Rotary Systems
Design & Technology: AQA GCSE, topic 1.5.4
Cams
Rotary systems can change the direction, type and/or speed of motion.
Cams and followers
- Cams and followers change a rotary motion into a reciprocating motion.
- A cam is a shaped piece of material with a hole for a cam shaft.
- The cam is rotated with a cam shaft.
- A follower rests on the cam and travels up and down as the cam is rotated.
- A dwell is when the follower does not move even though the cam is still rotating.
Circular cam
- Different shaped cams give different types of motion...
- Circular cam:
- This is a circular disk with an off centre hole.
- When the cam is rotated the follower rises and falls smoothly.
Circular cam
Pear shaped cam
- Pear shaped cam:
- This is a pear or egg shaped cam with a hole.
- When the cam is rotated the follower rises and falls quickly and then dwells for a short time.
Pear shaped cam
Snail cam
- Snail cam:
- This is the shape of a snail shell with a hole.
- When the cam is rotated the follower rises steadily and then suddenly drops.
- Only works in one direction.
Followers
Rotary systems can change the direction, type and/or speed of motion.
CAMs and followers
- CAMs and followers change a rotary motion into a reciprocating motion.
- A CAM is a shaped piece of material with a hole for a CAM shaft.
- The CAM is rotated with a CAM shaft.
- A follower rests on the CAM and travels up and down as the CAM is rotated.
- A dwell is when the follower does not move even though the CAM is still rotating.
Knife edge follower
- There are different shaped followers for different jobs:
- Knife edge follower:
- Good for precision.
- Not good for heavy loads.
- Low friction - however tip wears easily.
Flat follower
- Flat follower:
- Not good for precision.
- Good for heavy loads.
- Large flat surface creates friction.
Roller follower
- Roller follower:
- Some precision.
- Good for heavy loads.
- Roller rotates reducing friction.
Types of followers
Gear Trains, Pulleys and Belts
Rotary systems can change the direction, type and/or speed of motion.
Simple gear trains
- Gear trains can be used to change the speed, direction and/or power of the output motion.
- Simple gear trains consist of two gears.
- The gears may be different sizes.
Simple gear trains cont.
- The driver gear (A) is attached to a motor.
- The driver gear (A) rotates, rotating the driven gear (B).
- Gear ratio = Teeth on gear A/Teeth on gear B
- If gear A is a larger gear then gear B will rotate faster.
A simple gear train
Pulleys and belts
- Pulley systems can be used to change the speed, direction and/or power of the output motion.
- A simple pulley system is made up of two pulley wheels and a belt.
- The pulley wheels may be different sizes.
Pulleys and belts cont.
- The driver pulley wheel (A) is attached to a motor.
- The driver pulley wheel (A) rotates turning the belt which turns the driven gear (B).
- A simple pulley system can be used to help lift a heavy load.
A simple pulley system
Test yourself on Rotary Systems
Which type of follow is good for precision, not good for heavy loads, low friction however tip wears easily?