Power Transmission

Moving power and torque through a drivetrain: gears and gear trains, bearings, belts/chains/clutches/brakes/power screws, shafts and keys, and motors/engines.

What the problems look like

Power-torque-speed bookkeeping through components — gear ratios and forces; bearing life (L10); shaft sizing under combined torsion and bending plus key shear; belts/chains/clutches/brakes/power screws (tension, torque capacity, lead/efficiency); and motor/engine power. Calculation-based.

By exam day you should be able to —

• work gear trains: ratios, output torque/speed, tangential/radial/separating forces;
• compute bearing life: L10 = (C/P)^p (p = 3 ball, 10/3 roller), load-life trade;
• size a shaft for combined torsion + bending and check keys (shear/bearing);
• handle belts/chains/clutches/brakes/power screws (tension ratio, torque capacity, power-screw lead & efficiency);
• compute motor/engine power — P = Tω, HP = T·N / 5252.

Where people lose points

• Gear ratio inverted — mixing up the speed vs. torque direction.
• Gear tooth forces — tangential W_t = T/r, radial W_r = W_t·tanφ, resultant W_t/cosφ; pressure-angle φ confusion.
• Bearing-life exponent p — using 3 for a roller bearing (it's 10/3) or vice versa.
• Bearing-life units — L10 is in millions of revolutions; converting to hours needs the rpm (×60). Dropping that conversion is common.
• HP = T·N/5252 unit slips (torque in lb-ft, speed in rpm).
• Power screw self-locking / efficiency handling.
• Key failure mode — shear vs. bearing.

Have these at your fingertips

L10 = (C/P)^p, HP = T·N/5252, and the gear-force relations — plus where they sit in the Handbook.

Going deeper

• Power transmission — gears, bearings & shafts

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