Interesting old crank design.

[Cicli]

Saw these PMP cranks in an old article. Interesting, even if they didnt work. Kind if cool though. Maybe they would have worked better if they were carbon.
There was the Z-Force also. These were earlier though.

[oliver1850]

They should have had a diagonal for extra stiffness.

[JStonebarger]

They look like they would work just fine. Or were they supposed to do something regular cranks don't?

[Pastashop]

^^^ Other than add unnecessary weight and reduce stiffness?..

[jumphigher]

Pics of these make forum rounds every few years it seems like. Cranks like that supposedly are more efficient than the regular type, and there have been several similar designs. Apparently though they didnt take the biking world by storm as their designers hoped. :banana:

[cmbicycles]

They should have had a diagonal for extra stiffness.
I have a great idea. Why not use just the diagonal, it could revolutionize the radius of a pedaling circle. ;)

[Louis]

Everyone knows that the shortest distance between two points is not necessarily a straight line.

Plus, that design gives you 7% more leverage for the same effort.

[regularguy412]

Everyone knows that the shortest distance between two points is not necessarily a straight line.

Plus, that design gives you 7% more effort for the same leverage.

There. Fixed it for ya :)

Mike in AR:beer:

[cmbicycles]

Everyone knows that the shortest distance between two points is not necessarily a straight line.

Plus, that design gives you 7% more leverage for the same effort.
The shortest distance between two points is almost always under construction. :)

[sales guy]

This isn't that old of a design. Actually if you check the books or the China/Taiwan bike shows and pavilions, they will have versions of this. There is also a couple other companies from Italy and I think Spain if I remember right that are making something similar too.

And actually, Caramba did their Double Barrel crank which had an offset pedal hole to BB bolt hole.

[CaptStash]

Clearly designed by someone who failed high school physics.

CaptStash....

[cachagua]

Right, but he ended up a marketing major, so... didn't matter.

[martl]

Pics of these make forum rounds every few years it seems like. Cranks like that supposedly are more efficient than the regular type, and there have been several similar designs. Apparently though they didnt take the biking world by storm as their designers hoped. :banana:

on a sidenote, not too long ago, a design like this ("Z-torque") received a US patent. Apparently, the basics of mechanics and physics are no requirement for working at the patent office.

-> http://pardo.net/bike/pic/mobi/d.pmp-cranks/US5899119

http://pardo.net/bike/pic/mobi/d.pmp-cranks/z-torque.html

[oliver1850]

The design puts me in mind of Popeye's arms.

[David Tollefson]

And then there is this...
http://www.velonews.com/2013/09/bikes-and-tech/reviews/reviewed-zencranks-pas-crankset_301441

And this one that's a little difficult to see, but it didn't seem to slow her down much:
https://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Paula_Newby-Fraser_Encinitas_1991_Photo_by_Patty_Mooney2.jpg/697px-Paula_Newby-Fraser_Encinitas_1991_Photo_by_Patty_Mooney2.jpg

[choke]

This isn't that old of a design.Crankarms with an offset go back at least to the 1930s... http://pardo.net/bike/pic/mobi/d.pmp-cranks/

[Mark McM]

Saw these PMP cranks in an old article. Interesting, even if they didnt work. Kind if cool though. Maybe they would have worked better if they were carbon.
There was the Z-Force also. These were earlier though.

No, no, no, they've got it all wrong! They've got the bend in the wrong direction! Everybody knows that to increase power and efficiency they need to have the bend in the other direction!

[choke]

I don't know why I didn't think of this one until just now...the Interdrive (http://pardo.net/bike/pic/mobi/d.interdrive-crank/000.html) crank.

[54ny77]

Is this the SMS crank?

http://cdn.funcheap.com/wp-content/uploads/2015/02/stop-making-sense.jpg

[dgauthier]

These certainly are "old crank designs". They all look like they were designed by an old crank.

[sales guy]

And then there is this...
http://www.velonews.com/2013/09/bikes-and-tech/reviews/reviewed-zencranks-pas-crankset_301441

And this one that's a little difficult to see, but it didn't seem to slow her down much:
https://upload.wikimedia.org/wikipedia/commons/thumb/2/2c/Paula_Newby-Fraser_Encinitas_1991_Photo_by_Patty_Mooney2.jpg/697px-Paula_Newby-Fraser_Encinitas_1991_Photo_by_Patty_Mooney2.jpg


I used to work on Paula's bikes. Her and a bunch of other pros-Mike Pigg, Karen Smyers, Peter Reid, Lori Bowden and a bunch of others. It was fun with tri people. I was into it then and working for Cevelo. Used to run and ride with them all the time. Swimming, not so much. I could never keep up with them.

[cadence90]

I just heard today that PMP has been sold to another Italian company, and that new ownership will be reducing the production of a lot of their products.

Bummer. :(

[avalonracing]

Manx Crank?

[sales guy]

Manx Crank?


I believe it's "if you're not a Manc you're a wank!"

[fiamme red]

http://road.cc/content/feature/181256-retro-l-shaped-cranks-bad-idea-just-wont-die

[tombtfslpk]

Kinda reminds me of the stem length/handlebar width debates of folks with MTB's.

[MattTuck]

PMP.... what, am I ordering cranks from hot truck now?


sorry, probably no one will get that.

[cachagua]

No, no, no, they've got it all wrong! They've got the bend in the wrong direction! Everybody knows that to increase power and efficiency they need to have the bend in the other direction!

Right, because if it bends that way it'll cause your frame flex to push your foot down in front, instead of pushing it up in the rear.

Wait, wait, all you'd have to do is mount them on the opposite sides, wouldn't you?

And then pedal backwards?

I'm getting dizzy.

[GOTHBROOKS]

there are some nos houdaille industries power cams in the display case at the shop. ive always wanted to try them.

[Mark McM]

there are some nos houdaille industries power cams in the display case at the shop. ive always wanted to try them.

I immediately though of the Houdaille Power Cam cranks when I first say the Rotor RS-4 cranks. The Rotor cranks also used a BB mounted cam, but for a different reason: On the Rotor cranks, the two crank arms move out of phase with each other, with one arm moving faster or slower than the other arm during different phases of the circle.

http://www.bentrideronline.com/archives/reviews/Rotors/Rotors4.jpg

[Kontact]

The Rotor and the Interdrive are just complicated ways of replacing oval chainrings.

[GOTHBROOKS]

out of phase like these things?
http://cdn.media.cyclingnews.com/products/components/cranksets/1265719475363-13qsytzzkppju_600.jpg

[Mark McM]

The Rotor and the Interdrive are just complicated ways of replacing oval chainrings.

That is true of the Interdrive, but the Rotor is a little different. As previously noted, the two crank arms don't move in unison, the rear (rising) crank actually moves faster than the forward (descending) crank. The idea is that with normal cranks, the power phase of the right crank is between about 1 o'clock and 5 o'clock and when the right crank is between 7 o'clock and 11 o'clock the left crank is in its power phase of 1 o'clock to 5 o'clock. Between 5 o'clock and 7 o'clock and between 11 o'clock and 1 o'clock there are "dead" zones, when neither crank is in its power phase. But with the Rotor cranks, each crank moves slower during it's power phase and faster when it is outside of its power phase. So when the right crank reaches 5 o'clock, the left crank has accelerated through its rotation (and through the "dead" zone) and is already at 1 o'clock to start its power phase. In other words, with the Rotor crank, there is never a time when both cranks are in the "dead zone".

[Kontact]

That is true of the Interdrive, but the Rotor is a little different. As previously noted, the two crank arms don't move in unison, the rear (rising) crank actually moves faster than the forward (descending) crank. The idea is that with normal cranks, the power phase of the right crank is between about 1 o'clock and 5 o'clock and when the right crank is between 7 o'clock and 11 o'clock the left crank is in its power phase of 1 o'clock to 5 o'clock. Between 5 o'clock and 7 o'clock and between 11 o'clock and 1 o'clock there are "dead" zones, when neither crank is in its power phase. But with the Rotor cranks, each crank moves slower during it's power phase and faster when it is outside of its power phase. So when the right crank reaches 5 o'clock, the left crank has accelerated through its rotation (and through the "dead" zone) and is already at 1 o'clock to start its power phase. In other words, with the Rotor crank, there is never a time when both cranks are in the "dead zone".

I understand that the cranks move differentially, but that is just the mechanism that allows the pedal stroke to vary, achieving a variable gearing output for each leg.

[David Tollefson]

out of phase like these things?
http://cdn.media.cyclingnews.com/products/components/cranksets/1265719475363-13qsytzzkppju_600.jpg

Those are the PowerCranks, where each crankarm is independently ratcheted. Great for one-leg pedaling drills. And for killing your hip flexors.

[Mark McM]

I understand that the cranks move differentially, but that is just the mechanism that allows the pedal stroke to vary, achieving a variable gearing output for each leg.

Yes, it does produce varying leverage (effective gear ratio) like asymmetric chainrings or the Interdrive cranks. The difference is that asymmetric chainrings and Interdrive cranks vary the leverage of the cranks in unison, whereas the Rotor cranks change the leverage differentially. So while the effective gearing increases during the power phase for one crank, at the same time the effective gearing decreases during the recovery "dead phase" of the other crank.

But the varying leverage is not the end goal of the Rotor crank design. The real purpose is to eliminate the "dead zone" entirely, by ensuring that the power phase of one leg starts just as the power phase of the other leg finishes. It just so happens that this requires varying leverage.

[Kontact]

But the varying leverage is not the end goal of the Rotor crank design. The real purpose is to eliminate the "dead zone" entirely, by ensuring that the power phase of one leg starts just as the power phase of the other leg finishes. It just so happens that this requires varying leverage.

I think that is kind of a distinction without a difference. But I get how it is different and why. I just doubt it would translate into different output than an oval ring designed to produce a similar effect.

[Mark McM]

I think that is kind of a distinction without a difference. But I get how it is different and why. I just doubt it would translate into different output than an oval ring designed to produce a similar effect.

Except that oval rings can not produce a similar affect. With standard cranks, because both pedals are in their "dead zones" at the same time, no matter how you shape an asymmetric chainring, you can't get rid of the "dead zones" in the power output. But because the Rotor cranks don't move in unison, they can be arranged so that there is only one pedal in its "dead zone" at a time, and therefore virtually eliminate the "dead zone" in the power output.

Of course, that doesn't necessarily mean that you can generate more power with Rotor cranks. The limitation on power output is largely the ability to deliver oxygen to the muscles, rather than the percentage of the circle in which the power can be applied to the pedals. If increasing the size of the pedal power zone was effective, then treadle bikes (like the Alenax below) would be able to produce the best performance, because like the Rotor cranks, there is no time that both pedals are in the "dead zone". Just like treadle bikes, Rotor cranks have also failed to provide more power or efficiency (and asymmetric chainrings haven't demonstrated they deliver on these promises, either).

In short, I'm saying that the power output will always be different from standard cranks (either with round or asymmetric chainrings), but not necessarily better.


http://farm9.staticflickr.com/8218/8293612401_a288c2b814.jpg

[dddd]

The bent crankarm just may return soon, now that Jan Heine has brought up the argument that flex in the drivetrain load path may improve a rider's output in certain situations.

There are other ways to increase a bike drivetrain's flexibility, such as using a smaller chainring (10% smaller causes a 23% increase in flex at the pedal) or using a sprag clutch to replace the freehub ratchet.

But there will need to be another biomechanical study to show performance improvement, very much along the lines of using BioPace chainrings, which never have entirely gone away.

Flex in the drivetrain load path tends to reduce the peak level of force that the muscles are subjected to, which may reduce fatigue and allow higher net power outputs or improve endurance, but which would benefit from further study at this time.
Imagine if steel frames were to be found to improve a rider's performance by flexing more!

So as soon as the disc-brake marketing bubble bursts, bring on the steel and titanium frames, they ride more comfortably anyway.

[Kontact]

Except that oval rings can not produce a similar affect. With standard cranks, because both pedals are in their "dead zones" at the same time, no matter how you shape an asymmetric chainring, you can't get rid of the "dead zones" in the power output. But because the Rotor cranks don't move in unison, they can be arranged so that there is only one pedal in its "dead zone" at a time, and therefore virtually eliminate the "dead zone" in the power output.

Of course, that doesn't necessarily mean that you can generate more power with Rotor cranks. The limitation on power output is largely the ability to deliver oxygen to the muscles, rather than the percentage of the circle in which the power can be applied to the pedals. If increasing the size of the pedal power zone was effective, then treadle bikes (like the Alenax below) would be able to produce the best performance, because like the Rotor cranks, there is no time that both pedals are in the "dead zone". Just like treadle bikes, Rotor cranks have also failed to provide more power or efficiency (and asymmetric chainrings haven't demonstrated they deliver on these promises, either).

In short, I'm saying that the power output will always be different from standard cranks (either with round or asymmetric chainrings), but not necessarily better.


Hey, I get what you're saying, I just don't think that having "both cranks in the dead zone" is the actual root problem, especially if you have eccentrically changed the gearing to extend the power zone. The Rotor system could be seen as a way to decouple the dead zones, or a way to steal power from one crankarm to push the other through its dead zone.

[Mark McM]

Hey, I get what you're saying, I just don't think that having "both cranks in the dead zone" is the actual root problem, especially if you have eccentrically changed the gearing to extend the power zone. The Rotor system could be seen as a way to decouple the dead zones, or a way to steal power from one crankarm to push the other through its dead zone.

Yes, I agree with this. Having "both cranks in the dead zone" is not an actual problem, but that's what Rotor was trying to address - and this led to their excessively complicated solution that didn't achieve anything useful.

[dddd]

Not only does this PMP crankset have more flex in the arms, I also notice that the bend is oriented so that such flex results in the arms getting a little bit longer as pedaling force increases!

So, as when trying to hold onto a gear as a hill gets ever steeper (remember, these cranks were from the days of downtube shifters, so no shifting while off of the saddle!), the leverage increases as well as the load path yields, further reducing the need for a shift to a lower gear.

Just the thing for grabbing hilltop primes.

[dnc]

But the varying leverage is not the end goal of the Rotor crank design. The real purpose is to eliminate the "dead zone" entirely, by ensuring that the power phase of one leg starts just as the power phase of the other leg finishes. It just so happens that this requires varying leverage.


Rotor Cranks eliminate the dead spot at 12 but not the dead zone between 11-1 o'c. When the lower crank is at 6 o'c, the upper crank is only about 10 deg. past 12 o'c. You still have that dead zone where both legs are idling.

[dnc]

But the varying leverage is not the end goal of the Rotor crank design. The real purpose is to eliminate the "dead zone" entirely, by ensuring that the power phase of one leg starts just as the power phase of the other leg finishes. It just so happens that this requires varying leverage.

https://www.youtube.com/watch?v=7hh2DcgpnkU

In TT's this man could simultaneously start his power stroke at 11 as his other leg ended its downstroke at 5 by using the most powerful and most fatigue resistant muscle in his hip/leg around TDC (the soleus in the lower leg), a muscle all other cyclists completely ignore. This gave the same torque at 12 as at 3 o'c.
" A good workman never blames his tools "

[martl]

But the varying leverage is not the end goal of the Rotor crank design. The real purpose is to eliminate the "dead zone" entirely, by ensuring that the power phase of one leg starts just as the power phase of the other leg finishes. It just so happens that this requires varying leverage.
As long as the bike is in motion, the needed force to pass the "dead zone" is marginally larger than 0.

Funny thing is hat there are a gazillion of inventions out there to "optimize" pedalling "efficiency", while scientists have yet to prove there is any performance to be gained that way, and not for lack of trying.
A test performed in the late 1990ies proved that one of the german top track riders (olymic gold medalist) was a very "inefficient" pedaller.


Another failed affort:
https://www.bikerumor.com/wp-content/uploads/2016/09/Cyfly-eliptical-crank-system-concept-moeve-bikesEurobike-day-3-4-325-600x400.jpg
https://bikerumor.com/2016/09/13/eb16-cyfly-drive-system-promises-more-torque-with-wild-elliptical-crank-system/