A flying device that flies like a bird by having flapping mechanical wings. We did this project when we were in our first year at college.
The basic parts of the ornithopter:
2. Flapping Mechanism and Gearbox
Procedure to join two C.F. rods at a given angle
Keep the C.F. rods at the given angle and tie a few rounds of thread around it. Then apply a couple of drops of cyano. Once again check the angle, if correct, nicely tie around the joins from all directions and then apply enough cyano.
Procedure for fixing the hinge on the spar
Making a small grove at the tip of the spar, place the hinge in its position. Tie a round of thread at both the ends and then again check for the position and angle. Extreme care need to be taken at this junction as the angle of attack of the wing is fixed in this step. Once this is done, the hinge is fixed firmly by tying it with C.F. tape soaked in araldite and is allowed to dry overnight.
Procedure for fixing the membrane
The membrane on either ends was stuck to 1m steel scales and then streteched. Now applying 'fevibond' on the wing skeleton and was placed on the membrane. Any slackings were removes with the use of heat gun. Care should be taken to prevent excessive usage of heat gun as the following may happen(!):1. The membrane slacken further.2. The C.F. rods may be in compression. And a slight radial force will bend the rods.3. The membrane may burn leaving a hole. This is very frustrating after all thehard work.
Gear Assembly - Purpose and Design
The gear assembly is the system which has been designed to enhance torque from the brushless motor. The gear assembly was designed for a dual crank system - it has two output drives.
Gear Reduction in 3 stages, each stage consisting of a reduction of 22/6. Gear type - Spur gearsModule - 0.5Material - EN24 high carbon steelGears are of two sizes:1) OD: 7mm, PC dia: 6mm2) OD: 23mm, PC dia: 22mm
Symmetry is extremely important throughout all the components of an ornithopter. Any unsymmetrical distribution of mass can have a very drastic effect during flight. The design for the gear box is made so that it is symmetric about the vertical. Also, having two output shafts helps maintain symmetry.
Putting the gear assemble together - part 1
The gear assembly plates are of GRP plates of 2 mm thickness. We have had used 'flange bearings' to hold the gears in place and keep friction low. Flange bearings have a sleeve on one side along the circumference this helps in gluing the bearing to the plate by providing greater surface for application of adhesive. The bearings are fixed on the plates such that, the flanges are on the inner side(side facing gears) of the plates this ensures that bearings don’t fall out of the plate. The bearings are fixed in the gear plates (the gear housing) with Loctite.
Putting the gear assembly together Part 2
The gears are milled to their shape and placed in between the gear plates and in the length on the gear shaft from the bearing surface to the gear surface we place SS tubes to restrict any linear movement of gears. Stainless Steel (SS) tubes also ensure that the bearing does not slip off over the gear shaft. Four spacers made of SS tubes are placed between the gear assembly plates so as to provide structural configuration required spacing for gears, and a screw-nut system is used to lock the gear assembly about the spacers. After the gear assembly is completely fixed reduce any extra lengths of shafts and screws by grinding them this is to reduce unnecessary weights. Now we fix the motor attached with its mount to the gear assembly.
V shaped tail
The tail of our Ornithopter is a characteristic V-tail at an angle of 135 degrees.A V-tail (sometimes called a Butterfly tail) is an unconventional arrangement of the tail control surfaces that replaces the traditional fin and horizontal surfaces with two surfaces set in a V-shaped configuration when viewed from the front or rear of the aircraft. The rear of each surface is hinged, and these movable sections or flaps,sometimes called as ruddervators, combine the tasks of both the elevators and the rudder.
Building the tail
We have tried out various designs of the tail before finalizing the V-tail. The first one was a typical copy of a bird’s tail made out of thin plastic sheet spread over 2 thin carbon fiber rods bound together at an angle of 70 degrees. This tail was mounted on a servo which allowed it to move left and right. This servo was in turn mounted on another servo which moved it in the vertical plane as shown below. This made the bird technically controllable. While testing this tail the reaction time of turning was very high and the bird was difficult to control. We then tried to increase the area of the tail, though this gave the required result, the weight of the tail was more than that of an equally good V-tail, hence we finalized on the V-tail.
Tail Servo control
The servos of the V-tail must be mixed in order to give us appropriate control. Mixing of servos is basically making one servo dependant on the others reaction, i.e. when you move the controller up both the servos move down and when you move the controller left one servo moves down and the other moves up at the same time giving the required result and making the control easier.
The fuselage is a simple structure made with just 2 carbon fibre rods one above another. These are supported by attaching some transverse CF rods at required intervals of the fuselage with thread and cyano –acrylic glue.All the electronic components i.e. battery, servos, electronic speed controller, micro receiver are mounted on the fuselage with the help of rubber bands.
To protect the prototype during trial tests ,to give a protective outer shield ,we used Thermocol and Styrofoam.
Prof. V G Idichandy, Dean Students, IIT Madras Prof. T S Natarajan, Co-curricular Advisor, IIT Madras Dr. H S N Murthy, Dept. of Aerospace Engineering, IIT Madras Rajendran, Dean Students Office, IIT Madras Dr. Sunetra Sarkar, Dept. of Aerospace Engineering, IIT Madras Mr.Winston P J,Senior Mechanic , Electrical Shop, Central Workshop, IITM Mr.Dilli Babu P,Senior Technician , Fitting Shop, Central Workshop, IITM Mr.Senthilkumar P,Junior Mechanic , FRP Lab, Central Workshop, IITM In-charge, CAD Lab, Machine Design Section, IITM And the two who contribution is most invaluable: Mr. Nandakumar K, Consultant for the SoE Mr. Ravikanth A, Student Guide for the SoE
Was build at CFI. A lot of parts was machined at IITM Workshop