Force, Power and Human Operated Machines
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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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