Hopefully this has not been thought of before. This was to be my senior design project before my team members vetoed it, please discuss, and please excuse the roughness of the AutoCAD sketch.
The purpose of the crankset design is to allow the benefit of a crankset with a 275mm lever arm in the most powerful part of the pedal stroke while maintaining only a 175mm radius of rotation thereby allowing the rider to keep a high cadence while pushing a 275mm crank arm.
The 4 separate views are of the same crankset at different 90 degree rotations. The crankset will rotate at a fixed point at the base of the 175mm crank arm similar to current cranksets. The views have been offset only to avoid visual interference from one view to the next. The 175mm crank arm will be attached to a standard set of chainrings. The sprocket at the base of the 175mm crank arm will be fixed by a welded connection to a pin extruding from the center of the bottom bracket and not allowed to rotate (I really should have a top view to see this.) The 2nd sprocket will be fixed to the 100mm crank arm. The 100mm crank arm through bearing connections will be allowed to rotate with respect to the 175mm crank arm. The two sprockets will be identical in size and the, and rotation of the 100mm crank arm will be constrained by a chain connection from the 1st sprocket to the 2nd.
I think this should do it, 275mm crank arm with a radius of rotation of 175mm.
Interesting concept but it is not absolutely clear to me that this will offer the advantage you think it will. In fact, I predict it will not. The foot is still going to move in a complete circle, except the center of rotation will be moved 100 mm forward of the axle. So, even though the crank length appears to be 275 mm long, the downward motion is retarded by the backwards rotation of the 100mm portion. I personally think this would work exactly like a regular crank except it would move the crank circle forward 100 mm (probably interfering with steering on a regular bicycle) and loose a lot in stiffness. The only way to know is to build one and find out if it offers the advantages you think it might. But, let’s assume it works as you think it should.
I see several problems associated with manufacture, the most important would be to make the device reliable for many millions of revolutions. Then you have the problem of a patent, since the design is already in the public domain (you just put it there). If you don’t have a patent almost anyone can do it and do you not think Shimano will do this as soon as you prove it could be an economic success for a lot less money than you can do it?
But, if you are still interested in pursuing this, before I would worry about that I would build a set for yourself and ride them to see if they really offer the advantage you think they might. Sometimes things don’t work out quite as you think they would (and, rarely, sometimes you discover the concept is better than you thought it would be which was my experience). Even if it does live up to (or exceed) your expectations, then you still have the problem of sales and convincing the masses this radical new idea is more than just a gimmick.
Yeah, she rode side-mount-pedals (of a sort) with a significant drop from the thread-in point to the cleat. That’s actually the easiest way to do this.
Yeah, she rode side-mount-pedals (of a sort) with a significant drop from the thread-in point to the cleat. That’s actually the easiest way to do this.
What Paula did was substantially different than this idea. It did not extend the lever arm in front or shorten it in back but allowed this piece (and it was quite short) to rotate freely as a way of lowering the amount she had to raise her leg for any crank length.
I think this idea would do what you want it to do IF you could move the bottom bracket rearward by that 100mm. But in order to do that, you’ll need to move the rear wheel back, thus both messing up the balance of the bike, but also extending the wheelbase beyond legal.
I think this idea would do what you want it to do IF you could move the bottom bracket rearward by that 100mm. But in order to do that, you’ll need to move the rear wheel back, thus both messing up the balance of the bike, but also extending the wheelbase beyond legal.
As I think about this more it will not work. If one is going to change the crank length one must change the pedal speed. This design keeps the pedal speed constant as near as I can tell. What he wants to do is what Rotor cranks does but in reverse.
No, the engineer in me is saying that. The inventor in my says: If he still thinks it should work he should build one and see. Or, he should analyze it more carefully, based upon my thoughts if he thinks I might be right and doesn’t want to waste his time and money if I am right.
