SACA Mechanical Power Transmission 4 — Questions and Answers
Question 1: A planetary gear system has a sun gear with 20 teeth, planet gears with 40 teeth, and a ring gear with 100 teeth. If the sun gear is the input and the ring gear is fixed, what is the gear ratio?
- 6:1 (Correct answer)
- 5:1
- 4:1
- 3:1
Correct answer: 6:1
With the ring gear fixed and sun gear as input, the ratio is (ring teeth / sun teeth) + 1 = (100/20) + 1 = 6:1.
Question 2: Which type of coupling is specifically designed to accommodate significant angular misalignment between two shafts?
- Sleeve coupling
- Oldham coupling
- Universal joint (U-joint) (Correct answer)
- Rigid flange coupling
Correct answer: Universal joint (U-joint)
Universal joints (U-joints) are designed to transmit torque between shafts at significant angular offsets, commonly used in driveshafts.
Question 3: In a flat belt drive, increasing the wrap angle of the belt on the pulley primarily affects which performance characteristic?
- Belt speed
- Power-to-weight ratio
- Friction-based torque transmission capacity (Correct answer)
- Belt width requirement
Correct answer: Friction-based torque transmission capacity
A greater wrap angle increases the contact arc, allowing more friction force and thus greater torque transmission before slippage occurs.
Question 4: What is the primary purpose of a backstop (holdback) device in a conveyor drive system?
- To limit maximum conveyor speed
- To prevent reverse rotation under load (Correct answer)
- To absorb shock loads during startup
- To synchronize multiple drive motors
Correct answer: To prevent reverse rotation under load
A backstop or holdback prevents the conveyor from running backward under load when the drive is stopped, protecting against uncontrolled reverse movement.
Question 5: Which gear geometry feature is measured by the 'pressure angle' in gear design?
- The helix angle of the tooth spiral
- The angle between the tooth profile and the pitch circle tangent (Correct answer)
- The angle of the gear shaft relative to horizontal
- The taper angle of bevel gear teeth
Correct answer: The angle between the tooth profile and the pitch circle tangent
Pressure angle defines the angle between the tooth's normal force direction and the tangent to the pitch circle, typically 14.5° or 20° for standard gears.
Question 6: A V-belt drive system begins slipping under load. Which corrective action would be MOST effective without replacing belts?
- Increase motor speed
- Reduce center distance to loosen the belt
- Adjust the center distance to restore proper tension (Correct answer)
- Replace the pulleys with larger diameters
Correct answer: Adjust the center distance to restore proper tension
Restoring proper belt tension by adjusting center distance is the most direct fix for belt slippage caused by insufficient tension.
Question 7: In power transmission, what does the term 'service factor' account for when selecting components?
- The efficiency loss due to lubrication
- Additional load capacity needed for application-specific shock, vibration, or duty cycle (Correct answer)
- The ratio of output speed to input speed
- Temperature correction for belt material stiffness
Correct answer: Additional load capacity needed for application-specific shock, vibration, or duty cycle
Service factors multiply the nominal load to account for real-world conditions like shock loads, frequent starts, or continuous heavy duty beyond rated conditions.
SACA Mechanical Power Transmission 4
A planetary gear system has a sun gear with 20 teeth, planet gears with 40 teeth, and a ring gear with 100 teeth.
If the sun gear is the input and the ring gear is fixed, what is the gear ratio?