EXPERIMENT No. 2

                                                                          EXPERIMENT No. 2

6.0 b)Geneva Mechanism:                                                                

This mechanism is used to convert rotary motion of driving link into intermittent rotary motion needed to be transmitted to the index table. This mechanism is used to feed the work (job) on turret lathe and machine tool indexing table. This mechanism consists of driving link ‘A’ which acts as a crank, It carries a pin which engages in a slot of the driven link ‘B’, which is called as Geneva wheel. The Geneva wheel has 4 to 16 slots as per the requirement of indexing table. When the crank (driving wheel) rotates one revolution, the Geneva rotates a fractional part of the revolution. When driven member has four slots, the driven member will rotate one quarter of revolution during one revolution of the driving link.

c)  ACKERMAN’S STEERING GEAR MECHANISM.:                                                                                    

The mechanism is based on four bar chain with two longer links RS and AB of unequal length. This linkage has only turning pair. When the vehicle is moving along a straight path the longer links RS and AB are parallel. and each of the shorter link RA and SB is inclined at an angle α , with longitudinal axis of the vehicle . When a  vehicle steers to the left the shorter link is to turn, there is an increase in angle alfa (α  ). When the vehicle is steering to the left , the positions of the gear are shown by dotted lines. In this position the lines of the front wheel axle intersect on the back wheel axle at I. for correct steering. When the vehicle is steering to the right the similar positions may be obtained. In order to satisfy the fundamental equation for correct steering the links SB and BA are suitably proportioned .  

                                                              

d) Foot operated air pump: The foot operated air pump is an inversion of single slider crank chain mechanism. It is based on oscillating cylinder  mechanism In this the force is applied on the foot rest leading to oscillating motion of link and cylinder, which causes alternative suction and compression of air in the cylinder. Fixed link is called base frame. Link 2 is piston with piston rod. Link 3 is a cylinder and link 4 is oscillating link called crank. The air pump is used for filling air in small tyres( inner tubes.)

 8.0      Observation Table

Name of part/ link	Description/Function of part/ link
a)    Bicycle freewheel sprocket mechanism
Main body	To support the mechanism
Pawl	To give freewheeling mode while anticlockwise pedaling and to give and to give motion to the rear axle when clockwise movement of the sprocket so that cycle can get positive motion.
Spring	To maintain the desired movements of the pawl. Get compressed due to anticlockwise rotation of the outer toothed rim
Outer toothed sprocket	The upper and lower pawl piece lock in ratchet groove of the outer toothed rim. Used to transmit motion to the rear axle. It engages with chain and transmits motion to rear axle.
	b)   Geneva Mechanism
Crank	driving link ‘A’ which acts as a crank, It carries a pin which engages in a slot of the driven link ‘B’, which is called as Geneva wheel. When the crank (driving wheel) rotates one revolution, the Geneva rotates a fractional part of the revolution.
Geneva Wheel	The Geneva wheel has 4 to 16 slots as per the requirement of indexing table. When driven member has four slots, the driven member will rotate one quarter of revolution during one revolution of the driving link.
	c)  ACKERMAN’S STEERING GEAR MECHANISM
Stub axle	Stub axles are connected to the front axle by king pins. Front wheels are mounted on stub axles arrangement for steering is connected to stub axles. Stub axle turns on kind pins. King pins is fitted in the front axle beam eye and is located and locked there by a taper cotter pin.
Tie rod	A tie rod is a slender structural rod that is used as a tie and capable of carrying tensile loads only. The tie rod transmits force from the steering center link or the rack gear to the steering knuckle and this will cause the wheel to turn then outer tie rod end connects with an adjusting sleeve, which allows the length of the tie rod to be adjustable and this adjustment is used to set a vehicle's alignment angle. The tie rod is part of the steering mechanism in a vehicle.
Front axle	Functions of front axle are listed below : (a) It supports the weight of front part of the vehicle. (b) It facilitates steering. (c) It absorbs shocks which are transmitted due to road surface irregularities. (d) It absorbs torque applied on it due to braking of vehicle.
	d) Foot operated air pump:
Oscillating Cylinder	the force is applied on the foot rest leading to oscillating motion of link and cylinder, which causes alternative suction and compression of air in the cylinder.
Spring	To bring the oscillating link to its original position.
Piston	Due to oscillating motion of cylinder , with the help of piston air is forced to go through the tube to inflate the tyre.

9.0       Student related Activity-

            1.

Tyre size	1188	1272	1354	1433	1547	1565
Air pressure	26	29	32	35	40	41

2. Ashoka Machord Private Limited, Greater Noida,      Ultraplast Chainbelts Private Limited, Faridabad,Standardized Designed Sprockets, Jay ngineering,  Mumbai, Ashoka Machine Tools Corporation, Greater Noida, United Engineering Industries, Chennai, Chennai, Malkar Industries, Mumbai, Mumbai, B. V. Transmission Industries, Mumbai, Gears & Gears, Mumbai, Spectra Plast India Pvt. Ltd., Coimbatore, Seema Conveyor Belts & Systems Pvt. Ltd., Mumbai, Unisoft Pheripherials, Rajkot, National Conveyors (India), Ludhiana, Ravi Transmission Products, Mumbai, Narayan Industries, Ahmedabad, Sahajanand Industries, Ahmedabad, S. R. Polychem, Pune , Sudarshan Gear, Rajkot.

10.0    Questions for confirmation of learning:

            1. Four bar chain.

2. This mechanism is used to convert rotary motion of driving link into intermittent rotary motion needed to be transmitted to the index table.

3. Single slider crank chain mechanism.

4. Mai body, Pawl, Spring, Outer toothed sprocket, Positioning washer, ball bearings, Front plate

11.0    1. Forward pedaling.

            2. continuous , intermittent.3 Four bar chain

Conclusion for foot operated air pump-  foot pumps are manually operated pumps driven by hand or foot via a handle or lever. This manual external force actuates an internal mechanism, which increases pressure for moving fluids such as gas, chemicals, or water. Hand lever and foot pedals are pushed up or down to begin the pump cycle, often requiring one stroke to draw the fluid and another stroke to discharge it, as is typical in many displacement pumps.

 12.0 1 If freewheel is not provided at rear wheel, the bicycle will move towards back side 

             during anticlockwise rotation of the peddle. That will affect the balancing of the  

            rider and as bicycle has not third wheel to stay on, the bicycle and rider will  

            collapse.

2.    During forward pedaling, sometimes pedals rotate in forward direction without carrying rear wheel. This happens when there is a slipping between  pawl and internal ratchet grooves, due to which engagement between outer sprocket and rear axle do not take place.

3.    If some ratchets of freewheel are worn out, slipping between ratchet groove and pawl will take place and motion will not be transmitted to the rear axle during slipping period.

4. Application in mopeds and light scooterates.
5. a) Spring and pawl should work in a desired way to give freewheeling mode.    

b) Ratchet grooves should be sharp enough to restrict the pawl from slipping.     

6.      This mechanism is used to feed the work (job) on turret lathe and machine tool indexing table.

7.      This mechanism is used to convert rotary motion of driving link into intermittent rotary motion needed to be transmitted to the index table.

8.    The Ackerman’s steering gear mechanism is much simpler than Davis gear. The whole mechanism of the Ackerman’s steering gear is on back of the front wheels; Where as in Davis steering gear it is in front of the wheels. The Ackerman’s steering gear consists of turning pairs, where as Davis steering gear consists of sliding members.

9.   Perfect steering-The intention of Ackermann geometry is to avoid the need for tyres to slip sideways when following the path around a curve.^[2] The geometrical solution to this is for all wheels to have their axles arranged as radii of a circle with a common centre point. As the rear wheels are fixed, this centre point must be on a line extended from the rear axle. Intersecting the axes of the front wheels on this line as well requires that the inside front wheel is turned, when steering, through a greater angle than the outside wheel.

10.     What is over steer and under steer- Under-steer and over-steer are vehicle  dynamics terms used to describe the sensitivity of a vehicle to steering. Simply put, over-steer is what occurs when a car turns (steers) by more than (over) the amount commanded by the driver. Conversely, under-steer is what occurs when a car steers less than (under) the amount commanded by the driver.

  11.     It is based on oscillating cylinder mechanism. If the spring is broken then cylinder will not return to its original position. And suction and compression stages will not take place.