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Armless cranks
Let's see your armless cranks - as I need an armless triple and can't find one.
At this rate I'm going to have to make one. |
Sorry, my cranks are only legless.
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Heh... well, my stoker isn't legless but she's only 6yo, the tandem is electric, and the rear crank will run faster than my one up front. So that'll be fixed footrests above an armless crank.
Having concluded that this isn't really a thing, i have this morning gone ahead and made my own. My tandem's cranks are some pretty standard early '90s Sugino GT 110s so no worries chopping one up (note the severed arm on the tool box). All three cranks from the bike look identical, but only the one in question takes three rings, and the other stoker crank is 5mm shorter, so i had to get it right first time. And finally, after plenty of filing and sanding... https://i.imgur.com/nugS3bX.jpg It needs a good polish and i'll be x-drilling the chainrings, but it's turned out fine. |
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Originally Posted by MikeyMK
(Post 20348029)
Let's see your armless cranks - as I need an armless triple and can't find one.
At this rate I'm going to have to make one. |
I have a crankset which neither arm has any chain ring attached to it.
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You might look at a "sto-kid" setup.
The kid gets a crank attached to the seat tube above the regular crankset. However, in general, I think they just leave the lower crankset intact for later use. |
Originally Posted by cny-bikeman
(Post 20348218)
The crank is the arm, so good luck making an armless arm.
Originally Posted by CliffordK
(Post 20348519)
You might look at a "sto-kid" setup.
The kid gets a crank attached to the seat tube above the regular crankset. However, in general, I think they just leave the lower crankset intact for later use. For one, the crank is an overdrive - it will be turning around 1.42 times faster than the one on the front, because a 40T front crank will be turning the 28T chainring (his changes my 11-36T freewheel into the equivalent of 8-25T, therefore solving my problem of trying to get a Capreo freehub on an electric motor). But i could gear her crank back down. Three chains and three BB's though.. well, it ain't gonna be a light bike anyway! Also, she'll be sat on a long lay-back seat post, partially over the rear wheel, so her feet will be quite far in front of her even to reach the seat post - It'd condition her for using a cruiser bike i guess...
Originally Posted by fietsbob
(Post 20348476)
I have a crankset which neither arm has any chain ring attached to it.
So... now just to shorten the butted frame by some 10ins... |
Originally Posted by MikeyMK
(Post 20348620)
Yeah. It's more a hub really, isn't it. I knew what i meant. It 'should' be an armless crank.. :innocent:
I've looked at that idea briefly, but she just doesn't need to contribute. I suppose it wouldn't be a bad thing for the involvement, but there are other things to consider with that; For one, the crank is an overdrive - it will be turning around 1.42 times faster than the one on the front, because a 40T front crank will be turning the 28T chainring (his changes my 11-36T freewheel into the equivalent of 8-25T, therefore solving my problem of trying to get a Capreo freehub on an electric motor). But i could gear her crank back down. Three chains and three BB's though.. well, it ain't gonna be a light bike anyway! Also, she'll be sat on a long lay-back seat post, partially over the rear wheel, so her feet will be quite far in front of her even to reach the seat post - It'd condition her for using a cruiser bike i guess... Hmm, this gives me the idea of using the stoker to sit there and just generate electricity with the pedals... So... now just to shorten the butted frame by some 10ins... If you put in the stokid config, then you could reverse it: 28/40T, and be back to a 1:1 ratio, or if you're a big time spinner, perhaps even more relaxed gearing. It might be nice to get a freewheel in there somewhere, like the autoshift bikes use at the crankset. I took my nephew out on a Tandem a few years ago. He didn't really want to do it, and did everything he could think of to make it difficult, including simply standing on the pedals and letting them push him up and down. Frankly, I couldn't feel it (noting, of course, that what goes up comes down). |
She's not gonna grow 10ins a year, but yes, there will come a time in a few years when she's a fair bit bigger. And maybe then i can put rear pedals on - after all, the seats are gonna be barely any closer together thanks to the lay-back post, it's just the crank and wheel will be further forward. And by then she'll be on her own bike all the time.
I really don't blame your nephew. I wouldn't wanna be pedalling with no steering, either. Being a stoker doesn't appeal at all (being on the front of a tandem isn't all that great, either). But she's been happy sat on the back of my normal bikes as a full passenger for the last couple of years, this will just give us a few more. |
You did a nice job on that
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Yes, well done there. Sorry for being a smarta$$, but as you figured out, there's no such thing as an armless crank. Probably would have helped had you described what your need was, but clearly you've solved the situation.
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a Machinist's lathe would have saved a lot of time..
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