project 2 - robcom: a combat robot
TRANSCRIPT
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Project 2-RobCom: A Combat Robot
Introduction
If you have dreamed of creating a combat robot that
can destroy or knock out the enemies, rivals, space
in vaders, or oth er supernatural crea tures, you must
take a look at this project. RobCol11 is the answer for
your aspirat ions-your dream coming into rca lity.
Using inexpensive anel C0111111 011 parts, even inexperi
enced readers who may not yet be prepared to build
complex circuits wi th microprocessors can build the
RobCom.
The evil genius will be ab le to bui ld the RobCom
and challenge his or her friends to a real combat of robots. You can also invite your colleagues to bui ld
combat robots. Ask them to put into the project all
thei r imagination. to create weapons. and to build
defenses so they won 't be knocked out in the first
encounter.
RobCom was one of the proj ects proposed by the
author to his pupils of the mechalronics course at
Colegio M ater Amabilis in Guarulhos, Brazi l. Figure
3.2.1 shows some of the projects made by the stu
dents. You can see how these evil geniuses con
structed their destruction machines.
What Is RobCom?
RobCom is a remote-controlled robot buill with
common part s. In the basic version, it is bui lt to calTY
a rubber ba lloon th at it is protecting and three nee
dles as weapons. The reader can add other weapons,
of course, depending on the rules o f combat agreed
upon by the other competi tors.
To make the project easier, the remote control
uses a cable. Some advantages ex isllo using a cable
in place of other remote conlrolmeans,such as
infra red ( IR) or radio/reqllency (RF). Beyond the
simplicity of the ca ble method (no spccial circui ts are
requ ired), the problems of interferences and noise,
common in the places where the combat takes place •
don't exist.
RobCom has two small DC motors di rectly driv
ing two rear wheels, which arc made of standard CD s.
The single front wheel is able to turn freely in any
directiol1. 1l1e recommended fron t wheel is one that
can be found in old office chairs or other furniture.
Figure 3.2.2 shows the wheel used in the robol.
Figure 3.2.2 From whee/used in fil e RobCol1l.
The control unit , which is placed at the end of a
cable, is simply a small box with two special switches
Figure 3.2.1 Close-lip sho lving (1 1'0 robo(s in combat.
,. and a joysLick. 1l1c switches can control two circuits (two poles) at the same lime, and each switch has three positions. When the j oystick is in the central
posi tion. the con trolled ci rcuit is disa bled; no power is
releascd to the motors. Certain positions of the
switches con trol certain fu nctions of the 1110 tor, as
shown here:
22 Mechatronics for the Evil Genius
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Position Motor
FOlward Molor fllns forward
Released r ... IOIor off
Backward Molor runs backward
Combining the three posit ions of the switches,
the robot can run in any direction. as the following
table shows.l11e arrows indica te the direction of
movement.
Robot Switch R Switch B Symbol Movement
Released Released Stalled
Pressed Pressed t R un fo rward in forward forwa rd st raight linc
Pressed Pressed
• Ru n backward in
backward backward stra ighlline
Pressed r-fo rward Released Turn right forward
Pressed L. backward Re leased Turn right backward
Pressed ~ Released forward Turn left forward
Pressed .J Released backward Turn left backward
RobCol11 is powered by four AA cells placed in
the contro lun it.lllis placement reduces the weight of
the mobile unit, increases the mobi lity, and is very
important in combat.
Objectives-The Combat
The basic idea of robot combat is to put two Rob
Coms in an arena formed by four pieces of wood , as shown in Figure 3.2.3, and let them try to pop the
other's ba lloon using needles as weapons.
Cont rolling the forward and backward movement
of the robot, the player can find the best position for
an attack without exposing his or her own balloon to
the attack of the enemy. Strategies must be created
by the RobCom evil geni us to wi n the combat.
The winner is the fi rst robot to pop the enemy's
balloon.llle balloons ca n have a tiny amount of flour
or talc injected in them, adding a realistic effect for
Section Three
Figure 3.2.3 The arena IIsed in the combat is a sqllare made by fOllr pieces of Ivood.
the explosion. A cloud of smoke wi ll then announce
that the balloon is popped and the combat is over.
A normal combat session usuall y lasts from 1 to 5
minutes (see Figure 3.2.3). [n an organized competi
tion, a simple elimination process can be used.
Rules are very important in order to avoid major
differences among the competitors and to level the
playing fi eld. Rules include specifications for maxi
mum d imensions of the robots, the size of the rubber
ba lloon, the use of defense screens, the length of the needles, thc typcs of motors used, the power supply
voltage, and so on.
Rules for the actual combat are necessary, too. At the end of this project is a list of rules that we have
found are usefu l in our combat.
Figure 3.2.LJ Scene of combat IVhere IIVO RobComs (es( (heir pOIve/:
Th e Pro j ects
Winner
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The Proj ect
The RobCom is a robot that runs on three wheels.
The front two are used to turn the robot in the
desired direction, and the third is a free wheel.
Two small DC motors are couplcd directly to the wheels, which are made with CDs or some other
material of the reader's choice.
The motors are controlled by a remotc cont rol,
wired to the robot by a 3-meter cable. As indicated
previously, the use of a cable makes the project easy
to bui ld and very inexpensive, as no special materials
are needed. TIle remote control also houses the cells that power the motors. Two switches allow the robot
to move backward and forward and to change direc
lion.
The chassis can be made using common materials
such as cardboard, CD boxes, plastic, wood, and so
on. It is up to the reader to use his or her imagination
to create his or her own version while fo llowing the
rules of the competi tion.
When creating your RobCol11, it is important to
reduce the weight, making it as fast and well balanced
as possible .
Building the RobCom
TIle basic RobCom is the one described in the intro
duction. Of course, the evil genius can change the
RobCom by adding new weapons or defenses
according to the combat rules.
The Electric Circuit
Begin your project by building the electric circuit. Thc simple schematic diagram for the RobCom is
shown in Figure 3.2.5.
As we can see in the fi gure, the single power sup
ply is formed by four AA cell s. TIlis supply powers
two small , 6-vol1 DC motors via SI and S2. SI and S2
are a special arra ngement o[ two switches with three
positions each. In the middle position, the switches
are off.
61 + 6V -
S1
Figure 3 .2 .5 Schemmic diagram fo r the electric circuit of the RobCom.
S1 and S2 determine the direction of the motors.
The switches send the power to the motors by a special four-wire cable. TIle recommended length of the
4 X 26 Americon wire gauge (AWG) cable is 3
meters.
The switches are pl aced in a small box (plast ic or
other material) form ing the joystick. TIle different
colors of the cable wires are important and will help
the reader know where each must be soldered. Figure 3.2.6 shows the electric circuit assembled.
Figure 3.2.6 The electric circllit ready to be installed in rhe RobCom.
Parts List-The Electric Circuit
S1, S2 2 poles x 3 through switches (see text)
B1 6 volls of power (4 AA cells with hOlder)
MI , M2 6-voll DC motors
24 Me c hat r onics for the Evil Geniu s
3 meters o f four-wire cable (4 x 26 AWG)
Plastic box
Solder
The Mechanical Part
Figure 3.2.7 shows the basic moun ting of the robot ,
deta iling how the motor is coupled to the wheel. Fig
ure 3.2.8 shows a rea r view of the robot.
Cable CD Cardboard ·V·
Figure 3.2.7 Side vie.v oflhe RobCom shGlving hall' Ihe 1I1010r is COliI' led 10 the CD.
Rubber Band
Glue / CDBOX
~~lt==;±:i, ~TubeOf Spherograph Pen
End 01 Axis Protection
CD Box
_ CD
Figure 3.2.8 Th e molars are gilled 10 the CD box. They are kepI ill contact lVith Ihe CD by Ihe force of a rubber balld. This makes it possible 10 trallsmil all the pO lva (0 the robol,
Putting the Pieces Together
The next figures show the seq uence of operat ions to
mou nt the robot. Figure 3.2.9 shows the free wheel
fixed to the CD box used as a chassis and how to
Section Three
Figure 3.2 .9 InserriJlg a metal sheet between/he CD boxes before gluing thell1 logelher.
insert a metal sheet between them to keep the struc
ture rigid.
Figure 3.2.10 shows how to add an isolation sheet
to the CDs to increase the adherence. Rubber bands
glued to the CD ca n a lso be used to accomplish this. TIle reader is free to create the best way to increase
the adherence, making the robot faster and agile.
CD
.-- Insulation Tape
or Friction Tape
Figure 3.2 .10 Placing all isolalion sllee/to the CD to increase Ille adherence.
The plast ic wheel, taken from a toy, is glued to the
CD. Small plastic cars and other toys are good
sources for this wheel. I prefer the type with metallic
ax les. Figure 3.2.11 shows how to glue the wheel.
Pieces of ca rdboard can be used to make supports
for the wheels. The spi ndles of the wheels are
inserted into the drinking straws. At the end of the
spindle, a small piece of a plastic cover connects the spindle to the cardboard support , as shown in Figure
3.2.12. This cover can be a small piece of the tube
from a ballpoint pen or even the casing from an elec
tric wire.
111e motors are gl ued to the box. 8 e sure that the
motors' sha ft s will be al igned with the wheels (the
The Projects 25
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Figure 3.2.11 Gluing the wheel to the CD.
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Drinking Straw
t Glove Wheel
Figure 3.2.12 The Ivheel is coll llected to a cardboard support, which is glued 10 the chassis.
Motor
Rubber Band
\ 0 Hole
Figure 3.2.13 Motors in place.
co
CDs). Figure 3.2.13 shows the motors glued and con-
~ tacting the CDs. The motors are forced to maintain
r contact with the CDs by a rubber band holding them
Q) in place.
'r To increase the transmission power of the motor to the CD, the spindle is covered with a small glove.
As mentioned previously, the glove can be made
llsing a piece of plastic tube taken (rom a ballpoint pen or even a plastic cover from an electric wire.
T11e arms of the robot are made wi th needles, placed in a piece of ca rdboard as shown in Figure
3.2.14. Figure 3.2.15 shows the RobCom ready for
combat.
Finally, you can attach the rubber balloon to the
robot using a rubber band.
~..-__ Rubber Balloon
~>L--r;:.-._ Cardboard
Figure 3.2.14 Th e a/'lliS are placed ill the frolll of the RobCom. This piece of cardboard also serves as ({ screen, protecting againstlhe atfacks of lit e enemies.
Figure 3.2.15 RobCom ready for combat.
Testing the Combat Robot
Insert the batteries in the cell holder. Pressing the
switches in the control unit , the motors should be
26 Mechat r onics for the Ev il Genius
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t
acti vated. If not, check the solder and the cable. If
one or both motors run in the opposite directions
(e.g., forwa rd when you press backward) , invert the wire of the motor.
With the robot o n the ground, test to see if the
robot will move freely in a ll directions when you
press the controls. If the motors have difficul ties in
moving the robol, verify that they arc pressing
against the CDs with the necessa ry fo rce. If all the
movements are sa tisfactory, your RobCom is ready
and the competit ion. The robot characteristics should be as follows:
• The length of the robot must be be tween 15 and 25 centimeters.
• The maximum number of needles used as arms sho uld be three.
• TIle maximum length of the need les should be 20 centimeters (includ ing the support ).
• -n,e screen in front of the robot should be lim-for combat. it ed to 10 X 15 centi meters.
The Combat
The reader is certain ly free to create his or her own
ru les for competit ion. H owever, we call offer some
suggestions based 0 11 the experience of many combat
sessions organized in the school where the author teaches. Figure 3.2.16 shows several RobComs in an
arena, wait ing for the beginning of the contest.
Combat Rules and Specifications for the Robots
To avoid major differences among the robots, it is
important to establish some rules regarding the robot
Figure 3 .2 .16 Corr/bat of RobCollls at Co /egio Mtller AlI1abilis in Gaara/has, Brazil .
Section Three
• All the robots should use the sa me type of motor.
• The power supply must be fo ur AA ce lls fo r a ll robots.
• The rubber balloons must be equal in size.
• 0 other weapon is allowed (or otherwise combi ned) .
• The arena is formed by four pieces of wood with the d imensions between 3 X 3 and 4 X 4 meters.
Combat Rules
• T he competi tors cannot enter the arena.
• The competi to rs ca nnot pu ll the robots by the remote-control cable.
• T he competitors must begin at opposite corners of the arena.
• The combat begins when the referee gives the order.
• TIle combat ends when the balloon of one competitor is popped.
• If the two ba lloons are exploded at the same time, the robots must compete against each
other in a second round to determine the wi nner.
The Projects 27
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Exploring the Project
Many changes can be made to the original proj ect specificat ions. 1l1c fol lowing are simple examples of
the changes that can be made:
• Wood rods can be used to substitute fo r thc plastic chassis.
• A plastic chassis with different fo rmats call be used.
'Tnc same project ca n also be lIsed with vehicles other than combat robots. ~1l1 e reader can mount his
or her own walking robot lIsing the control system described here. Figure 3.2. 17 shows such a robot.
t Cells and Switches
o
Gear BOl(
• • Figure 3.2 .17 A common robollfsillg the remote control described in this project.
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Cross Themes
TIle control of movement is a theme that translates
easily in to the physics curriculum. Teachers who want
to explore this as a cross theme can invite the pupils
to research the next items:
•
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Analysis of movcmcnt : Describe the type of movement the robot makes during combat and how fast changes in directi on or speed can alter the equilibrium.
Friction: Analyze the effect of fr icti on in the robot mObility.
Transmission: Find the best way 10 transmit the power from the 1110tor to the wheels. Think about the use o f gea rs.
Additional Circuits and Ideas
l1le basic circuillised in the project is very simple. It lIses no electronic pieces and no complex clements.
TIle reader who is experienced in electronics can upgrade the circuit and create some interesting proj
ects.
Using a Joystick
Figure 3.2.18 shows how a common joystick, such as
the ones found in video games or pes, can be used to
control the two motors in the RobCom.
TIle circuit' uses four relays to controllhe two
motors. ll1e fou r switches o f the joystick arc used to power the motors on and off or to reverse the current
across them.ll1e position of the joystick affects what
happens to the motor:
Joystick Position
Center
Up
Down
Righi
Left
Upper ri ght
Upper left
Lower right
Lower left
Left Motor
Locked
Forward
l3ackward
Forward
Backward
Forward
Locked
Locked
Backw<lrd
Parts List- Using a Joystick
Right Motor
Locked
Forward
l3ackward
l3ackward
Forward
Locked
Forward
Backward
Locked
01 to 0 8 1 N914 or equivalent si licon diodes
Kl to K4 6 V to 12 X 50 mA reversible relays (select voltage according the motor)
28 Mechatronics for the Evil Genius
D3
K1 D1
Ri9ht~ K2 D2
D5
Down
Left Motor
o
D4 ....
~fO, -~
D6 ,-
1 ,~
o
D7
D8
+ 6/12V
I~ -K3 t
K4 I ~ -t ~
Right Motor
-- -- - -Figure 3.2.18 Controlling the combnt robot Ivith a game joystick.
Adding a Pulse Width Modulation (PWM) Control
A PWM control for the motor wi ll allow the reader
to change the speed of the RobCom. The PWM control is described in detail in Project 3.3.
Figure 3.2.19 shows how to add a I'WM block to
the RobCom. Notice that only one I'WM control is necessary to change the speed of both motors. Or if
the reader wants, he or she can use one PWM control
for each motor.
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Figure 3.2.19 A PWM control is added to the RobCol11 10 control the speed.
Adding Weapons
The reader can put his or her imagin ation to work creating new weapons for the RobCom. Of course, it
is important to be sure the weapons meet combat
rules.
Figure 3.2.20 shows how a small DC motor can be
used to add movement to the needle, making it much
more dangerous as a tool aga inst the enem y_
Another idea is to couple a rotary ball wi th nee
dles, as shown in Figure 3.2.21. In this case, the reader
must take care that the ball does not pop his or her own ba lloon.
Drinking Straw Solid Wire
t I ~r:::::) /~\ ~·<ltit=Tt ~ - _ _ Needle
Motor
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Figure 3.2.20 The mOlOr coupled 10 the needle can be activated by diodes when the RobCom runs fo rward.
3~------------------------------------------------______________________________________ _ Section Three The Pro jects 29
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.... --- Molor
------.~ Figure 3.2.21 A rOlary weapon fo r Ihe combal robol.
Rdding a Death Circuit
An interesti ng improvement fo r the project is a dealh
circuit. This circuit is formed with two reed switches
and a magne t, placed as shown in Figure 3.2.22.
As we call see, the current flows across the motors
and passes through the reed switches. 111e magnet is
attached with a ru bber band inside the balloon. If the
o balloon is full , the magnet touches the reed switches,
U and the motors are powered.
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If the balloon pops, the magne t fa lls and the reed
switches open. TIle motors are no longer powered,
and the robot stall s.
SWl
SW2
Magnet
Saloon
Figure 3.2.22 Placing the magnet in the balloon.
Rdding Sound
Figure 3.2.23 shows a simple sound-effect circui t for
the RobCom .
If a 47 oF capacitor is used, the circuit generates
sounds like a siren produces when the motors are
activated. If a 10 f.LF capacitor is lIsed, the circuit gen
erales pulses imitating a machine gun.
From Switches
C2 47 nF
113 To
"",---<~_+-_ Ml or 214 M2
SPKR 4/Sn
4X IN4148
Figure 3.2.23 SOllnd-effect cirCllit for RobCom.
Using an H-Bridge
111e digital control o f the RobCom can be imple
mented by usi ng an H-bridge. Th is idea is based on
the fact that fOllr transistors can be used to control
the current across a motor in the sa me way a double
pIIII/dollble-thrOlv (DPDT) switch cont rols the cur
rent. 111e circu it proposed in Figure 3.2.24 is a full
bridge or H-bridge using fou r D a rli ngton transistors.
Using an H -bridge for the control has two advan
tages. First, the curre nt across the cable is reduced.
Second , logic signals can be used in the control. In
th is case, even a computer can be used to control the
RobCom.
'1l1e circui t works as follows: When the forwa rd
(FWR) input is high, Ql a nd Q 4 are on and the cur
rent flows across the motor in the direction indicated
by a rrow 1. When the rewind (REW) input is high,
Q2 and Q3 are on and the current flows as indicated by arrow 2.
Notice that Ql and Q3 can 't be turned on at the
same ti me, as can Q2 a nd Q4, because that would
30 Mechatronics for the Evil Genius
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FW
J o-A ......--'IMr+-l:
B
J RW
Figure 3.2 .2lj The circuir for an f-1- bridge.
mean a short circuit [or the current be l ween + 12
volts and ground . It is a fo rbidden state that can
cause the transistor to burn. The circuit can be con
tro lled in the fo ll owing ways:
+v
Rt A 4
10kfi
Input R Input B Motor
Low Low Stalled
High Low Run forward
Low H igh Run backward
High High Forbidden
Figure 3.2.25 shows how to add a fifth transistor
a nd a logic system to avoid this forbidden state.
Parts List-Using an H-Bridge
Qt TI P122
Q3
lCl 4011 -4 NAND gates (CMOS integrated circuits [ICs])
Q l to Q5 TIP122 negative-positive-negative (N PN) Darlington tra nsisto rs
R l to R5 10 kfl X 1/8-watt resistor (brown, black, orange)
M D C motor (up to 500 m Al
+v o
M
Q2 TIP122
Q4 TIP122
R3 10 kfi
R4 10kn
TIP122
R3 10 kG
o o-----JtN~-_+K QS
Figure 3.2.25 I-I-bridge wilh logic.
Section Three The Projects 31
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The bridge works in the following manner:
Low
x (don' t care)
High
H igh
Low
Run forward
Ru n backward
Stalled
This same bridge can be implemented using the
same bipolar transistors used in the BD13S (500 rnA) or TI P31 (2 A) , as shown in Figure 3.2.26.
Rl lkn
A o---+J\N\r-+K
R2 lkn
B e>-<t-+J\N\r-+K
Figure 3.2.26 H-bridge using com l11OI7 bipolar transistors.
Using Gearboxes
The mechanics of the RobCom can also be improved
with the use of gea rboxes. As shown in Figure 3.2.27,
Common Plastic
Gear Boxes Wheel
I
~\ ~ Motors
Figure 3.2.27 Gearboxes can be used to pOlVer the robot. The photo sholVs a gearbox suitable for th is project.
the RobCom can be powered by small gearboxes, increasing the effic iency and a llowing the robot to be
built in a more compact manner. The gearbox can be
used to power the CD wheels or plastic wheels.
Remote Control
Starting with the ideas in this project, the reader who knows a lot about electronics call easily install a wire
less remote control in the combat robot. Small trans
mitterlreceiver modules, such as the ones shown in
Figure 3.2.28, are idea l for this task .
When using wireless remote controls, care should
be taken by the builders to choose different freq uencies for the systems. If two robots use the sa me fre
quency, interference problems will put the combat in
jeopardy.
Figure 3.2.28 Common hybrid modll ies fo r transmitters and receivers .
Technology Today
Combat robots are rea l these days. Mili tary robots ca n be used to fight, to carry resources, on rescue mis
sions, or to go where it is too dangerous for a human
soldier.
32 Mechatronics for the Evil Genius