rc car build

8/8/2019 RC Car Build

1/35

Design and Fabrication of IC Engine

Powered Radio Control Car

Guest article by Srihari.B

The Radio control dates back to the nineties when it first evolved. It is a hobby for most of the

engineering and automobile enthusiasts. It is proved by its rigidity, precision and ability.

The design of such RC cars has become a great market in the western nations. The design ofsuch RC car involves precision, rigidity and team work too

This project involves the design of the chassis and steering system of a 3cc IC engine poweredradio control car and to match its performance with that of the originally available components.

The main objectives of this project are

y To design a specific chassis system to accommodate all the components of the RC car tobe mounted on to it.

y The design of the steering system which should be capable of steering the car like thealready available mechanism and also to eliminate the ball joints present in the steeringmechanism.

y To fabricate the suspension arms to improve strength.y To fabricate a suitable body for the RC car.


2/35

1. Introduction:1.1 Radio Control Car:

A radio-controlled car (R/C car) is a powered model cardriven from a distance using a radio

control system. Inputs fromjoysticks (or a wheel and a trigger) on a transmitterare sent to the

car's onboard receiver. The receiver interprets the radio signals and sends electrical pulses to the

servo and electronic speed controller, making the model turn its wheels and the motor run.

RC Buggy (Scale 1:8)

Radio-controlled (orR/C) cars are usually categorized as either "toy" or "hobby" grade. Remote-

controlled vehicles differ from radio-controlled by the presence of a wire cable connecting thetransmitter and the car, limiting their movement

Cars are powered by various sources. Electric cars are powered by small but powerful electric

motors and rechargeable nickel-cadmium, nickel metal hydride, orlithium polymercells. Thereare also brushed or brushless electric motors. Most fuel-powered models use glow plug engines,

small internal combustion engines fueled by a special mixture ofnitro methane, methanol, andoil (in most cases a blend ofcastor oil and synthetic oil). These are referred to as "nitro" cars.

Further these cars can be classified as Off-road and on-road models. Off-road models, which arebuilt with fully-functional off-road suspensions, can be used on various types of terrain. In

comparison, on-road cars, which generally have a limited or non-existent suspension, are strictlylimited to smooth, paved surfaces

1.2 IC Engine Powered Car:


3/35

An R/C car can be powered by motors or engines. The cars that are powered with engines arecalled as Nitro-powered RC car. They use methanol as a basic fuel with a percentage of nitro

methane as booster and castor oil for lubrication.

Fuel-powered engines allow model cars to reach moderate speeds unmodified. Maximum power

is generally achieved at medium to high speeds and a slightly slower throttle response thanelectrically powered vehicles are to be expected. Electric motors effectively produceinstantaneous torque, where nitro engines, like full-sized gasoline engines, take time for the

engine to spool up and for the clutch to engage. Nitro- (and fuel) powered cars may be refueledand returned to action in a few seconds, as opposed to electrics needing to remove the body shell

and battery fasteners to replace a discharged battery. Nitro cars are completely air cooled, andmay be run continuously with no need to take breaks for cooling down. Nitro cars tend to be

larger than electric cars on average

1.3 Principle of Operation:

Radio-controlled cars use a common set of components for their control and operation. All carsrequire a transmitter, which has the joysticks for control, or in pistol grip form, a trigger forthrottle and a wheel for turning, and a receiverwhich sits inside the car. The receiver changes the

radio signal broadcast from the transmitter into suitable electrical control signals for the othercomponents of the control system. Most radio systems utilize amplitude modulation for the radio

signal and encode the control positions withpulse width modulation. Upgraded radio systems areavailable that use the more robust frequency modulation andpulse code modulation. The radio is

wired up to eitherelectronic speed controls orservomechanisms which perform actions such asthrottle control, braking, steering, and on some cars, engaging either forward or reverse gears.

Electronic speed controls and servos are commanded by the receiver through pulse widthmodulation; pulse duration sets either the amount ofcurrent that an electronic speed control

allows to flow into the electric motor or sets the angle of the servo. On the models the servo isattached to at least the steering mechanism; rotation of the servo is mechanically changed into a

force which steers the wheels on the model, generally through adjustable turnbuckle linkages.Servo savers are integrated into all steering linkages and some nitro throttle linkages. A servo

saver is a flexible link between the servo and its linkage that protects the servo's internal gearsfrom damage during impacts or stress.


4/35

Belt Driven On-road Car (Scale 1:10)

Fuel powered models utilize a servo for throttle and braking control; rotation of the servo in one

direction will cause the throttle on the carburetorto open, providing more air and fuel mixture tothe internal combustion engine. Rotation of the servo in the other direction causes torque to beapplied to a piece which causes friction with the braking material. The brake is located on the

driveshaft and stops only two wheels on a two-wheel drive car and all four wheels on a four-wheel drive car.

The whole machine is divided into three major categories:

1) Engine

2) Chassis and Suspension

3) Control

2. Engine

2.1 Introduction


5/35

Engine

Most gas R/C models use a 2- or 4-stroke glow engine, sized specifically for that model. Glowengines have a simple ignition system that uses a glow plug rather than a spark plug so theres

no coil, magneto or points. The glow plug is heated by a battery-operated glow starter. Whenfuel enters the combustion chamber, its ignited by the heated glow plug and with that, the

engine springs to life, instantly gaining the momentum to continue running after all the starteraccessories are removed. The engines carburetor supplies the fuel and air needed for

combustion. It has several adjustments. A rotating throttle arm controls the amount of fuel andair that enters the combustion chamber. The high-speed needle valve controls the mix or

proportions of fuel vs. air at mid- to high-speeds. The idle mixture screw is similar to the high-speed needle valve, except that it controls the mix of fuel and air when the engine is only idling.

2.2 Glow plugs

Glow plugs


6/35

A gasoline combustion engine uses a spark plug to ignite the fuel-air mixture within thecompression chamber, so a glow or nitro engine uses a small glow plug. Although the plug needs

to be heated up using a glow plug igniter initially, once the engine is running, the heat generatedwithin the combustion chamber keeps the plug glowing constantly and is thus able to ignite the

fuel-air mixture on each revolution.

To start a glow plug engine, a small direct current (around 1.5 volts) is applied to the glow plug,initially heating the filament. The engine is then spun from the outside to introduce fuel to the

chamber. Once the fuel has ignited and the engine is running, the electrical connection isremoved. Each combustion keeps the plug's filament glowing hot, allowing it to ignite the next

charge, thus sustaining the power cycle.

Technically a glow plug engine is similar to a diesel engine in that it uses internal heat to ignitethe fuel, but since the ignition timing is not controlled by fuel injection (as in an ordinary diesel),

or electrically (as in a spark ignition engine), it must be adjusted by changing fuel/air mixtureand plug/coil design. A richer mixture will tend to cool the filament and so retard ignition,

slowing the engine. This "configuration" can also be adjusted by using varying plug designs for amore exact thermal control.

2.3 Fuel

Glow engines cannot be operated with the same gasoline you get at a filling station pump. Theyrequire a special fuel, called glow fuel. It contains methanol as the base, with varying amounts

of nitro methane to increase the energy that the fuel can provide. Oil, pre-mixed into the fuel,lubricates and protects the tiny engine as it pounds out amazing power. The mixture of the fuel is

85% methanol and 15% castor oil.

2.4 Carburetor


7/35

Carburetor

Sitting at the front of the engine on top of the crankshaft is the carburetor, which is the part of

the engine that introduces the fuel into the crankcase. The fuel / air mixture is ignited by a glowplug which is screwed into the top of the cylinder head.

3. Chassis & Suspensions:

The chassis should be light in weight, strong and also able to accommodate all the components.

It can be made of aluminum or carbon graphite. The chassis should bear the whole weight of thecar. So it should be rigid and also accommodate the other forces acting on it.

The basic components of a car are

1) a) Rear drive shaft or dog bone b) Front dog bone

2) Front and rear disk brakes.

3) Center bulkhead.

4) Fuel tank

5) Center differential and spur gear.

6) a) Rear chassis brace

b) Front chassis brace

7) Servo tray

8) Battery and receiver box

9) Rear shock tower. The shock tower has many different mounting holes for both the shock andcamber link.

10) Rear camber link turnbuckle (adjustable)

11) Rear hub carrier.


8/35

12) Rear suspension arm.

13) Rear sway bar.

14) Rear CVD shaft.

15) Rear hub.

16) Rear differential housing, differential and rear bulk head.

17) Rear springs.

18) Rear shocks

Rear suspensions


9/35

Front steering and suspensions

19) Upper and lower pivot/pillow balls. They thread into both the upper and lower A-arms. Thisgives you the ability to change camber.

20) Front CVD

21) Front lower suspension arm

22) Upper suspension arm - A-arm.

23) Front shock tower.

24) Front drive shaft or dog bone.

25) Steering knuckle.

26) Front hub.

27) Front sway bar.

28) Front differential, differential housing and bulkhead.

3.1 Suspensions


10/35

The main component of a suspension is its springs. Coil springs are used commonly. These areusually placed around the damper housing to form a spring-damper unit. A spring is an elastic

device that resists movement in its direction of work

The main job of the suspension system is the following,

1. Maintain the ride height2. To provide damping3. To give the best suspension travel for a typical car4. To prevent the car from rolling5. To protect the car and all its components

3.1.1 Ride Height

This refers to the clearance between the ground and the chassis, both at the front and the back of

the vehicle. The spring adjusters on the shock can be adjusted (which are at the top of each shock

spring) until the appropriate height is achieved after the drop test. If you have an on-road vehicle,you should place it on a flat hard surface, compress the suspension a few times by pressing onthe chassis and let it return to its normal position

Deflection of different springs

3.1.2 Toe-In/Toe-Out


11/35

It is the angle of the front tires when viewed from above when the suspension arms are level. Ifthe fronts of the tires angle in, it is called toe-in and if the fronts of the tires angle out, it is

called "toe-out. This is adjusted by turning the steering rods - the rods that run between the fronthub and the steering linkage that is mounted on the chassis.

3.1

.3 Camber

Camber is the angle of the tops of the tires when viewed from the front. Negative camber is

when the tops of the tires are angled towards the center of the vehicle. Positive camber is wherethe tops of the tires are angled away from the center of the vehicle. Positive camber is very rarely

used, if ever. A small amount of rear negative camber is helpful to increase traction in the rear.Negative camber at the front will increase stability.

4. CHASSIS FABRICATION

Comparison withFabricatedChassis (Left - Modified Chassis, Right - Original Chassis)


12/35

4.1 Fabricated chassis

The chassis has very minimal flex and is very rigid. The chassis is hand worked in a tincture

shop and all the holes and the spur clearance and starter box provisions are drilled to match withthe required dimension to suit the layout of the car.

The following alterations are made on the new chassis:

Added material for extra strength at the corners

Bent sides which will act as a bumper in one way and also reduces the longitudinal torsion

Specifications Fabricated Chassis Readymade ChassisMaterial

Thickness

Mass

Length

Width

Maximum thickness

Aluminum 6061

3mm

750gms

392mm

225mm

12.2mm

Carbon Graphite

2mm

500gms

392mm

190mm

7mm

Table 4.1Comparison between the fabricated and readymade chassis

4.2 Method of Fabrication:

The raw material taken was Aluminium 6061 and of thickness 3mm.

Then the various processes that were done on the sheet were

1. Cutting and parting off: The chassis was cut to the required dimension with the help ofthe readymade chassis

2. Drilling: The required holes for the mounting of the various components were measuredand then drilled on to the chassis


13/35

3. Slot Drilling: The slots for the flywheel for starting and stopping the engine are alsoprovided. It was machined using a hand drill

4. The corner bends were provided in order to prevent the flexing and bending of themember

5. The slots were also given for the mounting of the servo motors in position.The fabricated chassis proved to withstand the various forces like the vertical bending,Longitudinal torsion, lateral bending and Horizontal lozenging.

5. STEERING MECHANISMS:

The steering mechanism of this on-road vehicle is totally unique where we have eliminated all

the ball and socket joints in order to make the mechanism as well as the fabrication part a bit

simpler.

Drag links with ball and socket joints

The challenge here was to eliminate all the joints with two or more degree of freedoms andrestrict it to one degree of freedom in two directions. The idea was inspired from the universal


14/35

joint. Usually the joints are made of plastics. The material selection was also a challenging tasksince it has to have the strength and functionality as that of the readymade one.

5.1 Steering Link Design

The objective of the design was to eliminate the ball and socket joint. So the single member wassplit into three different components. The one was a rod with external threads. The other memberis to hold the joint and the third member will have one rotational degree of freedom.

Steering Components

Stud


15/35

The component in Fig 5.1 is fastened with the stud and on the other end is a freely rotatingmember which will be fastened with the hub on one end and to the servo link on the other end. It

will provide the two DOF and also is easy to fabricate.

5.2 Steering Link Assembly

It bears some similarity with a universal joint but how ever the application part is new!!! Thebrown member is a stud on which two brackets are screwed into. Then the green member is a

free to oscillate kind of member which will effectively allow both the degrees of freedom that aball and socket joint would do.


16/35

Steering Mechanism Assembly

For example the member on the left is oscillating along the XX axis then the member on the rightwill oscillate along the YY axis thus satisfying the conditions of a steering link.

Steering links

The links shown here will be substituted instead of the ball and socket joints. The small memberis the member that will move both in X and Y directions and the bigger member is the coupling

member.


17/35

Steering Link in the car

6. ENGINE: O.S. 18 TZ (S)-T

OS ENGINE

6.1 Specifications:

DISPLACEMENT: .183ci (3.008cc)

BHP: 2.27 at 31,761 rpm

TORQUE: 84.58 in.-oz. at 24,000 rpm

BORE: .629 in. (15.97mm)

STROKE: .590 in. (14.986mm)

PORTS: 5-port


18/35

Practical rpm: 3,000-34,000CRANKSHAFT O.D.: .471 in. (11.963mm)

CRANKSHAFT I.D.: 305 in. (7.747mm)

CRANKSHAFT PIN: .175 in. (4.445mm)

PIPE: X12 Turbo

PLUG: O.S. Turbo P3

ENGINE TEMP: 230F

EGT: 625F

HEAD SHIMS: (1) .007 in., (1) .0035 in.

HEAD VOLUME: .21cc

POWER STROKE: .370 in. (9.398mm)

COMPRESSION RATIO(S): Trapped 7.89:1 Geometric 11.99:1

INDUCTION DURATION: 208 degrees

EXHAUST DURATION: 164 degrees

TRANSFER DURATION: 124 degrees

BOOST DURATION: 108 degrees

6.2 Port Configurations:


19/35

0 degree, 90 degree, 180 degree, 270 degree Port Configurations

The exhaust port is widest at the top to allow more exhaust gases to escape quickly. The port inthe sleeve very closely matches the shape and position of the exhaust port in the engine block,

and that allows exhaust to flow much more smoothly. The Schnuerle ports are two separate ports

on each side of the cylinder, and theres a vane cast into the transfer passage in the block thatmatches the ports. A single boost port features moderate port timing.

6.3 Dyno Tests:

Dyno test

Green Line: Peak torque 83.1 oz-in @ 25850 RPM torque83.1 oz.-in.

Red Line: Peak Bhp 2.28 @ 30500 RPM

6.4 Advantages:


20/35

Oversize fins on the case dissipate heat to help keep engine temperatures lower.

Five ports in the liner increase air flow for more power.

The rear bearing is 12 mm in diameter, which lessens vibration and allows the engine to handle

more torque.

A super-hot turbo P3 plug is included for better burn, more power and improved fuel economy.

The 18TZ-TX version features a new compact recoil starter that's smaller and lighter, making iteasier to install.

7. Basic Components - Specifications:

Basic layout

Length: 431mm

End to end width: 310mm

Distance between wheel centers: 325mm

Ground clearance: 25mm

Diameter of wheel: 100mm


21/35

7.1 MECHANICAL COMPONENTS:

The following components are classified under the mechanical components,

1. Chassis2. Engine 3.0 cc (0.18TZ OS)3. Air Filter4. Exhaust manifold5. Muffler6. Clutch7. Gear Box8. Differentials9.

Front & rear hubs10.Drive Shafts

11.Steering System12.Disc Brake13.Front & Rear Lower & Upper Arms14.Shock Absorbers15.Fuel Tank (150ml)

7.1.1 Exhaust Muffler


22/35

Exhaust muffler with the engine

The exhaust muffler is an attachment along with the engine. It is tuned in such a way as to reduce

the exhaust pressure and hence the noise of the engine to its minimum.

7.1.2 Clutch


23/35

Centrifugal clutch

The centrifugal clutch is an automatic clutch. The spring tension determines is engagement and

disengagement. The clutch engages at 2000- 3000 RPM. The material it is made of is an alloy ofbrass, so that it can withstand high temperatures and also it has a good coefficient of frictionalso. The flywheel is a solid aluminium block to store energy during the non-power strokes.

7.1.3 Gear box:

Gear box assembly

y The gear is made of Nylon materialy It is mounted at the center of the chassis and gives power to the two drives that goes to

the front and the rear wheelsy It has a gear ratio of 1:2.4 and 1:1.5

2 speed No of teeth: 1st

speed: 50, 2nd

speed: 42

Brake: Disc type

Material: Fiber glass

7.1.4 Differential with casing


24/35

Differential and casing

The RC car is a four wheel drive with a central drive and two differentials on both the sets ofwheels. The material of the bevels used in the differential is a heat treated steel. The basic

function of the differential is to control the speed of the wheels rotation while encountering aturn. The differential is lubricated with crease and it is sealed with a plastic casing. The drive

shaft is a dog bone shaft and is connected with the differentials using a CV joint. From thedifferentials the power is transmitted to the wheels using the dog bone shafts.

7.1.5 Suspension system:

The suspension system of the RC car is a wish bone type of suspensions with all the upper and

lower arms made of plastic. The suspension is again an individual suspension.


25/35

Suspension components

Spring type oil damped

Spring material: carbon steel

Free length: 35mm

Pitch: 5mm

No of turns: 7

Damping is provided using the suspension oil.Damping is needed to absorb the energy associated

with suspension travel. That suspension travel can be induced by bumps, or lateral orlongitudinal acceleration. Without damping, the magnitude of the suspension movement would

never stop increasing, leading to a very humorous situation. In terms of energy, damping absorbsmost of the energy the car receives as it moves, unlike springs stores the energy, and release it

again

7.2 ELECTRICAL & ELECTRONIC COMPONENTS:

The electrical and electronic components basically aids in the control of the steering and the

throttle. The electronic components in the RC car are,


26/35

1. Crystal Transmitter

2. Battery pack

3. Servo motors

4. Radio Pistol

7.2.1 Crystal transmitter:

The crystal transmitter transmits AM radio waves which is received by the receiver and controls

the servo motors. The frequency of the transmitter is 24.045 MHz

Transmitter

Battery pack for the radio box (4 numbers)

1.5 v AA size batteries

7.2.2 Servos


27/35

Servomotors

One for the steering and the other for throttle and breaks

HS311 Servo Specs:

Speed: 0.19 sec/60 degrees at 4.8V

Speed: 0.15 sec/60 degrees at 6.0V

Torque: 42.00 oz-in at 4.8V

Torque: 51.00 oz-in at 6.0V

Length: 1.60" (41mm)

Width: 0.80" (20mm)


28/35

Height: 1.40" (37mm)

Weight: 1.5oz (43g)

Servo motor

7.2.3 Radio:


29/35

Pistol radio controller

Pistol grip radios contain the transmitter. The trigger is used for the acceleration and braking.

The steering is controlled by the steering wheel kind of control. The pistol grip radio is a threeway control as it controls acceleration, braking and steering

Pistol grip radio

AM Transmitter/Receiver

27.045MHz band

Output power:


30/35

The body of the car is tinkered from a 3mm thick mild steel sheet and is welded to obtain theshape of the sedan.

The shape of the body was achieved by sheet metal working and welding of the ends.

9. Work progress in phases:


31/35

Phase -1 Body fabrication, Welding, Painting


32/35

Phase -2 Basic work, Chassis modification, Parts matching, Suspension mounting


33/35


34/35

The following results were obtained during the final testing,

Price - Rs.16,618

Length: 431mmEnd to end width: 310mmDistance between wheel centers: 325mm

Ground clearance: 25mmDiameter of wheel: 100mm

Turning Circle: 400mmKerb Weight: 5 Kgs

Engine: 3cc OS enginePeak Bhp 2.28 @ 30500 RPM

Peak torque 83.1 oz-in @ 25850 RPM torque83.1Steering Type Bell crank mechanism with universal joints

Suspensions Double wish bone suspensionsBrake transmission disc brake

Top Speed 60 KMPHFuel tank capacity 150 ml

Steering control: High torque Servo motor:Throttle and braking control: Servo motor

1st

Gear engagement: 0-5000 RPM2

ndGear engagement: 5000-35000 RPM

Braking: 50-0 KMPH in 3 secondsAcceleration: 0-50 KMPH in 3.5 seconds

Courtesy and References:

y Mr. Murarie Kumar. Personal and professional supporty OS 18 TZ Engine manualy www.towerhobbies.comy http://www.rc-truckncar-tuning.com/RC-Nitro-Engine-Carburetor.htmly http://www.raptortechnique.com/enginetuning_beginner.htmy http://www.redrc.net/2007/01/team-associated-launch-rc8-first-pictures/y http://www.rchobby.co.uk/radio_controlled_cars.htmly http://www.rc-airplane-world.com/model-airplane-engines.htmly http://www.easyrc.com/index.htmly http://www.easyrc.com/cars-trucks/carstrucks4.htmly IIT Bombay, Techfest 08, FTGP tutorial.

Tribute


35/35

The successful completion of this project is a glittering hallmark of academic achievement and Iam greatly indebted to scores of individuals who have contributed their mite for the jubilant

finish of this project work. I would like to express my sincere thanks to the following people,who in one way or the other helped or inspired me in the success of this project.

Mr.Murarie kumar, Mentor, guide and sponsor of this project

Dr. P.V.Mohanram, Head of Department of Mechanical EngineeringMr. B.Giriraj, Faculty, Department of Mechanical Engineering

Sowrirajan K, Team memberRakesh Narayanan, Team member

Ramani S, Team memberRagunathaprabhu S, Team member

About The Author

Srihari.B

BE.Mechanical Engineering, PSG College of Technology.

Webpage:-http://teamrhtp.googlepages.com

email id:- [email protected]

rc car build

Documents