10-09-2016, 10:34 AM
1454318416-RemoteLawnMower.doc (Size: 590 KB / Downloads: 4)
Abstract:
This project was about designing a remote control lawnmower that eliminated the need of
physical power. In completing this project, there were numerous steps that were taken; finding
parts, designing and testing H-Bridges, and having a microcontroller to interface the H-bridges to
the RC receiver. Throughout this report you will learn more on how we went about completing
this project and what various parts were used that replaced the physical power needed in moving
the lawnmower.
Introduction:
The purpose of this project is to design and build a remote controlled lawn mower. This
would be beneficial because man power is not required in mowing the lawn on those hot summer
days, where you would prefer not to be out in the sun. The remote will allow the user to control
the speed and direction of the lawn mower by moving the joy sticks. For safety purposes, the
engine of the lawn mower can be turned off via remote and also turns off automatically when
there is a loss of signal.
Design specifications:
The main objective of this project is to convert a push lawn mower into a remote control
lawn mower, where pushing is eliminated by battery power. The battery will be used to power
the dc motors, which will turn the gears and cause the wheels to turn with greater torque then
what the dc motor can produce. The steering of the lawn mower will be done in a skid steer
fashion by having the wheels turn in the opposite direction causing the lawn mower to turn either
left or right, with the help of swivel wheels in the front.
Project circuitry and component explanation
H-Bridges:
An H bridge is an electronic circuit which enables the current to flow in either direction.
The H-bridge consists of four transistor arranged in H shape (see figure 1). A transistor is an
electronic switch which can be turned on or off by applying the appropriate voltage. This H-
bridge consists of two P-channel transistors on the top and two N-channel transistors on the
bottom. To turn on the P-channel transistor we need 0 volts and to turn it off we need 12 volts
where for N channel we need 12 volts to turn on and 0 volts to turn off. The Arduino
microcontroller outputs are 0 volts and 5 volts which is not enough to turn the transistors fully on
or off. In order for the microcontroller to control the transistors, we designed four drivers, two
for P-channel transistors and two for N-channel transistors. The drivers which control the P-
channel (High Side) transistors takes 5 volts in and converts it to 0 volts which turns the high
side transistor on. To turn the high side transistor off, the driver takes in 0 volts and converts it to
12 volts. The other two drivers which control the N-channel (Low Side) transistors, take in 5
volts and converts it to 12 volts which turns them on and 0 volts turns them off.
The way this circuit works is fairly straight forward. To turn the motors forward, the Q1
and Q4 transistors (Fig. 1) need to be on, but Q2 and Q3 should be off. In order to turn the
motors backward, Q2 and Q3 transistors (Fig. 1) should be on, but now Q1 and Q4 should be off.
The H-bridge is also used to control the speed of the motors; this is done by varying the duty
cycle of the transistors. Duty cycle is basically the amount of time for which the transistor
remains on, of the total time under consideration. The duty cycle runs at a frequency of about
490 Hz. For example at 50% duty cycle looks like a square wave where the on and off time is the
same, this means that the transistor will remain on for half of the time and as a result, the motors
will turn at half speed.
Two H-Bridges will be designed to control the direction of the DC motors; turning the dc
motors clock-wise or anti-clock-wise. This will force the lawn mower to go forward or
backward, and in either direction, left or right. The lawn mower will be turned left or right by
turning the wheels in the opposite direction. Turning the wheels in the opposite direction gives us
skid steering maneuvering which allows one to make very sharp turns allowing the lawn mower
to get around tight corners. We have also installed LED’s in our H-bridge circuits for direction.
There is a yellow LED which represents forward and the other LED is red that represents
reverse.
Wireless remote and receiver:
A 2.4 GHz Spektrum DX5E remote and an AR500 receiver is used to control the
operations of the lawn mower, such as speed, direction, and safety shut off. The remote has a
range of 300 feet which allows the user to control the lawnmower from a great distance. The
remote will send pulse position modulation signals to the receiver; which then will be used by
the microcontroller to control the operations of the DC motors. The speed and direction of the
lawn mower is controlled by two joysticks on the remote. The left joystick controls the left wheel
and the right joystick controls the right wheel. Pushing the joysticks forward makes the
lawnmower go in forward direction and pushing them backward makes it go backwards. To turn
the lawnmower left, push the left joystick backward and right joystick forward, and to turn the
lawnmower right, do the opposite.