P14462: Tethered Glider
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Build, Test, Document

Table of Contents

Build, Test, and Integrate

Glider & Bridle

The tethered flights added a new challenge to flying the plane, because the glider would lose control and crash when the tether became taut. After attempting to enter a flight path in different methods, we discovered ways to retain stability when the tether became taut. When there was minimal wind, the glider was flown in increasingly large circles until the tether just became taut. The glider would smoothly reorient itself into the flight path. When there was large amounts of wind, it became too difficult to fly the plane smoothly into a flight path. We discovered that it was more beneficial to enter the flight path as soon as possible. We would try to gain altitude and become taut quickly. The plane would lose stability when the tether becomes taut, but with enough altitude, the pilot may regain control before crashing. Another challenge we encountered after entering the flight path was that the glider would not gain altitude with any control surface inputs. We first thought that this would be fixed by increasing the rudder area. While this did increase the controls entering the flight path, we still did not gain altitude after the tether became taut. After viewing our flight videos, we realized with a symmetric bridle caused the lift forces to be horizontal to the ground. In order to make our glider gain altitude, we reoriented the bridle so that the lift force would be pointed towards the center of our flight radius.

Base Station

The potentiometers and load cells were connected to the DAQs and processed in LabVIEW to establish proper working condition.

The base station's design is robust yet still compact. The most vulnerable part of it is the exposed load cell and vertical potentiometer however any impact damage to these components would remain localized. The rest of the base station is made of steel, aluminum, or half-inch plywood. The ball bearings used for the vertical potentiometers provide a smooth range of motion. The tapered roller bearings provide smooth range of motion for the horizontal potentiometer while dissipating the vertical loads that are applied. Preliminary testing shows that tracking occurs by the base station with approximately 2 lbs of tension on a 1 m tether. While the base station works well, it was difficult to manufacture for inexperienced machinists. After consulting with professional machinists, the parts were re-machined to a higher degree of precision. This greatly improved the bearing alignment resulting in minimal turning resistance. Installing the base station in a field was very easy. The auger installation is simple and is secure when in the ground. A rod is used to attach the auger to two hooks on the underside of the base station. The three adjustable legs are use to level the base station with the aid of a 2D bubble level.

Last Updated - 15 May 2014

Test Plans & Test Results

Due to environmental conditions, flying experience limitations, glider damage, and loss of elevation during the flight, experimental testing was limited to obtaining sustained looping flight. Instead of testing the theoretical model at various setups as intended, we worked to create a sustainable glider setup. The loss of elevation throughout the tests prevented us from having a long enough looping flight to meet the engineering requirement. Without this, we did not move on to testing each flight parameter.

Engineering Requirements Test Plan

The following table is the complete list of Engineering Requirements for our project

Figure: P14462 Engineering Requirements

Figure: P14462 Engineering Requirements

A test plan to test each "testable" metric was developed. The following test plans correlate back to the Engineering Requirements via the labeling on each.

Metric 1 and Metric 15 Test Plan:

Figure: P14462 M1 and M15 Test Plan

Figure: P14462 M1 and M15 Test Plan

Metric 2 Test Plan:

Figure: P14462 M2 Test Plan

Figure: P14462 M2 Test Plan

Metric 4 Test Plan:

Figure: P14462 M4 Test Plan

Figure: P14462 M4 Test Plan

Metric 5 Test Plan:

Figure: P14462 M5 Test Plan

Figure: P14462 M5 Test Plan

Metric 6 Test Plan:

Figure: P14462 M6 Test Plan

Figure: P14462 M6 Test Plan

Metric 7 Test Plan:

Figure: P14462 M7 Test Plan

Figure: P14462 M7 Test Plan

Metric 9 and Metric 10 Test Plan:

Figure: P14462 M9 and M10 Test Plan

Figure: P14462 M9 and M10 Test Plan

Assembly Instructions

  1. ‘’Connect motor to electronic speed controller (ESC) and battery’’

The motor, ESC, battery, and receiver (Rx) all connect to provide power to the glider. Figure 1 shows all these components laid out before any permanent connections were made.

Figure 1: Motor, ESC, Battery, and Receiver Laid Out

Figure 1: Motor, ESC, Battery, and Receiver Laid Out

The components are connected together using bullet connectors (BCs) and protected with shrink tubing.
Figure 2: ESC with the BCs and Shrink Tubing

Figure 2: ESC with the BCs and Shrink Tubing

The three wires on the ESC are color coded red, yellow, and black. These wires are connected with the respective wire color on the glider motor. The BCs mate the wire ends. They fit on the motor wires as shown in Figure 4.

Figure 3: ESC and Motor with BCs

Figure 3: ESC and Motor with BCs

Figure 4: ESC and Motor with BCs - Zoomed

Figure 4: ESC and Motor with BCs - Zoomed

Figure 4 also shows the shrink tubing on the wire ends of the ESC so when the motor and ESC are soldered together, the shrink tubing will be secured atop the connection. Figures 5-7 show the soldering process. Figure 8 shows the completed soldering job and the connections are ready for shrink tubing. The connection was then wrapped in electrical tape because past experience revealed the connection would come loose when the glider crashed.

Figure 5: Motor and BC Solder Process

Figure 5: Motor and BC Solder Process

Figure 6: Motor and BC Solder Process

Figure 6: Motor and BC Solder Process

Figure 7: Motor and BC Solder Process

Figure 7: Motor and BC Solder Process

Figure 8: Motor and BC Solder Completed

Figure 8: Motor and BC Solder Completed

Figure 9 shows a close up of battery, ESC, and Rx not yet connected. This close up better shows how the power is delivered from the battery, to the ESC, to the Rx via PWM cable, and finally to the servos that will be plugged into each Rx channel. The Battery and ESC are connected using an EC3-F to XT60-M adaptor as shown in Figures 10 and 11.

Figure 9: ESC and Battery with XT60 Adaptor and Rx

Figure 9: ESC and Battery with XT60 Adaptor and Rx

Figure 10: ESC and Battery with XT60 Adaptor

Figure 10: ESC and Battery with XT60 Adaptor

Figure 11: ESC and Battery with XT60 Adaptor - Zoomed

Figure 11: ESC and Battery with XT60 Adaptor - Zoomed

Figures 12 shows the soldering process of the ESC power wires to the EC3-F end of the adapter. Figure 13 then shows the two stage shrink tubing. A larger shrink tube was used to cover the adaptor and solder connection, while the smaller shrink tubing covers the larger shrink tubing and the ESC power wire.

Figure 12: ESC and Adaptor Soldered

Figure 12: ESC and Adaptor Soldered

Figure 13: ESC and Adaptor with Shrink Tubing

Figure 13: ESC and Adaptor with Shrink Tubing

Figure 14 shows the completed soldering process between the motor, ESC, and battery adaptor. The components were tested and are now ready to be installed in the glider.

Figure 14: Motor, ESC, and Adaptor Connected

Figure 14: Motor, ESC, and Adaptor Connected

Glider

  1. Gather all the glider components. View the glider components here.
    • Left & right halves of the fuselage
    • Left & right wings
    • Elevator
    • Rudder
    • Wing spar
    • Motor, ESC, and battery assembly
  2. Verify fuselage and wings mate together.

    Figure 8 shows the testing of the wing and fuselage mating. The purpose of this is to ensure the holes between the fuselage and wing align to allow the two center screws to hold them together. Note: the electronic components shown in figure 8 are not necessary for this test.
    Figure 8: Fuselage and wing mating

    Figure 8: Fuselage and wing mating



    This glider had misaligned holes that required modification.
  3. Modify the glider
    • Use a dry erase marker to mark the bottom of the screw
    • Insert the screw into the holes. When it gets stuck, twist the screw slightly to mark the stuck spot.
    • Disassemble the glider.
    • A dremel grinding tool was used to modify the hole until it aligned with where the screw actually hit.
    • Repeat steps 1-4 for both holes until the screw goes through all holes
      Figure 8: Fuselage and wing mating

      Figure 8: Fuselage and wing mating

      • Note: The plastic holes were dremeled off completely. The nut was also removed. See figure 10.
        Figure 10: Ground down internal plastic screw guides

        Figure 10: Ground down internal plastic screw guides



  4. The servomotors then are connected to the receiver. Each wire connected to the servomotors is labelled with a number.
  5. This number is matched up with the channel on the receiver with the exception of the ailerons which are instead connected to a splitter cable. The splitter cable is then connected to the receiver, see figure 11.
  6. The wires must be inserted with the black wire facing the edge of the receiver.
  7. Attach the motor to the cut out at the top of the fuselage. The wires attached to the motor need to be connected with the matching color wires at the ESC.
  8. Test the servomotors with the transmitter to ensure that the controls and directions are correct.
  9. Stick velcro to the bottom of the inside of the fuselage and the bottom of the batteries and receiver. This velcro should be positioned at the front of the glider because the glider is naturally tail heavy.
    Figure 11: Servomotor wires connected to the splitter cable and receiver

    Figure 11: Servomotor wires connected to the splitter cable and receiver

  10. Slide each wing into the slot on the appropriate side of the fuselage.
  11. Slide the carbon fiber rod into the metal hole in the wing.
  12. Place the carbon fiber rod into the matching hole on the other wing and slide the two parts together. Be careful to not damage any parts during this step because the two halves of the plane have a tight connection.
  13. Glue the fuselage together starting with the nose. Pull the fuselage apart slightly and insert a line of glue into the seam. Press shut, remove excess, and hold until secure. Repeat this on the top and bottom sections of the glider working from the nose to tail of the glider.
    Figure 12: Gluing the fuselage together

    Figure 12: Gluing the fuselage together

    Figure 13: Glued fuselage

    Figure 13: Glued fuselage

  14. Glue the motor cover in place
  15. Apply glue to all the mating surfaces of the vertical and horizontal stabilizers
    Figure 14: Gluing the tail together

    Figure 14: Gluing the tail together

  16. Glue the tail to the fuselage. Apply glue to all mating surfaces. This is the most fragile part of the glider.
  17. Let dry. Re-apply glue to any section where the EPO foam hasn’t mated properly.
  18. Apply more glue to the exposed tail seams. Let it soak into the crack and dry.
  19. Connect the servo arm to the attachments on the control surfaces. Adjust until properly trimmed, typically in line with the rest of the lift surface

    *Note: We set our elevator to be trimmed down as the glider is tail heavy.
  20. Attach the propeller and tighten. Verify it’s in the correct orientation.
    Figure 15: Assembled Propellor

    Figure 15: Assembled Propellor

Assembled Glider Pictures

Figure 16: Assembled Glider

Figure 16: Assembled Glider

Figure 17: Assembled Glider

Figure 17: Assembled Glider

Figure 18: Assembled Glider

Figure 18: Assembled Glider

Tether-Wing Attachment Disk Machining

Obtain a sheet of 1/8” thick polycarbonate. Using a band saw, machine the polycarbonate into a 2” by 2” square. Then remove the corners of the square, using a band saw to create an octagon, see Fig. 1. Because the tether-wing attachment disk does not have to be precision machined, an octagon will be faster to machine than a circle. The disk does not require a specific shape and only needs there to be no sharp corners.
Figure 1: Machining the polycarbonate into an octagon using a band saw

Figure 1: Machining the polycarbonate into an octagon using a band saw

Next, using a 1/4” drill bit and a vertical milling machine, drill two holes into the polycarbonate, see Fig. 2. These holes need to be 2/3” from each other and 1/3” from the center of the disk. Using a countersink, create small chamfers on both sides of the two holes. These chamfers will reduce stress concentrations on the tether reducing the risk of tether damage.

Figure 2: Machining two holes and a chamfer into the polycarbonate

Figure 2: Machining two holes and a chamfer into the polycarbonate

Next, the polycarbonate should have rough edges on the outside edges and the chamfers. These need to be removed because they could cause unnecessary damage to the tether or glider. Using a grinding stone as a tool bit for the dremel, remove all burrs and sharp edges from the part, see Fig 3. Then use the dremel tool to apply a light chamfer to all outside edges and corners. This will reduce stress concentrations from the edge of the tether-wing attachment disk on the glider.

Figure 3: Removing all burrs and sharp edges from the tether-wing attachment disk using a dremel with a grinding stone tool bit

Figure 3: Removing all burrs and sharp edges from the tether-wing attachment disk using a dremel with a grinding stone tool bit

Sensor Calibrations

Potentiometers

Both vertical and horizontal potentiometers were calibrated to work within the range of our system (vertical: 0 to 90 degrees, horizontal: -90 to +90 degrees). This was done by in a set number of steps:

1. Rotate the system a known number of degrees (about one axis at a time, keep other rotation fixed).

2. Record voltage output for a few seconds to gather significant data.

3. Average voltage output.

4. Repeat for 10-20 different angles within the desired range.

5. Plot the results on a degree vs. voltage scale.

6. Use a linear trend line to find the slope and y-intercept.

7. Incorporate the slope and intercept values into LabVIEW code.

8. Test to make sure angle readings are accurate.

In order to rotate the system a known number of degrees, a laser and measured linear distance were used. For the vertical potentiometer calibration, the laser was attached by two magnets, one taped to the bottom of the laser and the other centered on the end of the vertically rotating ("vertical") shaft. For the horizontal potentiometer calibration, the laser was placed centered on top plate which is the center of the horizontally rotating ("horizontal") shaft. The laser light was kept on during tests by tightening a zip tie around the button. The system was brought close to the whiteboard so it will be able to measure a wider range of degrees. For both the vertical and horizontal potentiometer calibration, linear measurements were made on the whiteboard from 0 degrees to the maximum angle the whiteboard space would allow and incremented in between to create 10-20 evenly spaced data points. For the test, the system was rotated to the desired angle by aligning the laser with the marking on the whiteboard. Trigonometry was used to calculate the angle the system was at during each recording and used to generate a linear plot.

The pictures below show the potentiometer calibration setups.

Laser Setup with Magnet and Zip Tie

Laser Setup with Magnet and Zip Tie

Laser Setup Close-up

Laser Setup Close-up

Vertical Pot Calibration Setup

Vertical Pot Calibration Setup

Vertical Pot Calibration Side View

Vertical Pot Calibration Side View

Vertical Pot Calibration Front View

Vertical Pot Calibration Front View

Horizontal Pot Calibration Setup

Horizontal Pot Calibration Setup

Horizontal Pot Calibration Front View

Horizontal Pot Calibration Front View

Horizontal Pot Calibration Top View

Horizontal Pot Calibration Top View

Load Cell Calibration

The first and second load cells that we calibrated were calibrated by tying two adjustable dumbbells together and hanging them from the load cell that was attached to a metal rod. This process proved very difficult as every time weight was added, the weights had to be carefully lifted and placed within the adjusting station, and then placed gently back to hag from the load cell. This system failed when, during the second calibration, the weight was dropped while still attached to the load cell. This caused a spike load to be sent through the system and permanently damaging the load cell and the bridge amplifier. The load cell was calibrated from 0lbs to approximately 100lbs.

A simpler calibration setup was created that consisted of a wooden plate that hang from the load cell and weights could be easily balanced on the plate one at a time. The steps for calibrating the load cell are as follows:

1. Measure and record the value of the weights with a scale to know the exact value of each weight.

2. Attach one end of the tether to the wooden plate and the other end to the load cell.

3. Attach the load cell to the steel rod and hang upside down between two identical heights on either side.

4. Record voltage output for a few seconds to gather significant data.

5. Average voltage output.

6. Repeat for 10-20 different weights within the desired range.

7. Plot the results on a weight vs. voltage scale.

8. Use a linear trend line to find the slope and y-intercept.

9. Incorporate the slope and intercept values into LabVIEW code.

10. Test to make sure weight readings are accurate.

The pictures below show the load cell calibration setups.

Original Calibration Setup That Resulted in Damages to the Load Cell and Amplifier

Original Calibration Setup That Resulted in Damages to the Load Cell and Amplifier

Load Cell Calibration Setup

Load Cell Calibration Setup

Load Cell Calibration Setup Showing Wood Plate Hanging and Ready For Weights

Load Cell Calibration Setup Showing Wood Plate Hanging and Ready For Weights

Weights Being Measured and Recorded

Weights Being Measured and Recorded

Weights Being Balanced On The Plate and the Output Voltage is Recorded

Weights Being Balanced On The Plate and the Output Voltage is Recorded

Maximum Amount of Weights Being Hung and Measured (~100lbs)

Maximum Amount of Weights Being Hung and Measured (~100lbs)

User or Operator Instructions/Manual

DAQ Instruction Video

This video gives a quick overview of how to set up, run, and save the data using the LabVIEW code generated for this project. This is similar to the written instructions within the LabVIEW code Front Panel tab "Instructions".

DAQ Instruction Video


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