Q1. Figure 1 shows a triple reduction spur gear gearbox as per design workshop week 3. Gears
are labelled sequentially from the input side to the output, such that gear a is attached to the
input shaft and meshes with gear b and so forth until gear f which is attached to the output shaft.
The gear box is driven by an electric motor running at 6000 RPM, at 7kW and each gear mesh
loses 2% efficiency.
Figure 1: Gearbox Technical Drawing.
Table 1: All required parameters for gear train.
Gear
Module m (mm)
Teeth N
Face Width b (mm)
Pressure Angle (°)
Diameter d (mm)
Seed n (RPM)
Efficiency η
Power 𝑊𝑊̇ (W)
Torque T (Nm)
Pitchline Vel V (m/s)
Tangent Ft (N)
Radial Fr (N)
a
4
23
135
20
92
6000
1
7000
11.14
28.90
242.19
88.15
b
4
89
135
20
356
-1550.56
0.98
6860
42.25
28.90
237.35
86.39
c
5
17
95
20
85
-1550.56
1
6860
42.25
6.90
994.07
361.81
d
5
125
95
20
625
210.88
0.98
6722.8
304.42
6.90
974.19
354.58
e
6
21
175
20
126
210.88
1
6722.8
304.42
1.39
4832.29
1758.81
f
6
129
175
20
774
-34.33
0.98
6588.34
1832.64
1.39
4735.64
1723.63
With the additional information provided over the page, carry out the stress analysis of the shaft
carrying gears d and e, and determine the critical stress element. Note, this may occur at a stress
concentration, rather than the position of maximum internal force. Also, for ease of analysis,
ignore radial gear forces and only consider the tangential components (AS IN THE LECTURE,
THIS ASSUMPTION IS WRONG AND WE’LL CORRECT IT LATER IN THE
SEMESTER).
Figure 2: 3D schematic of gears and shafts.
Figure 3: Dimensioned drawing of shaft carrying gears e and d and carried by self-aligning
bearings at each end. All dimensions in mm. All steps filleted with 2mm radius.
EGB210: Applied Mechanics
Stress Concentration Factors
Figure 4.35, page 163
From: Juvinall, R.C. and Marshek, K.M.
(2011). Fundamentals of machine
component design. 5th Edition. John- Wiley
and Sons, Brisbane.