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# Force, Power and Human Operated Machines

For man operated machines the force and power must be kept within certain limits.

• for a sitting person with a solid backrest the maximum horizontal force acting on a pedal is typically 1000 N
• for a sitting person the maximum vertical force acting on a pedal is typically 300 N
• for a standing person the maximum vertical force acting on a pedal is typically 500 N
• for a standing person the maximum force required to repeatedly act on a vertical level - like a pump - should not exceed 90 - 100 N. The frequency should not exceed 20 beats per minute
• for a standing person operating a rotating wheel or crank arm - the length of the arm (or radius of the wheel) should be approximately 0.4 m and maximum force should not exceed 130 N. The wheel or crank arm speed should not exceed 25 - 30 rpm. The center of the axle should be at approximately level h = 1 m.

The power produced by a force acting on a rotating wheel or crank shaft can be calculated as

P = F r π nrpm / 30                 (1)

where

P = power (W)

F = force (N)

π = 3.14...

nrpm = rotations per minute (rpm, 1/min)

The power produced by a person at ideal conditions as indicated above can be calculated as

P = (130 N) (0.4 m) π (25 rpm)/ 30

= 136 W

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