FIRGELLI APPLICATION CALCULATOR
Cable-Driven Telescopic Signal Mast Calculator
Design a cable-driven telescopic signal mast that slides straight upward. A linear actuator retracts to pull a cable downward, raising two nested mast stages through a moving pulley and cascade cable. Enter the required rise, tube length and moving weights, then compare actuator stroke and pulling force.
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How the telescopic mast cable drive works
The outer tube is fixed to the base. The main cable starts at a fixed anchor, travels under a pulley carried by the intermediate tube, passes over a fixed redirect pulley and connects to the actuator rod. Pulling the rod downward raises the intermediate tube by half the actuator movement.
A second cable is anchored to the outer tube, routed over a pulley at the top of the intermediate tube and attached to the bottom of the inner tube. This cascade makes the inner tube and signal head rise twice as far as the intermediate tube. The combined arrangement gives one inch of mast-head rise for each inch of actuator retraction.
Stroke and actuator pulling force
Required actuator stroke equals the requested mast-head rise for this particular cable routing. The ideal cable pull is the signal-head weight plus the inner-tube weight plus half the intermediate-tube weight. The calculator adds your measured equivalent resistance, applies 90% mechanical efficiency and a 1.5 design factor, then checks actuator force, stroke and upright mounting space.
The Super Duty family is the starting choice. Changing actuator family automatically selects its closest qualifying stroke unless the stroke is locked. Longer selected strokes need travel limits: the animation retains your requested mast rise rather than overextending the tubes.
Tube overlap, return motion and installation
The model uses equal-length tubes, two moving stages and a 2-inch collar offset per stage. Both interfaces must retain the entered overlap at full extension. The cutaway enlarges tube widths and pulley diameters to make the cable paths visible; these are not fabrication dimensions.
The actuator extends to pay out cable while gravity lowers the mast. A cable cannot push a stuck stage downward. Provide controlled lowering, guards, positive end stops and independent load retention. Separately verify cable and sheave ratings, anchors, bending, column buckling, wind loading, guying and the supporting base. Do not treat a matching actuator as approval of the complete mast structure.
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