GATE Agricultural Engineering Farm Machinery Syllabus

Farm Machinery syllabus — full chapter and topic list

Expand any chapter to see its topics and sub-topics. This is the whole examinable outline for Farm Machinery in GATE Agricultural Engineering, not a summary of it.

1. 1

   Machine Design

   3 topics

   • Design and selection of machine elements
     • gears
     • pulleys
     • chains
     • sprockets
     • belts
   • Overload safety devices
     • used in farm machinery
   • Measurement of force, stress, torque, speed, displacement and acceleration on machine elements
     • shafts
     • couplings
     • keys
     • bearings
     • knuckle joints
2. 2

   Farm Machinery

   5 topics

   • Soil tillage
     • forces acting on a tillage tool
   • Hitch systems and hitching of tillage implements
   • Functional requirements, principles of working, construction and operation of manual, animal and power operated equipment
     • tillage
     • sowing
     • planting
     • fertilizer application
     • inter-cultivation
     • spraying
     • mowing
     • chaff cutting
     • harvesting
     • threshing
   • Calculation of performance parameters
     • field capacity
     • efficiency
     • application rate
     • losses
   • Cost analysis of implements and tractors

Farm Machinery flashcards for GATE Agricultural Engineering

18 of 49 cards from the Farm Machinery deck — real questions with worked answers.

1. In machine element design, what are the two principal modes of failure that govern the design of a component, and how do they differ?

   Failure by yielding (permanent plastic deformation when stress exceeds yield strength, governed by static strength) and failure by fracture/fatigue (sudden breakage under fluctuating loads below yield, governed by endurance strength). Ductile materials are typically designed against yielding; brittle materials against fracture.

2. Define the factor of safety (FoS) for a machine element and give its formula in terms of stresses.

   Factor of safety is the ratio of a material's limiting (failure) stress to the allowable (working) stress: $$FoS = \frac{\sigma_{failure}}{\sigma_{allowable}}$$ For ductile materials $\sigma_{failure}$ is the yield stress; for brittle materials it is the ultimate stress.

3. What is the law of gearing (fundamental condition for constant velocity ratio)?

   For a constant angular velocity ratio between two meshing gears, the common normal to the tooth profiles at the point of contact must always pass through a fixed point on the line of centres called the pitch point. Involute and cycloidal profiles satisfy this law.

4. State the relationship between module $m$, pitch circle diameter $d$, and number of teeth $T$ of a spur gear.

   $$m = \frac{d}{T}$$ where module $m$ (in mm) is the ratio of pitch circle diameter to number of teeth. Circular pitch $p_c = \pi m$ and diametral pitch $p_d = \frac{T}{d} = \frac{1}{m}$ (in inch units).

5. Write the Lewis equation for the beam (bending) strength of a gear tooth.

   $$W_t = \sigma_b \, b \, m \, y$$ where $W_t$ = tangential tooth load, $\sigma_b$ = allowable bending (working) stress, $b$ = face width, $m$ = module, and $y$ = Lewis form factor. The tooth is treated as a cantilever beam of uniform strength.

6. Give the velocity ratio for a simple gear train of a driver with $T_1$ teeth and a driven gear with $T_2$ teeth.

   $$VR = \frac{N_1}{N_2} = \frac{T_2}{T_1}$$ The speed ratio is inversely proportional to the number of teeth (and to the pitch circle diameters). Idler gears in between do not change the magnitude of the velocity ratio.

7. Classify gears by the relative position of their shaft axes, giving one example of each type.

   Parallel shafts: spur and helical gears. Intersecting shafts: bevel gears (straight, spiral). Non-parallel non-intersecting (skew) shafts: worm-and-worm-wheel and hypoid gears.

8. What is the formula for belt tension ratio in a flat or V-belt drive (Eytelwein's / capstan equation)?

   For a flat belt: $$\frac{T_1}{T_2} = e^{\mu \theta}$$ and for a V-belt: $$\frac{T_1}{T_2} = e^{\mu \theta / \sin(\beta)}$$ where $T_1$ = tight-side tension, $T_2$ = slack-side tension, $\mu$ = coefficient of friction, $\theta$ = angle of wrap (rad), and $2\beta$ = groove angle.

9. Write the expression for power transmitted by a belt drive in terms of belt tensions and belt velocity.

   $$P = (T_1 - T_2)\,v$$ where $P$ = power (W), $T_1, T_2$ = tight- and slack-side tensions (N), and $v$ = belt velocity (m/s). $(T_1 - T_2)$ is the effective driving (net) tension.

10. How is the centrifugal tension in a belt calculated, and what is its effect on power transmission?

    $$T_c = m v^{2}$$ where $m$ = mass of belt per unit length (kg/m) and $v$ = belt speed (m/s). Centrifugal tension adds equally to both sides, reduces the effective driving tension, and the maximum power occurs when $T_{max} = 3 T_c$, i.e. $v = \sqrt{T_{max}/(3m)}$.

11. Distinguish between an open belt drive and a crossed belt drive.

    In an open belt drive both pulleys rotate in the same direction (used for parallel shafts rotating alike). In a crossed belt drive the belt is crossed so the driven pulley rotates in the opposite direction to the driver; the crossing causes more wear but allows reversal of rotation.

12. What is creep in a belt drive and what causes it?

    Creep is the small relative motion (slip) between the belt and pulley caused by the alternate elongation and contraction of the belt as it passes from the tight side to the slack side. It reduces the velocity ratio slightly (about 1\%) and is distinct from gross slip.

13. State the formula for the length of a chain in terms of pitch and number of links.

    $$L = K \cdot p$$ where $L$ = chain length, $p$ = chain pitch (distance between adjacent roller centres), and $K$ = number of chain links. The pitch line is the line through the roller centres, equal to the sprocket pitch circle at the wrap.

14. What is the chordal (polygonal) action in a chain-and-sprocket drive?

    Chordal action is the periodic rise and fall of the chain pitch line (and the resulting variation in chain speed) as the chain wraps around the polygonal sprocket. It causes velocity fluctuation that decreases as the number of sprocket teeth increases; a minimum of about 17–25 teeth is recommended.

15. Give the velocity ratio of a chain drive in terms of sprocket teeth.

    $$VR = \frac{N_1}{N_2} = \frac{T_2}{T_1}$$ where $T_1, T_2$ are the numbers of teeth on the driving and driven sprockets and $N_1, N_2$ are their speeds. Chain drives give a positive (non-slip) constant average velocity ratio.

16. List three advantages of chain drives over belt drives.

    1) No slip, giving a positive and constant velocity ratio. 2) Higher transmission efficiency (~96–98\%) and ability to transmit large power. 3) Compact (shorter centre distance) and can drive several shafts from one chain; also less load on shafts than tight belt drives.

17. What is the function of an overload safety device (slip/safety clutch) in farm machinery, and name three common types.

    It protects the machine and prime mover from damage by disconnecting the drive or limiting the torque when an overload (e.g. obstruction) occurs. Common types: shear-pin (bolt) device, friction (slip) clutch, jump/ratchet (spring-loaded jaw) clutch, and the over-running (free-wheel) clutch.

18. How does a shear-pin overload device work, and what is its main limitation?

    A shear pin connects the drive members and is designed to shear when torque exceeds a preset limit, breaking the drive to prevent damage. Limitation: the pin must be replaced after each overload, causing downtime; it also gives only one protection event per pin.

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