Mechanical Systems & Control, Ratchet & Pawl, Cleats, Disc brakes Bicycle brakes.

Ratchet & Pawl The device below is called a ratchet and pawl. The wheel with the teeth is the ratchet, and the other object is the pawl. The ratchet and pawl is also a one way control system like the one way valve and cam cleats we discussed in previous sections.

Purpose of a Ratchet and pawl? The ratchet and pawl allows movement in one direction while preventing movement in the other direction. When the ratchet is rotated in one direction by the axle, the pawl slides up and climbs the curved edge of the teeth. As the pawl passes over the tip of each tooth, it falls down the flat edge of the tooth into the dip and a spring clicks it into a locking position. The gear cannot slip back as the straight edge and the spring loaded pawl block the motion of the gear, allowing rotation to occur only once the ratchet axle turns in the correct way again. Watch the videos below, kindly provided to us by Robocop and Older brother guy.

Examples of where Ratchets are used. Ratchets are useful in devices such as: i.Mechanical Jacks - ii.Winches - iii.Devices in mountain climbing iv.Hand tools - v.Fairground rollercoasters - (Some of the links you will have to copy into your browser)

The Disc brake Mechanical Systems and Control

Disc brakes

Different components of disc brakes. Components: 1.The brake pedal is a lever connected to a piston. 2.The piston is connected to a master cylinder filled with brake fluid. 3.The master cylinder is connected by pipes filled with brake fluid to slave cylinders with pistons on all four wheels. 4.The pistons are attached to callipers, which are gripping mechanisms of two levers mounted over each wheel of the car. 5.Brake pads made of metal covered with a friction material are attached to the end of each piston. 6.A cast Iron or carbon composite brake disc is attached to the wheel of the car. Disc brake

How does a disc brake system work? 1.When the driver presses on the brake pedal, the small input on the brake pedal exerts pressure on the brake fluid and the whole system. 2.The fluid in the system forces a equal pressure through the whole system into the pistons on each wheel. ( Pascal's Law) 3.The piston then squeezes two brake pads mounted on the callipers against the disc, which is mounted on the wheel. 4.Friction between the pads and the disc slows the car, causing the wheels to slow down, and the car eventually stops.

Videos to watch! Disc brakes - Disc brakes PART Disc brakes PART 2-

Bicycle brakes Mechanical systems and control

Bicycle brakes Most bicycles use rim brakes- a braking force is applied to the rim of the wheel. Rim brakes are cheap, easy to maintain and mechanically simple-nevertheless very effective control system.

Different components of a bicycle brake system. 1.Operates brakes from brake lever on handle bars. 2.As pressure is applied ( lever forced to the handlebars) a metal cable inside the handle is pulled tighter. 3.The metal cable is attached to two callipers above the rim of each wheel. 4.The callipers are pivoted by a single bolt above the tyre, long enough to reach the wheel. 5.Rubber brake blocks are attached to the callipers.

How does it work? 1.When the rider operates the brake handle, a pull action on the cable causes the callipers to pull together. 2.This causes brake blocks to apply pressure against the rim of the wheel. 3.The rubber creates friction, which converts kinetic energy into thermal energy ( heat), causing the bicycle to slow down and eventually stop.

Cleats Mechanical systems and control

What is a cleat? A cleat is a safety mechanism used to control movement of the rope used in a pulley. It secures the rope by pinching it between or locking it around two pieces of metal or plastic.

Jam cleats 1.The simplest type of cleat. 2.It has two arms around which you wrap a rope to fasten it. 3.When wrapped around these arms the rope is pinched in the V- shaped slot. 4.To release this cleat the rope is pulled in the opposite direction.

Cam cleats 1.Has two spring loaded cams that pinch the rope. 2.Ridges or teeth on the rope stop the rope from slipping backwards. 3.When the rope is given a tug in the right direction, the cams are released.

Clam Cleat 1.Has two curved halves which look like the two halves of a clam. 2.The rope is pinched between the two grooved pieces and held in place by ridges or teeth.