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What are the relevant NEMA standards for calculating wind load torque on a rotating antenna system to properly size the azimuth/elevation drive motors?

 I'm specifying motors for a rotating parabolic antenna system (2m dish) in the U.S. I know the TIA-222 standard is for towers, but I've heard NEMA has standards for motor and gearbox sizing under wind load. Which specific NEMA standards (e.g., NEMA MG 1, NEMA ICS) cover the torque, duty cycle, and safety factor requirements for antenna positioning systems? How do I translate the wind force calculated from TIA-222 into the required motor torque, accounting for gearbox ratio, efficiency, and the need to breakaway from stiction after a storm?

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By Testing Answered 1 year ago

You're correct that TIA-222 provides the wind force. NEMA MG 1 (Motors and Generators) and NEMA ICS (Industrial Control Systems) govern motor performance and selection. Here's the workflow: 1) Use TIA-222 to calculate the total wind moment (torque) on the antenna at its worst-case orientation. 2) Divide this by your gear ratio to find the motor shaft torque required. 3) Apply a service factor (typically 1.5 to 2.0) for stiction, ice loading, and motor start-up. This gives your required motor torque. NEMA MG 1 defines motor torque capabilities (locked-rotor, breakdown). You must also consider duty cycle (NEMA classifications); antenna tracking is often intermittent. Select a NEMA-rated gearmotor whose published output torque exceeds your calculated value with the service factor. Don't forget to factor in drive efficiency (often 80-90%). For breakaway, ensure the motor's starting torque exceeds the static friction torque, which can be 2-3 times the running torque.

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