redesign assignment utwente IDE first year construction

1. CONSTRUCTION
TRANSMISSION RE-DESIGN ASSIGNMENT
COURSE ID: 201500230

2. 2017nov 2
LEARNING GOAL
Use a practical example of a servo
motor to apply knowledge learned in
lecture 3 and 4:
 Kinematics of gears
 Mechanical drives – Spur gear
design.
 Electric Motor
GOAL:
1) Re-design the transmission of a
servo-motor considering changes in
operating condition – Torque/speed
changes.
2) Apply structured design steps and
calculations on stress factors to
motivate new gear dimensions, OR
3) Select a different material for the
gears.

3. 3
LEARNING GOAL
https://www.youtube.com/watch?v=_FP1u
DmUhjk&t=1s

4. 2017nov 4
WHAT YOU RECEIVE
You receive:
 An assignment which you need to
work in groups of two.
 You also ‘borrow’ a motor which
you need to return on the date of
the final exam.
REQUIRED:
1) A 10-page max. report which you need
to upload in Canvas (a link will be
created to assist you to do this).
2) The report should be prepared in
word/pdf.
3) It should document your logic/steps for
the re-design assignment.
4) 20% of total grade of construction.

5. 2019nov 5
TASKS NEEDED
STEPS
Prerequisites:
 Find a colleague to work with.
 You only do the tasks which are
marked (unique for different
groups).
Step 1:
 Open/disassembly the servo motor.
 Sketch the gear stages, before taking
apart the gear one-by-one.
 Take apart the gears and measure
their dimensions.
 Take photos/videos for your memory,
i.e. different stages, how they mesh,
etc.
 The photos should help you assemble
the motor back to its original state.
 NOTE: re-assemble back the gears
before handing it back during the
exam (01/02/2023)

6. 2019nov 6
TOOLS NEEDED FOR DISASSEMBLY AT HOME
1) Vernier Caliper: 2) Screwdriver set:

7. 2019nov 7
EXAMPLE OF IMAGES SHOWING GEAR STAGES!
Pinion
(motor)
Pinion
(motor)

8. 2017nov 8
TASK LIST (MANDATORY FOR ALL GROUPS)
STEPS
Task 1: Gear kinematics
 Make basic calculations to
determine gear dimensions,
number of teeth, gear (face)
width,…
 You will need the calculations to
compute the velocity ratio (VR),
train value (TV), torque/speed
transmitted per stages.
 For an inspiration, use the slide
from lecture 3 on kinematics of
gears.

9. 2019nov 9
KINEMATICS OF GEARS
DIMENSIONS
https://www.myodesie.com/wiki/index/retur
nEntry/id/3000

10. 2019nov 10
KINEMATICS OF GEARS
DIMENSIONS
Metric module system DIN867
table is for standard gears.
 m - metric module (mm)
 D - pitch diameter (mm)
 Do - outside diameter (top)
 DR - root diameter (bottom)
 ht - height of tooth
 hk - projected tooth height
 t - tooth thickness
D = mN
DO = mN + 2m
DR = D − 2b
ht = a + b
hk = a + a
t = π. m/2
Outside Diameter
Root Diameter
Whole Depth
Working Depth
Tooth Thickness
Pitch Diameter
Preferred values for m
0,5 0,8 1 1,25 1,5 2,5 3 4 5 6 8 10 12 16 20 25 32 40 50

11. 2017nov 11
TASK LIST (MANDATORY FOR ALL GROUPS)
STEPS
Task 2: Velocity ratios, TV
 Calculate the velocity ratio (VR), train value (TV), torque/speed
transmitted per stages.
Pinion – Stage 2
Gear – Stage 2
Pinion – Stage 3
Gear – Stage 3

12. 2018nov 12
KINEMATICS OF GEARS
VELOCITY RATIO
VR is ratio of input speed to
the output speed of two gears.
 VR - velocity ratio
VR > 1 reduces speed
 TV - train value
(system property)
In DIN-base literature
 i - Űbersetzung
 ω - Winkelgeschwindigkeit
 z(N) - Zähnezahl
𝑉𝑅1 =
𝜔𝑃
𝜔𝐺
=
𝑁𝐺1
𝑁𝑃1
𝑇𝑉 = 𝑉𝑅1 . 𝑉𝑅2 . . 𝑉𝑅𝑛
1
2
2
1
z
z
i 




13. 2017nov 13
TASKS (MANDATORY)
STEPS
Task 3:
 Calculate the torque transmitted
by each pinion/gear at each
stage:
 Be careful of the motor
specification you have.
 Maximum stalled torque,
transmission speed,……
 !!! Only consider the
operating torque and radial
speed!!!!!!!
 65% (of max. speed) and
35% (of max. torque).

14. 14
TORQUE-SPEED RELATIONSHIP
Point to note:
• Max torque (Tmax) when stalled (not rotating).
• T = 0 at maximum speed ωmax
• So we use operating torque and speed (radial) 2019jan
𝜔 = 0
𝑇 = 0

15. 2017nov 15
TASKS NEEDED
STEPS
TASK 3: NOTE
 The maximum torque (stalled torque
given is at the output gear of the last
stage.
 Tip: Use the velocity/transmission ratio
to calculate torque/speed transmitted
by each pinion/gear.
 Tip: the pinion connected to the motor
normally will transmit the lowest
torque/highest speed of the entire
transmission.
 Tip: for several stages, the pinion/gear
are connected -> same
speed/torque……

16. 2017nov 16
TASKS NEEDED
STEPS
TASK 3:
 Next calculate the bending and
contact stresses for each stage:
 Require:
 Tangential forces transmitted
per stage!!!
 Tip, only one tangential force
at each stage!!!!!
 Tip: use the torque of the
pinion as the basis of
calculating the Tangential
force.
Ft
T = Ft × Rp

17. 2019nov 17
SPUR GEAR DESIGN
TOOTH STRENGTH (BENDING STRESS)
 To compensate for tooth form and tooth size,
the form factor YFA is introduced. It is a
function of m (compensates for tooth
thickness).
σb =
Ft
bm
YFa
σb - bending stress (N/mm2)
Ft - tangential force (N)
b - gear width (mm)
m - module (mm)
Yfa -form factor acc. to DIN 3990
In the module system, L (sum of addendum
and dedendum) and h (tooth thickness) are
related to module (m).

18. 2019nov 18
SPUR GEAR DESIGN
DIN 3990
Form factor YFa
for standard metric
module-based
gears.
z - number of teeth
x – profile shift,
standard x = 0
Z1 = 19 teeth
x = 0
No. of teeth of pinion (driver)
Form
factor
Yfa
Profile shift (X)
YFA = 2.9
Always read on the line x=0
for standard profile design!!

19. 19
SPUR GEAR DESIGN
2) CONTACT STRESS
 But for a gear: we need to compensate for tooth form to calculate contact
stresses.
σH - contact stress (N/mm2)
b - gear width (mm)
u - teeth ratio z2/z1 > 1
ZH - curvature factor (2.5 for standard spur
gears)
ZE - elasticity factor (√ N/mm2)
E - reduced E modulus for different
materials (N/mm2)
E – use material stiffness E in case of same
material!!
𝜎𝐻 = (𝑍𝐻𝑍𝐸) ∗
𝐹𝑡
𝑏𝐷1
𝑢 + 1
𝑢
𝑍𝐸 = 0.175𝐸
 We introduce three factors to the Hertz equation in the previous slide.
These are u, ZH and ZE are introduced to compensate radius of curvature
and material stiffness.

20. 2017nov 20
TASKS NEEDED
STEPS
TASK 4: Safety Factors!!
 Determine the safety factor at
bending and contact:
 Require:
 Material properties for the
gears you have.
 Gear dimensions, and
tangential forces.

21. 2019nov 21
SPUR GEAR DESIGN
FACTOR OF SAFETY (BENDING AND CONTACT STRESSES)
min
lim
min
lim
2
H
A
H
H
H
F
A
b
F
F
S
K
S
S
K
S








DIN 3990
𝜎𝐹𝑙𝑖𝑚 - limiting bending stress
𝜎𝐻𝑙𝑖𝑚 - limiting contact stress
 On average a minimum safety factor of between 1.5 is valid, up to 3 for high risk
applications (𝑆𝐹𝑙𝑖𝑚) and (𝑆𝐻𝑙𝑖𝑚).
SF - safety factor bending stress
SH - safety factor contact stress

22. 2017nov 22
RE-DESIGN TASKS
(ONLY WHAT IS MARKED FOR YOUR GROUP!!)
Step 5: Re-design Tasks
 Select the stage with the lowest safety factor (bending/contact).
 Re-design to fit new operating conditions:
 Replace your transmission with all brass gears?
 Use lighter, high strength gears?
 Use a combination of gear materials, e.g., brass + aluminium

23. 2017nov 23
TASKS NEEDED
STEPS
Step 5:
 Re-design task:
 What gear dimensions would
you recommend considering
new retro-fitting?
 Do you require to re-design to
have stronger gears (larger
module, or thickness)?
 …………….
 Show/document in your report
your logic or argumentation.
 WHAT NEW GEAR DIMENSIONS WILL
YOU SUGGEST KEEPING IN MIND A
SAFETY FACTOR OF MINIMUM 3?

24. 2017nov 24
QUESTIONS/HELP WITH THE ASSIGNMENT?
Deadline:
 Preliminary report should be submitted on or before 13th
January, 2023 (uploaded on canvas). Tasks to be performed
are indicated on the reader.
 Final report uploaded via Canvas on or before Wednesday,
01/02/2022 at 23:59 hrs.
 Canvas upload link will be created and available before the
submission deadline.

25. 25
DIY
EXPECTED SERVICE LIFE
2017nov