Guys I'm making a post for searchability reasons. Also, it is meshed from another forum, apologies if I dropped an ef bomb carelessly. Ask questions if you have them, and give me a shout if you see me backwards pedaling around campus!
Retro-Direct Concept: Pedal forwards in 39/18. Go forwards. Pedal backwards in 39/16. Go forwards. No derailleurs or gear changes. 1 chain. Freewheel whenever you want.
Last Known Production: 1903 by Hirondelle
Purpose: To make a bicycle that is excessively complex and only works some of the time (although this one is 98%) =P
Reason I made a new thread was because there were very few resources available when I was building this bike involving any details. This way, it will be searchable through the goog and such. I left the explanation a little dumbed down. I'm also predicting right now that this will be the next "trendy mobile".
This bike is assembled off of my old Sekai 400 (rusted) frameset (I DO NOT CONDONE STRIPPING OF PERFECTLY GOOD OLD BICYCLES). I ended up stripping the fixed side of the hub trackstanding on a hill.
There is nothing special about this bicycle in the assembly. I "built" the rear hub myself using parts of cassettes and bottom brackets as well as other hardware.
There is another fellow who has just posted pictures of this design, literally using the EXACT same setup as me. I am not claiming that he copied my design as I don't think there was any way he could have. But I am stating that I certainly did not copy him as my design had been conceptualized roughly 10 months ago.
This bicycle has taken nearly 6 months to get working properly. I am now able to successfully commute around town with literally zero flaws in the drivetrain. The drivetrain has been assembled and dis-assembled completely no less than 20 times to get the smoothness and reliability of a normal bicycle.
This is a closeup of the drivetrain. On the rear hub it is worth noting that the 18t freewheel is on the inside section of the cluster while the 16t freewheel is outboard on the cluster.
The chain when pedaling forward and starting from the top of the crank heading backwards will go directly over the 18t freewheel as it would normally. From here, it will wrap around heading directly to the chain tensioner. Chain tension is very key to the successful operation of this bicycle. The Kore tensioner is set at maximum tension and oriented in such a position in which it can be no tighter relative to leaving slight flex aftward, as well as spring tension. It is also worth noting that I have seen significant reliability issues with wether the chain loops through the tensioner from above or below. You'll note that I have the chain coming up from the bottom of the chain tensioner and passing back over the top. I would be happy to explain the physics behind this if necessary for your own information. The chain then heads directly back to the BOTTOM of the 16t freewheel at the cluster and loops back over the top. From here it will pass THROUGH the Kore chain tensioner (using it as a chain aligner at the same time (If any of you were around during version 1 of this bicycle you'll recall I was after a separate piece to accomplish this, but was unable to find a piece that would accomplish it in a successful manner. This has been the solution)) the chain rub here must be carefully adjusted. Too much pressure on the chain and you will regularly snag your chain tensioner providing a "catastrophic" hangup of the drivetrain. Too little and the chain will regularly derail at varying points on the drivetrain. You can also notice that I have experimented with many different positions of chain routing (marks on the chainstay) including running it outboard of everything. It will not work.
The chain continues through the tensioner to the bottom of the crankset completing the loop.
Tips: I have the rear axle completely respaced VERY far to the left to allow for the accommodation of the "cluster" (two independent freewheels and associated spacers). There is also almost no axle left as the rear spacing is now in the vicinity of 150mm! This factor also limits this build to steel framesets in my opinion. I also recommend starting with the wheel as far back in the dropouts as possible (against the stops). This is advised because it gives you a consistent variable when trying to adjust the chain size, and consistent positioning when adjusting chain alignment. I also highly recommend using a Sram or quick link capable chain as you WILL need to re-route the chain several times to experiment with positions relative to your frameset. Version 1 used a 9 speed chain with limited success and this current version is using an 8 speed chain (exaclty 3 1000ths wider) with great success.
To do this project correctly, some advanced bicycle knowledge is necessary, specifically understand hubs and respacing and disassembling them.
This bike is otherwise assembled with spare parts as more of a proof of concept than anything else. If you have questions about how to work it out, ask away as there were almost no resources available to me when I was assembling this bicycle.
You'll notice that while there are a few other RD bikes on the web, many of them use cut chainstays rewelded for clearance and more primitive tensioning mechanisms. My build was intended to directly avoid using any crazy ideas. A build in your garage out of spare parts type of approach.
The gearing is currently 39/18 forwards, and 39/16 backwards allowing me to successfully accelerate away from people/cars while pedaling backwards. I've also used a 52t ring with poor success and a 46t ring with decent success.
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Here's a pic of the rear hub. Things to note: With the wheel not dished, you can see how far left it sits relative to the brake mount on the frame. (what is that little bar called? Brakestay?)
Also, the inner freewheel is a Dicta SPECIFICALLY because it uses internal teeth for removal so it is able to sit flush as opposed to the Shimano freewheel on the outside which has external disengage teeth. There is a 1mm cassette spacer between the freewheels to allow free spinning. Also note that the freewheels were not able to be threaded all the way onto the hub, because you would have no threads for the bb cup.
So the 18t freewheel is threaded partway on (about half, but adjusted to accommodate spacing and frame clearance). Then nylon spacers are packed into the void while a BB cup is threaded on tight. This makes the hub and the BB cup and the freewheel 1 unit. Then the spacer is put on followed by the 16t Shimano. This is threaded tight and axle spacers are threaded back on as appropriate for spacing. This axle is designed for 135 spacing, and there is VERY limited threading left to thread the locknuts on. For the next round of updates, I'll be searching for a longer solid axle to use, as well as re-dishing the wheel as appropriate.
The bike is definitely a cruising bicycle. I will still however be experimenting with various gears. The next change though will be tire size, for comfort and winter functionality. This will also change my gear inches up slightly.
It has worked very well with gearing in the 65 or less gear inch range. Higher than that, and the chain continuously tries to derail. (also when putting real power on the pedals so no sprints). I experimented using an 1/8" chain as it is not designed to derail, but ran into flexibility issues.
It is still a work in progress. But as I've learned with this bike, when it functions at 90% or greater reliability, and you go after that last 10%, you end up with about 60% reliability at the end.
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Basic schematic of the hub setup.Black is the freewheel side of any hub. Remove everything from the solid axle down to the cone. Replace the spacer closest to the cone with an appropriately sized set to maintain adequate pressure for the bearings to function. Then, thread the 1st freewheel on approximately half way (in this case the 18t (red)).
Take your adjustable english BB cup and package of nylon washers (purple) and pack the bb cup with the appropriate amount that lets it fit over the axle and fill the void of the BB cup. The nylon washers are primarily to help stabilize the axle, and primarily to keep a uniform pressure across the system. It removes pressure points from the face of the cup both from the axle and the frame.
Thread this (green) into the remaining half of the freewheel (red) ensuring that the freewheel doesn't thread further onto the hub. You can adjust your chainline by adjusting the positioning, but you can only move it so far in either direction before you A. run out of space, or B. compromise the structural integrity of the "cluster". The BB cup (green) should be packed with nylon spacers (purple) and threaded tight into the freewheel (red) tight up against the hub (black).
Note: some micro adjusting may be necessary to ensure that the threads line up ideally creating a hub thread extension. I used nail polish to mark the thread positioning so that I could get it as close as possible.
From here you should have some threads from the BB cup remaining. Place a spacer of your choice (I used a 1mm) (light blue) to do this. This spacer is necessary, otherwise when the two freewheels are turning in opposite directions (all the time) they will rub and/or cease.
Now there should still be some threads left from your BB cup. Thread the remaining 16t freewheel onto the cup (dark blue). This will likely (although not ideally) extend out beyond the threads of the BB cup. This you may notice is a problem since the axle needs to remain stationary and the hub and freewheels needs to move. If you have an extra long BB cup (does that exist?) you could use that and eliminate that problem. I simply re-spaced my axle at this point and then used axle spacers to extend out beyond the removal teeth (what are those things called? The things that you lock the tool into to take the freewheel off?). This allows the pressure holding the wheel in the frame to be between the axle spacers and the tracknuts as it was designed for originally. Otherwise, the pressure would be on the longer BB cup if you had one, or on the freewheels and it would eff everything up.
Its sort of tricky to explain without just video-taping me build the damn thing. Hopefully this helps out until I can get some sort of better schematic or until I do a dis-assembly.
Pic hath been taken down for updatenessingston.
Topic: Retro Direct Build Complete. (Read 4068 times)
