ASME Student Design

Competition
Tutorial
 Overview:

 Objective
 Algorithm
 Gripping Mechanism for picking up the object
 Motors used (eg. DC motors ,Stepper motor )
 Power source for the motors
 Sensors (eg. Metal , IR , Bump )
 AVR Atmega 16
 External links
Objective: We have to design, build, and test a system capable of rapidly and
accurately sorting the four waste materials noted above into distinct waste
containers. This system must operate autonomously and be capable of both
material identification and waste handling.

Thus following are the fields in which we need to work:

 Gripping mechanism for picking up the object.

 Different types of Motors.
 Power source for the motors.
 Sensors.
 AVR.
 Drop the object.
 Algorithm:

Pick up an object

Use metal detector

If yes,
If no, check its size
use electromagnet

If no, drop in the If its size is around If its size is around

If yes, drop in the
non-ferrous 220cm, drop in 95cm, drop in glass
ferrous container
container plastic container container
Picking up the waste object: Gripping Two-Pincher Gripper The two-pincher
gripper consists of two movable fingers, somewhat like the claws of a crab. This
model is really one of the most basic types of gripping mechanism. Its
components are easily available and it is also very easy to build. Look at the
diagram below. You just require 4 metallic pieces (or can be wooden or plastic),
nut-bolts and some screws. Parts of Mechanics kit would come pretty handy.
The basic gripper is finished. In order to grip, you must move the two fingers.
This can be done by rotating the angular shafts by motors.

Apart from this any other clamping mechanisms can be used.

 MOTORS
DC MOTORS:

DC electric motors are also split into

types. These include brush motors,
brushless motors, and stepper
motors.Of these types, brush electric
motors are by far the most common.
They are easy to build and very cost
effective. Their major drawback is that
they use carbon brushes to transfer
electrical current to the rotating part,
and these brushes wear over time and
eventually result in the failure of the
electric motor.

The DC brushless motor eliminates the brushes, but is more costly and requires
much more complicated drive electronics to operate.

A stepper motor is a special type of brushless motor that is used primarily in

automation systems. A stepper motor uses a special type of construction that
allows a computerized control system to “step” the rotation of the motor. This is
very important when controlling a robotic arm.

Stepper motor

Stepper motors consist of a permanent magnet rotating shaft, called the rotor,
and electromagnets on the stationary portion that surrounds the motor, called
the stator. Figure 1 illustrates one complete rotation of a stepper motor. At
position 1, we can see that the rotor is beginning at the upper electromagnet,
which is currently active (has voltage applied to it). To move the rotor clockwise
(CW), the upper electromagnet is deactivated and the right electromagnet is
activated, causing the rotor to move 90 degrees CW, aligning itself with the
active magnet. This process is repeated in the same manner at the south and
west electromagnets until we once again reach the starting position.

Figure 1

In the above example, we used a motor with a resolution of 90 degrees or

demonstration purposes. In reality, this would not be a very practical motor for
most applications. The average stepper motor's resolution -- the amount of
degrees rotated per pulse -- is much higher than this. For example, a motor with
a resolution of 5 degrees would move its rotor 5 degrees per step, thereby
requiring 72 pulses (steps) to complete a full 360 degree rotation.
You may double the resolution of some motors by a process known as "half-
stepping". Instead of switching the next electromagnet in the rotation on one at
a time, with half stepping you turn on both electromagnets, causing an equal
attraction between, thereby doubling the resolution. As you can see in Figure 2,
in the first position only the upper electromagnet is active, and the rotor is
drawn completely to it. In position 2, both the top and right electromagnets are
active, causing the rotor to position itself between the two active poles. Finally,
in position 3, the top magnet is deactivated and the rotor is drawn all the way
right. This process can then be repeated for the entire rotation.

Figure 2

There are several types of stepper motors. 4-wire stepper motors contain only
two electromagnets; however the operation is more complicated than those
with three or four magnets, because the driving circuit must be able to reverse
the current after each step. For our purposes, we will be using a 6-wire motor.
Unlike our example motors which rotated 90 degrees per step, real-world
motors employ a series of mini-poles on the stator and rotor to increase
resolution. Although this may seem to add more complexity to the process of
driving the motors, the operation is identical to the simple 90 degree motor we
used in our example. An example of a multipole motor can be seen in Figure 3. In
position 1, the north pole of the rotor's permanent magnet is aligned with the
south pole of the stator's electromagnet. Note that multiple positions are
aligned at once. In position 2, the upper electromagnet is deactivated and the
next one to its immediate left is activated, causing the rotor to rotate a precise
amount of degrees. In this example, after eight steps the sequence repeats.

Figure 3
The specific stepper motor we are using for our experiments (ST-02: 5VDC, 5
degrees per step) has 6 wires coming out of the casing. If we follow Figure 5, the
electrical equivalent of the stepper motor, we can see that 3 wires go to each
half of the coils, and that the coil windings are connected in pairs. This is true for
all four-phase stepper motors.

Power source for the motors

The motors used for making the robot are DC motors. They usually need current
near 1 A to run properly. So rechargeable batteries of proper current rating must
be used. The following link gives the various batteries available that can be used
in robotics.

SENSORS
METAL DETECTOR
The metal detector circuit shown here must represent the limits of simplicity for
a metal detector, yet the design works surprisingly well. It uses just one 40106
hex Schmitt inverter IC, a capacitor and a search coil – and of course the
batteries. A lead from IC1b pin 4 needs to be attached to a medium wave radio
aerial, or it should be wrapped around the radio. It can be used even like those
hand held metal detectors.
As shown, the metal detector gives a respectable range for beat frequency
operation (bfo) up to 90mm for a bottle-top. In fact, for the ultimate in
simplicity, capacitor C1 may be omitted. In this way the author achieved am
amazing 150mm range for the bottle-top. However, with the frequency then
being raised to more than 4MHz, instability becomes a significant problem.

Metal detector circuit diagram

As shown, the circuit oscillates at around 230kHz. One may also experiment with
the frequency by changing the value of C1. A Faraday shield may be added to
reduce ground effect and capacitive coupling, and this is wired to 0V.
Since the inductor resists rapid changes voltage, the charging of C1 is slightly
delayed as the logic level at IC1a pin 2 changes. This sets up a rapid oscillation,
which is picked up by a MW radio. Any changes in the inductance of the search
coil (through the presence of metal) bring about a change to the oscillator
frequency. Although 230kHz is out of range of the Medium Wave band, an MW
radio will clearly pick up harmonics of this frequency.
Metal detector calibration
The making of search coil L1 allows a lot of room for error and is far from critical.
The author used seventy turns 30 s.w.g. (0,315mm) enamelled copper wire on a
120mm diameter former.
The metal detector is set up by tuning the MW radio to pick up a whistle. Not
every such harmonic works well, and the most suitable one needs to be found.
The presence of metal will clearly change the tone of the whistle.

Metal detector faq :

This is not a industrial metal detector circuit and is not even close to loma or
eriez metal detection products. It’s just a portable metal detector.

For more information on metal detector

http://www.robotix.in/metaldetector_part2

IR SENSOR WITH TSOP :

For detecting object , we can use Infra Red(IR) proximity detectors. This is
basically an IR emitter-IR receiver pair. The emitter emits IR rays, which bounce
back from the obstruction and reach the receiver. The voltage drop across the
receiver is dependent on the distance.
Infrared Emitter Detector Basic Circuit

R1 is to prevent the emitter (clear) LED from

melting itself. Look at the emitter spec sheet
to find maximum power. Make sure you
choose an R1 value so that
Vcc^2/R1 < Power_spec.
Or just use R1 = 120 ohms if you are lazy and
trust me.

R2 should be larger then the maximum

resistance of the detector. Measure the
resistance of the detector (black) when it is
pointing into a dark area and then choose the
next larger resister. This means Vout is close to
zero when there is no signal.
Or just use R2 = 11kohms
Or use a 20kohm Pot here in series with a
100ohm resistor for white line following
calibration.

To check whether your IR LED is working or not, simply view the LED using a
phone's camera or any digital camera available, and the LED can be seen
glowing.

But, if you have bought a ready made one, then you shouldn't have any problem
with it. If, in any case you are facing problems, you are free to post it on the our
forum.
These generally work till distances of 25 cm.

The above sensor is a quite complicated one, it works on a single frequency. i.e.
TSOP sensor.

Now, In the current problem statement, we can attach many spaced sensors in
one direction of the bot , so that knowing the distance between the sensors we
can calculate the desired size of the object .

BUMP SENSOR
A bump sensor is probably one of the easiest ways of letting your robot know it's
touched something. The simplest way to do this is to fix a micro switch to the
front of your robot in a way so that when it collides the switch will get pushed in,
making an electrical connection. Normally the switch will be held open by an
internal spring.

Micro switches are easy to connect to micro controllers because they are either
off or on, making them digital. All micro controllers are digital, so this is a match
made in heaven. Micro switch 'bump' sensors are easily connected to the
Robocore, simply plug them into any free digital socket and away you go.
The following diagram shows a typical circuit for a micro switch bump sensor.
The resistor is important because it holds the signal line at ground while the
switch is off. Without it the signal line is effectively 'floating' because there is
nothing connected to it, and may cause unreliable readings as the processor tries
to decide if the line is on or off.

If you dont get these microswitches you can make one easily , using a spring
mechanism.

AVR

The ATmega32 is a low-power CMOS 8-bit microcontroller based on the AVR

enhanced RISC architecture. By executing powerful instructions in a single clock
cycle, the ATmega32 achieves throughputs approaching 1 MIPS per MHz
allowing the system designer to optimize power consumption versus processing
speed.
For coding ATmega32 one have to use softwares like WinAVR , CodeVision and
there are many more. The code is first written in C language and this softwares
give a platform to compatibility of the program. This program have to be burn in
the ATmega32 using AVR Burner.
The Atmel ATmega32 is a powerful microcontroller that provides a highly-
flexible and cost-effective solution to many embedded control applications. The
ATmega32 AVR is supported with a full suite of program and system
development tools including: C compilers, macro assemblers, program
debugger/simulators, in-circuit emulators, and evaluation kits.

Fig : Pin Outs Of ATmega 32

External Links:
http://www.8052.com/
http://winavr.sourceforge.net/
http://hubbard.engr.scu.edu/embedded/avr/avrlib/
http://www.beyondlogic.org/serial/serial.htm
http://robokits.co.in/shop/index.php?main_page=index&cPath=13&zenid=5fbcn
rsq89g7hha0vepv5cda37

Contacts :
Sagar Agrawal Aayush Agarwal
+91 9775193881 +91 9735485110
Sagar.agrawal@ktj.in aayush.agarwal@ktj.in