Include formula to calculate desired gear ratio #1

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opened 2025-03-17 00:22:11 +01:00 by Filip · 0 comments

Filip commented

2025-03-17 00:22:11 +01:00

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from math import pi, sin, atan, degrees

# Configurable variables
power = 140
cadence = 75
crankarm_length = 0.1725
total_mass = 85
slope = 0.2
tire_circumference = 2.105

# Calculated values
circumference = crankarm_length * 2 * pi
pedal_speed = circumference * (cadence / 60)
pedal_force = power / pedal_speed
slope_radians = atan(slope)
slope_degrees = degrees(slope_radians)
gravity_force = total_mass * 9.80665 * sin(slope_radians)
pedal_torque = pedal_force * crankarm_length
wheel_radius = tire_circumference / (2 * pi)
wheel_torque = gravity_force * wheel_radius
gear_ratio = pedal_torque / wheel_torque
speed = (cadence / 60) * tire_circumference * gear_ratio

print(f"[{power} W] Desired pedal average force: {pedal_force}N - Desired cadence: {cadence} rpm")
print(f"Incline/Slope: {slope} - {slope * 100}% - {slope_degrees} degrees")
print(f"Slope force down: {gravity_force}N")
print(f"Required gear ratio: {gear_ratio}")
print(f"Speed: {speed} m/s - {speed * 3.6} km/h")

```py from math import pi, sin, atan, degrees # Configurable variables power = 140 cadence = 75 crankarm_length = 0.1725 total_mass = 85 slope = 0.2 tire_circumference = 2.105 # Calculated values circumference = crankarm_length * 2 * pi pedal_speed = circumference * (cadence / 60) pedal_force = power / pedal_speed slope_radians = atan(slope) slope_degrees = degrees(slope_radians) gravity_force = total_mass * 9.80665 * sin(slope_radians) pedal_torque = pedal_force * crankarm_length wheel_radius = tire_circumference / (2 * pi) wheel_torque = gravity_force * wheel_radius gear_ratio = pedal_torque / wheel_torque speed = (cadence / 60) * tire_circumference * gear_ratio print(f"[{power} W] Desired pedal average force: {pedal_force}N - Desired cadence: {cadence} rpm") print(f"Incline/Slope: {slope} - {slope * 100}% - {slope_degrees} degrees") print(f"Slope force down: {gravity_force}N") print(f"Required gear ratio: {gear_ratio}") print(f"Speed: {speed} m/s - {speed * 3.6} km/h") ```

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Reference: Filip/cyclinglib#1

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