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1.0 THE USAGE OF MOTORCYCLE SIMULATORS

Motorcycle simulators have been used for many purposes such as:

a. Entertainment : used as a racing game that reproduces the experience of driving a racing motorcycle in an existing racing class

b. Training and improve road safety: used for training drivers all over the world. It consists of motorcycle standing on a moving platform that is linked to driving software. It can generate different weather conditions, traffic volumes and hazards. This could lead to safer driving on the roads, reducing the likelihood of collisions and possibly leading to lower bike insurance premiums for some drivers.

c. Research: used for research purposes in the area of human factors and medical research, to monitor driver behavior, performance, and attention and in the car industry to design and evaluate new vehicles or new advanced driver assistance systems (ADAS).

Mostly they are used in educational institutions and private businesses.

Click here to read about the differences between these 3 types of simulator in pdf.

2.0 MOTORCYCLE DYNAMICS

There are some motorcycle’s dynamics that we need to consider on a motorcycle simulator to allow the rider experience riding.

- Balance and Instability

- Turning

- Braking

- Vibration

Balance and Instability

A bike remains upright when it is steered so that the ground reaction forces exactly balance all the other forces it experiences, such as gravitational, inertial or centrifugal if in a turn, and aerodynamic if in a crosswind.

This self-stability is generated by a combination of several effects that depend on the geometry, mass distribution, forward speed, Gyroscopic effects of the bike.

There are three main unstable modes that a bike can experience: capsize, weave, and wobble.

Turning

In order to turn, bikes must lean to balance the relevant forces: gravitational, inertial, frictional, and ground support. The angle of lean, θ, can easily be calculated using the laws of circular motion:

N is the normal force, F_f is friction, m is mass, r is turn radius, v is forward speed, and g is the acceleration of gravity.

There are a lot of ways to turn, example like counter steering, steady-state turning, no hands.

Braking

Front wheel braking-

Allowing a maximum deceleration of 0.5g, but there is limiting factors:

* the maximum, limiting value of static friction between the tire and the ground,

* the kinetic friction between the brake pads and the rim or disk,

* pitching (of bike and rider) over the front wheel.

Rear wheel braking-

The rear brake of a upright bicycle can only produce about 0.1 g deceleration at best therefore more stable than front wheel braking.

Vibration

An important factor in any vibration analysis is a comparison of the natural frequencies of the system with the possible driving frequencies of the vibration sources. A close match means mechanical resonance that can result in large amplitudes.

In addition to the road surface, vibrations in a motorcycle can be caused by the engine and wheels, if unbalanced. At high speeds, motorcycles and their riders may also experience aerodynamic flutter or buffeting.

For more information, click here to download the pdf.

3.0 Degree of Freedom

Degrees of freedom are very important to develop the actuator system to make the simulation like the real situation. The number of degrees of freedom of a bike depends on the particular model being used.

The multi-body model of motorcycle consists in a system of six rigid bodies. They are: the rear wheel, the rear frame (including engine, tank and driver), the front frame (handle bars and sprung fork components), the front wheel, the swinging arm, the unsprung fork components (including brake system).

Actual cases of motorcycle have 11 degree of freedom, as showed below:

In order to make a simulation more realistic, the presence of all degree of freedom is ideal. But there are some degrees of freedom that are important and some are not to produce a simulator. The most vital degrees of freedom that we will consider are vertical lateral and longitudinal displacement, roll, pitch, and yaw angles, and steer.

To download the DOF pdf, click here.

4.0 MATHEMATICAL CALCULATION

STEERING CONTROL OF TWO-WHEELED AND TILTING VEHICLES

When a motorcycle executing a steady coordinated turn, it tilts to an angle such that the vector combination of the acceleration of gravity and the centrifugal acceleration lies along a symmetry axis of the vehicle.

Development of the Mathematical Model

FIGURE 4.1

Fig 4.1 shows a number of the dimensions and variables associated with the mathematical model of a tilting vehicle. For a single vehicle, the sketch in Fig 4.1 is to be imagined as existing in the ground plane.

For a multiwheeled vehicle, the two wheels represent equivalent single wheels for the front and rear axles much as was done for the “bicycle” model for automobiles. The “ground” plane would then pass through the roll center of the suspension. The dimensions a and b relate to the distances from the projection of the center of mass to the front and rear axles in the ground plane. The velocity component U and V describe the velocity of the center of mass projection on the ground plane. (Because of the time-varying tilt angle, the center of mass has other velocity components beside these components of the projection in the ground plane.)

The coordinates x and y locate the ground plane projection of the center of mass in inertial space, and the angle Φ, which may be large, represents the orientation of the vehicle with respect to the y-axis. Slip angles are negligible as long as the tires do not skid. Forward velocity U is assumed constant and with all those assumptions, motion in the ground plane is determined purely kinematically. Using the small angle assumption,

......................................(4.1)

Simple geometric considerations result an expression for the turn radius.

........................................(4.2)

Eq. (4.2) is a generalization of the steer angle relationships encountered previously in the “bicycle” model of an automobile.

The yaw rate r is given by the expression

.....................(4.3)

The lateral velocity in the ground plane is found again purely kinematically by considering the lateral velocities at the front and the rear.

................................(4.4)

Finally the “slip angle” for the center of mass projection in the ground plane, b, is

..............(4.5)

To track the location of the center of mass projection in the ground plane during computer simulation, for example, the following equations can be used:

.........(4.6)

With the assumption of zero slip angles for the front and rear wheels, the motion in the ground plane is completely determined by the time histories of the front and rear steer angles.

For More Calculation, click here to download the pdf.

5.0 BODY POSITIONING

Riding a motorcycle is not easy as driving a car. Our body positioning is very important to control and stabilize our bike especially during taking the corner. Figure below shows the body position to lean during taking the bend.

Motorcycle rider taking the lap

Besides body movement, controlling the steering is also important to prevent instability during taking the corner. Figures below show some skills of controlling the steering and throttle.

Steering in the opposite direction is required at corner entry and when changing directions in S-curves

In mid-corner at a stable lean angle the bike will steer itself by castor effect

Counter steering is required again at corner exit to reduce lean angle

Counter steering is required to increase or decrease lean angle in every curve

5.1 FALL ANALYSIS

This simulation planned to cover the safety aspect. Hence, some fall analysis had to take into account. Figure below shows a model of a rider consists in a total of 13 main and 25 contacts, connected together by means of 22 kinematic joints.

Stand alone model of a rider

Assembled model with black indicating contact elements

Front Low Side Fall

For more information on Rear Low Side Fall and High Side Fall, click here to download the pdf.

6.0 Material Selection

Before deciding which material is most suitable for any particular component, we clearly need to know something about material properties. The main properties of concern to us are:
• Stiffness
• Strength
• Density
• Ductility
• Fatigue resistance
• Available joining methods
• Cost of material
• Cost of machining and working
Typical properties of some common materials

Click on the Table to enlarge it.
Note: The above properties are a rough guide only

6.1 Raw Materials

The primary raw materials used in the manufacture of the body of motorcycle are metal, plastic and rubber. Sometimes, metal is being ousted in order to save weight but in this case thermoplastic mouldings are commonly used, some of which have greater flexibility. A disadvantage, however, is their tendency to look tatty in time as a result of scratching and other surface blemishes. The motorcycle frame is composed almost completely of metal, as are the wheels.
The frame may be overlaid with plastic. Steel is the most common material. There are several reasons for its choice. There are:
• Raw material cost is relatively low
• Ability to be formed into tubes of all shapes and sizes, its great strength, the ease with which it can be bent and welded
• Well developed manipulating and joining techniques are available
• Young’s Modulus is high, so the required stiffness can be obtained with small tube sizes.
Steel is used for fabricating both round and squared tubes, since, if they are properly designed, it makes round ones easier to bend and squared ones easier to prepare for mating and subsequent welding. These constructions may be characterized by a high moment of inertia as well.

For more information on Material Selection, click here to download the pdf.

7.0 ACTUATORS

There are many types of actuators used for the motorcycle simulators to produce the movement requires. The common actuators used are as below:

• Hydraulic: Hydraulic actuator is a mechanical actuator that is used to give a linear force through a linear stroke. Hydraulic actuators or hydraulic cylinders typically involve a hollow cylinder having a piston inserted in it. The two sides of the piston are alternately pressurized/de-pressurized to achieve controlled precise linear displacement of the piston and in turn the entity connected to the piston.

• Pneumatic: A pneumatic actuator converts energy (in the form of compressed air, typically) into motion. The motion can be rotary or linear, depending on the type of actuator. A Pneumatic actuator mainly consists of a piston, a cylinder, and valves or ports.

• Electrical: Electric motors driving screw-jacks can be “beefed-up” to produce a large thrust but they cannot be designed to have also the extreme sensitivity and fast response which is vital to the simulation illusion.

• Mechanical: Mechanical actuators typically convert rotary motion of a control knob or handle into linear displacement via screws and/or gears to which the knob or handle is attached. For accurate and repeatable positioning, index marks may be used on control knobs. Some actuators even include an encoder and digital position readout.

• Electromagnetic (PEMRAMTM): Electromagnetic actuator is a combination of the properties of a DC motor with those of a pneumatic ram. The mathematics proven a wide range of ram thrusts from off-the-shelf magnets and these fall into exactly the right ranges that is needed for simulator motion bases.

For more information on Actuators, click here to download the pdf.

8.0 CONCLUSION

After we have done our research on motorcycle simulator, we found out the differences between three type of simulator which are, training , gaming and research purposes. We understand more and we now know what we need to focus on, which is, the research simulator purpose.

There are many things to be considered and one of them is dynamic factor. Dynamic factors influence the directions and movements of a motorcycle such as balance, turning, braking and vibration of the motorcycle too has an impact on the dynamic analysis. We understood the functionality of degree of freedom(DOF) in motorcycle and we found out 7 of the most vital DOF for a simulator.

The mathematical calculation that we found is more on steering which helps us understand and calculate the limit of movements when turning or banking. The fall analysis, which comes under body motion, assist us in designing the simulator.

However, we obtained little information regarding the materials required to estimate the cost of designing a motorcycle simulator. But we did found more on types of actuators. This alone aids us as an extra information for our future design.