There was a strong wish for a crankset in CNC, in nice and strong - a "own" crankset.

 

What is the ideal structure of a crankset ?

 

Is it hollowtech?

Is it with steel, aluminium, maybe carbon?

 

Due to the pedalthreads and the axle-profile there are aluminiumparts necessary. To avoid to have a combination of  3 different components, aluminium is the best solution. One singe piece of aluminium.

 

If you attach two pieces together, welding, pressing or clamping - there is always the risk, that this joint fails. The best engineering is, to avoid this joints. That's why every crankarm is from a single piece of aluminium.

 

The raw material is a round profile. This promises a solid and ideal structure of the raw aluminum.

 

If you look at a crankarm like on a limb of a tree, there are 2 kinds of loads on it.

 

On the left side you see how the crankset gets loaded under pedaling. This results in the 2 kinds of loads seen on picture 2 and 3.

 

  • 1. kind of load is seen in the middle, a normal force
  • 2. kind of load is seen on the left, a torque on the crankarm

 

To handle best with the first load the crankarm has to have a massive structure on the side of the main axle. The more material there is, the more resistance it has against load 1. The material on the side of the pedal does not play a huge role in this kind of load.

 

To maximize the resistance for load 1, the crankset is made with a conical shape. This also looks graceful.

 

 

Addional to this, there is a small trick:

 

Like you can see on the picture on the left, there is a diagonal rib in the H-profile. This gives even better stiffness then a hollow-construction, because this does not allow the outer parts to move.

 

 

 

 

 

 

Exactly like the old houses have it.

 

And this buildings last now for hundreds of years

To maximize the resistance against load 2, the rest of the crankset has to have lots of material as far away from the middle, the neutral area.

 

That's why the Rocksteady crankarms are drilled out in the middle, this saves about 15 g per side, without any restriction for stiffness and durability.

 

The next point is the clamp of the left arm and the axle.

 

The best, easiest and most noiseless combination of this two parts is the same like shimano cranks have. 

 

With one difference: I use a 10mm hollow titan bolt. This gives a lot of clamping force.

 

To improve the clamping force further, the bolt has to be as near as possible to the axle outer surface. That's why the profile of the axle is interupted in this area, and the titan bolt can come as close as possible.