Gipemme Colrut ranks and integrated pedals. Unknown vintage and background. Marked various places with
Gipiemme Italyand the vanity groove is marked
COLROUT'
Background on Gipemme: from http://www.classicrendezvous.com/Italy/Gipiemme_main.htm as of 2007/06/15:
Gipiemme is still involved in the bicycle trade but has realigned it's product offering. In the 1970s it offered, among other levels, the Special series components that rivaled Campagnolo.
"Gipiemme a world-renowned brand synonymous with top-end cycle components for race and MTB was acquired by Isca SpA group in 1989."
The crank has a standard square taper, but the pedal eye is approx 82mm diameter. A bearing is fitted in the eye. The inner race has a pedal stub rigidly attached at about 62mm diameter (31mm radius). A pedal is attached rigidly to the stub. The bearing has rubber seals on both the inside and outside. the bearing layout is unknown but is likely double-row ball.
There are no bearings between the pedal and the stub, so the pedal has a fixed relationship to the inner race. The pedal and race are oriented so when the pedal is level, the pedal cage is forward of the crank, in all crank positions.
Not much is known about these cranks or their original marketing.
It appears the goal is to place the pedal farther from the spindle on the downstroke for increased leverage -- as with a longer crank, but without increasing the total distance traveled by the foot and thus without other disadvantages of longer cranks.
The pedal cage follows an offset path -- it travels in a circle, but the "dust cap" of the pdeal is further from the crank spindle when the pedal is ahead of the bottom bracket, and closer when the pedal is behind.
To analyze the true operation it is useful to first consider a standard pedal in isolation, say bolted to a stand. The foot presses on the cage both in front of the spindle and behind the spindle. The average force is always centered on the spindle. If more force is behind the spindle, the pedal rocks until the front comes up and presses hard enough on the underside of the shoe to balance the force on the rear. Similarly if more force is ahead of the spindle, the pedal rocks until the rear comes up and balances the force in the front.
Now consider the Colrut: the center of rotation is not about the pedal "dustcap", but about the center of the bearing in the pedal eye. The whole pedal cage is ahead of the center of rotation, so load placed anywhere on the pedal body causes the pedal to rotate down and back about the bearing. If the Colrut used only a simple cage, the rider's foot would wind up pressing on the back of the pedal cage. However, the Colrut uses a metal support that reaches back. When the rider's foot presses on the cage, the cage rotates down until the rear support comes up enough to balance.
Thus, while the visual effect is a pedal offset from the pedal eye, the true mechanical effect is still a platform which rotates about the pedal eye. The sole effect which is different than a standard crank and pedal is the rider's foot is shifted forward, as if a 31mm longer toe clip were used. However, the Colrut achieves this at greater weight, cost, and friction, and with reduced reliability.
Note that an offset pedaling circle could be achieved using a standard pedal and a Vietor/Erich Split Crank/Kingsbury K-Drive with 1:1 gearing instead of the usual 2:1. The same (or similar) shape may also have been achieved by the "Power Pedal" (see http://www.sonic.net/~ckelly/Seekay/weird_bike_stuff.htm as of 2007/09/02).
More at http://pardo.net/bike/pic