New Blades Please!
Another idea inspired by the paralympics... but this time it's an idea for the actual athletes. Although it could form part of the thinking for everyday use prosthetics.
Watching the paralympic sprinters such as Oscar Pistorius, I was fascinated by their blade prostheses and how it affected their running and overall physical performance.
I noticed that particularly for the one legged sprinters, who therefore employed only one blade, a great deal of the effort they put in was in compensating for the balance issues, that is, not just standing up, but balancing the forces both generated, and to which they were subject between the two legs.
Firstly, the blades themselves are flat surfaces which describe a curve for the purposes of shock absorption, and springing off to the next stride, and in order to keep the weight down, the simplest design is used of one piece of carbon fibre or suitable plastic material, but this flat surface presents a sail effect as they cast the blade leg forward, which creates wind resistance, which the athlete's other leg does not... our legs being rounded in cross section, allowing the air to slip around even a larger volume of leg by being more aerodynamic than the blade on the other leg. This requires extra effort to overcome the wind resistance, especially as they are sprinters who are attempting to move the leg through the air very quickly... so any gains made by having a more simple one piece design may be cancelled out by this effect.True Blades
To Counter this, I think that the calf/shin area of the blade needs to be turned 90 degrees in order that the profile of the blade cutting into the air is ultra slim.
And this requires that both the strength and flexibility aspects of the blade have to be accounted for by other means, as my hastily drawn sketches show.
The first sketch (1)
shows a blade design where the back is a thin tube of the appropriate material incorporating the desired strength/flex properties, on which are anchored shorter lengths of tube projecting horizontally forward, where a shorter bar of the tube is fixed at the front. Several of these forward projected tubes with bars are placed at regular intervals throughout the height of the blade, with these collection of short bars following the same line at the front of the blade, but therefore not being joined to each other, but rather with regular gaps between them. Creating the overall effect of a single continuous tube at the back of the blade, and a tube with breaks at the front.
Between these gaps, or breaks, hard rubber balls are placed which will be compressed between the bars as the weight of the athlete is applied, and springing back out to shape when the weight is released, so assisting the propulsion of the athlete as he runs.
The back tube provides most of the strength and only a small amount of the flexibility, but the front tube/ball arrangement provides less strength, but more flexibility, until the weight is applied, causing the front tube to gain strength as the whole arrangement closes up and stiffens.
The second sketch (2)
provides the same effect for the athlete, but by alternative means.
Here, the whole arrangement is made of tubes, still providing the slim frontal profile, but the blade compresses and springs by means of each shorter tube, anchored to the long back tube, but able to move through a collar which attaches the other end of this short tube to the next a limited distance and returning to position by a spring located inside the collar, and attached to the tube to which the next tube is also attached, with the cumulative compression and release having the same effect as the previous blade.A Weighty Issue
And one final thing... I observed that the athletes upper leg- the thigh- where they still had them, moved outward and round from back to front as the leg with the blade moved forward, which the other whole leg did not... and this I think, was because the leg has one other effect which a blade does not account for, namely the weight of the lower leg and foot, which the running action uses to generate force. Because when we run, we lift our legs and throw them forward, which amplifies the effect of the weight of the shin and foot and pulls the whole leg straight forward, against, the natural action of the hip ball and socket arrangement, which without the weight of this lower portion of the leg, wants to move in the manner described earlier, meaning that the athlete has to compensate by forcing the leg more forward than out, and not letting it be pulled naturally that way, and this extra effort is transferred to the other leg, through a twisting motion of the torso, which has to be corrected by the upper body muscles.
So, counteract this, the addition of a simple sliding weight on the toe of the blade (3)
can recreate this effect, which, if calibrated to the athletes physique, until balance is achieved, can reduce the effort required to run, as more of the force and energy applied goes to propelling the athlete forward rather than countering this unbalanced twisting effect.
The weight is situated on the toe, and mounted on a rod, along which it can move forward and back along the foot plate, and when the athlete is at rest, the weight is held at the ankle area by a spring, so it does not require undue effort to lift the foot, and cast it forward... but when he does, the weight is thrown out toward the toe end, stretching the spring and the force this flung weight generates pulls the leg straight from the hip, and in the racing line of the athlete along his desired path