1. The document describes the design and optimization of an alternative, cost-effective rain sensing wiper system called the electrochemical rain sensor (ERS). 2. The ERS uses an electrochemical cell that is displaced by rainwater to complete a circuit and activate the wiper motor. This provides faster response time than conventional systems. 3. Analysis shows the ERS system requires 18% less torque from a smaller, lighter DC motor, reducing weight and costs by 66% compared to conventional wiper systems while achieving similar performance.

1. Modeling and Design Optimization of
an Alternative Cost Effective Rain
Sensing Wiper System
Dr. Amol M Khatkhate Nitin Dhamal
Professor, Department of Mechanical Engineering PhD Student, Department of Production Engineering
Rizvi College of Engineering (RCOE) Veermata Jijabai Technological Institute (VJTI)
Bandra (W), Mumbai - 400050 Matunga(W), Mumbai - 400028

2. Motivation : Analogous to Classical Control
Theory
Classical control theory
evolved with all the
mathematics so as to
model linear systems
Further advancements
took place to identify
solutions for nonlinear
systems
Control of DC motor is well
established using Arduino
UNO microcontroller
Modular software systems
can be built on top of the
same with advanced
control algorithms to
develop innovative
solutions for auto industry

3. Motivation and Introduction
v Rain sensing wipers form an important part of a vehicle which operates in a region where there is heavy
rain and considerable reduction in visibility due to such events. This may also lead to accidents and
may prove to be fatal.
v Rain sensing wipers reduce the drivers distraction and his attention span so that he can focus on the
driving and ensure the safety of the passengers in the vehicle.
v In a place like Mumbai, there is heavy downpour and neck to neck traffic which requires a lot of
alertness and energy of the driver to ensure smooth and controller driving. In such a scenario, rain
sensing wipers and such units which are sensitive to rain will result in an alarm system which can be
very useful for the driver to park his vehicle in case of heavy rainfall thus avoiding vehicle disability.
v This work introduces a novel idea of making an modified electrochemical cell to work as a rain sensor
and also to further utilise the rainwater for cooling purposes. This sensor has been adapted to suit the
conditions of the tropical climate and hence provide good level of automation to the driver during the
rain.
v The work presented also shows that the system is very cost effective (66% less costly) as compared to
the conventional one and achieves the same functionality as required.Also, the system is independant
of the microcontroller or the current manufacturing process of the vehicle and can be installed with
proper procedure as a seperate unit.

4. Electrochemical Rain Sensor (ERS)
Procedure for preparing Rain Sensor
v Use a container of suitable size with a
seperation to seperate the electrolytes
v Construct a salt bridge from an accordion joint
plastic straw
v Use a container typically usedfor giving
medicines to adults or babies as a container
for collecting rainwater
v Use a spring from a normal ball point pen to
complete the straw-spring-container assembly
v Allow a spacing of 50 microns (thickness of
paper) between the salt bridge and the
electrolytes
v Place the rain sensor in the hood of the
vehicle just below the area where there is
collection of rain water from the windshield.

5. Performance of the Electrochemical Rain Sensor (ERS)
Impulse response of rain sensor
v A single droplet of rain produces a 3.2 micron
deflection of the salt bridge
v Assuming the damping of air to be 0.01, the
response dies down after oscillating as shown
in the Figure
v Sensitivity of the sensor is 227 micron/ml
of rainwater
v Test were conducted to find the life of the
accordion salt bridge using a plastic straw
v Cell life was found using the following formula
v Cell life in days = (No of cells x Molarity x
Volume (liters) x No of electrons/mole x
96485)/(60 x 60 x 24 x (Final current +
Initial current)/2) )
v The life was found to be 18 days in practice
while it was found to be 22.9 days
thoeretically.

6. Comparison of different rain sensors
DIFFERENT TYPES OF RAIN SENSORS
Plate based
sensor
Piezo- electric
sensor
Probe based
sensor
Optical based rain
sensor
Electro-chemical
rain sensor
Operating
principle
Micro controller
based
Micro controller based External circuits
connected to micro
controller
Micro- controller based Independent of micro
controller
Working Small drops of
water change the
resistance
Water between plates
decrease resistance
Contact of water with
probe completes rain
circuit
Change in reflection due
to rain water
Rainwater energy is
converted into
displacement of
electrochemical switch
False rain
detection rate
Very high Less than 5% Less than 2% Less than 2 % Less than 2%
Voltage required 12 – 5 V DC 12 – 5 V DC 2 – 6 V DC 12 – 5 V DC 1 – 3 V per single cell
System response
time
Not mentioned 500 ms after rain contact On collection of 10
cu.cm
Very low 550 ms after rain
contact
Sensor surface size Very large <= 4 cm x 4 cm >=2.58 cm x2.58 cm Not applicable 1 cm x 1 cm
Placement of
sensor
On the windshield On the windshield Inside the font hood Inside the car cabin Inside the front hood
Cost of
replacement
Quite high Quite high Around Rs 1000 Around Rs 7000 Around Rs 200
(sensor ONLY)
Adaptivity Changes the
aesthetics of the
vehicle
Embedded on
windshield
Volume of rain
collected is high
Seamless integration
with vehicles
Adaptable to all
vehicles

7. Comparison of Conventional Lucas Wiper System and
Electrochemical Rain Sensing (ERS) system
28/11/19
Parameters Conventional
Lucas Wiper
Motor
DC Geared Motor
with rack-pinion
Weight of wiper arm 330 gms 330 gms
Length of wiper arm 450 mm 450 mm
Crank rod length NA 25 mm
Connecting rod
length
NA 50 mm
Diameter of pinion NA 79 mm (Module
1.41,Teeth – 56, Pitch
- 18)
Length of rack NA 100 mm
Weight of motor 800 gms 180 gms
Stall torque of motor 180 kg-cm 80 kg-cm
Stall Current 14 A 7.5 A

8. Details of the Electrochemical Rain Sensing
Wiper System
v Water collected in the container displaces
the salt bridge and connects the
electrolytes
v The base current to the transistor makes
it forward biased
v Transistors are connected in Darlington
pair to amplify the current and run the
motor at the desired speed
v Rack and pinion with slider-crank
mechanism is used to actuate the wiper
v The motor needs to be run only in a single
direction without reversal
v Li-ion batteries connected to a solar panel
can act as a power source

9. Performance comparison between the two wiper
systems
Motor Configuration
45 RPM 65 RPM 100 RPM
Cost Of
System Per
Vehicle
Tavg
N-m
Iavg (A) Imax (A) Tavg
N-m
Iavg (A)
Imax
(A)
Tavg
N-m
Iavg
A
Imax (A)
Conventional
Lucas Wiper
motor
arrangement
2.44 1.71 2.18 2.44 1.71 3.29 2.44 1.71 6.2
4400/- (MIN)
(TVS
SINGLE
WIPER
SYSTEM)
DC Geared
Wiper motor
with Rack-
pinion
mechanism
2 1.68 2.13 2 1.68 3.2 2
1.68
6
1500/-
1000 (DC
GEARED
MOTOR) +
200 (RACK
AND
PINION) +
100 (SLIDER
CRANK) +
200 (ERS)
% Change in
parameter from
conventional
arrangement
-18 -1.75 -2.75 -18 -1.75 -2.75 -18 -1.75 -3.23
66%
reduction

10. Location of sensors in vehicle
A suitable “ERS KIT – ELECTROCHEMICAL RAIN
SENSING KIT” will be designed using the following
components as shown in the Table 5.
Table 5 : ERS Kit Components
Components Manufacturing
Cost
Rain Sensitive Cell 200
Accordion Joint Salt
bridge (12 QTY)
70
Rack and Pinion 180
Slider crank 50
DC geared motor 1000
TOTAL 1500

11. Mathematical modeling of the Conventional Lucas Wiper
System
where:
T = torque to move one wiper arm (N-m)
F = force onto blade on screen (N) = (W + 0.8)cos(β + λ)
W = 90 gms weight
Frictional force, 0.8 N = maximum frictional force on blade
β = angle of travel by wiper (rad) = max 180 – 2λ
λ = relief angle on windscreen = 15 degree
μ = maximum dry coefficient of friction, which is 2.5
fs = multiplier for joint friction, which is 1.15
fl = tolerance factor, which is 1.12
l = wiper arm length, m = 0.24 m
ωa = maximum angular velocity of arm, rad/s
ωm = mean angular velocity of motor crank, rad/s
e = efficiency of motor gear unit which is 0.8
Rh = motor winding resistance, hot-Ω = 1.05 Rc = motor
winding resistance, cold-Ω = 1

12. Mathematical modeling of the Electrochemical Rain Sensing (ERS)
Wiper System
Taking downward direction as positive
W + mg = N.................(1)
Taking right side positive
-Ft + µN = -mddot(x)....................(2)
Moment about O taking clockwise
positive
-T - WLcos(β + λ0)/2 + FtR - µNR =
Iddot(β) =
(WL2/3g)ddot(β).........................(3)
Also, for the pinion and rack
arrangement, β = -x/R
dot(β) = + dot(x)/R ddot(β) = -ddot(x)/R
Substituting in the equation (3), we get

13. Torque requirement and Current drawn by the
two wiper motor arrangements

14. Salient features of the ERS wiper system
v Since, the electrochemical reaction is spontaneous,
the actuation by this kind of a cell will result in very
less response time. (approx 700 ms – 550 ms by
rack and pinion + 150 ms by the ERS
v The DC geared motor consumes almost 18% less
torque than the conventional Lucas motor and runs
with very minimal parts.
v Also, 80% weight reduction by replacement of
Lucas motor with geared DC motor and the easy
off the shelf availability of the rack and pinion setup
are a lucrative point to choose this alternative.
v Compactness of this arrangement as seen in
Figure 6 which has a dimension of 36 inches to a
reduction of 6 inches which is 1/6th the original size
is a great advantage for the auto industry.
v The cost reduction estimated with the alternative
wiper system is around 66% per vehicle.
v Experimental verification of the same is a part of
ongoing work.
Following enhancements will be done in
due course of time which will lead to value
addition of the above rain sensing wiper:
v Automatic speed control of wiper
based on rate of rainfall
v Automatic mist and fog removal
v Design of parking mechanism for
wiper
v Design of vibration isolation system
for cell and effect of temperature on
the performance.
v The introduction of this new type of
system in current cars needs to also be
checked in terms of its effect on the fuel
economy especially the effect on
reduction in usage of air-conditioning
and the gains/losses that it has as
compared to an existing rain wiper
system.

15. Future Open Research Areas
1. Design of a linear variable
electrochemical transducer
2. Stabilisation of agar agar
gel with plastic
3. Embedment of ERS and
other sensors for SHM of
civil infrastructure
4. Development of
miniaturised rain sensor
for Indian conditions
Acknowledgements
The presenters are grateful to
Mina Bairagi for helping in the
fabrication of the ERS
We thank Ramkumar Maurya
for providing us guidance in
electronics
We thank Husain Jasdanwala
and Dr Sujata Rout (ex-HOD
Mechanical Department) and
our principal Dr Varsha Shah
for motivating us in doing the
project

16. THANK YOU
Dr Amol M Khatkhate
amolmk@eng.rizvi.edu.in/amol.khatkhate@gmai
l.com
Look up our other projects from Mechatronics
and Robotics Lab at ResearchGate
28/11/19