Doolittle

I just had the opportunity to visit the archives of the Canada Science and Technology Museum in Ottawa and spotted this oddity in the warehouse. Unfortunately I forgot to charge my camera battery, so I was only able to get some cellphone shots. I have never seen a crankset like this and can only assume that when climbing/pedaling hard the chainring effectively shrinks making the gearing easier. I couldn't find anything about this online. Anyone familiar with "Dura Drive International?"

A few more fun photos:

non-fixie 

Wow! Automatic transmission?

rhm

That's a new one for me as well. One of those ideas where one is tempted to speculate: if it was such a great idea, it would have caught on.

Soylent 

Someone went for a ride

John E

Evolutionary dead ends are interesting. I have seen an expanding chainring before, but that one was manually controlled. It did evidently provide something of a CVT effect. I am still trying to get more information on Otto Cap's unusual shortlived rear cog innovation from the 1950s.

Blue Belly

That gear set had to weight more than the bike

Kactus

I'm thinking that was its big drawback.

smontanaro 

The frame looks pretty decent. Modolo anatomic brake hoods? Some sort of fluted seatpost.

Unusual pedals as well.

Jeff Wills

IIRC, that one was made of reinforced plastic- not super heavy, but not particularly durable, either.

A similar, manually controlled unit was made of stamped steel. Imagine a 8-inch diameter, 1/2" thick, solid steel chainring and you'll get an idea of how much it weighed

dddd

I think you're right about that, and I'm glad that I didn't struggle to build something like this when I had the same idea about 20-25 years ago.

What has occurred to me in more-recent years is that it's important that the leg muscle's effort be met with instant resistance when force/effort is increased, otherwise the bike would feel quite sluggish, and the physiological response of gearing down instantaneously would make the rider's effort inefficient imo.
Thus I am also suspicious of claims that a flexible frame or crankset will "store and recover" the pedaling effort lost to elastic flex, since the rider's increased leg/body force is not fully met by the anticipated resistance that would get the most power out of the rider's effort.

Similarly, gearing stategies that reduce chainring size similarly cause an "X-squared" (doubly increasing) drivetrain flex as felt at the pedals, one reason that I always set up bikes with short enough bb spindles so as to allow staying in the big ring while crossing over fully into lower ratios on the cassette/freewheel.
On many bikes I can literally feel the increase in drivetrain flex after shifting to the smaller ring, which alters the rider's "ignition timing requirement" WRT pedal position and realizes an immediate decrease in biomechanical/physiological efficiency imo.

The pictured crankset's "yield" effect in response to pedaling forces would seem to be orders-of-magnitude worse than even the flexiest of frame/crankarm/gearing setups as encountered on conventional-drivetrain bikes, but could be adjusted to yield according to a higher force-to-yield ratio or perhaps have the springs(?) tensioned to a high pre-load (eliminating yield altogether except when a maximal force is applied, or perhaps even according to an electronic algorithm(???).
I would have to ride the pictured bike to know how well this invention was developed. Perhaps then I would have a different opinion.

juvela

reminds one somewhat of the Hagen Allspeed Drive of the early 1970's.

Jeff Wills

Ah, so... the plot thickens. From https://www.zoxed.eu/photos/bikes_drives.html :

The Deal Drive







Hagen All-Speed

dddd

That crank sure aint pretty, but wow, there's a lot going on in there.

Reminds me somewhat of a VCR transport mechanism, Rube Goldberg at his very best!

Sixty Fiver

Staff parking actually.

juvela

the spokesperson for the Hagen was Fred Cox, placekicker for the Minnesota Vikings football team. was never able to see any connection there... ;^\