primary design

8/4/2019 Primary Design

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Primary Design

STATEMENT OF THE PROBLEM

A quadcopter is a four rotor hovering platform. Each rotor is mounted directly to a motor, andthe motoris mounted onto the frame. The frame is shaped like a+ with a motor mounted atthe end of each extremity.

Without a skilled human pilot at the controls, the foremost problems in realizing amodel helicopter-sized flying robot are stability and control. It is necessary to investigate the

stability and control problems, define solutions to overcome these problems, and build aprototype vehicle to demonstrate the feasibility of the solutions. The proposed HoverBot will
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have six input sensors (Roll, Pitch, Yaw, X, Y, Z) for stability and control. The resultingcontrol system is a very complex, highly non-linear Multiple-Input Multiple-Output (MIMO)system, in which practically all input signals affect all output signals. A surprisingly simpleexperimental control method, called additive control, is proposed to control the system. Thismethod was successfully used in the current experimental prototype of the HoverBot

(although with fewer input signals). It is also proposed to investigate two alternative controlmethods, adaptive control and neural networks, both of which appear to be especially suitablefor the Multiple-Input Multiple-Output control problem.

One of the main design goals was to obtain a high controlling frequency throughout thesystem. To support this, our platform features a custom built onboard high-speed sensingsystem which consists of gyroscopes to give relative measurements for the robots angles.High control frequency precludes the use of commercially available brushless motorcontrollers, such as those found in model aircrafts, as they only allow motor speed updaterates of 50 Hz. This controller has very low dead times and supports very dynamicmovements. Intensive manual acrobatic flights with loops, flips, spins, sharp turns and

combined maneuvers proofed the stability of the controller in extreme situations. Havingsuch a high control frequency allows us to create an extremely stable platform, even with

payloads of up to 350g. Many applications for such a platform exist. The outstanding stabilityof the platform makes the integration of onboard and off board position tracking system

possible. In this project we demonstrate the performance of the system using an externalmotion tracking system to provide closed loop position control. Cameras mounted on the

platform also benefit from a stable image.

Electrically Powered Rotorcrafts

We propose to develop an electrically powered rotorcraft. To date, electrical powerhas been found unsuitable for rotorcrafts, except for the very lightest of model-helicopters.
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The reason for this can be explained with a few first approximation design guidelines forrotorcrafts. As a rule of thumb, the powerPrequired developing thrust (i.e., lifting capacity)Tis given byP T3 .

This function is sketched in the Power vs. Weight chart of Fig. The offset P0represents the power required for lifting the motors and structure. The battery power vs.

battery weight (for a given maximum flight duration) is plotted as a group of dotted lines,each for a given flight duration. Because of the non-linear nature of Eq. electric helicopterscannot be scaled: It is impossible to simply design around a larger motor and larger battery,to get a larger (read: strongerrotorcraft). As Fig. shows in principle, there is only a smallrange of feasible designs. Commercially available model helicopters demonstrate this

principle: only extremely lightweight (2 - 3 lb) models with 5-6 minutes flight duration areavailable. These models use ultra-light building materials and control elements.

A robotic rotor-craft would need an onboard computer and sensors, in addition to theconventional radio-control components. For this reason, we conclude that it is unfeasible to

build a robotic rotorcraft based on current electric power model helicopter technology. Toovercome this seemingly inherent limitation, we propose to design a multiple rotor platform,called theHoverBot. In principal, theHoverBotcan be considered as four individual electricmodel helicopters, linked together at their tails. While this design slightly increases theweight of the structure, its advantage is that certain components needed in every conventionalmodel helicopter (such as gyros and the receiver and its power source) can be shared amongthe four units, and so can special components for autonomous operation (such as a computer

board, more gyros, and other sensors).

In preliminary experimental battery endurance tests, we achieved 3-minute flightswith our prototype HoverBot and conventional NiCad battery packs. The tests weresomewhat flawed by inferior charging equipment that wouldn't allow optimalcharging of thecells. Rotor blade loading, power transmission and motors were also far from optimal in ourearly experiments. We expect that by the end of a one-year project, we will have improved onthese factors to achieve flight times of 4 5 minutes with standard NiCad batteries. Moreimportant, new battery technologies promise additional two to threefold improvement inweight-to-charge ratios. Driven by the rapidly expanding market of notebook computers,more powerful nickel-hydratebatteries are already in use, which provide 1.5 2 times higherenergy densities, and recently Byte magazine reported on the development of new lithium-

iron and lithium-polymer batteries that promise 3 times longer operation than Alkalinebatteries of the same size2.

Four-Rotor Design

In the earlier days of vertical flight experimentation (before the development of theingenious cyclic/collective pitch concept, which is now used by all modern helicopters)developers looked atthe intuitively easy control functionality of 4-rotor designs. While someof these prototypes did indeedfly, none ever made it into production. The reason most oftenquoted was the fact that the 4-rotor machines were difficult to control and stabilize: Withmanual controls, the pilot would have to coordinate at least four control parameters (for

example, the pitch of the rotor blades), which wererather counter-intuitive. Another reason toconsider multiple rotors is to achieve larger pay-load capacities then what ispossible with
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single rotor designs. The reason for this is the fact that the thrust of a rotary wing isproportional to the square root of the area swept through by the rotor. This area is also calledthe rotor 2Ultimately, of course, we are interested in weight-to-energy ratios. Yet, theliterature quoted size to energy ratios (relative to existing products). We quote these exampleshere to show the feasibility of electric power, while the focus of the proposal is on the

stability and control problem. Other words, the larger the rotor disk, the more thrust isdeveloped. Obviously, there are technical limitations to the maximal size of the rotor disk.Multiple rotors multiply the effective rotor disk area, although there are, of course, losses.Most notably are losses caused by the additional weight of the structure and losses due toturbulent interaction of the air underneath the disks. Nonetheless, tandem rotor designs areclearly superior to single rotor helicopters in terms of pay-load capacity.

Control of the HoverBot

The control system of the HoverBot is designed to allow either fully autonomousoperation or remote operation by an unskilledoperator. To either, the HoverBotwill appear

as an omnidirectional vehicle with 4 degrees of freedom: (1) up/down (2) sideways, (3)forward/backward, and (4) horizontal rotation. Up/down motion is easily controlled bycollectively increasing or decreasing the power to all 4 motors. Control over (2) can beachieved as explained in Fig: For example, increasing the power to the two left rotors lifts theleft side up and generates a thrust component to the left. Consequently, the HoverBotmovesto the right. By the same principle, adding power to the two rear rotors causes theHoverBotto fly forward. The implementation of horizontal rotation control is less obvious:

When a rotor turns, it has to overcome air resistance. The reactive force of the air against therotor causes a reactive moment called the induced moment. The induced momentacts onthe rotor in the direction opposite to the rotation of the rotor. As everyone knows,conventional helicopters require the tail-rotor to counteract the induced moment. In the

HoverBotboth sets of diagonal rotors turn in opposite directions (as indicated by the oppositedirection of the arrows in Fig). As long as all rotors experience the same induced moment,which is mostly a function of speed of rotation and rotor blade pitch, the sum of all inducedmoments is zero and there is no horizontal rotation. If one set of rotors, for example the onethat turns counter-clockwise in Fig., increase their rotational speed or their pitch, the resultantnet induced momentwill cause theHoverBotto rotate clockwise. It is important to note that

because of the diagonal arrangement, this operation has no effect on translation in x or ydirection. The effect on up/down motion can be compensated by reducing the pitch or speedof the other diagonal pair, although in practice this is not quite so easy without some sort of

feedback control.


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Stability

We believe that stability is the foremost challenge for any effort to build a model-sized robotic rotorcraft. As explained before, in the absence of natural damping, all

rotorcrafts must be constantly stabilized by the pilot or auto-pilot. In model-sized helicoptersthis presents a formidable difficulty, because of the much smaller time-constants. This is thereason why model-helicopter pilots need months and months of training, just to keep theirhelicopters in stable hovering. Model helicopter pilots we talked to confirm that stabilizing asmall model helicopter is even more difficult than stabilizing a larger model helicopter.

Larger Time-Constant with the Proposed HoverBot

The 4-rotor design of our proposed HoverBot is originally motivated byconsiderations of payload is appears to have one unique advantage over conventionalhelicopter designs: the distributed weight of the 4 rotor heads increases the moment of

inertial and thereby the time constant of the system. To illustrate this point, we can roughlyestimate that the moment of inertia, J, of a 6 kg conventional (single rotor) helicopter modelaround its longitudinal axis isJ= 0.06 Kgm2. By comparison, the 4-rotorHoverBotwith thesame weight has a moment of inertia ofJ= 1.53 Kgm2 around its least favorable axis. Inother words, the moment of inertial of the HoverBotis approximately 1.53/0.06 = 25 timeslarger than that of a comparable conventional helicopter. Since the time-constant J of thesystem is proportional to the square root of the moment of inertia (J % J2), the time-constantof the HoverBot is (25)2 = 5 times larger than that of the conventional helicopter design.Stabilization of this rotorcraft will be greatly facilitated by the much larger time-constant.


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The Dual Control Approach

Another important advantage of our 4-rotor design is the control flexibility gained from the

useof four independent motors. As we explained, the HoverBotcan be fully controlled bycontrolling the thrust of the four rotors. In conventional helicopters thrust is controlled in twodifferent ways: a) by adjusting the motor power and b) by adjusting the rotor blade pitch (theangle of attack of the rotor blades). Adjusting the motor power is usually not an efficientmeans of control, because gasoline powered engines do not respond quickly enough(especially with the large inertia of the rotor)to the pilot's commands. By contrast, adjustingthe rotor pitch has an immediate effect on the thrust: a larger pitch angle increases the thrust.However, a larger pitch angle also increases the power needs of the rotor and must therefore

be accompanied by an increase in motor power. Because of the kineticenergy stored in therotor, the increase in motor power does not have to be available immediately, ashort delay isacceptable. Thus, the immediate action of pitch control combined with the slightly delayed

action of motor power control works well. In normal-sized helicopters (without automaticcontrol), determination of the proper mixture between pitch increase and motor powerincrease is left to the skill of the pilot. The problem is different in the HoverBot. Here,controlling the motor power is somewhat moreeffective because we use electric motors. Wefound that we can perform the typical control functions (up/down, forward/backward andsideways tilting, rotation) just by controlling the rotor thrust. However, in our system thecraft must also be stabilizedby varying the rotor thrust. In ourexperimental system we foundthat the thrust control must react at least ten times faster in order to dampen undesirableoscillations caused by external disturbances. Thus, we propose a dual controlapproach, inwhich fast-acting pitch control is the primary means for damping and stabilizing, andmotor

power control is the primary means for controlling the steady state thrust and thus the motionof theHoverBot.

In practice, both control actions are strongly interrelated. Any control signal going to, say, thefront left motor must also generate a secondary control signal that affects the pitch actuator ofthe front left rotor, and vice versa. The exact nature of this interaction is extremely difficult todetermine analytically. The interaction is highly non-linear and there are numerous

parameters that are practically impossible to measure. Our focus in the work will be todevelop experimentally a new controller capable of performing this complicated stability andcontrol task.

Areal Photography

Cameras mounted on quadcopter, and photographs may be taken, triggered remotely ortriggered automatically.

GPS Tracking

Using GPS we can determine the position of the quadcopter during flight.

Remote Target Pointing

We can point a remote object using camera and laser beam. Using this we can easily aim amoving object.


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The aerial robot proposed here, called HoverBot, is highly stable robot helicopterprototype, which is developed to demonstrate its mechatronics technology and to explore thepossible use of aerial robots and the development of component technology applications. Thegoal of this project is to create a semi-autonomous hovering platform, capable ofvertical lift-off and landing, and capable of stationary hovering at one location . The HoverBot uses

four rotor heads and four electric motors (so called Quadcopter), making it whisper-quiet,easy-to-deploy, and even suitable for indoor applications. Special applications for theproposed HoverBot are inspection and surveillance tasks in nuclear power plants and wastestorage facilities.

This project built upon the Universal Aerial Video Platform (UAVP), an open-sourcequadcopter project, with the ultimate goal of creating an autonomous, GPS-guidedquadcopter fitted with a digital camera module. The project utilized a microcontroller-baseddaughterboard to provide the UAVP with simulated input from the RF receiver module. The

board interfaced with GPS to facilitate waypoint based navigation. Laser pointer used in thisfor remote point targeting. We used motion capture technology and laser pointing for the

accurate aiming of moving target. We can successfully attach a remote control gun or bomberand can use for preventing terror attacks. Highly complex control systems using InertialMeasurement Unit (IMU) prevents the recoil effect of gun and UAV cannot crashes.

It has many distinguishing features, some of them are

High efficiency: motors are connected directly to rotors no losses throughgearboxes, swash plates, or other couplings

High payload capacity: our platform has 4 motors providing an estimated 600g ofthrust each; therefore we aim to have a payload capacity of about 1kg

Vertical lifting & landing: no need of runway.

High Stability and Reliability: highly stable and reliable platform compared to otherUAVs.

6 Degree of Freedom (Roll, Pitch, Yaw, X, Y, Z) and highly suitable for indoorapplications.


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APPLICATIONS

Applications In Hazardous Environments Like Nuclear Power Plants

Defense

Security & Surveillance

Inspection and Surveillance Tasks in Nuclear Power Plants and Waste StorageFacilities

Spy work & Anti terrorism application for police and military

Visual photography

Space Exploration

Remote Sensing Applications

Disaster Rescue

Mapping Applications

Applications in the Domain of Disaster Monitoring, namely Forest Fires

COMPONENT1. Propellers (Maxx Products 10x4.5 EPP1045 Counter Rotating Pair Propellers for RC

2.Airplanes + RC Helicopters)

Length: 10 inches Pitch: 4.5 inches per revolution Type: Counter Rotating Matched Set Material: 1 Piece Composite Shaft Diameter: 3 mm (Works with GWS type gearboxes)

3.Battery( Rhino 2620mAh 3S 11.1v Low-Discharge Transmitter

Lipoly Pack )
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4. Motor and ESC (TowerPro BM2410-08T / 18A BEC / 1047 Prop Combo)

Motor: BM2410-08TBESC: 18A

Current: 18-25ABEC 3S LipoSize: 43x38x10mm / 20grams

5 .Boom ( Carbon Fiber Square Tube 750x6mm)

Carbon Fiber Square Tube 750x6x6mm
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