1.0 Introduction
The first spring-powered car was designed by Leonardo Da Vinci in 1478 with the name of self-
propelled car. The car was spring driven that had to be wound up before it would move.
Although a full scale production model was made, the machine has not yet been tested due to its
powerful mechanism that might run into something and damage everything (Galluzzi, 2004).
However, this brilliant invention failed to work properly when constructed in a full scale sized
vehicle over the last century. Today, inventors and engineers are pulling together in making this
theoretical concept a miracle. Over the past century, various kind of springs are used and been
modified to match the concept of Leonardo’s inspiration so that it won’t fail. Somehow, the
closest we get for this idea is the manufacturing of millions of toy cars. The cars are rather
skeptical, but the infamous version known worldwide is the pullback car. It still uses the concept
of spring but the type of spring used is a flat spiral spring attached to a gearing mechanism.
This report will discuss the design of a spring-powered car powered by a mousetrap from all
aspects from its design approach, the testing and its mechanism. Mousetrap cars are known in
physics, sciences and engineering classes to help building problem-solving skills, spatial
awareness and team building experiences. It is a way to help creating a desired and fulfill
inventors that can learn to budget time and practice cooperative behavior. The general style for a
mousetrap car varies depending on the shape and size of a spring, whether it is build for a
distance or speed and also depending on the accessories that can be added. A number of
commercial vendors offer plans, kits and complete cars for sale (Kelvin, 2007).
1.1 Theoretical Background
A mousetrap is powered by a helical torsion spring that obeys an angular form of
Hooke’s Law. When a mousetrap is assembled, the spring is initially twisted beyond its
equilibrium position so that it applies significant torque to the axle when the trap is
closed. The string is attached to the mousetrap’s hammer and wrap around the axle thus
creating enough torsion to rotate the axle and the wheels when released.
2
, The calculation of energy stored in the spring denotes as U in correlation to a torsion is
defined in the following formula:
U = ½ kθ2
The k is a constant with units of Newton-meters / radian, variously named as spring
constant or torsion elastic modulus. The U is in joules where θ is the angle of twist from
equilibrium position in radians.
The torque exerted by the spring is calculated using the following angular Hooke’s Law
formula:
τ = - kθ
where τ is the torque with units of Newton-meters.
To added extra distance, the design is attached with friction motor, a simple mechanism
to propel toy cars. The motor consists of a large flywheel which is connected to the drive
wheels via a low gear ratio, so that the flywheel revolves faster. The flywheel stores
kinetic energy of initial acceleration and propels the toy after it is released.
A gear train can be analyzed using the principle of virtual work1 to show its torque ratio.
The input torque, τA applied to the input gear and the output torque, τB on the output gear
are related by the ratio:
R = τB / τB
The R is the gear ratio of the gear train.
1
Virtual work is the total work done by applied forces and inertial forces of a mechanical system as it moves
through a set of virtual displacements.
3
, 2.0 Design of Spring-Powered Car
The spring-powered car is designed to meet specifications of a long travelling distance with the
usage of an only power source, a mousetrap. This particular section discusses every vital aspects
of a design approach for this mousetrap spring-powered car.
2.1 Design Considerations
The concept of spring-powered car can be implemented at a variety of scales and in a
variety of contexts, from school projects to new development setting. The scale and
concept of any mechanical project depends on several factors including materials quality,
spring power, intended application and regulations. The design process must be flexible
and rigorous enough to address these factors. There are few considerations that have to be
taken before designing this mousetrap car. The idea is to design an optimum distance
travelling car tested in the testing track with suitable parameters.
Design Codes And Standards
The spring-powered mousetrap car design must follow the criteria, codes and standards
set by Board of Engineers Malaysia (BEM) in order to avoid any further or future
complications. As stated in Engineering Programme Accreditation Manual, 2012 by
BEM, Section 4.0 (iii), under Design/Development of Solutions, “Design solutions for
complex engineering problems and design systems, components or processes that meet
specified needs with appropriate consideration for public health and safety, cultural,
societal and environmental considerations”. (See Appendix B)
In terms of safety, when dealing with a mousetrap, some precautions needed to be
addressed. The sharp edges of the trap are taped to avoid any injuries during installment
and tested. The hammer is also handled with extra care and locked when setting up so
that it will not snap unwillingly causing unwanted incident.
4
The first spring-powered car was designed by Leonardo Da Vinci in 1478 with the name of self-
propelled car. The car was spring driven that had to be wound up before it would move.
Although a full scale production model was made, the machine has not yet been tested due to its
powerful mechanism that might run into something and damage everything (Galluzzi, 2004).
However, this brilliant invention failed to work properly when constructed in a full scale sized
vehicle over the last century. Today, inventors and engineers are pulling together in making this
theoretical concept a miracle. Over the past century, various kind of springs are used and been
modified to match the concept of Leonardo’s inspiration so that it won’t fail. Somehow, the
closest we get for this idea is the manufacturing of millions of toy cars. The cars are rather
skeptical, but the infamous version known worldwide is the pullback car. It still uses the concept
of spring but the type of spring used is a flat spiral spring attached to a gearing mechanism.
This report will discuss the design of a spring-powered car powered by a mousetrap from all
aspects from its design approach, the testing and its mechanism. Mousetrap cars are known in
physics, sciences and engineering classes to help building problem-solving skills, spatial
awareness and team building experiences. It is a way to help creating a desired and fulfill
inventors that can learn to budget time and practice cooperative behavior. The general style for a
mousetrap car varies depending on the shape and size of a spring, whether it is build for a
distance or speed and also depending on the accessories that can be added. A number of
commercial vendors offer plans, kits and complete cars for sale (Kelvin, 2007).
1.1 Theoretical Background
A mousetrap is powered by a helical torsion spring that obeys an angular form of
Hooke’s Law. When a mousetrap is assembled, the spring is initially twisted beyond its
equilibrium position so that it applies significant torque to the axle when the trap is
closed. The string is attached to the mousetrap’s hammer and wrap around the axle thus
creating enough torsion to rotate the axle and the wheels when released.
2
, The calculation of energy stored in the spring denotes as U in correlation to a torsion is
defined in the following formula:
U = ½ kθ2
The k is a constant with units of Newton-meters / radian, variously named as spring
constant or torsion elastic modulus. The U is in joules where θ is the angle of twist from
equilibrium position in radians.
The torque exerted by the spring is calculated using the following angular Hooke’s Law
formula:
τ = - kθ
where τ is the torque with units of Newton-meters.
To added extra distance, the design is attached with friction motor, a simple mechanism
to propel toy cars. The motor consists of a large flywheel which is connected to the drive
wheels via a low gear ratio, so that the flywheel revolves faster. The flywheel stores
kinetic energy of initial acceleration and propels the toy after it is released.
A gear train can be analyzed using the principle of virtual work1 to show its torque ratio.
The input torque, τA applied to the input gear and the output torque, τB on the output gear
are related by the ratio:
R = τB / τB
The R is the gear ratio of the gear train.
1
Virtual work is the total work done by applied forces and inertial forces of a mechanical system as it moves
through a set of virtual displacements.
3
, 2.0 Design of Spring-Powered Car
The spring-powered car is designed to meet specifications of a long travelling distance with the
usage of an only power source, a mousetrap. This particular section discusses every vital aspects
of a design approach for this mousetrap spring-powered car.
2.1 Design Considerations
The concept of spring-powered car can be implemented at a variety of scales and in a
variety of contexts, from school projects to new development setting. The scale and
concept of any mechanical project depends on several factors including materials quality,
spring power, intended application and regulations. The design process must be flexible
and rigorous enough to address these factors. There are few considerations that have to be
taken before designing this mousetrap car. The idea is to design an optimum distance
travelling car tested in the testing track with suitable parameters.
Design Codes And Standards
The spring-powered mousetrap car design must follow the criteria, codes and standards
set by Board of Engineers Malaysia (BEM) in order to avoid any further or future
complications. As stated in Engineering Programme Accreditation Manual, 2012 by
BEM, Section 4.0 (iii), under Design/Development of Solutions, “Design solutions for
complex engineering problems and design systems, components or processes that meet
specified needs with appropriate consideration for public health and safety, cultural,
societal and environmental considerations”. (See Appendix B)
In terms of safety, when dealing with a mousetrap, some precautions needed to be
addressed. The sharp edges of the trap are taped to avoid any injuries during installment
and tested. The hammer is also handled with extra care and locked when setting up so
that it will not snap unwillingly causing unwanted incident.
4
