TABLE OF CONTENT: 1)
PROBLEM STATEMENT
2)
HOVER THEORY
3)
ELEMENTS OF A HOVERCRAFT
4)
DESIGN CONSEDERA CONSEDERATIONS TIONS
5)
ELECTRONIC ELECTR ONIC EQUIPMENT
6)
HOVERCRAFT BUILD
7)
TROUBLESHOOTING
1) PROBL PROBLEM EM ST STA ATEME TEMENT NT :
To design design a remote controlled hovercraf hov ercraftt or ACV(air cushion vehicle) that will be tested for speed, maneuverability and handling on various terrains like like sand, mud, water water,, gravel, concrete. concrete.
Fur urther ther details are pro provided vided on the website www.technozion.org
2) HOVER THEORY :
WHAT IS A HOVERCRAFT ? WHAT
A hovercraft is an amphibious vehicle that can move with equal ease on both land and water or any other terrain. It is also known as an “ACV” (air cushion vehicle).
How does a hov h hovercraft overcraft ercraft work ?
A hovercraft hovercraft works on the air cushioning effect of air trapped at high pressure underneath the hull which seeps slowly through a flexible surface known as “skirt” .The pressure due to this trapped air is responsible for for lifting lif ting the craft craf t a few inches above the ground.
3) ELEMENTS OF A HOVERCRAFT HOVERCRAFT :
MAIN PARTS OF A RC HOVERCRAFT :
HULL It is the main body of the craft which parts par ts of the hovercraft hovercraft
LIFT SYS SYSTEM TEM The lift lif t system consists of a fan or prope propeller ller attached to a motor or an engine ,which provides air for filling the cavity underneath the craft (called as plenum chamber) and also for filling the skirts.
It is the same as the lift lif t system system with a difference that it propels the craft forwar forward d by the virtue vir tue of reaction force applied by the air. The propeller used for generating thrust is generally provided with a duct to increase the velocity of air and hence to increase the thrust.
THRUST FAN LIFT FAN
SKIRT
SKIRT It is the flexibl flexible e wall that is attached all around the periphery at the bottom of the craft .The skirt prevents the pressurized air from escaping from the plenum chamber .
CONTROL SY SYSTEM STEM This consists of a set of rudders that steer the craft by directing the air from the thrust system toward either leftt or right which consequently lef steers the craft.
RUDDERS
4) DESIGN CONSIDERATIONS :
WEIGHT Light weight materials must be used for construction ,but at the same time the model must have good strength. PRESSURE IN PLENUM CHAMBER Lift force= pressure x area of the craft Sufficient pressure must be generated so that lift force > weight of the craft MOMENTS As rotating parts are involved .the unbalanced moments moments particularly due to the lift fan must be balanced to avoid spinning of the craft POWER SYSTEM or an genera y mo or- prope er sys em av av ng s a c rus > 0.4x(weight of the the hovercraft) hovercraft) will generate hover hover , provided provided skirts are properly attached. SKIRT DESIGN a bag skirt skir t is generally preferred as it is easy to build and gives good performance DUCT DESIGN The duct although do not have much effect on thrust due to propellers ,they must be used for safety from propeller blades. In design a duct should have a decreasing area towards exit, such that velocity of air ,leaving the duct increases i ncreases and hence thrust increases
5) ELECTRONIC EQUIPMENT:
MOTORS; DC motors motors used for for rc rc models are categoriz categorized ed as BRUSHED DC MOT MOTORS ORS
BRUSHLESS DC MOT MOTORS ORS
Of these two motors brushless motors are generally preferred because of High power to weight ratio Low maintenance
ELECTRONIC SPEED CONTROLLERS (ESC) These are used for controlling controlling the speed of the motor. They are generally classified on the amount of current they can handle eg. A 30 amp esc can handle 30 amperes of current draw and will burn if current exceeds this value.
So while choosing an esc for brushless motor the max. current draw of motor should not exceed the rated value of esc used.
BATTERIES: Li-po or lithium lithium polymer batter batteries ies are used because because of High discharge rates Light weight High charge retaining capacity
Li-po batteries are rated by the amount of charge the theyy can store and the discharge d ischarge rate and the voltage eg. A 11.1v 11.1v ,2000mAh ,20C battery can provide 2 amperes of current for two hours at 11.1 volts and the maximum current can be C ratin rating g x mAh mAh rat rating ing i.e. 20 x 2amp= 40 amp
RECEIVER/TRANSMITTER :
Receiver and transmitter are used to control the electronic electro nic equipments on the model. A receiver or transmitter is categorized by no, of channels and frequency of operation. The no. of channels define how many equipments can be controlled through the transmitter A three channel radio is suitable for running a hovercraft
SERVO A servo is a kind of electronic actuator that rotates by only a fixed angle ,like 45 degrees, from the neutral position. It can hold it’s position at an angle and is used in rudder rudd er mechanism for the model
A 9gram servo is ideal id eal for rudder mechanism
BRUSLESS MOTOR SETUP: choosing the right motor Lift motor motor-- a high kv mot motor or is genera generally lly used with a 6”-7” 6”-7” propeller. Thrust motor-a motor-a low kv motor is generally used with a 9”-11” inch propeller.
Suggested motor setups: setups Lift motor ” ” EMAX BL221 BL2210/25+ 0/25+ 20amp esc+8”x4” propeller Turnigy 2730 1500kv + 10 10 amp esc + 7”x3.5” propeller Thrust motor Turnigy 2830 100kv 100kv + 20 amp esc +10”x +10”x 4.7” propeller Hobbyking Hobbyk ing 800kv +12 +12 amp esc +10”x6” +10”x6” propelle propellerr Turnigy 221 2217 7 860kv+20 amp esc +11”x4.7” propeller propeller Batteries 11.1v batteries with rating from 1800mAh to 2700mAh and a discharge rate of 25-30C I recommended.
•
A 3mm prop saver or prop adapter should be used for attaching the propeller to the motor shaft
Prop adapter
6) HOVERCRAFT BUILD
MODEL – UH10F MODEL UH10F Materials used: Plywood ;thickness -2mm Thermocol Alumin Alu minium ium pla plate te Glue gun or fevitite Polythene Garbage bags (black coloured)
Building the hull: The hull is built by sandwichin sandwiching g thermocol sheet in between between two plywood sheets using fe fevicol. vicol.
The duct (hole ) at the front is for the lift fan
MOT MOTOR OR MOUNT MO UNT :
Alumin Alu minium ium pla platte is used; used;
DRILL HOLES FOR SCREW
MOUNT SECTIONS ATTACHED
the mount are joined using Now the parts of the nuts and motor is mounted
Motor mount for the lift motor is also made
using usi ng alu alumin minium ium pla platte
lift fan motor mount
Hull with the motors attached
BUILDING THE DUCT :
Thermocoll is used Thermoco used for for making making the duct. duct. A 9” thick block of of thermocol thermocol is formed formed into into the required shape by sanding using a sand paper. The e therm thermoco ocoll duc ductt is reinf reinfor orcr crd d by wra wrapp pping ing Th thin cott cotton on cloth dipped dipped in diluted diluted fevicol fevicol tigh tightly tly around the duct.
REINFORCED THERMOCOL DUCT
THRUST MOTOR AND PROPELLER
RUDDERS : rudders are are made made using cor coro o shee sheets ts and cycle cycle
spokes
Coro sheet Passing a spoke through the coro
Hinge for rudder
Four bar mechanism for synchronizing rudder movement
Completed
rudder
RUDDER
CONTROL HORN
CLEVIS SPOKE SERVO
SKIRT : •
•
•
The skirt is a bag type skirt made using garbage bag as an alternate any thin airtight materiall can be used materia The skirt is basically a round balloon type structure that gets inflated when lift motor is switched on. For inflating the skirt a fraction of air from the lift fan should be directed into the skirt
SKIRT (inflated)
For step by step skirt construction refer the following link •
://www.johntom.com/hovhttper/MiscHoverPhoto/skirt.swf
SKIRT CUTOUT
Join at bottom of the craft
SKIRT COMPLETE D
Join at the top of the craft
ATTACHING THE SKIRT AND DUCT : •
Glue gun is used for attaching the skirt and duct to the hull ,alternat ,alternately ely fevitite fevitite or any any epoxy based glue can be used. skirt is attached using transparent tape.
DUCT BATTERY CASE
SKIRT PLENUM
PROPELLER
AIR FLOW FOR INLATING THE SKIRT
AIR FLOW FOR LIFT
THIS COMPLETES THE BUILD
7) TROUBLESHOOTING :
CENTRE OF PRESSURE AND CENTRE OF GRAVITY : The centre of pressure is basically the geometric centre of the plenum chamber chamber .But the lift is in general contributed both by thrust due to motor and the pressure force,such force,such that the point where total total lift force force acts gets shifted towards the lift motor. The centre of pressure and the point of action of lift force must coincide for leveled hovering The line of action of lift force is fixed for a model, the . . . INSUFFICIENT TURNING: Increase the rudder area or the servo throw throw.. NO HOVER: Check if the skirts are fully inflated The skirt skirt should allow allow a minimum amount of air leak from the plenum chamber. chamber. check for any rapid air leaks Insufficient power of the lift lif t motor UNCONTROLLED SPIN: Provide a slight rudder trim in direction opposite to to spin
WHERE TO BUY: RC stuff is available at following sites which
deliver in 3-4 days www.rcelectro.com www.rcdhamaka.com www.rcdhamaka.com www.rchobbyaddict.com www.rcforall.com www.rcbazaar.com alternate building material
Deprron foam (BIO (BIOFO FOAM) AM)-- ava vailab ilable le at at some some Dep stationery shops around stationery around ramkote ramkote cro crossr ssroad oad ,Hyderabad Cor Coropla oplast st (sunpa (sunpak k or sunbo sunboard ard)) SOME USEFUL LINKS: www.john-tom.com www.rchovercraft.com www.gohover.com www.model-hovercraft.com
For any queries contact-
RAHUL RATHORE email :
[email protected] Ph. : 9466862434
There is nothing that cannot be achieved by firm imagination
