead stop only the freewheel for the low gear would engage, once you spooled up on the pedals with or without motor assistance (just gear the motor to one side of the input shaft and the pedals to the other with freewheels on each for either-or drive) to get the output shaft spinning fast enough to engage the mid gear centrifugal freewheel it shifts up and the slower moving low gear sprocket just freewheels, then you accelerate further until the high gear centrifugal freewheel engages which shifts you up to high gear with both the low and mid gear sprockets still moving but at slower RPM's then the inner shaft so they both just freewheel. As soon as you let off the input power engagement of the mid and high gear is no longer "load locked" and the transmission will thus downshift if necessary.

Riding a bike with such a transmission would give you a 225% gear range which is wider then your average three speed hub and about the same as a bike with only one front chain-ring and just a rear derailer only for gears. Up-shifts would be automatic and adjusted by swapping out spring strengths in the transmission. Downshifts would be induced by backing off on the pedaling and/or throttle for a moment. Put the low gear with the regular freewheel in the middle of the triple with the mid and high gears out the two outside edges with the springs outboard to allow easy adjustment and I think it could work like a dandy especially for an electric motor assisted bicycle.


the problem i see with this is the pawls and centrifugal, just before they engauge it will start to judder trying to put the pawls fully into the locking position, they with start grinding them self down more then likely.
adam
 
No more so then the wear on the pawls of a regular freewheel, probably less since there wouldn't be full force trying to push them outwards all the time.

Edit: Or do you mean the tips of the pawls being just barely out and just barely hitting the tips of the engagement sockets on the outer sleeve? I suppose that could be an issue. Could relocate the spring holes up to just shy of the outer edge for a cam effect on spring tension so the leverage on the pawls due to the spring tension is greatest when they are held in tight and as they open up the leverage is reduced so once they open they "pop" open and when they close they "pop" closed due to the cam effect on the leverage point for the spring tension.
 
spinningmagnets said:
And if it was fun to make, and fun to use...that alone makes me happy to know.

file.php

Can testify to them being 'fun to use' ^ dat be my two speed there! 8)
as far as the enjoyment Thud gets from making them i don't know but damn glad he does!!

That plexi box looks sharp, i think it was linked too on ES not too long ago i dont recal where though?

KiM
 
Threw together quick mod (sorry no time to do proper colorized print just raw CAD screen capture) to give a heavy cam effect to the spring tension. Leverage arm quickly drops off to less then half as the pawls open so that once they start to open they are going to open all the way because the net spring force holding them closed actually reduces as they open. Thus once they start to open they are going to open all the way and once they start to close they are going to close all the way. Only in-between is travel time between the two positions. Acting leverage arm is in green (decimal fractional inches). Not finalized or anything just good enough to show the cam effect of moving the spring hole location to get the "pop" effect that ensures they are either in or out and not in-between except for travel time between the two positions, probably would not need that much cam effect in the spring leverage arm.

 
turbo1889 said:
Threw together quick mod (sorry no time to do proper colorized print just raw CAD screen capture) to give a heavy cam effect to the spring tension. Leverage arm quickly drops off to less then half as the pawls open so that once they start to open they are going to open all the way because the net spring force holding them closed actually reduces as they open. Thus once they start to open they are going to open all the way and once they start to close they are going to close all the way. Only in-between is travel time between the two positions. Acting leverage arm is in green (decimal fractional inches). Not finalized or anything just good enough to show the cam effect of moving the spring hole location to get the "pop" effect that ensures they are either in or out and not in-between except for travel time between the two positions, probably would not need that much cam effect in the spring leverage arm.


don't get me wrong i no where your going with this but this all depends on what speed your going to use this at, i can see it working at low rpm. but high ? even if the pawls flick out straight away if its spinning at high speed you will still have a prob with them eating themselves when engaging, or the sudden stop at speed will make them fail.
adam
 
xadmx said:
. . . don't get me wrong i no where your going with this but this all depends on what speed your going to use this at, i can see it working at low rpm. but high ? even if the pawls flick out straight away if its spinning at high speed you will still have a prob with them eating themselves when engaging, or the sudden stop at speed will make them fail.
adam

The "impact event" when the pawls engage into their slots I believe is what you are refering too. That same thing happens on a regular freewheel assembly when someone goes from coasting to slamming on the pedals. Your average normal bicycle freewheel has three significantly smaller and more fragile pawls with multiple small notches in the entire outside ring. So engagement of a normal freewheel occurs with much less radial travel but never the less it is still an impact event under force and speed on much smaller pawls and notches which provided the grade of metal used is identical should be accordingly weaker due to their smaller size.

Long story short, so long as the forces and speeds are not substantially higher then what a normal bicycle freewheel is subjected too I think it should stand up. I could be wrong, only actual prototype testing would tell for sure.

Took the time to do a full spec. out and colorized print with the spring holes positioned for a cam effect on spring tension. Tension let-off due to shortening of the acting torque arm is about 30% in the open position so that if for example they were set to pop open at 100-RPM the wouldn't close back up without overrunning pressing them in unless speed dropped below 70-RPM. Should be sufficient to get the desired "pop" in or out effect so they can't linger only slightly open and have just their tips making contact with the tips of the notches in the outer ring.



(And yes I do realize that the acting torque arm was not measured correctly on the previous image because it was not taken on the line directly perpendicular to the spring.)
 
I should also note that my idea isn't entirely unique. There is an automatic two speed hub on the market (can't remember which company) that uses this exact same kind of centrifugal engagement pawl to kick up into high gear. It has only one small pawl that engages the ring gear on the in-hub planetary gear assembly (1:1 low gear, 4:3 high gear). It works, but its only a two speed an its built into the hub based on internal planetary gear hub technology and you can't adjust the engagement speed without tearing the entire hub down to get at the spring inside.
 
That idea seems really good for a low power bike. On an RC bike I could see it slamming into gear at high throttle and throwing you off the bike :lol:
Too bad the go kart centrifugal clutches don't work at high torque and low speed.
 
I was thinking 200watt minimum up to 1,000watt maximum mid-drive set-up. Of note you would use a regular freewheel on the first gear and only these centrifugally engaged freewheels on the second, third, etc . . . gears for the up-shifts. So since you are already moving in a lower gear I doubt when the next gear engages it would throw you off the bike especially since the change in gear ratio would tend to bog down the motor for a second when the shift occurred. You are correct though that under a lot of power (multiple Kw builds) the shifts could be a little hard and abrupt.
 
turbo1889 said:
I was actually thinking of the currently available one which I took the time to look up and is made by Sram:

http://www.bikeparts.com/search_results.asp?ID=BPC377569
http://www.bikeparts.com/search_results.asp?ID=BPC377570

I want one of those.

One nice thing about most traditional gearhubs is that if they are shifted under heavy torque, they just wait until the load diminishes before executing the shift. That seems particularly desirable if it's the machine deciding when to shift.

I was amused at all the bulk and resources spent on the Instructables project, just to do the same basic job that Sturmey Archer was doing back in 1905. Clearly it's more about the joy of making things from scratch than it is any kind of practical concerns, because $80 full retail will buy a Shimano Nexus 3 coaster hub that's all worked out and fully commoditized.
 
Back in the mid 80s when racing BMX i tried a 'Torpedo' rear hub was a automatic two speed dunno if you can find them still?
Was a coaster brake, was no good for me my little legs couldnt push the 2nd gear. Gave it to the side hack rider i swang for he loved it.

KiM
 
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