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Lab 04 - Ground Test Believer

15 points

Nathan Tyler Rose

Anestis Athanasios Tsagris

Last edited 18 days ago by Jacob Daniel Sieber.

Weekly writing:

This week, the Believer build was finished. This was an immense weight off the shoulders of the group. The ESCs were calibrated, the weight and balance was recorded, and the trim was exacted. In the coming weeks, I will perfect my ability to fly the fixed wing drones. The group is confident in the airworthiness of the aircraft, and the future is limitless.

Overview

In this lab, teams will perform ground testing of their Believer aircraft to complete final setup prior to flight operations. At this stage of the project, the aircraft is assumed to be structurally complete and transitioning from build to operation.

The purpose of this lab is to verify that all control systems and propulsion components are configured correctly and behave predictably before any attempt at flight.

Objectives

By the end of this lab, teams will be able to:

Confirm correct servo centering and control surface neutral positions

Verify correct control direction at both the servo and control-surface level

Calibrate ESCs and verify propulsion system operation

Identify and correct discrepancies using the Ground Control Station (GCS)

Document aircraft readiness

Warnings!

Propellers must not be installed at any time during this lab.

DATX Power On:

Safe State must always be followed for now on. There is a great risk of unintentional connection to another aircraft. This is an enforced rule

DATX Refresh

When powering on your Transmitter it must be in safe state. Please use this PDF as a refresher on the configuration of your switches. Do not bypass the warning screen that appears when you power on. The warnings will go away automatically if the switches are in the correct configuration.

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Servos

When installing servos on the aircraft, they must be mechanically centered in order to operate correctly. Proper servo setup requires both physical alignment and software alignment/verification. These steps must be followed carefully and in order.

Part A – Servo Mechanical Installation and Centering

Before beginning this section, ensure that:

The servo is not installed in the aircraft and servo horn is disconnected

This prevents unintended movement of the control surface during centering.

Important:

If the servo gear is manually moved at any point after this process, the centering procedure must be repeated from the beginning.

The DATX must not have any flap input during this step. Make sure your flap is set to 0%.

Servo Centering Procedure

Obtain a GCS laptop

Power on the Cube

Ensure proper telemetry connection

Set the aircraft status to Manual mode

Plug in the servo

Allow the servo to self-center

Unplug the servo

Servo Horn Installation

Before fully securing the servo in its mounting location:

Install the servo horn so that it is as close as possible to perpendicular relative to the wing and control surface

Minor deviations are acceptable, but gross misalignment is not

Push-rod Adjustment

Adjust the push-rod length to make the associated control surface appear as level as possible when the servo is centered.

Do not connect the push-rod to the servo at this time

The goal is visual neutral, not final trim

Change the push-rod length to try to make control surface as level as possible. But do not install the rod to your servo

After completing these steps, the servo is mechanically centered.

Part B – GCS Trim and Control Adjustment

In previous labs, teams uploaded parameter sets based on a standard Believer configuration. While many parameters are universal, aircraft trim is unique and must be adjusted on a per-aircraft basis.

Teams must identify which control surfaces require trim and determine which direction the servo must move to achieve neutral control surfaces.

GCS Mechanical Trim Verification

Power on GCS Laptop, DATX and aircraft

Set the aircraft status to Manual mode

Observe the distance between the push rod and servo horn connection spot

If the distance is minimal

Power down aircraft and connect your push rods to the servo horn

You may continue to GCS Trim

If the distance is large and major control surface deflection is necessary to connect the push rod to servo

Repeat Part A and alert instructor

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Trim verification in progress

Trim verification in progress

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GCS Trim

Connect your GCS Laptop, DATX, and aircraft

Move all control surfaces and observe:

Which values change

How the servo responds to each input

Identify the parameter associated with the control surface requiring trim

Modify the parameter value based on observed servo movement to achieve a neutral control surface and fill out the table below

Ensure all control surface params are in the table even if no values are modified

Obtain instructor sign-off of trimmed aircraft: AT

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Parameter change image

Parameter change image

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*It should be noted that during this lab there were many problems with the trim. One ruddervator deflected greatly in one direction and not the other, and the opposite was true of the other ruddervator. To fix the issue, the TA, professor, and others studied the issue as well as our group, and it was finally solved. The remedy was to change the mixing gain parameter, as pictured above, to 0.6 instead of 0.5, allowing for more predictable ranges of motion.*

Trim Parameters

Trim Parameters

Param Name

Corresponding Control Surface

Original Value

Modified Value

SERVO1_TRIM

Right Flaperon

1,495

1,425

SERVO2_TRIM

Left Flaperon

1,450

1,500

SERVO6_TRIM

Right Ruddervator

1,600

1,475

SERVO5_TRIM

Left Ruddervator

1,500

1,550

There are no rows in this table

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ESC/Motor

Esc Calibration

Power on your GCS laptop, DATX and Aircraft. Ensure that the aircraft is not armed. Following the instructions from

Lab 11 - Motors and Controls · AT 209⁠

calibrate both ESCs.

What was your method for calibrating the ESCs?

We followed the visual guide found on the ESC web page from the lab 11 resources section. After completing this, the ESCs were calibrated and rotated in sync.

Instructor sign-off: AT

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Proper battery connection confirmed all systems worked, including ESC power

Proper battery connection confirmed all systems worked, including ESC power

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Motor Direction

Observe the direction of your motor rotation under power. Take note of the initial direction.

Which direction should the motor be spinning?

Change the relevant parameter to make the motor spin in the correct direction.

Motor

Initial Direction

Correct Direction

Port

Starboard

There are no rows in this table

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Weight and Balance

Each group assembled their Believer independently. Variations in wiring, battery placement, adhesive use, reinforcement, and hardware placement can shift the aircraft’s center of gravity (CG). Before flight, CG must be calculated and verified.

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CG Guiding Questions

What is a datum? Where is it?

A datum is essentially a reference point people use to measure arms when conducting weight and balance on aircraft. It is located at the marked indent on the right and left sides of the fuselage by the forward wing spar.

If I state that a sensor is installed at -3 in and an additional battery is installed at +20 in, where are those components located relative to the datum?

The sensor would be located 3 inches forward relative to the datum and the additional battery would be located 20 inches aft relative to the datum.

What two configuration conditions must the aircraft be in during CG calculation?

The two configuration conditions the aircraft must have during CG calculation are level flight attitude and all equipment installed.

What are some ways to verify that the aircraft is in both of those configuration conditions?

Some ways to verify that the aircraft is in both of those configuation conditions are making sure all control surfaces move (ensuring that all wiring and electrical components are present), performing a visual check, and consulting the user manual.

What is Tare? How is it depicted in a CG Table?

The tare the weight is the weight of the equipment used to weight the aircraft such as the weight of the jacks. It is subtracted from the weight and balance of the aircraft as a negative value (as something like the jacks would not be equipped in flight).

What is a plumb bob? How is it used?

A plum bob is usually a weight on a string used to level the aircraft relative to the earth. It’s a piece of metal on a string in our lab, and it was placed under a variety of components to understand their placement relative to the datum for measurement.

Verify answers with instructor

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Aircraft calibrated and waiting to be weighed in position

Aircraft calibrated and waiting to be weighed in position

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Calculating CG

Make sure that this portion is done on one singular table that is not finished to be able to draw on the table.

Discuss within your group and have consensus on your methodology of calculating the CG

Determine where the datum is located

Obtain CG jacks and scales

Weigh each jack individually and record the weight (grams) in the table below under Tare.

Decide where to place the two forward jacks on the aircraft and determine their distance from the datum.

Note: The forward jacks must be placed at the same longitudinal station on both sides of the aircraft.

The forward jacks were placed near the indent of the underside of the wing closest to the front wing spar.

Determine where to place the rear jack in order to satisfy the required configuration conditions.

The rear jack was placed in such a way that it balanced well with the aircraft and was easily measured.

Place each jack on a scale and carefully rest the aircraft on the three jacks.

Verify that the rear jack is in the correct location and adjust as needed

Record the weight depicted on each scale in the table below

Using a plumb bob, mark the exact longitudinal location of each jack stand on the physical table and the datum on your CG Table

Ensure that the measuring method used for each jack is consistent.

Determine the centerline between the two forward jacks.

Determine the centerline of the rear jack.

Determine the centerline of the datum.

Measure the horizontal distance from each jack location to the datum and record the value in inches.

CG Table

CG Table

Item

Location from datum(in)

Weight (grams)

Moment

Port Jack Tare

1.44

-204

-293.25

Star Jack Tare

0.81

-203

-164.94

Rear Jack Tare

29.19

-58

-1,692.88

Port Jack with aircraft

1.44

2,365

3,399.69

Star Jack with aircraft

0.81

2,235

1,815.94

Rear Jack with aircraft

29.19

275

8,026.56

There are no rows in this table

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Total Weight

4,410

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Total Moment

11,091.13

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2.51

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Evaluation of CG

What does

2.51

⁠

in mean?

“2.51 in” means that our center of gravity for the aircraft is

Do you think that this number is acceptable? How would you fix this if not?

It is not clear where the CG limits are for this aircraft. Neither the manual nor the resources were found to contain guidance for this. However, this number would appear to be acceptable because of its fairly noticable nose-heavy weight distribution, which would provide positive longitudinal stability (and easy stall recovery). If this is eventually found to be less than acceptable, the battery can be moved forward or aft in order to shift the center of gravity of the aircraft.

Based on your CG Location, what flight characteristics would you expect during flight?

Our CG is very close to the datum, and is slightly aft of the datum. Largely, it should be noted that the CG is fairly forward on the aircraft, and this would result in easier stall recovery, greater longitudinal stability, less efficient cruise, higher stall speed, and more ruddervator authority compared to an aircraft of the same weight with a further aft CG. If it turns out that the flight characteristics are not optimal, the CG can be shifted by moving the battery around as a form of ballast.

Discuss your results with your instructor. You may need to fix your CG.

The instructor was not in COMP at the time of the completion of the weight and balance results, but more discussion will follow come Monday. Furthermore, a most recent version of the parameters could not be downloaded because access to the COMP 101 laptops was not available in the after hours time the lab was completed. This will be updated Monday as well.

Deliverables

Fully completed document exported as a PDF to Brightspace

.json of exported parameters file name “MMDDYYYYGroup#Param” imported into this document

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IMG_0802.HEIC

3.1 MB

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IMG_0806.HEIC

2.8 MB

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IMG_0803.HEIC

3.3 MB

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IMG_0804.HEIC

3.6 MB

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