A stepped-pulley drive changes shaft speed by moving a belt to a selected pair of pulley steps. For one selected pair, ideal speed ratio equals driver pitch diameter divided by driven pitch diameter; this reference adds an explicitly selected fractional speed-loss parameter.
Motion-control checks for actuator use
Actuator-driven shaft step adjustment mechanism needs a control review as well as a mechanical review. Voltage, current, switching, feedback, and limit behavior all affect whether the motion is repeatable in the real machine.
For structural members, the actuator load should be applied through brackets that do not introduce unintended bending. Check both static load and the extra load created when the mechanism starts, stops, or binds.
Speed should be checked as a loaded value whenever the application has meaningful force. A high-force actuator is often geared slower, so the correct choice is the one that meets both the load requirement and the timing requirement.
- Use loaded speed, not only no-load speed, when timing the motion.
- Confirm voltage, controller rating, and limit-switch behavior before wiring.
- Use feedback when synchronized or repeatable position control is required.
For FIRGELLI actuator control, use the linear actuator wiring diagram generator before wiring the final circuit and compare suitable actuator families in the FIRGELLI linear actuator range. If the machine already has an actuator, the linear actuator replacement finder can help shortlist replacements.
Selected Stepped-Pulley Belt Ratio Reference
Explore one selected stepped-pulley ratio, hypothetical speed loss and exact open-belt geometry.
Equation Used
- The belt is open and both pulleys rotate in the same direction.
- The selected ratio equals driver pitch diameter divided by driven pitch diameter.
- The selected speed-loss percentage directly reduces driven speed.
- Belt design, power capacity, tension, efficiency, loads, shifting and safety are excluded.
The ratio input represents a selected driver/driven pitch-diameter pair, not a complete pulley stack.
Selected open-belt step pair
The animation draws two pitch circles, their exact common external tangents and a continuous open belt. The driver and driven markers rotate in the same direction with the selected kinematic ratio after the entered fractional speed loss.
It shows one selected pair, not a complete historic step stack or a belt-shifting operation.
What the calculator determines
Select driver speed N₁, pitch-diameter ratio r = D₁/D₂ and a hypothetical speed-loss fraction s. The calculator reports effective speed ratio r(1−s), driven speed N₂, the ideal no-loss torque ratio 1/r, and the selected speed difference N₁r−N₂.
Selected speed identities
N₂ = N₁r(1−s/100); Rspeed = N₂/N₁; ideal torque ratio = 1/r; and ΔN = N₁r−N₂.
Selected-input arithmetic
At 1,750 rpm, r = 0.542857 and s = 0%, ideal and selected driven speed are 950 rpm, effective speed ratio is 0.542857, and the ideal no-loss torque ratio is about 1.842.
Intentionally partial mechanism
The selected loss percentage is an input, not a slip prediction. Real pitch diameters, belt section and length, wrap, tension, power rating, service factor, efficiency, bearing loads, pulley balance, guards, available discrete steps and shifting procedure require manufacturer design data.
Questions
Is 1/r the delivered torque multiplication?
No; it is an ideal no-loss kinematic ratio.
Does the calculator predict slip?
No.
Does the drawing show every step?
No; it shows the selected pair.
References & Further Reading
- Wikipedia contributors. Pulley. Wikipedia
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