Note that the blade length and width used are higher than those assumed previously. This was done to overestimate the required torque value and in case there are any unknown discrepancies in the future. According to NASA’s article, Important Scaling Parameters For Testing Model-Scale Helicopter Rotors, “the rotational velocity of the scale-model must be multiplied by the reciprocal of the geometric scale factor”. In this case, the geometric scale factor was one-tenth, so the rotational speed was multiplied by 10, giving the value of 100 RPM. The corresponding drag and lift coefficient values are assumed to be .2 and 1.2, averages for low speed applications with low Reynolds number.

The Blade Element Theory for the standard process of airfoil theory to the rotating blade integrates the elementary forces along the rigid length of the blade gives the following drag, D, and lift, L, equations:

D = (1)

L = (2)

These equations yield values of 8.54 and 51.21 Newtons respectively for drag and lift. To take into perspective, a 150-lbs person plus a 100-lbs helicopter will need at least a 250 lbs lift, which is an equivalent of about 1110 Newton. Scaling that amount by one-tenth gives a number of 111 Newton, which is about twice the lift calculated. Keep in mind that HPH team is designing for the range of minimum input required to drive a 72”x5” blade. In other words, it is trying to draw a big picture of the possibilities of what can happen and make necessary accommodations in terms of inputs and data readings for the extremes. The element of blade yields the torque, τ, as:

D = (3)

Integrates the element throughout the length of blade gives:

(4)

The torque needed to rotate the 72”x5” blade at 100 revolutions per minutes to produce the aforementioned drag and lift values is 3.9 N*m. Applying the power, P, equation, we have:

P = τΩ (5)

For 2 blades, P = 2*τΩ, which gives 81.8 Watts, or .11 horsepower. At full-scale, a person can output little over one horsepower, which is comparable to the power computed when the scale factor is removed.

So now that the values under which the test stand will need to operate, HPH team can decide on the range of inputs and outputs each load cell and sensor will have to accommodate. Naturally, determining the load cells’ and sensor’s capacities will have to take into considerations that the rotor designers will conceive different variations of designs, some very likely to be innovative ideas, that could produce highly proficient values for the critical elements, or otherwise. These capacities will be discussed in more details in each component’s section.

The calculations gave HPH a set of specifications it will plan to meet or exceed. The range of rotor speed needs to be from 50 to 100 RPM. The ranges for drag and lift that the test stand must be able to measure are set to be 4 – 15 N*m and 40 – 60 N*m respectively. And all materials cost should not be more than $2500.

AC Motor

Theory

Three-phase AC induction motors are composed of rotor and stationary (stator) windings. Applying three-phase power to these windings produces a rotating magnetic field. This rotating field serves two purposes. It induces current flow in the squirrel-cage rotor, which in turn, produces a magnetic field in the rotor that helps to drive the rotor. (Unicous.com)

In order to achieve the needed response as well as controlling speed, three quantities of the electrical power are varied to the ac motor:

· Frequency, which determines the motor speed

· Voltage to keep the volts per Hertz constant (in order to prevent overheating the motor, yet it must be large enough to enable the motor to develop sufficient torque)

· Phase relationships (vectors) between the three electrical phases.

Controlling three phase motors

The actual rotation speed of AC induction motor depends on the motor design. If there is a need to change the rotation speed, the frequency of mains voltage must be changed.

Also, the rotation direction of a three-phase motor is controlled on the order of the phases applied to the motor. If the order of two-phase wires is changed, the rotation direction can be changed.

Approximately, a 3 phase motor draws

At 575 volts, a 3-phase motor draws 1 amp per horsepower.

At 460 volts, a 3-phase motor draws 1.27 amps per horsepower.

At 230 volts, a 3-phase motor draws 2.5 amps per horsepower.

1hp=746 watts

Specifications

Rotor experimental system was powered by a variable frequency AC motor rated at 3 horsepower output at 157 RPM. These ratings were obtained due to the group’s torque calculations. The most successful attempt on previous HPH projects was using 5 RPM. Therefore, on 1/10 scale our group decided to draw the motor around 50 RPM.

The motor was connected to the rotor shaft through three-phase speed control system, which would allow us to vary the speed of the motor; thus the lift and drag forces could be obtained at different speeds. The motor, which spun the rotor, sit on a plate that rested on a load cell. As the rotor was spun, thrust was measured by the difference in apparent weight of the motor acting on a load cell. The obtained data gathered at a computer program called Lab View, which was connected to motor speed control unit.

The motor was decided to be mounted vertically inline as shown in figure 2 due to our design specifications. The motor output shaft was threaded in order to allow installation of a nut. Therefore, nut prevented the rotor pulling the hub off of the shaft. The lift generated by the rotor would pull on the hub. Moreover, the output shaft was drilled through the nut so that a cotter pin can be inserted inside the nut, which kept the nut in its place.

Figure 2: Vertical mounting position of motor

The table 1 below shows the properties of the motor selected. The data obtained from the manufacturer’s web site (nord.com). Throughout this selection it is emphasized that motor has capability of our design specification of 3 hp power and output speed of 157 rpm.

Table 1: Properties of motor

Type	Part number	Ratio	Max Output Torque	Input power	Output speed
Helical Unicase	SK52-100L/40	10.7	1204	3 hp	157 rpm

The figure 3 and table 2 below shows the exact dimensions of the motor selected that group will need during the installation of motor. The pictures and table are taken from manufacturer’s website.

Figure 3: SK12-100L/40 (nord.com)

Table 2: Dimensions of Motor (taken from nord.com)

The group decided that the shaft should be threaded and drilled by the manufacturer motor company so that more precise results can be obtained. Group has been conducting with motor distributors and prices for the required motor have been collected.

AC Motor versus DC Motor

HPH team had to make an important choice concerning what kind of motor would give the best results for our project. Therefore, it was necessary to identify the differences between AC and DC motor.

In the beginning of project HPH team considered DC motor as the first option. The reason why was simply due to the fact that speed controllers are more simple to build for DC motors. However, DC motor is dedicated to a power supply so that it would be necessary to purchase an extra power supply. Due to limited budget for the project, it was decided that would much more money compared to the AC motor. For an AC motor all we had to do was to plug in the motor into the wall.

MOTOR CONTROLLER

Group has decided a need for speed control unit for our test stand; therefore motor could be run at different speeds, which will help to gain a data of forces gathered by a computer program.

After a long research, it has been found that most suitable speed control unit is for our project is MC 1000 motor controller provided by AC Tech Company. This control system was chosen as a result of consulting faculty members and technicians from the industry.

Theory

Motor controller units convert the fixed frequency and voltage of the AC power line source to a sine coded pulse width modulated (PWM) adjustable voltage and frequency output that will control motor over a wide speed range. This can be adjusted by varying the applied voltage and frequency.

Controllers are rated in amperes, volts, and speed of response called bandwidth. This is measured by applying a sine wave input at various frequencies and comparing the output to the input. The usual unit for quantifying the bandwidth is radians per second. At low frequencies, the output stays in phase with the input and the magnitude remains constant, Figure 4. However, as the input frequency increases, the output lags the input; and the output magnitude decreases. (Unicous.com)

Figure 4: Frequency response vs. phase lag and amplitude ratio (taken from Unicous.com)

Specifications

Table 3 below shows the specifications for the speed control unit. The data is taken from manufacturer’s web site.

Table 3: MC 1000 Specifications

Input line voltages	240/120 Vac, 240/200Vac, 480/400 Vac, 590/480 Vac
Input Voltage Tolerance	10%, -15%
Input Frequency Tolerance	48 to 62 Hz
Output Wave Form	Sine Coded PWM
Output Frequency	0- 120 Hz, Optional up to 1000Hz
Carrier Frequency	2.5 KHz to 14 kHz
Efficiency	97% throughout speed range
Cverload Current Capacity	150% of output for 60 sec. 180% for output rating for 30 sec
Speed Reference Follower	0- 10 VDC, 4-20 mA
Control Voltage	15VDC
Analog Outputs	0-10 VDC, or 2- 10 VDC (proportional to speed and load)
Digital Outputs	From C relay: 2 A at 28 VDC or 120 Vac

Function Description

The MC Series is a variable speed AC motor drive with 16-bit microprocessor based, keypad programmable unit. Speed control unit consists of four major sections, which are an input diode bridge and filter, a power board, a control board, and an output intelligent power module.

The MC1000 series is designed for constant torque or variable torque applications.
Motor speeds are controlled manually from the drive keypad and remotely using the serial communications port.

Briefly, the power board contains the control, protection and charging circuits. Protection circuits eliminate excessive output current. Input diode bridge converts incoming AC voltage to DC voltage. Control board consists of keypad, display and a 16-bit processor. Output power module basically converts incoming DC voltage to three-phase sinusoidal output current wave, which optimizes motor performance.

Potential Disadvantages

A motor speed controller typically costs several times the cost of the motor it is controlling. In addition, controllers are available in different levels of sophistication, such as those that can very precisely control motor speed and can sense the actual position of the motor/load shaft, if necessary, to control the process. Obviously more sophisticated controllers do cost more. Therefore group had to pick one that will not exceed the potential budget.

During the installation of the controller there were some other considerations must be taken place. The controller installed between the power supply and the motor means another piece of equipment has been inserted into the system. Naturally, installing the controller will decrease system reliability. As now there were two pieces of equipment that can fail rather than just one. Moreover, it is an electronic device and is more susceptible to negative environmental conditions, such as dust and temperature changes, than are electromechanical devices, such as motors. Thus, during the experimentation, lab conditions should have been appropriate.

Implementation

The figure 5 below shows the final design of the motor. As it can be seen in the figure motor was vertically mounted. The motor was connected to speed controller and to the power supply. Speed control had led to vary the speed within the range of 0 to 10 volts through electronic programming module. Moreover, digital LED screen showed frequency applied. Therefore, load cell and the torque sensor could measure the data obtained. Figure 6 shows the picture of the speed control unit.

The speed control system also had an emergency stop at the other side of the room, which was connected to power board in series.

Figure 6: Speed controller

Figure 5: motor vertically placed

Torque Sensor and Load Cell Objective

The objective of this paper is to explain the importance of the load cell and torque sensor that are being used in the human-powered helicopter project. This includes the fundamental of the sensors, the method of obtaining the data from the sensors, and description of the chosen sensors.

For the human-powered helicopter project, the test stand needs to be able to measure important output data from the rotor so the data can be used to improve the overall design. The rotor creates mainly two forces: drag and lift forces. Drag force creates a resistance to the rotor in the opposite direction of the rotor rotation. Therefore, the drag force creates a moment acting on the whole test stand. This force can be measure by the use of torque sensor in which the total torque is equal to the total drag of the rotor.

Lift creates vertical force acting on the test stand. Lift force is created by the momentum of the fluid, which can be calculated by using Bernoulli’s Equation:

(6)

From this equation, the result can be applied to the momentum equation as shown in Equation 7:

(7)

With the fluid momentum equation, the shear stress is combined into the equation to get drag and lift equation as shown in Equation 8 and 9:

(8)

(9)

Typically, it is rarely possible to determine the flow direction analytically. Instead, the calculation would rely on the dimensionless values such as Reynolds number, Re, Mach number, Ma, Froude number, Fr, and relative roughness of the surface, of the body in fluid; therefore, drag can be found by using drag coefficient equation:

(10)

as, (11)

Since the test stand is vertically aligned, the load cell is able to measure the force from one direction, which is measuring the force relative to displacement. In addition, the load cell is torque resistant which adds the accuracy to the reading.

For torque, it is described as:

(12)

Typically dynamometer is used to measure the torque, but reaction torque sensor is found to be more convenient in measuring the torque in this case. The dynamometer is operating on measuring torque relative to angular displacement. This method is not suitable for measuring the drag since the torque output here is the torque of the motor not the drag. The drag creates the reaction torque on the entire test stand; therefore, the reaction torque sensor is more suitable for this application base on the Equation 12.

Apparatus

The load cell is designed to be aligned at the center of the rotor directly below the motor. The reading will be zeroed out after the rotor is loaded on the test stand. The test stand is constrained at each leg to be fixed to the ground; therefore, the load cell is measuring the force only in one vertical direction.

The torque sensor is also designed to be located axially aligned with the center of the rotor. The benefit for aligning every component axially is to prevent the rotor to wobble which will result in unstable condition for the test stand.

Description of the Load Cell

The load cell is a tension and compression type in a cylinder shape with capacity of at least 500 lbs. The team chose the Futek T2920 Tension/Compression Load cell for this design. The sensor is made out of stainless steel. It has threaded holes on both ends so it can be easily bolted to the structure of test stand. The treaded holes actually extruded out of the body so the load does not contact with the non-loading surfaces of the load cell, which could produce an error in reading. Additionally the load cell has flat surfaces which will prevent the load cell from rotating. This is key, as the load cell will experience torque during testing. Figure is a Pro E drawing of the load cell.

Figure 7: Futek T2920 Load Cell

Description of the Torque Sensor.

The torque sensor is the flange to flange reaction type with capacity of 2000 in-lbs. The team chose the Futek LM5400 flange to flange reaction torque cell for the design. This means that each face of the torque sensor can be attached to the structure by using another flange. The torque sensor is designed to measure the reaction moment. The flange will need eight bolts to hold down the flange to prevent the movement between the flanges, which will provides the maximum stability to prevent the error in reading. The sensor is made out of aluminum. Figure is a Pro E drawing of the torque sensor.

Figure 8: Futek LM5400 Flange to Flange reaction torque sensor

Load Cell Calculations

Tension and Compression Load Cell

Torque Sensor Calculations

Test Stand

Our project was build test stand for the human powered helicopter. The basic concept of design for test stand was tripod stand which is using widely in the today’s world. The actual height for our design is less then 11 feet. The material for our design needs are 40 feet solid cylindrical steel, 2.5 inches diameter and 13 inches long steel pipe, 2 inches diameter and 4 feet long steel pipe, 10 inches by 9 inches by 22 inches solid cube, and 4.47 inches diameter and 1 inches solid cylindrical steel. In this paper, we are going to describe the process of our design.

Test Stand Design Process

At the beginning of the semester, our team has a brainstorm about the shape of the test stand. We have some different idea for the test stand for this project. The ideas were cube, cylindrical, trapezoid, and tripod. Therefore we have searched for some information. And also we have some experiments for each stand.

Actually we built test stand with chop stick and straw (see Figure 9), after that we checked which stand need more force to lift it over. After testing the each design, the tripod and trapezoid was good to use for our design, but the cube and the cylindrical shape test stand was failed. Actually the trapezoid was better test stand then the tripod; however, we decide to use tripod test stand because tripod test stand was still good for the our design and its lot more chipper then the trapezoid.

Figure 9: Alternate Stand Designs

After we made the decision for the design of our project, we have another brainstorm for the material for the test stand, and we have come up with some different materials. The materials which we can use for our design were a metal, aluminum, and steel. After brainstorming we decided to use steel because the weight for the metal would be too heavy and for aluminum would be too light for our design. After make decision for the material, we have to come up with some solution for torque from rotating blade. Therefore, we searched some information about this and we come up with using torque load cell which can eliminate the torque from rotating blade. Also in our design, the balancing is really important. Therefore we design all the weight on centroid, so that we don’t have to worry about the losing balance.

Figure 10: Pro E drawing of Test Stand Base

Stand Calculations

In this design, we have to make sure about the flexure about the shaft since there will be a toque when rotating a blade. However, we will have torque load cell to avoid torque from blade to shaft. Other thing that we have to worry about is stay in balance. Since blade is rotating, some force will be creating to X-direction. Since Blade is 5 ft long and has 3.9 Nm torque for one blade, it will create 2.55 N; however, our design weights about 6.9 N so that we don’t have to worry about lift over.

Measuring Signals

To successfully complete the design of the rotor test stand, it is paramount that the team is able to measure the reaction torque which is equivalent to the drag on the rotor. The torque will be measured utilizing a Futek LM5400 flange to flange reaction torque sensor. The problem with torque sensors is that they don’t actually measure anything. They simply have a variable resistance inside which corresponds to the strain on a strain gage affixed to a flexure. While this is extremely useful, it is not quite as simple to measure this varying resistance as it would initially appear. To successfully measure the torque using a torque sensor, signal conditioning techniques must be implemented. These techniques include the application of a voltage to the strain gages which are typically one leg of a Wheatstone bridge circuit. This voltage is commonly referred to the excitation voltage. Application of the excitation voltage allows measurement of the varying resistance of the strain gage as a voltage. This is essential, as computers that collect data are not typically able to measure current or resistance, but instead measure voltages.

Additional problems associated with the measurement of torque using this arrangement is the affect of signal noise. This is a phenomenon that occurs in all circuits that are exposed to electro-magnetic fields. This is especially visible in low voltage level circuits. In some instances, especially in the presence of fluorescent lighting, and unshielded AC Circuits, the induced voltages on a circuit due to environmental noise can equal or exceed the voltage level that one is attempting to measure. This makes deciphering the measured voltage especially problematic. While signal noise is a problem in circuits, it has long been recognized, and proven methods exist to deal with it.

One method frequently implemented to eradicate signal noise is to implement signal filters. This is a simple circuit that utilizes an RC circuit to attenuate the noise present in the signal. By choosing a capacitor of the appropriate size, one can attenuate waveform voltages with frequencies above a cutoff level. Voltages with frequencies above this cutoff level will be allowed to pass through the circuit to be further conditioned.

Once the noise is filtered out of the circuit, signals often need to be amplified. This is beneficial for two main reasons. The first reason one may choose to amplify the signal is that this will make the signal easier to read using available methods. The second reason is that this will increase the resolution of the instrument. In the case of a torque sensor, the instruments that the team has chosen utilize excitation voltages that are approximately 10VDC in magnitude. By conditioning the output signal such that the output voltage is at a maximum when the torque being sensed by the instrument is at its’ maximum value with some safety factor, and conditioning such that the output signal is at 0 VDC when there is no torque applied, the team is maximizing the resolution of the torque measurement.

This sort of signal condition will also be applied to the signal generated by the load cell. The team has chosen to implement the Futek T2920 0- 250 pound tension/compression load cell for the test stand. This instrument uses technology very similar to those found in the torque sensor.

Once the signal has been generated in the instruments, the team will have to measure and record the produced voltages. In addition to the requirement to measure the voltages corresponding to the drag and thrust in the stand, the team will need to control the speed of the gearmotor that is being used to drive the rotor. Controlling the speed of the motor has many available options, but the simplest and easiest solution that the team found was to select a 220 VAC 3Phase motor, and control the input frequency to the motor in order to control its’ corresponding speed. The frequency will be varied using an AC Tech MC1230 solid state controller. The benefits of this particular controller are price, simplicity and functionality. This particular motor controller allow for controlling output frequency by applying a voltage to one of the input channels on the controller. A minimum and maximum speed for the motor can be selected and the output frequency can be controlled linearly based on the varying input voltage between 0-10 VDC. For example, if the minimum speed is set at 100 rpm and the maximum is set at 150 rpm, the speed can be set at 125 rpm by applying 5 VDC to the input channel.

Based on all the requirements listed above, the team chose to select the National Instruments NI PCI-MIO-16E-4 data acquisition card. This particular card is a twelve bit card with eight analog input channels and two analog output channels. While many cards have sufficient channels for this application, the NI PCI-MIO-16E-4 can produce and acquire voltages in the ±10VDC range. This will easily allow the team to acquire the signals from the torque sensor and the load cell, and also allows for controlling the motor output speed with one of the output channels. The twelve bit feature of the card will allow for much more resolution than require by the sensors, especially since we are only utilizing two of the input channels. Figure 1 is a picture of the NI PCI-MIO-16E-4.

NI PCI-6040E

Figure 21: National Instruments NI PCI-MIO-16E-4 data acquisition card

While the DAQ card makes it possible to read the signal, an issue still remains. The team must be able to interface between the signal that we have conditioned, and the card. The team chose to attack this task utilizing the National Instruments SCB-68. This component is often referred to an input output or I/O block. Some key benefits of the SCB-68 are the fact that the enclosure is made of metal which shield the circuitry from noise, and the fact that it has some pre-built signal conditioning onboard. The SCB-68 also has two prototype areas which allows for building additional signal conditioning circuits, and simple screw-type connectors for attaching wires from circuits and sensors. Figure 2 is a picture of the SCB-68 I/O block.

SCB-68

Figure 32: National Instruments SCB-68 I/O block

The team will implement a National Instruments SH-68-68 cable to connect the SCB-68 to the NI PCI-MIO-16E-4. Figure 3 is an image of the SH 68-68 cable. Of course the team must also acquire a personal computer in order to install the hardware. The PC must have an open PCI slot in order to accept the DAQ card, and must be capable of running Microsoft Windows software.

SH68-68-EP

Figure 13: National Instruments SH 68-68 cable

The last detail necessary for reading the signal from the instrument is the user interface. For simplicity and cost considerations, the team will interface with the instruments using National Instruments LabView software. LabView is a programming environment in which simple operator interfaces can be created. These interfaces are executable files called Virtual Instruments. Within this environment, a person can manipulated input and output signals using visual instruments that simulate the “real thing.” Since the team only recently obtained our instruments, and has yet to obtain a PC or sensors, no virtual instruments have been developed to date.

Budget

The budget set aside by the Mechanical Engineering department for this project is $2,500. Through much negotiation, the team has obtained sponsorship from National Instruments. National Instruments has decided to provide all Data Acquisition instruments required for this project. In order to receive this sponsorship, the team will be required to make our progress on the project available to National Instruments. Additionally, the team will display the company logo and link to their website on the teams’ website. A total of $1400 in instruments have been receive from National Instruments under this agreement to date.

Similar sponsorship has been promised from Futek but to a lesser extent. So far Futek has agreed to a 20 percent discount on their instruments if we link to their website on the teams’ website.

The following table is a breakdown of the required parts to complete the project.

	Before Discount	After Discount
M 1230 B 240 Volt 3 Phase AC Motor Controller	359	359
Nord SK12-100L4 3 HP Gearmotor	415.56	415.56
Futek T5400 2000 in-lb Flange to Flange Reaction Torque Cell	1187.5	1000
Futek L2920 0-500 lb Tension and Compression Load Cell	736.25	620
National Instruments SC-2075	395
National Instruments DAQCard- 1200 DAQ Board	900
National Instruments Cables	200
Pipe	100	100
Speed Measurement	90
	4383.31	2494.56

Manufacturing Process

One of the main objectives of HPH team was to design with simplicity to account for the ability to manufacture the product without requiring extensive machining skills. The test stand’s function is to acquire data to aid in the rotor-blade design analysis; therefore, measuring instrumentations are the critical components of the product. With the motor simulating the human power output to the rotor shaft and the torque sensor and load cell are the devices used in reading the drag in terms of reaction torque measurement and lift respectively, HPH team’s manufacturing responsibilities include constructing a sturdy structure and mounting arrangements to have the instrumentations assembled appropriately. The components HPH team set out to manufacture are the structure stand, the motor mount and adapting flange for the flange-to-flange torque sensor attachment.

As the rotor spins, it creates a moment acting on the entire body in the opposite direction. The purpose of the structure is to stably secure the unit in counteracting the resulting forces due to movement of the rotor-blades. The drag and lift values from the Torque Calculation section gave HPH team a range of specifications that it can choose the motor and motor controller on. The motor selected was a three-phase AC induction motor of rotor and stator windings. The motor weighs about 64 lbs. The motor will be mounted vertically on a motor mount. The entire weight of the unit of approximately 100 lbs will be lined up at the center and is distributed into the three tripod pipes equally. The process of selecting the tripod stand was discussed in the concept design report.

A secondary function of the stand structure is to adjust the unit to different heights to observe the significance of ground effects, if any. Ground effect, in theory, improves the lift of the unit due to interference of the ground on the induced airflow pattern by reducing the velocity of the downward flow. The effect would be less drag, thus improved lift.

HPH team machined the solid cylindrical pipe stock down to three 84 inches-long leg pipes. Three 18-in braces were also milled from the solid pipe stock. The main vertical pipe was cut from the ¼-in thick and 2.5-in diameter pipe stock to a length of 26 inches and has two holes at one and two inch from the top of the pipe. The smaller riser pipe was of 2-in diameter and 48 inches in length and was drilled with 24 holes, each being 1.5 inch apart. This riser pipe can be adjusted up and down inside the main vertical pipe and can be affixed still with a ¼-in bolt through both the riser and main pipe. All pipes were grinded to smoothen all sharp edges and ready for the welding process. The bottom of the three leg pipes are appended with three sleeves, each with three threaded holes to be bolted down to the shop floor. HPH team then attempted to machine the load cell adapter (see drawings 1 and 2 in Appendix A) and the torque sensor flange (see drawings 3 and 4 in Appendix A) would assemble the load cell onto the riser pipe and connect the torque sensor to the load cell respectively. After spending hours in the shop and numerous failed attempts to fabricate the parts to the desired dimensions and tolerances, HPH team decided to outsource the manufacturing of the parts to a local machine shop. The decision was based on the wasted efforts being spent would outweigh the cost of outsourcing. The output flange (see drawing 5 in Appendix A) was also fabricated by the machine shop. HPH team then obtained a 1/8-in thick metal plate stock to cut one 26”x8”, two triangular 26”x8” plates and an 8”x8” base. The plates were welded together to make up a vertical motor mount that is big enough to cover the dimensions of the motor, and the pipes were welded to form the structure stand (see figure 10). The welding process was done by a local machine shop, Trucraft. With the load cell adapter being welded on top of the riser pipe, the load cell was attached to the side with the intruding square-slot by the threaded center hole. After the welding process was completed, HPH team connected the torque sensor and load cell using the torque sensor flange-adapter via the 6 1/8-in bolts. The top side of the torque sensor was then attached to the bottom of the motor mount with 6 1/8-in bolts. The motor was mounted onto the side of the mount vertically with 4 1/8-in bolts. The output flange is affixed on top of the rotor shaft by inserting the keyway (see drawing 5) onto the shaft. The wiring from the motor to the motor controller was completed next. Load cell and torque sensor cables were hooked up the data acquisition panels and into the computer. Labview program was developed to control the input voltage and take data. The test stand product was finally completed and ready to do testing.

Instrumentation

Background

In order to design a successful Human-Powered-Helicopter, the rotor must be tested to be low in drag, light weight, and produce high lift force. With these criteria in mind, the test stand must be able to detect slight changes in force. The load cell and torque sensor are needed in the test stand to measure the drag, lift, and weight of the rotor in the scaled down model. The calculation can be done to estimate the forces of the rotor in the full scale whether the rotor would be able to create enough lift for the helicopter to compete in the Igor Sikorsky Human Powered Helicopter Competition.

Measurement Requirement

The theoretical design of the helicopter is based on the successful design that has the 100 foot long diameter rotor with approximate speed of 10 RPM. The helicopter and a person should weigh about 250 lbs, which means the rotor must produce at least 250 lbs of lift or 1110 Newton. With the scaled down model, the rotor will be 10 foot long in diameter with rotational speed of 100 RPM. The scaled-down model yields the lift of about 25 lbf, or 111 Newton.

With these requirements, the load cell and torque sensor were chosen to have ±200 lb and ±2000 in-lbs respectively. The load cell is preloaded of about 100 lbs according to the configuration of the test stand; therefore, the load cell is capable to measure up 300 lbs of lift. The capability of the load cell is well enough to measure the lift of the full scale, but it is being used for only the scaled down model.

Instrumentation Capabilities

The DAQ card for this project is a 12-Bit card, which was available before the beginning of the project. For cost-cutting purpose, the accuracy is designed to be within this DAQ card.

The load cell is a ±10 V; therefore, the resolution is 0.004883 V. With ±200 lbs, the resolution in pound is 0.0957656 lb.

The torque sensor is a ±10 V, and with ±2000 in-lbs, the resolution is found to be 0.004883 V or 0.976563 in-lb.

Experiments and Results

The experiment was conducted to check the repeatability and accuracy of the measurement whether the DAQ card has enough Bit to give good results. It was found that both the load cell and torque sensor are able give measurement with accuracy well within the resolutions. The torque sensor was used to measure an experiment rotor blade, and was found to have 31.41 in-lbs of drag by using LabView. From theoretical calculation, the drag was found to have 31.49 in-lbs. The difference is 0.08 in-lb, which is a very small difference and within the resolution specification. The load cell was tested by measuring known weights for repeatability. The results showed that the reading from LabView is different from trial to trial, but is small enough to be ignored. However, a 16-Bit DAQ card might be considered to increase the accuracy of the reading.

Final Budget

At the completion of the project, the cost of the materials, instrumentation and outsourcing manufacturing come out to be $534 above the allotted amount of $2500. Here’s the breakdown:

Sensors and Calibration cables: $2490

Motor : $444

Motor Controller: Free

All DAQ instruments: Free

Computer: Free

Welding: $100

Total $3034

Conclusion

HPH team set out to design and build a test stand that will be able to perform analysis of different rotor blades based on previously semi-successful projects’ parameters. The end product is one that met specifications and function properly. The test stand is now ready to be taken on by the next HPH team that will do actual testing to help build the complete helicopter to compete in the Sikorsky Competition. The complete procedure to execute the test is found in Appendix B.

Perform the following to conduct Human Powered Helicopter Scaled Rotor Testing.

Text Box: NOTE: The amplification circuits and the sensors are color coded by dots which are attached to the sensors and amplifiers. The load cell instrumentation is currently marked with yellow dots and the torque sensor instrumentation is marked with red dots. Figure 4 shows the instrumentation color coding scheme. F

Figure 4: Instrumentation color coding.

Ensure that the rotor that you intend to test is securely attached to the Output Flange of the Gearmotor.

Determine the desired rotor speed(s) you wish to test and enter it(them) in Table 1 on page 5.

Connect the instrumentation cables to the load cell and the torque sensor.

Ensure the Motor Controller is plugged in to the 3 phase outlet on the side of the column adjacent to the Data Acquisition computer

Power up the Data Acquisition Computer by depressing the Power button on the front of the computer case

Power up the Data Acquisition Computer Monitor by depressing the Power button on the front of the Monitor.

When prompted, enter the BIOS password and then depress “Enter”

Once the DAQ Computer has completed its startup routine, double click on the Labview file shortcut named “Rotor Test” which is located on the computer desktop.

Power up the excitation power supply for the instruments by flipping the toggle switch located on the side of the small black box labeled “HPH STAND”. The green arrow in Figure 5 is pointing to the power supply toggle switch.

Power Supply Toggle Switch

Figure 5: Instrumentation Power Supply Box

To collect “Zero” data for the rotor, left click on the “Zero” button which is located on the lower left portion of the Controls window of the Rotor Test Labview file. The “Zero” button has been circled in Figure 6 below.

Figure 6: Rotor Test “Controls” Screen

Verify that the Zero button toggles from a silver button labeled “OFF” to an orange button labeled “ON”

Text Box: NOTE: When Labview prepares to write new data, the operator is notified that previous files are about to be overwritten

Verify that previously gathered data has been copied to a secure location

Left click on the small white arrow in the upper left portion of the Controls screen

Left click on Replace to allow “C:\Labview\Raw.xls” to be overwritten

Left click on Replace to allow “C:\Labview\Calculations.xls” to be overwritten

Left click on Replace to allow “C:\Labview\Data.xls” to be overwritten

Labview will now begin gathering zero lift and drag data for the current rotor. After a brief pause, the Zero timer will begin to count up to 29. After gathering data for 30 seconds, you will be prompted to allow the previous zero data to be overwritten. Figure 7 is a screenshot of this prompt.

Figure 7: Zero data replacement prompt

Left click on Replace to allow Zero.xls to be overwritten.

Left click on the arrows next to “Controls” to navigate to the “RPM Table & Trial Collection” Screen as shown in Figure 8 below.

Figure 8: Rotor Test “RPM Table &Trial Collection” Screen

Scroll through the Voltage to RPM Table to select the voltage(s) that correspond(s) to the desired RPM(s) for this series of tests and enter the input voltage value(s) in Table 1.

Table 1: Desired Rotor Speed and Corresponding Input Voltages

Test Number	Desired Rotor Speed (RPM)	Corresponding Input Voltage (V)
1
2
3
4

Return to the Controls screen

Place the cursor in the Voltage Display (located below the red dial) by left clicking in the Voltage Display Box

Type in the voltage selected for Test Number 1 in Table 1 above.

Depress <Enter>

If counter clockwise (looking down on the rotor) rotation is desired, move the switch located on the top right hand side of the Power Supply Box to “START REV” and release.

If clockwise (looking down on the rotor) rotation is desired, move the switch located on the top right hand side of the Power Supply Box to “START FWD” and release

Text Box: CAUTION: Prior to beginning the test familiarize yourself with the locations of the rotor stop buttons: 1) On the Motor Controller labeled STOP, 2) On the Power Supply Box labeled STOP, 3) On the wall around the corner from the bulletin board (Large red button labeled “HPH TEST STAND EMERGENCY STOP”)

Left click on the “Begin Test Button”. Figure 10 shows the “Begin Test” button toggled.

Figure 10: "Controls" Screen Showing the "Begin Test" Button toggled

Verify that the “Begin Test Button” toggles from a silver button labeled “Test Complete” to an orange button labeled “Begin Test”.

Ensure that everyone is clear of the rotor

Left click on the small white arrow in the upper left corner of the “Controls” screen

Perform steps 13, 14, and 15 to allow Excel data files to be replaced.

Verify that the “Stabilizer” timer begins counting

Verify that the motor ramps to the desired speed

If you do not desire to perform an additional test on this rotor, skip to step 36.

Enter the voltage value in the “Voltage Display” box that corresponds to the output speed for the next sequential Test Number in Table 1 above

Depress <Enter>

If you desire to perform an additional test, return to step 31.

Left click on the “Begin Test” button

Verify the “Begin Test” button toggles to a silver button labeled “Test Complete”

After the data collection “Timer” reaches 29, verify that the motor ramps to a stop

If the motor did not ramp to a stop, depress one of the three STOP pushbuttons

NOTE:      The data for the test will be located in the folder C:\Labview.

·        Raw data from the instruments will be located in Raw.xls

·        Calculated lift in pounds and drag in inch-pounds is located in Calculations.xls

·        The earliest data are in the lowest row numbers, later data in higher row numbers

Open the Excel file that contains the data you wish to evaluate.

Left click “Finish” on Text Import Wizard Window

Highlight the data

Copy the data by depressing <Ctrl> and <c> simultaneously

Paste the data into another file by depressing <Ctrl> and <v> simultaneously

$Text Box: CAUTION: Failure to close the Excel files in the C:\Labview folder could lead to future errors as Labview may not be able to write to these files during upcoming tests. Additionally, altering these files in any way may make them incompatible with the Labview application.$

Close all the Excel files in the C:\Labview folder without saving

Subsequent steps are to shutdown the Data Acquisition Equipment

Power down the Instrument Excitation Power Supply by flipping the toggle switch located on the side of the Power Supply Box labeled “HPH STAND” to “OFF”

Disconnect the cables from the Load Cell and Torque Sensor.

Stow the test cables on the storage straps

Close the Rotor Test Labview program

Shutdown the Data Acquisition Computer

Background

Project Descriptions

Torque Calculations

AC Motor

Theory

Specifications

Type

Part number

Theory

Specifications

Function Description

Torque Sensor and Load Cell Objective

Load Cell Calculations

Test Stand

Test Stand Design Process

Measuring Signals

Works Cited