A HEAT SHIELD FOR THE FLIGHT CONTROLLER’S IMU CONTAINING SENSITIVE ACCELEROMETERS AND GYROSCOPES.

Wait… why do we need a heat shield for drone’s flight controller. Here comes the problem statement.

The gyroscopes and accelerometers present in the INERTIAL MEASUREMENT UNIT of the drone’s flight controller are very much sensitive to temperature.

So on a hot day, at noon if a drone flight has to take place. Then there is a high probability of EKF failure. i.e. EXTENDED KALMAN FILTER FAILURE.

WHAT HAPPENS ON EKF FAILURE, WHEN THE DRONE IS AIRBORNE?

⦁ Drone malfunctions with heavy power draw and heavy acceleration.

⦁ The gyroscopes and accelerometers may get fixed in one single direction and the drone goes in that fixed direction either with the heavy acceleration / no acceleration based on the positions fix accelerometers.

⦁ Bizarre actions of the drone may take place like quick jerky roll, pitch, and angular movements which seems devastating for the drone pilot and the people around. This is all due to the gyroscope failure which makes the gyros and accels keep fluctuating in directions in a jerky manner, which generally happens due to high temperature.

MY APPROACH TO PREVENTING EKF FAILURE?

This problem when digged deep redirects us to regulate the temperature of the flight controller. And my idea is to create a heat shield with some heat-resistant material on it, to be placed on the drone’s flight controller so that it doesn’t allow the temperature of hot noonday to enter into the flight controller.

UNDERSTANDING THE PROBLEM

What is heat exactly?… it is just the energy radiated from a source and in our case it is the sunlight which is an electromagnetic wave.

Okay, that’s fine how is the heat getting transmitted to IMU which is inside the flight controller’s shell ( of course how the heat is getting transmitted simply )?

⦁ LIGHT: Any object which is exposed to sunlight gets a energy radiation hit from the electromagnetic wave which results in temperature rise — simply RADIATION.

⦁ GASES: The gases in the air absorb the heat radiated from the sunlight’s electromagnetic wave. The hit of these gases with the object results in transfer of heat within the gas molecule — simply CONVECTION.

So in order to solve the problem, we should avoid the entry of LIGHT and isolate the air within the vicinity of the flight controller with the external atmosphere ( INSULATION ).

SELECTING THE HEAT-RESISTANT MATERIAL?

I’ve searched for the cheap heat-resistant material on google and I found them to be:

⦁ Polyimide

⦁ Polyimide aluminum alloy

⦁ Asbestos

⦁ Kevlar

⦁ Galvanised Mild steel

⦁ Kapton

⦁ BoPet

These are the list from which I’ve to finalize a material to put it on the shield.

I’ve analyzed the material properties of all the materials listed.

POLYIMIDE PROPERTIES

⦁ Radiation resistance

⦁ Superior temperature adaptability

⦁ Transparency in many microwave applications

⦁ High mechanical performance

⦁ High tensile and compressive strength

⦁ Superior bearing and wear properties

⦁ Outstanding chemical resistance

CONS

1. Low impact strength
2. Expensive.

POLYIMIDE ALUMINIUM ALLOY PROPERTIES

1. Increased thermal stability than Polyimide.

2. Decreased Electric breakdown voltage

CONS

1. Polyimide is itself expensive. It’s alloy is even more expensive.

Source: https://iopscience.iop.org/article/10.1088/1757-899X/782/2/022096/pdf

ASBESTOS PROPERTIES

1. High thermal resistivity
2. Fire resistant
3. Chemical resistant
4. Very low biological breakdown

CONS

1. Needs careful operation or else inhalation of asbestos fibers leads to Asbestosis and Mesothelioma

KEVLAR PROPERTIES

1. High thermal stability
2. high tensile strength
3. High modulus
4. High toughness

CONS

1. Quick moisture absorbent
2. Difficult to cut such high tensile strength material.

GALVANISED MILD STEEL PROPERTIES

1. Extreme heat resistant
2. Waterproof

CONS

1. More in weighT
2. Low tensile strength as compared to others.

KAPTON PROPERTIES

1. high temp-resistant ( -269 to 400 ) degrees celsius.
2. high electrical insulation
3. strong hydrogen bonds
4. very strong adhesive nature
5. very low outgassing nature — does not allow gases

BOPET PROPERTIES

1. high tensile strength
2. High reflectivity
3. Low outgassing properties
4. electrical insulation

MYLAR PROPERTIES

1. Electric insulator.
2. Transparent.
3. High tensile strength.
4. Reflective.
5. Gas barrier.

Upon taking the following things into consideration i’ve finally selected the Kapton as our heat-resistant material

1. High heat resistance
2. Low weight
3. Low cost
4. Availability
5. Easy to use for any kind of modification.

HEAT SHIELD DESIGN

The heat shield I’ve created on fusion 360 is a hollow rectangular array upon which the Kapton tape will be sticked.

ARRAY CONSTRUCTION

The reason I’ve made it in an array construction is that the 3d printed material may interfere with the heat-resisting process and that would entirely threaten the aim of the idea.

DIMENSIONS

Dimensions are taken as per the measurements of the flight controller and the upper squash plate.

As you can see here the distance between two internal screws on an edge is 70mm.

The dimensions of the pixhawk cubepilot orange are 38.25mm x 38.25mm x 22.3mm.

Heat shield dimensions :

Length : 150mm

Width : 50mm

Height : 40mm

MAKING IT AERODYNAMICAL

To make it more resistant to the aerodynamical drag when the drone experiences in flight, I’ve Filleted every edge of the design so that this construction would not create a drag on the drone.

Here is the design of the heat shield.

Hope you liked it, thank you soo much for reading:)