Is there anything on the market like a hub that looks like a freehub but that doesn't use a freewheeling/ratcheting mechanism? Or is it possible to open up a freewheel and 'fix' it from ratcheting (and if so, how difficult would this be?) What I'm after is a way to build fixed multi-gear bike, so that one wouldn't be able to 'cruise' but would still have an entire cassette of gears available and accessible using a shifter/derailleur.

As far as I am aware, the only multispeed fixed hub in production today is the Sturmey Archer S3X.

I am not sure of the feasibility of 'fixing' a normal hub gear.

See this discussion on the singlespeed forum for a review, or google for more details.

You really can't use a sprung tensioning device on a fixed gear. Because you're applying force in both directions, tensioners (derailers included) have a tendency to crumple. You might be able to rig together something like a Campangolo Corsa, but that would be a significant project. It would be awesome though, so I strongly encourage you to try.

The S3X could be combined with a Schlumpf...

I have never tried this, but the early NuVinci 170 hubs seemed to require an external freewheel, and from what little I know about their design, it seemed like there was nothing directional about the way they worked inside. The new 360 has an internal flywheel though.

Get somebody to weld/braze the back of the freewheel. Should be easy and cheap.

[edit] Not sure how you'd keep it from unscrewing from the hub, though...

The only problem with a fixed multi gear is in order to change gear you will be using a RD, unless you can come up with a Campy Corsa setup as already mentioned. Now on a fixed gear with a RD any backwards pedaling will cause the chain to loose tension and strain/bend/break the RD springs and possibly bend the RD and hanger. Or cause the chain the chain to come off at a real in-opportune time which causes you to become road kill. Overall not a good situation.

OK, this thread is now about how to build a fixed gear Corsa.

First obvious problem is you have to pedal backwards to shift on a conventional corsa, but that's because the changing mechanism is on the top of the cassette. It's not inconceivable to move the changing mechanism to the bottom, so you can shift when pedaling forward, right?

Hey, if you run it down the back of the seat-stay, it should work out perfectly.

Second obvious problem is to come up with the parts for a Corsa. Sure you can find the levers and stuff occasionally on eBay, but the dropouts and the custom frame are a whole other issue....

Cambio Corsa uses a rack & pinion axle and dropout combination in which the wheel actually moves forward and backward in the dropouts to maintain chain tension over different gears. The backpedal action is needed to move the axle back in the dropout when using higher gears; I'm not sure how well this would work with a fixed cluster.

Not to mention the special fixture that keeps the rack mechanisms on the dropouts properly aligned with each other.

I thought about that before buying my NuVinci hub. Unfortunately the power transfer setup of the NuVinci hub design is one way, not reversable. If you build an older pre N360 version of the hub up w/o the freewheel there is some minor drag on the pedals with the bike moving when not pedalling but not a solid connection like with a FG bike. This info is from a BF member who reported that he tried building a bike with the original hub and w/o the freewheel.

I have a bike with the S3X hub and cannot see any reason the Schlumpf 2 speed drive crankset should not work with it. Be an expensive drivetrain though. I believe that you would want to use the speed drive for the project as IIRC it's step is about the same as the overall range of the S3X so it should give 5 speeds effectively and a overall ratio range of about 250%, similar to a SRAM P5 or new SA 5 wide IGH hub.

The Schlumpf Mountain drive would give broader dynamic range than the Speed Drive.
It might give you too much torque throught he hub, though there were faqs out there from SRAM on how to mate the S7 to the Mountan Drive.
A Schlumpf with track/fixie rear hb could give you a 2 speed as well.

Sheldon Brown acquired an ASC hub in 2005 and mated it to a Schlumpf to give him a 6 speed.

There are other 2 speed crank options besides Schlumpf. The Sram Hammerschmidt, although it freewheels so there goes the fixed gear, also FSA is coming out with one called the Patterson. Not sure if that one has hit the market yet or when it will.
From what I've read about it, the FSA unit has the fewest requirements for mounting. No chamfering required as there is for the Schlumpf, and ISCG mounts not required as they are for the Hammerschmidt.

The mountain drive has way too big a step between ratios to work well with the range of the S3X or ASC IMO. Ity would give two three speed ranges with a large gap between them. The step between low and high is 250%.

Schlumpf [its in the manual] wont tolerate fixie use..
KiSS method : , S3X, Dingle cog , bring along a wrench to loosen the axle bolt,
stop and change,
2 chainrings with tooth total F+R same , 2 more tooth on larger dingle cog,
2 less teeth on the chainring on the front. [F+R(a)] = [f+r(b)]

so chain length remains same , but drive range is wider than S3X on its own..

Perhaps a QR axle will grip enough to not need wrench in the pocket.

I have an AW3 and a schlumpf MD on my Brompton, its a wide ratio set

the equivalent to a 50t/20t crankset ..

What's so bad about freewheeling/coasting , its my favorite part of cycling.

The thought of using a system where the axle or BB has to come loose to allow the change pretty much fills me with dread. Reading the procedure for that Campy system it is obvious that this is not something you want to be doing in the heart of any downtown traffic. Not to mention that with a fixie the need to maintain the pedal cadence would make all that balancing and pedalling while maintaining a neutral chain load pretty tough.

What about a derrailleur like shifter/tensioner that actually locks up solid between shifts? There would need to be a way to unlock it then shift to the desired side and shift the chain with it and then once in place to relock. The rider would need to plan the shifts such that they did NOT suddenly have to back load the pedals during a shift or the obvious bad things would happen. But I can see where this could be done using some manner of a control pod on the bars that declutch for the first portion of the lever or twist travel and then shifts and then allows for relocking as the control is released. It would likely be a longer travel than usual due to the added function. Much like upshifting two gears at a time with the Shimano MTB rapid fire pods or a double shift with a road brifter. For shifting down to the smaller rear cogs the throw would be more like a single upshift to de-clutch and then have the normal small click at the end of it.

The other and far more ideal option to my mind is that Sturmey-Archer fixie 3 speed hub mentioned above. It would look a lot less Rube Goldberg like than any sort of external changer that deals with shifting chains and multiple sprockets.

Is the preclusion on all Schlumpf bike hubs or just certain models?

Since the epicyclic gear on the MD is low vs high for the Speed Drive and High Speed Drive, any torque driven by the rear through the BB would milder with the High Speed Drive worst due its high ratio.

Schlumph [in their FAQs] say their Speed-drives manufactured since summer 2009 can tolerate fixie use.

tcs

That link says all there BB drives so that would also include the Mountain and High Speed Drive.

It's your $700+, for the Schlumpf crank .. do with it as you wish.

fwiw , a flip flop double fixie hub and 2 dingle cogs will give you 4 cog pitches . aka 4 speeds .

Just get the S3X and be done with it. Short of installing a hydraulic derailleur, there's not really any way to build something that can deal with the forces involved.