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Small Robot Drive TrainsBy Ibrahim Kamal

Last update: 4/4/08

1-Traction and steering mechanisms There are many types of mechanisms that have been developed to move a robot from a place to

another, more than you could imagine, however, we will only study some of those techniques

which are the most adequate to relatively small robots:

1.1- Differential Drive system: This is the most common locomotion scheme in the world of

robotics. It's easy to build, easy to control and can permit the robot to move in all requireddirections. In that system, two motors are connected, one to each of the two drive wheels at the

right and at the left of the robot's base. Those two motors are responsible of driving the

Table of content:

Overview

Traction and steering mechanisms

Mounting the motors

Transmitting power to the wheels

Diameter of the wheels, speed and torque

Mass distribution and robot stability

Acquiring small motors and Building materials

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Overview

This Tutorial Aims to introduce to beginner thedifferent techniques used to build the chassisand drive trains of relatively small robots.W h a t I m e an b y sm a l l r o b o t s , i s t h e c a t e g o r y o f l ig h t

w e ig h t r o b o t s w h e r e a s p e c t s l i k e a er o d y n am i c s a n d

v i b r a t i on d am p i n g a r e n o t t a k e n i n a c co u n t .

Most of the fundamental theory remain the same for all

sizes of robots, Theory such as robot stability, traction

and steering techniques. However, This tutorial is

dedicated tothe construction of relatively small robots,explaining how to the implement your designs using

material and equipment at the reach of any average level

hobbyist.

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As you can also notice in the figure 1.A, this system needs one or more caster wheels (also called

free-wheels) to support the rest of the chassis while freely following the movement of the robot

engaged by the two main drive wheels. Some robots use 2 caster wheels, adjacent to the drivewheels for better stability, but again, in the category of small robots, one caster wheel can be

enough.

in a horizontal position. This technique becomes interesting when used for lightweight robots,

where caster wheels can cause even more friction than the skids, and add additional and

unnecessary weight to the robot.

You can also notice in the figure 1B that the rear skid is not touching the ground, and thus is nota primary skid, but rather a secondary one just in case the robot pivots around the drive wheels

to the back during a sudden acceleration for example.

1.2- Four wheel differential drive system:

robot back and forth as well as steering in

any required direction. This system can

even allow a robot to pivot in its place.

The word "differential" comes from the fact

that this system relies on the velocity

difference between the two wheels to drive

the robot in the required path and make it

move in any required curve.

Figure 1A shows in a simplified way the

principle of operation of differential drive.

When the left and right motors are turningat the same speed, the robot moves

forward or backward in a straight line. In

order to turn right for example, the right

motor is slowed down and the whole robot

steers to the right. The bigger the

difference of speed between the two

wheels, the tighter will be the steering

curve. F i g u r e 1 . A : D i f f e r e n t i a l d r i v e s y s t em

Many roboticists

even replace this

single freewheel with

a piece of bent metal

or any other low

friction surface to

act as skid that slips

on the ground under

the action of the

driving wheels.

Figure 1B shows the

chassis of one of our

line follower robots

where skids are used

along with the drive

wheels to support itF i g u r e 1 . B : Sk i d s u s e d o n a d i f f e r e n t i a l d r i v e t r a i n


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friction, it requires relatively powerful motors, as compared to the previous differential drive

scheme. The advantage of this system is that it is very easy to build and is most suitable for

running on low friction and dusty surfaces where other drive systems would suffer.

1.3- Car-type drive system: This drive system has many names, but calling it "car-type" make it

clear to any reader, that it consists of 2 wheels coupled on the same axe at the back and one or

two wheels capable of steering to control the displacement of the robot. While this technique is

very difficult to implement mechanically, it provides two major advantages over other tractionsystems: Ease of control and accuracy (because traction and steering are connected to two

independent motors). The best way to build your first 'car-type' drive train is to look at any old RC

toy car. You can also use some parts of it's drive train to build your own, or even use the

allowing the green axe (in the figure) linking the two front wheels together to move freely along

the axis of the chassis.

There can be many other configurations based on the same idea, like a 2 wheel traction / 1 wheel

steering drive train, which may be a little simpler to construct because the front wheel can be

directly connected to a gearhead DC motor.

1.4- Divided chassis drive train:This is another locomotion scheme that we experienced, which has the advantage of being very

powerful and highly configurable. Inneed, this system relies on 4 independent motors, each one

coupled to one of the four wheels, allowing the robot to move forward or backward with the

Another variation of the differential drive system, is the 4

wheel differential drive system, which resembles the drive

trains of tanks and bulldozers.

As figure 1c shows, it consists of only two motors and 4

wheels. Each pair of wheels are mechanically connected

together, usually by the mean of a belt forcing them to

move together, driven by a single motor.

The behavior of this drive train is similar to the previous

differential drive system; If the the two motors turn at the

same speed, the robot moves forward or backward, if there

is a difference between the speed of the two motors, the

robot will steer in the direction of the slower motor.

This drive system implicates a great deal of friction,

specially during steering, and thus, to overcome this F i g u r e 1 . C: 4 w h e e l d i f f e r e n t i a l d r i v e s y s t em

chassis of a brand-new RC toy car

for your robot, as we did in the

WFR project. Figure 1.D shows a

simplified layout showing the

principle of operation this drive

system. Connecting the front

(steering) wheels to the motor can

be very complicated, but a basic

rack and pinion arrangement can be

enough for very low steering angles,

otherwise, for relatively high

steering angles, the rack and pinion

arrangement will have to be

enhanced with a sliding mechanism F i g u r e 1 . D : B a s i c c a r - t y p e d r i v e t r a i n
http://www.ikalogic.com/wfr2.php


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the two rear motors are used either to push it or to bend the chassis (like a toy train) to turn

right or left by running one of the two motors faster than the other.

One last special feature of this system is that it has no head nor tail, in other words, there is no

difference between the front part of the chassis and the rear one, making it possible for the robot

to change it's direction, to adapt to any situation, without having to execute a 180 degrees

rotation.

2-Mounting the MotorsWhen you are settled on a traction and steering mechanism for your robot, you have to find a way

of fixing the motors firmly to the chassis. At this point, in order to construct a professional drive

train, you have to take those points in consideration:

You have to be able to mount and dismount the motor easily. Gluing, soldering and other

permanent fixing solutions are not good ones. As a roboticist, building a prototype, You have to

able the make any modifications easily.

The outer shell of a motor is not designed to bear high, undistributed stresses. whatever the

method you are using to mount and hold your motors in place, you have to increase the contact

area between the motor's body and the mechanical part linking it to the chassis to prevent stress

concentration and eventually damaging the motor.

There are many items that you can buy at your nearest hardware store, to use it to mount themotor on the chassis, I present some ideas that I find to be the most adequate to this category

of robots.

2.1- Pipe Clamps:

accumulated power of four motors

or to turn right and left with

approximately equivalent power, but

with minimum frictional losses.

Figure 1.E shows how to implement

such a configuration, and shows

how the the chassis is divided into

two parts, hinged together, allowing

it to change it's shape to turn in

tight curves.

Usually, the two front motors areused only to drag the robot, while F i g u r e 1 . E: P i ct u r e a n d l a y o u t o f t h e d i v i d e d c h a s s i s

Because they come in any size you want, because they

are cheap, and because it can be used with any motor,

this is my favorite choice. Initially, at the name implies,

pipe clamps are used to fix water pipes on walls. Due to

the resemblance of size and shape between the outer

shell of a standard DC motor and water pipes, those

clamps are very adequate to the job of holding motors

firmly in place, while distributing any eventual stress along

the whole contact surface.

Figure 2.A shows a standard pipe clamp, where the right

bolt was replaced with a longer 4mm screw, to be used

later to fix the motor-clamp assembly to the chassis. Note

F i g u r e 2 . A : P i p e c lam p


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2.2-U-bolts:

2.3- Building your own bracket:

If your motor is too small, too big or just not adequate to any of the previous solutions, building

your own bracket to hold your motor is not that difficult. You have to use your imagination, and

cope with the components, tools and materials that are at your reach. At this point i'll only give

you hints of materials you could use to easily attach your motors.

that there are many varieties of pipe clamps, so it's up to

you to pay a visit to your hardware store and find the one

that would be the most suitable according to your design.

Most Pipe clamps come with a nut welded to it, allowing

easier fixation to any adjacent plan (that plan can be a

wall as it can be the chassis of your robot).

Figure 2.B shows how a motor fits in that pipe clamp.

Adding small parts of rubber between the surfaces of the

motor and the clamp can be a good idea, as it will absorb

any eventual vibration, and protect the motor's body.

Figure 2.C shows how a pipe clamp can be used to mountthe motor on the chassis. As you can notice, one of the

main advantages of using a pipe clamp, is that you can

easily adjust the distance between the motor and the

base of the robot to which the motor is fixed, which is not

the case with other solutions, like the U-Bolt idea..

F i g u r e 2 . B : DC m o t o r & pipe clamp

F ig u r e 2 . C

If for any reason the pipe clamp solution cannot be used,

this is the second best choice. I've never used thistechnique to fix motors, but i've seen it used by many

hobbyists. The two reasons making this technique less

effective that pipe clamps are:

1- The contact area is relatively small, thus stress

concentration can be a problem. This problem can be

solved by using more than one U-bolt for each motor.

2- The U-bolt is designed to hold a circular object by

pushing it against a fixed surface. As figure 2.E shows, in

our application, the circular object is the motor and the

fixed surface is the chassis. so the height of the motor

from the ground depends on the height of the part of the

chassis where the motor is fixed. In contrast, with Pipe

clamps, you can easily adjust the distance between the

chassis and the motor.

Figure 2.D: U-BoltPicture from: http://www.gibsonstainless.com/

Figure 2.E: U-Bolt on a motor

- A rubber band (figure 2.F) can hold your motor in place

exactly like a U-Bolt, while giving it some elasticity to

absorb shocks and vibrations. You can obtain really strong

rubber belts from old cassette players.

Figure 2.F

- Thick copper wire can also be used instead of the U-

bolt, although it has the major disadvantage of being a

permanent solution, any modification will be destructive and

new wires will have to be installed. Figure 2.G shows actual

pictures of DC motors that's I've mounted on one of my firstrobots.
http://www.gibsonstainless.com/


6/13

- Metal sheets formingis the best alternative to U-Bolts and pipe clamps if you have the tools,

skill, and material to do the job. Then you can form the exact required shape to firmly hold your

motor in place. I personally recommend Aluminum as a working material. It's corrosion resistance,

it's light weight and it's machinability, make it a perfect match for small robots.

3-Transmitting power to the wheels There are many way of transmitting the power from the motor's shaft to the wheels, but in any

case, friction is your biggest enemy. The frictional losses increase when the weight of the robot

increases, specially if you're not using any ball bearings to support the shaft, which is usually thecase in small robots. I am going to categorize the various techniques used for power transmission

into two main categories: Direct transmission and Un direct transmission.

3.1 -Direct transmission

3.1.1- Direct transmission from a DC Motor, Which is when the wheels are directly mounted on

the motor's shafts. This technique is only acceptable when working with very light weight robots,

otherwise, those relatively small DC motors are not mechanically designed to bear any bending

stresses that could be caused by directly mounting a wheel on it. Usually the internal

3.1.2- Direct transmission from a gearhead DC motor is the most common method used by

roboticists, specially for the category of robot we are talking about. That's because the output

Figure 2.G

- Plastic strap fastener, is still a permanent solution, but

has the advantage of providing a strong attachment, while

being easily introduced and fastened in small places where

it would be harder to install copper wires or rubber bands.

Figure 2.H

bearing of those motors are designed to withstand the

stresses required to keep a gear in place in a gearbox,

or to withstand the tension in a rubber belt. In Mostcases, directly mounting the output shaft of a DC motor

to a wheel is rarely the best choice because without

any speed reduction, the developed torque wont be

enough to easily move a robot around. Figure 3.1.1

shows an example of how a small plastic wheel can be

mounted to the tiny shaft of small motors. As you can

see this is the same idea used in most toy cars, where

parts are simply forced in their place. This is more

interesting than more advanced shaft coupling

techniques when you're working with tiny motors,

because it would be very difficult to drill it's output

shaft to install setscrews or pins.Figure 3.1.1


7/13

3.2-Undirect transmission

Undirect transmission means that the shaft holding the wheels is on a totally different plane than

the output shaft of the motor. Usually, between those two shaft is a reduction belt/gears

arrangement. Undirect transmission is more suited to heavy robots, where rolling bearings are

installed to support the shaft holding the wheels, to minimize any frictional losses due to the

technique on one of our early robots, where each wheel is mounted to a 6mm steel shaft,

supported at both ends with rolling bearings. There is no obligation to put the rolling bearing at

both sides of the wheel (the two rolling bearing can be placed at the same side of the wheel as in

figure 3.2A) but you have to put two of them, each one as distant from the other as possible, to

reduce shear stresses on the rolling bearings. (rolling bearings are designed to withstand very high

radialstresses). While you're looking at the pictures, you can notice how the motors are mounted

with i e clam s as ex lained before.

shaft from the gearbox of a gearhead motor are

designed withstand higher stresses than the output

shaft of the motor itself and has a very suitable output

characteristics (low RPM and high toque). That can be

noticed from the shape of the output shaft of a

gearhead DC motor in the figures 3.1.2A and 3.1.2B,

which is not fully circular to be able to firmly secure it

to a shaft coupling or to a wheel in our case.

There are many ways to fix a wheel to the output shaft

of a gearhead DC motor, one of the simplest ways is to

drill a hole in the body of the wheel, of the exact

diameter of the screw to be used. Forcing the screw inthe drilled material for the first time will form a helixmating the thread of your screw, allowing you to fasted

the shaft in its place by simply driving the screw.

If the wheel you are using doesn't have an extended

shaft as shown in figure 3.1.2A, you will have to find

another mean of fastening the motor's shaft to the

wheel, but virtually any wheel you will find is designed

to be mounted on a shaft, so using your imagination,

you'll end up finding a solution to that problem,

depending on the shape and size of the wheel.

Figure 3.1.2B shows the output shaft of an old PITMAN

GearHead DC motor.

Figure 3.1.2 A

Figure 3.1.2 B

weight of the robot. Mechanically speaking, any wheel is to be

fixed with rolling bearings, so this is the best method of all, but

again, you have to remember that there are some compromises

that can be made with small robots, to reduce cost, weight and

complexity.

Figure 3.2A shows a classic undirect transmission system,

where the rotation of the motor's shaft is transmitted through a

reduction pulley arrangement, lowering the RPM of the wheel,

while increasing the torque. Notice how the the full weight of

the robots is distributed only on the two rolling bearings, makingthis drive train much more robust than other where the wheels

are directly mounted on the motors.

Figure 3.2B and 3.2C shows a practical implementation of this Figure 3.2A


8/13

4-Diameter of the wheels, speed and torque With a constant output RPM from a motor, The diameter of the wheel is the last criteria that can

affect the the balance between the torque of the robot and it's linear velocity.

Consider the wheel in figure 4, having a radius rturning with a constant angular velocity (RPM) wwww,

Pa point on the circumference of the wheel, Tthe torque developed from the motor acting on the

ground plane and F the reaction force of the ground on the wheel.

that increasing the radius of the wheel will increase the velocity of the robot, but also increase

the resisting torque that the robot have to overcome. Thus, varying the radius of the wheel, you

can make a compromise between linear velocity and torque of the robot.

5-Mass distribution, Moment of Inertia and robot stability One of the most important phenomenon that can affect the behavior of moving robots is the

moment of inertia. The moment of inertia, which is different for each shape, size, weight and

trajectory of a moving rigid body, is the ability of that rigid body to resist a change in its

velocity. The force developed by the moment of inertia appears at the center of gravity of the

body, and acts as a mechanical moment around the pivot point of the robot (usually a wheel) in

the a direction opposing the change of velocity.

In order to better understand the effect of mass distribution on the moment of inertia and

consequently on the stability of a moving robot, let's imagine this scenario where a simple robot

(as shown in figure 5.A) is moving at a constant velocity in the horizontal direction. Recalling the

secondlaw of Newton, and noting that theacceleration of the robot equals zero,

Figure 3.2B Figure 3.2C

Let Tfbe the torque developed by the ground as reaction

to the wheel's movement. This is the torque resisting the

robot's movement. For the robot to move from rest (or to

accelerate), Tmust be bigger than Tf.

The toque Tf = F.r.......(1)

Also note the that the linear velocity of the robot equals

the linear velocity of any given point on the outer

circumference of the wheel,

Then the velocity V = wwww.r.......(2)

From the relations (1) and (2), you can easily deduce Figure 4


9/13

of inertial depends on the rate of change of velocity (the acceleration). You can greatly decrease

the effect of inertia by controlling the acceleration and deceleration of your robot, through

ingenious speed control algorithms

6-Finding motors and building material

The easiest way to acquire all the material and equipment you need to build a robot, is to buy it!But that's not the cheapest way, and sometimes you won't find all what you need in the stores.

That's why - if you plan to dig your way in the field of robotics - you should start collecting all

the force F1 moving the robot forward

equals the resistance force R1 (which is the

sum of all mechanical friction losses in the

system). The stability problem will start to

appear when this moving robot will suddenly

stop.

In that situation, there is a change of

velocity, a deceleration or a negative

acceleration as some books states and the

moment of inertia of the robot will resist this

change of velocity, by generating a force

acting in the previous direction of motion,tryingto keep the robot moving in the same

direction, with the same velocity.

In figure 5.B, the effect of the moment of

inertia is somehow exaggerated to clearly

show the unstability that can be caused by

this problem. To solve this problem, and

design robots that have very low inertia,

you have to understand those two main

factors that affect the inertia of a body:

A- The position of center of gravity has tobe as near as possible from the ground or

from the eventual pivot point (which are the

wheels in case of our example robot). This is

verified by the mathematical relation that

state that:

I = m.(r^2)

Where I is the moment of inertia, m the

mass of the body, r the distance between

the center of mass of the body and the

pivot point

To change the position of the center of

mass of your robot, you have to lower the

position of the heavy parts of the robots like

the batteries and the motors.

You also have to design the chassis to be as

near as possible from the ground (as shown

in figure 5.C). If all that is not enough, or if

the chassis simply isn't heavy enough, it's

common practice to add additional weights

as near as possible from the ground with the

sole purpose of lowering the overall centerof mass of the robot.

B-The torque developed by the moment

F i g u r e 5 . A

F i g u r e 5 . B

F ig u r e 5 . C


10/13

kind of devices from which you can scavenge all kind and sizes of DC motor, mechanical parts,

gears, pulleys, etc.

From my experience, I tried to classify the kind of devices from which you could extract useful

items, at least, this is what I do with those devices before throwing them away.

Old cassette players and walkmans: Small Motors, pulleys, belts, gears.

Old Floppy disk and CD-ROM drives: Very small motors, worm gear, sliding mechanism, gears, limit

switches

Old Photocopier machines, printers and scanners: quality Gearhead DC motors, sliding mechanisms,

rubber wheels, gears.

As for the chassis, it can be built with a multitude of materials. My preferred material is Copper

boards (made for PCBs) as you can solder many metals to it like screws and nuts, you can also

design the main board of the robot on the same board to reduce size, weight and cost.

My second best choice is the Fiberglass. It can be easily formed with a a cutter, can be easily

drilled, can sustain high stresses, and looks very neat an professional.

Another good choice for building the chassis of the robot is the 3mm Medium Density fibers (MDF

wood) which has the advantage of being very cheap, and can be very easily cut, drilled and

grinded to any shape you want. The only disadvantage of this material is that it can easily

deteriorate with water or even too high humidity.

Those were the material I found to be more suitable for this category of robots.

Discussion (Last 15 posts preview...)Preview of the last 15 messages discussing this page. Messages are sorted from the newest to the oldest.

Follow this discussion in the Full-featured forum

Posted by:

demonhackeron: 10 Jun 2009

Re: Small Robot Drive Trains ['Quote]

Q u o t i n g i k a l o g i c :

buddy your question is irrelevant.please elaborate your query so that the other person getsthe clear idea of your concern.

Q u o t e : sir , i am verythankful for all this guidance but i want to know that howaerodynamics is used to make robotics?

Posted by:

ikalogicon: 07 Oct 2008


Search on e-bay for modeling and hobby wheels, you should find what you

need

small advice from a mechatronics engineer: start by chosing your motors,

and depending on their couple, chose the biggest possible diameter for the

wheels, that will still be small enough to deliver enough couple to move your

robot around all those terrains...

Q u o t in g a b h i g em _ 1 2 6 : hey, i am building a differential drive that can move on all kind ofterrains, namely sand, peebles, greasy path, water ditch, bumper... etc. can u guys help me

with what kind of wheels to use??? what kinda grip to use???

Posted by:

abhigem_126on: 07 Oct2008

Small Robot Drive Trains ['Quote]

hey, i am building a differential drive that canmove on all kind of terrains,

namely sand, peebles, greasy path, water ditch, bumper... etc. can u guys
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11/13

help me with what kind of wheels to use??? what kinda grip to use???

Posted by:

ikalogicon: 19 Aug 2008


I could, but the first thing you have to know is that it would be big mistake

to put all that weight on the robot. you have to keep all the batteries,

motors, and electronics on the fixed base, and use wire systems to transmit

the mechanical power to the different parts of the ARM...

Q u o t i n g g y a a n g u r u : hellowe are working on a project in which we trying to make a robotic arm on a moving base. .since we are all electrical students we are having a bit of difficulty in designing base andfinding motors. the total weight of the arm + batteries (lead acid) +electronics = 7 kg .could you please tell me the type of motor required in terms of torque. how do we calculatethe torque requirements in general. preferably a speed of 0.6m/s (2 ft/sec) is required.could to teach us how to go about these calculationsthank u

Posted by:

gyaanguruon: 18 Aug 2008


hello

we are working on a project in which we trying to make a robotic arm on a

moving base. . since we are all electrical students we are having a bit of

difficulty in designing base and finding motors. the total weight of the arm +

batteries (lead acid) +electronics = 7 kg .could you please tell me the type of motor required in terms of torque. how

do we calculate the torque requirements in general. preferably a speed of

0.6m/s (2 ft/sec) is required.

could to teach us how to go about these calculations

thank u

Posted by:

ikalogicon: 23 May 2008


15cm is more than enough, and with that size of robots, you can use the

PCB material for the chassis, as in our mini line follower robot project. I

think it is the most suitable for that size

Q u o t i n g s a if : about 15cm dia... v had decided on 20cm but since most of the collegecompetitions here in bangalore(india) fix the maze width at abt 20-25cm max.. nd aso theyfix a max limit to ur chassis width as sumthin lik 20cm.. so that is it-15 cm... u think its too

less?

Posted by:

saifon: 23 May 2008


about 15cm dia... v had decided on 20cm but since most of the college

competitions here in bangalore(india) fix the maze width at abt 20-25cm

max.. nd aso they fix a max limit to ur chassis width as sumthin lik 20cm..

so that is it-15 cm... u think its too less?

Posted by:

ikalogicon: 22 May 2008


circuilar is ok, but, as fr the material of the chassis, i can't tell you unless

you tell me, what is the size of your robot?

same thing for the battery.

Q u o t i n g s a if : salam... hey vr actually designing a chassis which v decided to be cicular withjust 2 wheels ndpassive skids.. is a circular chassis ok wid u? v decided on it coz it canrotate freely in any direction easily... even a 360 turn... nd wot material do u recommend 4the chassis? it shud be light as well as sturdy..nd do u recommend a lead acid or nicad battery?
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so, what's the size of your robot?

Posted by:

saifon: 22 May 2008


salam... hey vr actually designing a chassis which v decided to be cicular

with just 2 wheels nd passive skids.. is a circular chassis ok wid u? v

decided on it coz it can rotate freely in any direction easily... even a 360

turn... nd wot material do u recommend 4 the chassis? it shud be light as

well as sturdy..

nd do u recommend a lead acid or nicad battery?

Posted by:

ikalogicon: 28 Feb 2008


Good question!

You can either do it the easy way, which is to use 'skids' that will act just

as a wheel but with more friction..

Or you can do it the hard way, wich is to build a robot with only 2 weels in

the midle, and to constantly accelerate and decelerate the wheels, acting

on the momentof intertia of the robot to stabiliseit.. or maybe you have tohave a mean of changing the center of gravity of the robot to give it the

ability to balance itself horrisontally.. there lot of ongoing researches about

this subject.. you may find some information on wikipedia..

hope this answers your question.

Q u o t e : how can we construct a small robort which has only 2 wheels and can turn and movein any direction

Posted by:



Well, unless you wroking with robots that go in the air on in the sea, or

that are very fast, aerodynamics usually is not a big concern. I honnestly

don't have a lot of experience in this field so i can't give you more

information.

good luck

Q u o t e : sir , i am very thankful for all this guidance but i want to know that how aerodynamicsis used to make robotics?

Posted by:



discussion for the page: [link]

Gearhead DC motors (which are normal brushed DC motors, with a gearbox

attached to it's output shaft, to decrease speed and increase torque)

Q u o t e : sir i have gone through the site,i want to know which motor is prefered for the betterefficiency of the robots.(what type it is?)

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