R05222106-mechanisms-and-mechanical-design

Set No. 1

Code No: R05222106

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 MECHANISMS AND MECHANICAL DESIGN (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. A nose wheel-assembly for a small aircraft is shown in figure 1. Classify the motion of this four-bar mechanism based on the configuration of the links.

Figure 1 2. (a) Why watt mechanism is so common to be used to generate an approximate straight line motion ? (b) Show that for the Tchebicheff straight line motion the point P which bisects the link BC will lie on a straight line parallel to AD when it is directly above A, D and the mid-point of AD, if the proportions of the links are BC : AD : AB :: 1 : 2 : 2.5. 3. A petrol engine has a stroke of 120 mm and connecting rod is 3 times the crank length. The crank rotates at 1500 r.p.m. in clockwise Determine: (a) Velocity and acceleration of the piston, and (b) Angular velocity and angular acceleration of the connecting rod, when the piston has traveled one-fourth of its stroke from I.D.C. 4. Locate all the instant centres for the mechanism shown in figure 4. Determine the linear velocity of slider B and angular velocity link AC. When the crank rotates at 60 rpm.

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Set No. 1

Code No: R05222106

Figure 4 5. The cam rotating clockwise at a uniform speed of 500 rpm with minimum radius is 40 mm and the line of stroke of the follow is offset by 15 mm from the axis of the cam and the displacement of the follower is to take place with uniform and equal acceleration and retardation on both the outward and the return stroke with the following data: (a) follower to move outward through a distance of 20 mm during 1200 of rotation (b) dwell for next 600 (c) return to initial position during 900 and dwell for the remaining 900 of rotation. Then determine maximum velocity and acceleration during out ward stroke and return stroke. [16] 6. The following data is related to symmetrical circular arc cam operating a flat faced follower: Least radius of cam = 28 mm, total lift = 20 mm, angle of lift = 750 , nose radius = 5 mm and speed of the cam = 300 rpm. Find (a) acceleration of the follower at the beginning of the lift, (b) at the end of contact with the circular flank, (c) at the beginning of the contact with the nose and (d) at the apex of the nose

[16]

7. (a) What are the differences between the type of assembly generally used in running fits and interference fits? Explain (b) Calculate maximum and minimum clearance for an assembly specified by 45 H7-g6. [8+8] 2 of 3

Set No. 1

Code No: R05222106

8. (a) Draw the diagram of a gear tooth and explain the nomenclature of gear and define all the terms. (b) What is beam strength of gear teeth? Explain the Lewis equation for the estimation of beam strength. [8+8] ⋆⋆⋆⋆⋆

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Set No. 2

Code No: R05222106

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 MECHANISMS AND MECHANICAL DESIGN (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define a fluid link and give any two examples. (b) Which of the following are the kinematic chains? i. figure 1(b)i

Figure 1(b)i ii. figure 1(b)ii

Figure 1(b)ii iii. figure 1(b)iii

Figure 1(b)iii iv. figure 1(b)iv

Figure 1(b)iv 1 of 3

Set No. 2

Code No: R05222106

2. The distance between the fixed centres O and O1 of a Watt’s straight line motion, as shown in figure 2 is 250 mm. The lengths of the three moving links OB, BA and AO1 are 150 mm. 15 mm and 100 mm respectively. Find the position of a point P on BA which gives the best straight line motion.

Figure 2 3. The mechanism of a variable-stroke feed pump is shown in figure 3. The drive is taken from the crank OA to the pin B on the connecting rod CBD. The end C of the connecting rod carries a die-block which moves along the curved slotted link EGF. The radius of curvature of the slot is equal to the length of the connecting rod CD and the stroke of the feed pump may be varied by rotating the slotted link about the fixed fulcrum G. If the crank OA makes 225 r.p.m. find for the given position of the mechanism. (a) the velocity of acceleration of the piston D, (b) the angular velocity and angular acceleration of the links AB and CD.

Figure 3 4. Figure 4 shows the mechanism of a moulding press used in plastics. The crank OA rotates counter clockwise from the horizontal through about 1500 , dragging with it the crank O1 B. Movement continues until OA and AB are in line. The crank O1 B operates, through the link BC, a ram at C constrained to move vertically. Determine the velocity ratio of C to A when OA is in its initial horizontal position. Use instant centre method.

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Set No. 2

Code No: R05222106

Figure 4 5. (a) Explain the functions of cams and followers. What are different applications cams in automobiles. (b) Derive the equations for the estimation of maximum acceleration and maximum velocity if the rotation of the follower follows simple harmonic motion. [8+8] 6. Derive the expressions for the displacement, velocity and acceleration for a tangent cam operating a radial translating follower (a) when the contact is on the straight flank and (b) when the contact is on circular nose.

[16]

7. An engine indicator has a plunger diameter of 20 mm. The indicator spring attached to the plunger is to be compressed 12 mm, when the steam pressure acting on the plunger is 5 N/ mm2 . Assume a stress in the wire as 460 N/ mm2 , and the mean diameter of the coil is three times that of wire diameter, Find the diameter of the wire, mean diameter of the coil and number of turns required. Take the modulus of rigidity as 84 kN/ mm2 . [16] 8. (a) Discuss the design procedure for helical gear from first principles. (b) Differentiate between bevel gears and warm gears with suitable applications. [8+8] ⋆⋆⋆⋆⋆

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Set No. 3

Code No: R05222106

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 MECHANISMS AND MECHANICAL DESIGN (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Define a rigid Kinematic link and give any two examples (b) Which of the following are Kinematic chains? Justify your Answer. (a) figure 1a

Figure 1a (b) figure 1b

Figure 1b (c) figure 1c

Figure 1c (d) figure 1d

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Set No. 3

Code No: R05222106

Figure 1d 2. (a) Under what conditions Scott-Russel mechanism traces out a straight line and an Ellipse. (b) A circle has OR as its diameter and a point Q lies on its circumference. Another point P lies on the line OQ produced. If OQ turns about O as centre and the product OQ . OP remains constant, show that the point P moves along a straight line perpendicular to the diameter OR. 3. The crank of an oil engine is 18.75 cm. long, the connecting rod is 82.5 cm. long and the crank rotates at a uniform speed of 310 r.p.m. Calculate the velocity and the acceleration of the piston for crank positions of 450 and 900 . 4. (a) State and prove Kennedy’s theorem. (b) Locate all the instant centres of the toggle press mechanism shown in figure4 The crank AB is rotating at a speed of 120 r.p.m. The dimensions of the various links are as follows : AB = 30 mm ; BC = 80 mm ; CD = 45 mm ; and CE = 120 mm. Find the velocity of slider E and angular velocity of CE. Use instant centre method.

Figure 4 5. Draw the profile of the cam when the roller follower moves with cycloidal motion during outstroke and return stroke as given below: (a) out stroke with maximum displacement of 31.4 mm during 1800 of rotation, (b) return stroke for the next 1500 of rotation, dwell for the remaining 300 of rotation. 2 of 3

Set No. 3

Code No: R05222106

The minimum radius of the cam is 15 mm and the roller diameter of the follower is 10 mm. The axis of the follower is offset by 10 mm towards right from the axis of the cam shaft. And also calculate the maximum velocity and maximum acceleration if the speed of the cam shaft is 100 rpm. [16] 6. A symmetrical tangent cam operating a roller follower has the following specifications. Radius of the base circle of cam = 40 mm, roller radius = 20 mm, angle of ascent = 750 , total lift = 20 mm, speed of the cam shaft = 300 rpm. Determine (a) the principal dimensions of the cam, (b) the equation for the displacement curve, when the follower is in contact with the straight flank, and (c) acceleration of the follower when it is in contact with the straight flank where it merges into the circular nose. [16] 7. (a) What are different types of helical springs used in automobiles? Explain their uses. (b) A helical spring is made from a wire of 6 mm diameter and has outside diameter of 75 mm. If the permissible shear stress is 350 N/mm2 and modulus of rigidity 84 N/mm2 , find the axial load, which the spring can carry and the deflection per active turn. i. by considering the effect of curvature and ii. considering the effect of curvature.

[6+10]

8. (a) Describe the design procedure of bevel gears and draw the suitable figures required. (b) Explain different applications of warm gears and helical gears in automobile industries and discuss their materials of manufacture. [8+8] ⋆⋆⋆⋆⋆

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Set No. 4

Code No: R05222106

II B.Tech II Semester Supplimentary Examinations, Aug/Sep 2008 MECHANISMS AND MECHANICAL DESIGN (Aeronautical Engineering) Time: 3 hours Max Marks: 80 Answer any FIVE Questions All Questions carry equal marks ⋆⋆⋆⋆⋆ 1. (a) Discuss witht the help of neat sketches the parallelogram linkage and Deltoid linkage. Discuss also the Inversions of the linkages. (b) Given any two kinematic chains which satisfy the relation l=2/3(j+2). What are the exceptions for the relation? 2. (a) What are straight line motion mechanisms? How are they classified? (b) Describe grasshopper mechanism with a neat sketch and prove that the tracing point describes an approximate straight line motion. 3. A quick return mechanism of a shaper is shown in figure 3. The crank O2 A rotates at 40 r.p.m. in the counter-clockwise direction. Determine the linear velocity of the cutting tool when the crank O2 A is at 45o with the horizontal. All dimensions are given in the figure.

Figure 3 4. Locate all the instant centres of an oscillating cylinder engine mechanism for any one configuration and discuss the velocity analysis of the mechanism. Assume the link proportions and the speed of the crank. 5. (a) Explain the functions of cams and followers. What are different applications cams in automobiles. 1 of 2

Set No. 4

Code No: R05222106

(b) Derive the equations for the estimation of maximum acceleration and maximum velocity if the rotation of the follower follows simple harmonic motion. [8+8] 6. (a) Derive the equation for the estimation of maximum velocity and maximum acceleration for circular arc cam with circular flank (b) Draw the profile of tangent cam with circular flank and explain the terminology and functionality of the cam [8+8] 7. (a) What are the differences between the type of assembly generally used in running fits and interference fits? Explain (b) Calculate maximum and minimum clearance for an assembly specified by 45 H7-g6. [8+8] 8. In an epicyclic gear train, an arm carries two wheels A and B having 36 and 45 teeth respectively. If the arm rotates at 150 rpm in the anticlock wise direction about the centre of the wheel A and is fixed, determine the speed of wheel B. If the wheel A instead of being fixed, makes 300 rpm in the clockwise direction, what will be the speed of B. [16] ⋆⋆⋆⋆⋆

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