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A cyclist will have the pedal spindle somewhere under the front part of their foot, usually around or just behind the ball of the foot. This means that the ankle is part of the driving movement - at a minimum, holding itself in a single position while the other muscles apply torque to the pedals, so the 'ankle muscles' are acting as a static stabilising force; or in some riders the ankle position changes throughout the pedal stroke, possibly helping to apply force around more of the pedal circle, possibly helping around the 'dead spots' where the pedals are at the 12 and 6 o'clock positions. This video illustrates it very well, from 3m08s: https://www.youtube.com/watch?v=E7K8VcBXUM4#t=3m08s

Are there any machines designed to utilise a similar mechanism? Off the top of my head something like a steam train doesn't, it uses the fewest, simplest parts to enable the linear movement of a piston to be translated to the circular movement of the wheels.

What would be the advantages/disadvantages of such a mechanical setup?

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This answer covers the disadvantages, as I am unable to find any advantages.

Your answer is something you've written into the question. "It uses the fewest simplest parts to enable the linear movement to be translated to circular movement of the wheels."

The reason cyclist use ankling is the "engine" driving the mechanism is very low powered and rarely has an excess of power available. One desires to transmit as much of that power to the drive system.

Creating a mechanism to mimic the ankling sequence would involve rods, bearings and additional weight. If there's sufficient power, or an excess of power, one need not add complexity and weight to have a well operating mechanism to convert linear to rotary movement.

If one is considering to implement such a mechanism on a bicycle, the weight is likely to be more of a factor than the complexity. Although the power output of the human engine is low, the mechanism would still require bearings and maintenance. I became familiar with ankling in the seventies and never developed the habit to use it consistently. When consciously applying the practice, it did allow for slightly better hill climbs.

Having such a mechanism might have forced me to adapt to the movements, but I suspect ergonomic factors may play an even bigger part of not having such a system on a bicycle. Even a few millimeters seat height change affects a rider. Attaching a forced foot pattern device to a cycle could be injurious.

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  • $\begingroup$ Thanks for this, interesting, especially the low power comment. The motivation for the question was 'Why don't cyclists have the pedal right under their ankle, taking the foot out of the process altogether' but that's not really in the scope of this stack. $\endgroup$
    – Wilskt
    Apr 20 '21 at 19:50
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    $\begingroup$ Part of the reason (perhaps all of the reason) is that the ankle absorbs some of the otherwise nearly dead stop at the bottom of the rotation. Back in the 70's, someone developed/marketed a bicycle with lever arms in place of pedals. The rotation was completely eliminated and replaced with movement cessation. Bad for the knees! This type of design appears periodically, then vanishes, as well it should. $\endgroup$
    – fred_dot_u
    Apr 20 '21 at 20:01
  • $\begingroup$ Also helps you push laterally on the pedal since our feet aren't usually bolted to the pedal like a steam train piston rod. Humans also don't stand on their heels. $\endgroup$
    – DKNguyen
    Apr 20 '21 at 22:39
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Ankling is to make up for the inefficiencies of turning a crank with a device designed to walk/run.

So unless you have a stupid designer who make the input power inefficient (thanks, evolution), there is no need to create complex linkages that help turn a crank that helps account for muscle contraction and extra movement. A crank is used to turn linear motion into rotary. The most efficient is turning rotary motion in to rotary, so if you really wanted to make it more efficient, you'd lose the linear motion entirely. Steam turbines versus old time piston steam engines.

Everything else is wasted motion and friction.

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