A specifier-grade method for sizing, motorising and integrating shading systems with intelligent building management — from Somfy tubular motor torque calculations to KNX, BACnet and Modbus interfaces, sensor logic and commissioning on South African commercial projects.
A specifier who writes 'supply motorised blinds' has deferred every decision that determines whether the system works. This masterclass gives registered architects and controls engineers a rigorous method to size tubular motors by torque, choose the control bus on feedback and integration grounds, design the power and cabling topology, integrate shading with the building management system over KNX, BACnet or Modbus, and build the sun, daylight and — critically — local high-wind logic that makes shading behave intelligently. All within the IEC 60335-2-97, SANS 10142-1 and SANS 10160-3 compliance frame that governs South African approval.
Motor sizing is where specification becomes engineering, and getting the torque calculation right is the single most important technical decision in motorisation. This lecture builds the torque calculation from first principles: the load the motor must overcome is the weight of the fabric or slat package plus the bottom bar acting at the radius of the loaded tube, and the required torque is that force multiplied by the effective radius, divided by mechanical efficiency, with a safety margin applied. We work the full calculation for a real roller blind — fabric mass per square metre, drop, width, tube diameter and the build-up of fabric on the tube that changes the effective radius — and select a Somfy motor from its Nm rating with the correct margin. We extend the method to the heavier cases that catch specifiers out: large external screens with windload, blackout fabrics, and curtain-track motors rated in pull-force rather than torque. A Johannesburg atrium where under-sized motors stalled on 4-metre drops anchors the consequences of skipping the calculation.
Torque sizing is the calculation that separates a specifier who engineers motorisation from one who guesses, and stalled, overheating or prematurely-failed motors are almost always traceable to a skipped or sloppy torque calculation. The physics is straightforward but must be applied with care. The motor on a roller blind must generate enough torque to rotate the tube and lift the suspended load. The load is the downward force F = m x g, where m is the total suspended mass (fabric area x fabric mass per square metre, plus the bottom bar/rail mass, plus any side-channel friction allowance) and g is 9.81 m/s2. That force acts at the radius at which the fabric leaves the tube, so the static torque demand is T = F x r, where r is the effective radius — and here is the subtlety that catches specifiers: r is not the bare tube radius but the radius to the outer wrap of fabric, which grows as fabric rolls onto the tube.
A 2.4 × 3.0 m screen-fabric blind: suspended mass 4.32 kg, F = 42.4 N; with build-up radius 0.030 m, T(tube) = 1.27 Nm; / 0.70 efficiency × 1.3 margin = 2.4 Nm required → select a quiet, conservative 6 Nm Sonesse 50.
Target audience: South African registered architects (SACAP), professional electrical and controls engineers (ECSA), interior design professionals (IID) and facade/shading specifiers responsible for motorised and BMS-integrated shading on commercial and institutional buildings.
Assessment: 10 application-based multiple-choice questions, minimum pass mark 70%. Certificate of completion on passing.
Your enrolment includes the full C21 package: the in-depth eBook, the practical how-to guide with the full assessment bank and per-lecture commissioning checklists, and the A4 quick-reference cheat sheet.