Welcome to Jom's

ENGINEERING FORUM

Scroll Down

Quick Click

 

________________

SOLID ROCKET FUEL

8 July 2021 -- Jomkhwan Borrirak   3 min read

Solid-propellant rocket is the most common type of rocket since the 13th century due to its simplicity and low-cost. As you might have guessed by its name, the chemical components that made up the fuel is consisting of two solid components; the solid oxidiser and the solid fuel. The oxidiser contains O2 (Oxygen) which is the most essential component to start a combustion. Typically, the common oxidisers for low-orbit rocket are Potassium Nitrate and Powdered Sulpher since those two are easy to find and legally purchase. Make sure you are looking for a pure Potassium Nitrate (Potassium Oxide + Nitrogen) with minimum of other substances since it could affect the performance of the engine. Up next is the fuel which is the components that we need to mix together with the oxidiser. The Black powder, Charcoal and Aluminium powder are considered to be the most common. For low-thrust engine, you might consider fined sugar with dextrose, sorbitol or sucrose as a fuel as well

 
4CD117FA-A718-4418-BC3A-BC2A0F108A3B.jpg

FUEL STIRRING PROCESS

Mixing two components together can be done through normal emulsification. This type of mixture is considered to be the safest way to mix up rocket fuels. However, you have to ensure that they are really well-mixed, otherwise the engine would have a discontinuous or uneven thrust which isn't a good result for a rocket. The ideal ratio of two components is 60-65% of Oxidiser and 35%-40% of fuel. For more effective mixture, I recommend to mix through heat. For instance, JOM-A10's fuel has been mixed through high-temperature stirring which melt Potassium Nitrate and Sugar together, making a brown solid fuel as a result. The advantage of this type of mixture is effective thrust. As the fuel is evenly mixed, the resulting thrust is very continuous with complete combustion. However, the scale of safeness reduced, compared to normal emulsification by which the high temperature could sparked the fuel while you stir. Therefore, you have to ensure that no component makes contact with fire. The duration of stirring depends on how high the temperature is. The indicator of the well-mixed fuel is its colour where you can stop the stirring when you see a good light-brown liquid. Make sure that you prepare a containment pipe first before do any mixture process since the light-brown liquid would turn into solid fuel after it cools down. After it cools down, it is important to make a hole at the middle of the solid fuel to allow oxygen to reach the entire fuel chamber. When you get yourself a solid fuel inside a containment, you are ready for engine ignition part.

_________________

HYBRID ROCKET FUEL

14 July 2021 -- Jomkhwan Borrirak   3 min read

 

Hybrid Engine is considered to be the safest fuel existed. It is also my favourite type of engine due to more reliability and safety. Although high safeness came with higher cost, the trade off is worth it for many individuals and Aerospace companies nowadays. The process still keep the simplicity. Instead of having two solid or two liquid chemical components, making up as fuel, Hybrid engine contains two entities of mixtures; either Solid and Liquid or Solid and Gas. Usually the solid component in the hybrid engine is the fuel and either liquid or gas is the oxidiser. High-Pressure Oxygen is the most common oxidiser, followed by Nitrous Oxide and Hydrogen Peroxide. Now comes to an interesting part. For Hybrid engine, we can use literally anything for the fuel. Yes, you can use your pencil as a fuel. You can use your clothes that you wear or even unused papers. Nevertheless, the efficiency of an engine will depend on the flammability of that substance and also the weight if you are dealing with rocket. Therefore, the most common components for the fuel are paraffin wax, charcoal and polymers. All of them are considered to be highly inflammable as well as low cost.

FUEL SETUP

In this part, you will see a clear difference between Hybrid and Solid engine. Instead of using only one containment as the solid engine does, hybrid engine need two containments; an oxidiser tank and the combustion chamber. For those who has a high-pressure oxygen, you usually have a tank to contain it. So, you only need to focus on the combustion chamber where you really have to ensure that the containment is high-temp resistance and most importantly, no leak. Polymer containment can be considered as well if the burn up process does not take long. Make sure you create two main holes in your containment where one side is the nozzle and another side is for the high-pressure oxygen pipe. Up next is the valve. Normally, high-pressure oxygen tank will already provide you a valve to control the pressure bar. The pressure bar is considered to be the safety measure for Hybrid rocket engineers since they could simply lower the pressure or turn it off when things gone wrong. Unlike solid engine that provide you no control once you commit an ignition. Like the solid engine, make sure that you create a hole inside the solid fuel as well to allow the flow of high-pressure oxygen to the nozzle.

_________________

LIQUID ROCKET FUEL

5 October 2021 -- Jomkhwan Borrirak   2 min read

Personally, I have not been tried this type of this engine yet due to its difficulty and time consumption. Its difficulty lies upon the fact that instant ignition will immediately occur if the oxisider and the fuel make contact such as Hypergolic engine, unlike both solid and hybrid engine where engine ignition system is required. The liquid rocket fuel is getting used quite often in Aerospace industries as it offers extremely low dry mass. SpaceX for instance has been interested in Liquid fuel, specially using the liquid methane since Mars is full of it. What's make the liquid fuel to be different from solid and hybrid fuel is its three containments; an oxidiser tank, a fuel tank and a combustion chamber. The first choice of an oxisider is LOX Liquid Oxygen and the fuel is RP-1 Kerosene. The reason behind many people's first choice is the fact that these two make up as non-hypergolic or cryogenic fuel which means that they don't ignite when contact each others like Hypergolic fuel. In this decade, you might also fine aerospace companies are using more liquid hydrogen as the oxidiser as well.

 
The-parts-of-liquid-rocket-engine.png

FUEL SETUP
As you may see the mechanism of Liquid-propellant rocket above, three chambers lined up where fuel and oxidiser will be pumped to the combustion chamber. To avoid instabilities such as chugging, which is a relatively low speed oscillation, the engine must be designed with enough pressure drop across the injectors to render the flow largely independent of the chamber pressure. This pressure drop is normally achieved by using at least 20% of the chamber pressure across the injectors. This process is very similar to the Hybrid engine where the flow of exhaustion can be controlled through the pressure bar. Safety must come first. Like other two type of engines, do not forget to ensure that all chemical and combustion chamber is high-temp resistance with no valuable part or leaking holes.

 

_________________

ENGINE IGNITION SYSTEM

28 July 2021 -- Jomkhwan Borrirak , Phruek Pimolsiri  3 min read

Now comes to the process that unite all three type of rocket engines. After you choose what type of engines you are going to build, up next is the engine ignition system. Well, of course you do not want to ignite the engine by yourself and risked being burned alive. Therefore, this system would come in handy since this system allows you to stand by in distance and ignite the engine whenever you want.

S__7725065.jpg

SETUP

The setup is simple. First off, we need a resistance wire of 600A or 25 Ohm to be our heater. As you might have known by its name the resistance wire resists the electrical loop and form into thermal energy. In order to spark enough fire for engine ignition, the wire can be surrounded by a powder of red phosphorus. This substance is very common among the lighting torch. The power house does not need to a high voltage battery at all. In fact, the series of two AA Batteries could already do the work. I personally used three AA Batteries since it provided more effective and faster igniting time. Last but not least is the switch. The switch acts as subject that simplify the ignition otherwise you have to manually connect the + - wires to the batteries yourself which does not allow you to ignite the engine in the great distance. Up next is the installation of the resistance wire to the combustion chamber. This process would be difference for a different type of engine.

INSTALLATION FOR A SOLID ENGINE 

For a solid engine, the fuel fires off once the resistance wire is heated. Therefore, it is important to install the wire at the end of the fuel chamber next to the nozzle, so the burn will be outside-in. Moreover, it is important to make sure that the wire make contact with the fuel otherwise no fuel is going to light up. Such as the picture below where the number four is the place for solid engine ignition system

INSTALLATION FOR A HYBRID ENGINE 

For a hybrid engine, the fuel does not fires off once the resistance wire is heated as the oxidiser doesn't do the flow. Therefore, it is important to install the wire at the opposite side of the nozzle or the side that connected to the high-pressure oxygen pipe, so once the wire is lit up, the flow of high pressure oxygen will spread out the fire to the entire fuel grain as you might have seen below.

 

INSTALLATION FOR A LIQUID ENGINE 

For a liquid engine with non-hypergolic fuel, the heated resistance wire will fire off the engine once the fuel is already mixed. Therefore, it is important to ensure that the fuel is already mixed before make contact with the ignition system otherwise there will be no ignition. Like the hybrid engine, the igniter have to be at the opposite side of the nozzle where two components are well-mixed and ready for ignition.

Hybrids_big-tosvg.svg.png
1024px-Solid-Fuel_Rocket_Diagram.svg.png
 

________________

HYDRAULIC ROBOT ARM

8 June 2021 -- Jomkhwan Borrirak   2 min read

Robot arms have been utilised by plenty of industries nowadays as it increases the productivity of the industry. The mechanism is simply a three-to-eight parts that are connected via joint to support its freely movement. There are different type of robotic arm but the type with the lowest cost and the simplest build is hydraulic robot arm 

Anyhow, the using purpose is essential. For lifting a heavy object, a hydraulic arm is still a bad choice since it tremendously increase pressure to the pipe and things can go very wet in any moment. For my design, the purpose is only to ignite the rocket engine before I later switched to the new Engine Ignition System. Therefore, the work of it was only to connect the +- wire to continue the electrical loop.

MECHANISM

In order to control the hydraulic arm manually, you need a couple things; water syringes, a clear pipe, a body of the arm and screws. The amount of syringes is depending on how many joints you want the arm to have. For instance, my design need eight syringes 1.) 180 degrees turn 2.) main lift 3.) secondary lift 4.) grabbing. each mechanism required two syringes because you need to inject the pressure from the controller to the arm itself as you may see it from the picture below. For the body, I simply use cardboard due to its low weight and low cost. Low weight is important since it reduces the input-pressure that needed to lift things up. For the screw, you might have seen that I literally use the wooden stick since it does the same job as the metal screw, to hold the body together.

S__7643163.jpg
cardboardRobot_2.jpg

_________________

BALANCE AUTOMATION MATHEMATICS AND SOFTWARE FOR AERIAL OBJECT

6 October 2021 -- Jomkhwan Borrirak    15-20 min read

S__7725074.jpg
 

This applicable formula is among the most used formula on Earth for balancing any kind of entity. This formula is called 'PID Controller'. The P stands for Proportional, I for Integral and Derivative as a D. All of them are combining into one single formula in order to reorder the error. To give you an idea of the PID controller, imagine an airplane that turns on the autopilot. When the plane starts to make error to left or right, the error will be sent to the processor in order to reorder back to the initial point. Let's say the plane of yours is making a 10 degree error to the left, the flight computer will be calculated through the PID formula and give the specific degree to turn right back to the initial degree without any swing. This principle could not only apply to just an aircraft but also the rocket as well as you may see below. The principle is very similar to when you try to balance the long stick on your hand.

 

PROPORTIONAL GAIN

The formula can break down into three main parts as discussed above. Proportional control takes part as Kp by which multiply by the error. Let's say that error = 1 and

Kp = 10, so 1*10 = 10. The 10 has to be convert to -10 since it is the correction to the error. So, if we apply the Kp alone, the result of error correction would be 10 degree correction but that would create a tremendous overshoot.

__________________________

S__7725076.jpg

__________________________

 

DERIVATIVE GAIN

The Derivative or Kd comes to fix the overshoot problem. The Kd has to multiply by the Δerror / Δtime. This will allow the derivative to act like a break system and resist the overshoot. For example of a provided diagram, the rising derivative number cause a different reply to the error whereby more number would result in more break. The PD controller has been utilised by many industries such as the Cruise Control Technology in modern cars. However, the disadvantage about the PD controller is the fact that the correction would consume time or might even create a droop. Therefore, Integral would come in handy in order to readjust the order.

S__7725078.jpg
S__7725079.jpg
 

__________________________

INTEGRAL GAIN

The Intergral or Ki is the most difficult part of all. Its work is to eliminate the droop and accelerate the process but also giving risk to mess up everything since its job of accelerating comes by higher swing rate. However, if the Ki number fit well with the machine or processor, the Ki become very useful. Where the Kd allows the controller to look forward in time, the Ki gains allows the controller to look backwards in time. The integral is storing up the error that the controller sees over time. If the error fails to reach the initial point, the formula will increase in magnitude.

__________________________

__________________________

S__7725082.jpg
S__7725084.jpg

__________________________

 

APPLY THE MATHEMATICS TO SOFTWARE FOR ROCKET AND AIRCRAFTS

LINE 1-5 : Import Setup

LINE 7-20 : Initial Setup for Servos and MPU-6050 Gyro

S__7725087.jpg
S__7725088.jpg

LINE 22-49 : Converting Raw's Gyro number to readable number (in degree)

LINE 51-53 : Activate the MPU-6050 Gyro

LINE 55-63 : Initial Setup for PID

LINE 65-80 : Standby Mode. Detecting any movement. If break, next while comes

S__7725089.jpg

LINE 82-98 : Gain contant error information  from the MPU-6050 Gyro

LINE 99-106  : PID Calculation 

        Line 99-100 : Proportional 

            Line 101-102 : Integral

            Line 103-104 : Derivative

LINE 107-110  : Set up for next loop

LINE 112-121 : Limit Servo's turn

LINE 124-125 : Turn the Servo