A Guide to Designing Chassis - Part1

We all know, chassis designing is not a day job and is very crucial for performance, stability, durability and strength of the car. Chassis (for beginners) is the bare-bone of the car. The most basic and most crucial component to which all other components of the car, like suspension, body panels, engine, front and rear fender assembly and everything else is integrated, which makes it also a specification dependent design component, meaning, to design it, you must already have all the specification sheets and a basic chassis idea in your head. And, the best way to design a good chassis to fit your all components is to start with a cube of a definable length x width x height and roughly start adding components into it. Well, in this series of chassis design I'll start from the basic of it and will take you through types of chassis, types of loads on chassis, contributing factors to chassis design, chassis design, stress and torsion analysis methods and finally Computational FEM.

Image Courtesy: images.google.com

Well, for the starters, we always need to remember one thing during chassis design, the higher the ground clearance, the reduced will be the stability of the car; thus, the COG always need to be at low as possible. Now, there are many layouts of chassis designs which are:

1) Ladder: This chassis is the most basic chassis design with good stress load capability but lacks torsional bearing capacity completely. The design is very simple, it used a uni-planar parallel shafts joined with each other using cross-members just like in a ladder and hence the name. The parallel shafts and cross-members are responsible for all load bearing capacity and all intersection points are the high stress regions, one should not reduce the load bearing capacity at these regions by adding holes.

image courtesy: images.google.com

2) Backbone: In simple words, it is opposite of ladder design when it comes to functioning. The backbone design is targeted towards reducing high torsional profile where the front and rear axle are connected with each other using a single multi-sectional solid/hollow rod which removes the torsional forces off the vehicle.

image courtesy: images.google.com

3) Body-on-frame: It is the most appreciated chassis design after unibody chassis design, every car manufacturer has used this design in every vehicle at one point or another. The body on frame design is very similar to ladder design but it takes into account components like center of gravity and torsional force very seriously. The design includes elongated parallel shafts for more reduced stress profiles and added reinforcements on intersections to reduce the torsional force profile. The benefit of the design is that body is mounted on the frame which reduces sprung mass and also reduces COG.

image courtesy: chevyhighperformance.com

4) X-Frame: A perfect fusion of ladder and backbone chassis design. The system looks into both stress and torsional profiles on the design. The design includes 2 parallel rods connected diagonally with X structure starting from front axle to rear axle. The design increases the surface area as to reduce stress profile and because of X intersextion, the torsional capability is increased.

image courtesy: images.google.com

5) Unibody: It is the most popular and advanced design which is specially designed for mass production and the whole process is carried out on a single piece of material from which material is then reduced to get the required shape. The designs are designed in softwares like CATIA V5 and they are of industry standards, because of mass production, CNC machines are used for the process. The design is carefully designed with regular updates with analysis using Computational FEM softwares like Ansys, Hypermesh etc.

image courtesy: images.google.com

6) Monocoque: The easiest way to understand monocoque design is to think yourself as you don't have bones and you are living because of strength of your nerves. The monocoque design doesn't have a designed structure but the body panels serve as the load bearing components. The design was high unappreciated due to obvious reasons and presented very poor results against stress and torsional analysis. One might easily confuse monocoque with Unibody, the difference is that, the Unibody design incorporate structural components that works as frame.

image courtesy: images.google.com

7) Spaceframe: Spaceframe chassis design is considered as the best design for prototyping and is highly popular in motorsports because of two reasons, first: the design is made of hollow narrow pipes of small lengths; second, it corresponds to pyramidal shape which is considered as strongest in dissipating force over the entire structure. The array of such shapes completely disintegrate torsional and lateral forces from the structure and the design shows best restrain towards car crash test.

image courtesy: images.google.com

8) Stressed member engine: One can also say it as minimal chassis design or frameless chassis design. The system is most popular for bikes and engine plays the major role in deciding the stress and torsional profile of the design. The design mounts the engine and make it the force bearing component. Also, it is made sure that COG of the vehicle is as close to engine as possible for best stability and control over the vehicle.

image courtesy: images.google.com

9) Subframe: The subframe chassis design is best for innovation in the field of chassis design, the chassis is  essentially divided into more than 1 component and each component may/may not be independent of each other. Subframe designs are most popular for kit cars and Do It Yourself Cars. Also, since each component is independent, one can easily do changes in the chassis to reduce stress and torsional forces as per the requirement.

image courtesy: images.google.com

10) Superleggera: Ring the bells? Superleggera or in Italian, "light weight" is a special division of chassis design which incorporates materials like carbon fiber rods, titanium pipes and other innovative components to increase strength of the design while reducing the weight of the car. Many high end vehicles like Lamborghini Murcielago/Aventador, Aston Martin Vanquish and many more have special superleggera editions.

image courtesy: images.google.com

Thus, in this article we discussed about various chassis design and their characteristics from which one can opt for making his/her own design, in upcoming articles we will start explaining different types of loads that are found in vehicle and then stress analysis methods.

Brakes: Design your own Disk Brakes - Part7

We all know drum brakes are an important part of life and learning to design them is extremely important but with the time of upgrading brakes into disc brakes, it is even more important that one must know the design aspects of disk brakes. In this article we will show how you can design your own disk brake and all the calculations and equations involved.

The above image represents a simple disc brakes and to understand the equations, one must understand the image above and now key to defining elements:

F = Force applied by the slave cylinder on the brake shoe

r = radius from center of disk to center of the brake pad

r_o = radius from center to outer surface of the brake pad

r_i = radius from center to inner radius of the brake pad

θ₁ = angle from horizontal to heel of brake pad

θ₂ = angle from horizontal to toe of brake pad
P_max = maximum applied pressure (depends on frictional material)
P = Uniformly distributed pressure along brake pad
Now, one more things to take into account is, in disc brakes there are 2 conditions that persists! 1) Uniform Pressure: which is applicable for new brakes & 2) Uniform Wear: which comes after a certain amount of use. Now, Work done is directly proportional to P_max X r_i therefore, W = k.P_max.r_i and since W & k are constants, let, W/k = K = P_max.r_i, Also, K = P.r, therefore,
P = P_max.r_i/r
Now, the force applied on the brake pads (F) is equal to

F = 

Replacing P with equation above and doing integration for θ, we get;

F = 

Again, doing integration for radius r, we get;

F = 

The equation above gives the force, now for torque;

τ = 

Replacing P with Pmax equation and integrating for θ, we get;

τ = 

Again, integrating for radius r, we get;

τ = 

Thus, the above equation gives torque for the disc brakes for uniform wear system!

Now to get equivalent radius (r_e) = τ/µF 

All the above equations hold good for Uniform wear system when work done is dependent on radius but when the brakes are new, then P = P_max because of which the new equations becomes;

F = 

Integrating for θ and solving for P, we get;

F = 

Thus, the final equations comes out to be;

F = 

Also for Torque (τ), the equations changes as;

τ = 

Integrating for θ and solving for P, we get;

τ = 

Thus, the final equation on integration of r comes out to be;

τ = 

With, this all the design equations have been discussed for the disc brakes, again, we know Torque = Force X Perpendicular length

Therefore, The Force applied by the force to stop the car will be F_brake = τ / r_e

Using this, we can solve any linear motion problem and calculate stopping distance and find time to decelerate the vehicle from velocity v to 0 using equations of motion.

Brakes: Design your own Drum Brakes - Part6

Well, we are nearly at the end of series with few more articles to go! Till date, we have already discussed nearly everything about construction, advantages, disadvantages and uses of each braking system but we, The Unicorn, understands that just understanding is not enough for anyone that is why we also make you understand how you can design the system yourself! As our motto says, Educate, Excel and then Innovate! To innovate you need to learn everything including how to design the system and the equations involved. In this article we will discuss the design aspects and equations involved in designing drum brakes.

To understand the design aspects of drum brakes, we have to understand the image above! First of all, as assumed we will say that direction of rotation of wheel is clockwise. Now the key to defining elements:

F = Force applied by the actuating device on each of the brake shoes.

P_max = Maximum Pressure applied

c = total displacement of heel and toe of the brake shoe

a = displacement from center of drum to the center axis of the brake shoe

r = radius of the drum from center of drum

b = displacement from center axis to the pivot point

Θ₁ = angle from center of pivot point to heel of shoe lining

Θ₂ = angle from center of pivot point to toe of shoe lining
Θ = average angle to distribute forces along the whole length of the shoe
and let µ = frictional coefficient of the shoe lining material

Since, the rotation is clockwise, the right shoe lining will attack first and its effect will be more than the trailing left shoe! and to calculate the force applied, we need to calculate the moment of inertia applied due to frictional force and also due to normal force acting on the shoe lining.
let's take k = P_max/SinΘ₂ therefore, k = P/sinΘ
equating both, we get; P = P_maxsinΘ/sinΘ₂ (where P is Uniformly distributed Pressure)
Now, Let M_f be the Moment of Inertia due to Frictional Force then,

M_f = 

Replacing P, we get:

M_f = 

Therefore, final formula after integration comes out to be:

M_f = 

Now, for calculating Moment of Inertia for Normal Force,

M_n = 

Replacing P in above equation,

M_n = 

After integration, final formula comes out to be:

M_n = 

Therefore, F = (M_f - M_n)/c

Also, Torque applied by the right shoe will be equal to

τr = 

replacing P, we get:

τr = 

The final equation becomes:

τr = 

Also, we need to add the force due to Left Shoe also called the trailing shoe;

For trailing shoe P'max = FcPmax/(Mf + Mn)

The torque applied by the left shoe will be:

τl = 

replacing P', the above equation becomes:

τl = 

The final equation becomes:

τl = 

The total Torque τ = τr + τl

Also, we know Torque = Force X Perpendicular length

Therefore, The Force applied by the force to stop the car will be F_brake = τ / Radius of Drum

Using this, we can solve any linear motion problem and calculate stopping distance and find time to decelerate the vehicle from velocity v to 0 using equations of motion.

Brakes: The Drag Brakes - Part5

Drag brakes as the name suggest are completely different braking system, both in characteristics and functioning! As the name suggests, it produces a force which opposes the motion of the vehicle. Drag in normal terms can be described as the force which is applied on a component of vehicle which does not fall in its aerodynamic foil. The ambient air at high speeds, due to relative motion of the vehicle against air, produces a massive amount of air channel in front of vehicle through which the vehicle has to go through else it'll hinder the top speed capacity of the vehicle. After a lot of research in the field of aerodynamics, the researchers mentioned that the shape of the "falling water drop" is the most aerodynamic shape and if somebody might have noticed, the shape of Airfoil is also shape of drop only.
The most common application of drag brakes is aircraft, the common name of drag surface is spoiler in aircraft which is present above the flap and even flap functions somewhat as the drag brake. These are together called as control surfaces and they include: flaps, rudder, aileron, slats, spoilers and elevators which control the 6 degrees of freedom of the aircraft!

Courtesy to NASA

The basic concept of functioning is very simple, when flaps and spoilers are deployed, they work as resistance to the air flowing through the flat surface thus making air as the working medium to stop the vehicle.

The same concept has been used in cars for a very long time, the spoilers in cars does the same thing. There are two types of spoilers, 1) Fixed geometry: which is usually used to create downforce 2) Variable Geometry: also called as Retractable spoilers, they serve as both drag brake system as well as downforce producing system.

Both above images show different types of spoilers.

The above image shows a very conventional drag method to stop high speeding cars like the high tuned drag racing cars! In them, the designers and enthusiasts used to install the parachute behind the car with a deployment circuit through which the driver can deploy it whenever he wants to stop the car. Drag brakes in automotives have been very useful especially in the stopping distance timings of super cars like Bugatti Veyron. They make sure that the Peak force of the friction brakes are always under control!

So, with this we end with the types of braking system and their functioning, in next series we will start with the calculations involved in designing if each of the braking system and we will start from drum brakes.

Brakes: Electromagnetic Brakes - Part4

Dear readers, I am sorry for the delay in 4th part of the brake series. Today we are going to talk about EM Brakes or Electromagnetic Brakes. We have already covered the basics, about disk brakes and about drum brakes in previous articles and they can be found in http://themechunicorn.blogspot.in/. So, let's come to the topic of EM Brakes, EM Brakes are usually seen in heavy vehicles like trams, trains etc. They serve as an alternative to friction brakes. The various advantages of EM brakes include high CPD (Continuous Power Dissipation) i.e. it's ability to remove excess heat energy very quickly thus increasing life span of system and reducing maintenance costs. In recent years, with development of hybrid and electric cars, the EM brakes have been used in  them also, and their functioning and construction is very different from conventional disk or drum friction brakes.

As can be seen from the image above, the EM brakes have a electric coil which produces controlled magnetic pole and energizes the Armature to have an opposite pole and with continuous change in strength, the magnetic forces push the armature towards the friction disk which produces the required braking action.

Now we will explain each component and their role in functioning of the EM brakes.

Lead Wire: It is the electrical wire that brings 24V or 12V DC from battery/alternator to the EM brakes coils.

EM Coil: On application of DC, the coil produces a magnetic force and pole on the concepts of Faraday's law of Electromagnetic Induction and Faraday-Maxwell Equation and also on Fleming's Right-Hand thumb rule.

Braking Spring: It is the return spring, after application of brakes and de-energizing of coils, the return brake springs detaches the armature from friction disks.

Friction disks: They are circular disks with friction material linings on outer surface, they are usually made of aluminium and are hollowed inside for maximum ambient air displacement and increased cooling effect on friction disk.

Hub: The component which attaches to the output shaft and finally with wheels.

The whole EM brake assembly is mounted on anti-vibration mountings in chassis and is fixed together with 3 fixed bolts. The EM brakes have a lot of advantages over conventional friction brakes and can be easily equipped with many other technologies like KERS (Kinetic Energy Regeneration System) to increase the efficiency and overall power of the whole vehicle.

Brakes: Disk Brakes - Part3

In last 2 articles we covered the basic terminology and basic knowledge of brakes and in second the concepts of working principle behind the drum brakes. Our previous articles can be found on http://themechunicorn.blogspot.in/. In this article we will continue our trend with working principle of disk brakes for automobiles in bikes. Well, the disk brakes have quickly become a spotlight feature in nearly all cars and motorbikes. The reason is simple, more power, more peak force capability and surely reduced weight! Disk brakes are usually found and known as hydraulic disk brakes, while mechanical disk brakes are also present, but hydraulic disk brakes are more powerful, durable and requires very less maintenance. Also, unlike drum brakes, the disk brakes have less reciprocating/moving components and due to use of hydraulic fluid as the working medium, the disk brakes are more responsive in nature.
In construction:

The above image shows a typical single hydraulic cylinder hydraulic disk brake. In the simplest of words, the caliper holds 2 brake pads which are of frictional material and when the pressure is applied by the piston, the brake pad rubs against the disk and because of this frictional combination, the braking action is achieved. Well, there are actually 3 types of hydraulic disk brakes, single cylinder configuration, dual cylinder configuration and full disk configuration. While, the first 2 configurations are differentiated by the no. of cylinders disk caliper will be housing, the full disk configuration is rather based on surface area the brake pad will be covering! In cases of single and dual cylinder disk brakes, the brake shoe is covering a particular angled surface area of the disk, while in case of full disk configuration, a full 360^o brake pad is used.

The first image shows the full disk configuration, while the second image is the common single cylinder hydraulic disk brake. The only reason, the full disk configuration aren't popular is because of the low durability due to high surface area contact and unbalanced forces acting on the actuation rod.

Now, we will explain each component of the single cylinder disk brake.

1) Hub: Like the brake drum in drum brakes, the hub is the component of disk brakes that is connected with the wheel of the vehicle.

2) Rotor/Disk: It is the metallic disk that's been abraded to produce a frictional surface over it. The disk has to be designed in such a way that it can withstand all the frictional heat and should implement best methods of aerial cooling or ambient cooling.

3) Brake Pads: The brake pads are made of frictional material like graphite or carbon composites. the brake pads serve the same feature as served by brake shoes in the drum brakes, but are more durable in construction and usage.

4) Hydraulic Slave Cylinder: Just like the drum brakes, Slave Hydraulic Cylinder also works as an actuator in disk brakes. The pressure created inside the cylinder serves as the way to move the brake pads towards the disk.

5) Caliper Return Springs: They are mediocre to high tension springs that helps in bringing back the brake pads to their original position when the pressure from the main and slave cylinder is removed.

6) Caliper: It is the main housing in which the brake pads, hydraulic slave cylinders and caliper return springs rests and helps the whole braking system to stay rigid and in required position.

While designing a hydraulic disk brake, a lot of things need to be taken care of and every design has its own specifications, the angle covered by the brake pads, the radius of brake pads, position of them from top, frictional coefficient of the disk caliper, and many more considerations need to be taken care of while designing the braking system. In the coming series of continuing articles, we will also discuss all the equations required to design hydraulic disk brakes and their derivations, so stay tuned. Remember, educate, then excel and then only innovate.

Brakes: Drum Brakes - Part2

In the previous article, we talked about the basic concepts that are related with brakes and terminology that is defined to understand brakes and its features. The previous blog can be found at: http://themechunicorn.blogspot.in/2014/04/brakes-general-part1.html
Now, in this part, we will start discussing about the components and construction of different braking systems, we will start with the simplest friction based drum brakes for vehicle and will continue towards disk brakes, aircraft drag brakes, jake brakes and will end towards electromagnetic brakes. This differentiation will be based on categories depending upon the vehicle i.e. we will first take brake systems used in cars, then aircrafts and then other vehicles.

The two images above show a basic drum-brake assembly for cars and motorcycle. These are the most common braking system till now for vehicles but are now being replaced by disc brakes at a very fast rate, the reason for this migration is quite simple, high brake fade, low peak force, less brake power when compared to disc brakes and less durability. The drum brakes work on a very simple principle of friction. The drum-brake assembly include the following:

1) Brake Drum - It is the brake cover that gets attached to the wheel while also serving as the friction surface for the brake system, the inner side of the brake drum is lined with frictional surface having a friction coefficient (µ) of anything between 0.4 to .45 while depending upon application, the µ might gets increases as high as 0.66. Brake drum also connects with the tire and is subjected to high torque when braking action is required.

2) Brake Shoe - It is the component that is attached with the brake lining material of the inner assembly and the actuation occurs here itself, the hydraulic slave cylinder is connected to both the brake shoes and when brakes are actuated, the slave cylinder pushes the brake shoe towards the brake drum and the shoe returning springs bring it back after actuation is completed.

3) Shoe Adjustment: It is the component through which you can set the initial position of the brake shoe! It is used to control the pedal play as well as to control the peak force, but increasing the initial value of shoe might result in reduced durability due to increased drag and more brake power.

4) Hydraulic Slave Cylinder: It is the actuator unit of the drum brakes, apart from hydraulic actuators like hydraulic cylinders, various drum brake designs also use mechanical actuation which is still commonly seen in motorcycles. Through a hydraulic pipe it is directly connected with the master hydraulic cylinder which in turn is connected with the brake pedal! As hydraulic systems are based on Pascal's law, the rest of the actuation method is nothing but a series of clever engineering architecture.

The brake power is directly related to the surface area of the brake pads or brake lining material in contact with the inner brake lining of the brake drum. Now, a days the application of drum brakes have been reduced considerably and are usually used as secondary braking system like the parking brakes while newer disk brakes have taken the place as primary braking system in the cars.

Thus, with this we conclude the information related to drum brakes, in next series of article, we will talk about other types of brakes and their constructions. Also, we will also bring in all the equations related to drum brakes and their designs in upcoming articles so that entrepreneuring designers can use the resources for designing their own drum brake systems and innovate!