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As some of you are aware I can't stand up on the pedals as whilst most of me was born in Twickenham my right leg was made in Austria. Mine is a through knee amputation, so unlike these soft below knee amps (I'm looking at you Pistorious) I have no knee, so no control over how the lower limb swings (it's just a damped hinge). As a result placing weight on it when anything other than locked straight causes it to fold under me. This means standing on the pedals with the pedals level, even on flat and level ground, doesn't happen. This is limiting my ability as I can't stand up off the seat for travelling over obstacles, or even one day landing a jump or two. I'm mainly interested in trail riding.
I had a theory that if I could lock the crank for a few moments I'd be able to stand up on the pedal thats locked (my meat leg is huge; it does all the work so its quite strong) so had wondered about using a disc brake on the crank (opposite side to the front gearset). I've got a lathe and can machine most things, but had noticed some crazy unicyclists have actually fitted disc brakes to their cranks. Why, I've no idea, surely hitting the brake on a unicycle is swiftly followed by an emergency trip to the dentist.
Has anyone got any experience of fitting a disc to a crank? I heard some fixie people thought about it but I don't know if anything came of it, mainly because there are no real advantages in their case. In my case however it would be ideal for getting more out of my cycling. My theory was a caliper mount on the seatpost down tube and a disk adapted crank arm. The lever would be mounted somewhere on the bars, possibly using a dropper lever.
I realise its a strange subject to raise.... Jon.
It's a perfectly achievable idea, there's a few examples about crank mounted discs I think on novelty fixies and the like.
It would be easiest if you went square taper and used a tandem LH crank with a custom disc rotor (with BCD to suit). An adaptor to fit the caliper to the seat post should be pretty simple, you might want to fit the caliper backwards to keep the mounting bolts, etc inboard which could make the cable routing slightly trickier... I assume you're thinking cable actuated, not hydraulic.
Couple of examples:
*like*
Fascinating idea - looking forward to seeing progress!
Speak to bencooper on here - he does this kind of stuff for a living.
It would be great if you could adapt a dropper seatpost so that it applies the brake as you stand up...
That is a great idea, something like a reverb might work as it’s hydrolic or you could use a bar mounted dropper switch connected to something like hopes v twin road brake. Then at the crank you could use something like a drive side race face cinch crank arm ( on the non drive side) and make a rotor mount instead of a chain ring. Then all you would need to do is mount the caliper. Perhaps if you had a frame with an isgs mount you cold make a caliper mount that fitted there. You could always use boost spacing (on a standard frame) that would give you some room to bring the disc away from the crank arm to allow for the caliper.
Excellent, glad to know I'm not having totally daft ideas. Only minor issue is the slightly funky shape to the frame on my bike (2009 Anthem X1) which means a little more effort required, but still not too bad. Thanks all, I'll investigate further.
You described the prosthetic as a damped hinge, just thinking outside the box, but is there an option to run a "lockout" mechanism on that?
Glenn Johnstone was using a Fox RP23 in his prosthetic leg so he could adjust it.
https://fat-bike.com/2014/08/glenn-johnstones-fat-biking-story-another-take/
although this photo shows a Monarch
The first unicycle disks used a standard 5 bolt crank and a custom made disk to fit. The newer ones use a standard 6 bolt rotor fitted to a custom crank or hub. I suspect the custom disk on a standard crank will be easier. Hope do custom laser cutting of disks or you could see if unicycle.com have any old ones. In fact it might be worth having a word with Roger at unicycle.com. He's does a lot of the design engineering work there and makes various unicycles and penny farthings. I'm sure he'll be happy to chat.
Does sound feasible though. I'm sure a few people on here will be happy to help as well. We have a few manufacturing toys between us. Keep posting updates
@nobbysideways - interesting post! Would you always want to lock the cranks out with your 'meat leg side' foot forward or back or both? ... Or at any point in the rotation of the crank?
Also, would you want to toggle the lockout on and off or just have it on when the lever or whatever is pressed?
If you always want the cranks locked in only a horizontal position, would it be easier to have some kind of sprung loaded locking pin that is normally held in a closed, compressed state.
When you release it with some kind of bar mounted lever, it would spring free against a machined surface that has a notch in it relating to horizontal crank position. Next time the cranks reach this position, the pin would spring into the notch and lock the cranks, until the lever was activated to reset the pin.
^^ that was the sort of line I was thinking on except you've been able to describe it concisely 🙂
Yes its a good point, it would be more positive as well. To be honest I don't know which would be better but now you mention it that would work well for me.
The NHS completely flip their bin when I say I've adjusted or modified my legs in any way, one time they said I'd voided the Otto Bock warranty and it was effectively scrap despite the fact I'd improved it. I can't change the leg (its not really mine) but the bike is all bought and paid for.
The locking pin idea would be fantastic in retrospect; smaller than a disc and capable of maintaining positive locking. I'm not completely off the disc idea (the ability to lock the pedals anywhere I like appeals) but more alternatives keeps things interesting.
Just to give more detail I use a flat on my real leg and an SPD on my false leg purely to keep it on the pedal. If it helps I'm in North Dorset.
If you go for the disc on crank option, you could use an ISCG adaptor to help mount the caliper. i think it should work on either side.
Doffs hat to nobbysw. Would love to see progress on this!
Good call on the ISCG adaptor. I don't want to make more work for myself than required!
Beaten to it, but I was going to suggest a pin that pops out and stops the relevant crank rotating down/back rather than a brake.
The other idea was if there is an easy way to stop any backpedalling ability, like a BB with a hub style ratchet. Obviously you'd want a quiet Shimano style, not an angry Hope buzzing away as you are pedalling!
I have a Banshee ISCG05 plate going spare a bit like this:
I may purchase that off you if it takes that route; I'm still in the bouncing ideas stage at the moment, thank you.
Lots of sketching going on here now...
No you won't - I'll sent it to you F.O.C.
Rules are: Keep People Riding.
The other idea was if there is an easy way to stop any backpedalling ability,
Some dirt jump BBs (including one I saw recently, but can't remeremember where!) have a 'keep the pedals level' function. I wonder if that could be bridged somehow.
Can I suggest a call to Hope? I'm sure I've seen them help out some other folks with added challenges.
Some dirt jump BBs (including one I saw recently, but can’t remeremember where!) have a ‘keep the pedals level’ function. I wonder if that could be bridged somehow.
It's usually just a bit of rubber to add friction and keep them from spinning when their feet are off, same on the pedal axles.
Would a trials crank mounted freehub give you the 'ratchet' idea in a convenient package on the granny ring if you mounted it in reverse? Just need to lock it to something.
The other problem is going to be activating it, I'm guessing it's going to need about the same power as a disk brake so a reverb button isn't going to cut it. You could somehow mount a 2nd brake lever, but that might make braking difficult. Has anyone tried activating something like a BB7 off a shimano dual control lever? I'm guessing the original plastic ratchet and cable stop wont be upto it but it might be moddable?
Or thinking outside the box, could you not just modify the crank so the spindle extended out past the crank a little, so you could rest your heel on it when your good leg is forward and not need any other mods?
Running with the locking pin idea, maybe a lefthand front shifter could be used to control it : shift up to push it out, shift down to let it pop back in. The pin just needs to be spring loaded to retract and put tension on the cable the locking and release mechanism is handled by the shifter.
What about a pin locking mechanism system for the crank? A bit like the ones used by Gravity Droppers to set the position of their posts maybe?
What a fantastic thread ! I’ve nothing practical to add, but am mightily impressed by all the contributions !
Not entirely sure of this one in my head yet, but could you use a couple of jockey wheels, mounted in a chain device, that you could brake to lock the chain?
I find myself wondering if a small clutch plate pressing on the face of the wheel would make for an easier solution than attempting to get a disc in there too. You could spring load it 'on', with a pull cable on a shock remote to hold it 'off'. It should let you hold the cranks at any position although it would likely have some rock back and forth.
No idea how small and light you could build an effective clutch though.
Similarly to the pin idea, my immediate thought was a dog clutch rather than a disc brake. I'd always be wary the disc would slip when I really really didn't want it to!
Do you use the granny ring? An adaptor to bolt half a dog clutch to the crank could go on there, the other half sleeved and bushed to a custom BB shell. You've got a lathe, so depending on BB type/clearance this should be very doable.
Top project!
Only thing I can add is non-drive side for disc as drive-side will pick up chain spatter and you'll be baking or replacing pads weekly/daily.
Good luck with the sketching.
I was thinking along the same lines as the pin lock, could it be used with a a solid plate mounted onto the inner ring on a triple crank? You could then drill holes for a couple of different crank positions. Iscg mounted pin system.
You'd need to be running 1x system and I don't know whether that's feasible.
company linked inpage (though the web page link is no longer valid which isn't good news)
Can I suggest a call to Hope? I’m sure I’ve seen them help out some other folks with added challenges.
Beat me to it.
I reckon a hydro brake on the the non-drive would work well as its a proven reliable thing and you can modulate it and may be able to use this for balance whereas any pins trying to lock stuff meh, an extra brake lever(or two could have them inboard and joined so you can pick whichever) gonna give you fine control over it.
Depends a bit on whether an on/off type action would work better than a momentary action - I imagine it would be a pain to hold a lever down to keep a brake disc locked (if that is what is required).
On/Off would work better with a detent pin of some sort - maybe you could use a modified front mech / shifter to flip a pin, etc. into a receiver bolted to the cranks in the granny ring position? Or have a spring loaded pin that the front mech could pull out?
Good luck, whatever!
It's amazing the ideas and expertise coming from this thread; I'm really grateful. I'll give Hope an email and see if they have any bright ideas also, thank you. As for the granny ring I do use it on some climbs as I don't manage sustained power with one strong leg and one weak one.
As for the donations for parts that is really kind, thank you. I won't shamlessly grab everything thats been offered but I will keep record of what has been offered and by whom so I can take you up on the offers as required; thank you.
In theory you should be able to stand with your prosthetic. You have to really drive your stump back to lock the knee out then keep the pressure on to stop it from collapsing, at least that's how I have done it with the 3r80.
I see someone has already posted it but have you looked at the Bartlet tendon knee? I have one and its made a huge difference in what I can do. You get much more stability when standing and makes things much more natural. It's not magic and is still a whole lot of work, I can't stand and peddle like you see others do but I couldn't do without it now.
Hmm.
Thinking of new ways to do this.
This may only work on a frame with one of those removable covers near the BB shell like some do for internal routing but...
Hydraulic push lever on the bar, like a fork lockout lever. Hose routed internally towards BB shell. Mechanim in the downtube at th BB junction which somehow grips the crank axle, maybe a pin into it, maybe a clamp around it. Pin into it might be easier given imited space.
Upsides: Sealed and away from mud and dirt, no moving parts on the outside to foul anything such as undegrowth or shoelaces.
Downsides. I suspect a right PITA to get it in there unless you have a massive BB shell.
Couple of questions Nobby:
1). Is it a threaded BB and if so what width...
2). Hardtail or FS?
3). Could you get used to riding weaker leg forward...?
If you go for the locking pin, it's worth considering whether it should lock in both directions or just one. In other words, does (A) the pin engage in a hole in the crank, or (B) just pop out and wait for the crank to come round to it? Also whether the cranks would lock in one position per 360º or at 180º, ie, with either leg forward.
(A) means you're not reliant on keeping the load on the pin with your meat leg but is harder to engineer and operate. There would be no problem having a hole that was bigger than the pin, so that the cranks could move a bit.
(B) might leave the risk that you inadvertently take your weight off the meat leg and rotate the crank backwards.
have you looked at the Bartlet tendon knee? I have one and its made a huge difference in what I can do.
Awesome. Read up about the knee and am impressed. Seems like it would be a much better idea than some bodge on the bike, although obviously I don't know if it would be suitable for you.
I think a disk brake will be a nightmare for contamination being as it's going to be in line of fire from the mud etc from the front tyre unless you have done sort of shield. Holding it on when you are riding a section that requires you to be standing up may also be problematic.
A mechanical systems with a positive lock like a pin that can be switched between engaged and not doed sound like a good solution and would be quite straightforward to make.
I dintd think you'll get the pin idea to work.
You'll either snap the pin or you'l struggle to get it to engage as you rotate it unless you heavy chamfer the hole.
Was going to suggest a back pedal lock but you wont be able to back pedal i guess.
You need a remote lock out knee?
Maybe a drum brake would be easier? More shielded, it only needs to be on or off so no real modulation needed?
Something like a coaster brake for the crank?
yes, i was thinking about the load on a pin and it would be pretty significant (but IANA Engineer) - but would something that the crank rests on directly be possible? like a bar that swings out when released and clicks into place - then when you press the catch it is pushed back into position when you down pedal?