Group 23: Gate 3

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Contents

Project Management: Coordination Review

As the project progresses, it is necessary to continually step back and assess how the team management plan under implementation is functioning. It is important to identify any factors in the team and work dynamic that are causing issues, and address them with a new corrective plan.

Cause for Corrective Action

At this point in our project, our group is working together very well. We continue to try to assign well defined expectations for each group member. So far each member has been completing all tasks assigned to them in a timely manner. If anyone has trouble with any of their assigned tasks, the group works together at our meetings and collaborates to solve the issue.

During our last management review, we changed how the group collaborates about meeting times. We have continued to use the plan used in the previous management review, we meet once during the week and then on Sunday afternoons in the Ellicott Complex. We have continued with this plan because all of our members have many commitments outside this class and testing for other classes continues to increase as we reach the end of the semester. Since all members face these problems, we try to work around members study schedules and be understanding of their commitments. The communications liaison or project managers are still responsible to text group members to plan out meeting times.

The one major change that we have made to our group dynamic since the last management review is that we decided to assign check stops for members of what work they should have completed prior to our meetings. Previously, each member had an assigned task, but we would usually work on them together at our group meetings. To become more time efficient, we have decided that certain tasks must be completed before the meetings, so at the meetings, we can review each other’s work and correct any problems. This also shortens the group meetings, and allows members to work on tasks when it fits into their schedule. The decision to assign check stops was decided by a unanimous group vote and was brought up to try to cut down the length of group meetings.

Product Archaeology: Product Evaluation

With the product now disassembled, the team can more thoroughly evaluate the product and its various components and subsystems. During the dissection process, greater knowledge of how the various parts of the product are interconnected was gained, and thus the assessment of the Barbie Power Wheels Dune Buggy can more properly be carried out.

Component Summary

The following figure displays the various components that make up the Barbie Dune Buggy Power Wheel. The figure lists the parts and their respective functions, materials, manufacturing methods, and quantities used in the product.

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Figure 1. Parts List

Product Analysis

FBD 1
Figure 2. Product Complexity Level Definition

12-Volt Battery

Component Function

• The function of the 12-Volt battery is to transfer energy. Chemical energy is converted to electrical energy and then this electrical energy is transferred throughout the electrical system. The electrical energy provided by the battery is user in the powertrain system. The energy is sent through various wires to the motors where the electrical energy is converted to rotational and translational energy. This energy causes the final motion of the toy. The battery is located in the hood of the Barbie Dune Buggy but is connected to groups of wire that transfer the energy throughout the car.

Component Form

• Shape: Rectangular Cube; The shape of the battery is based on the alignment of the cells of the battery.
• Part Geometry/Part Features: There is a plastic coating around the battery with an inlet for wires to connect to the positive and negative terminals of the battery.
• Dimensions: 4.25 in x 5.375 in x 5.50 in
• Weight: 9.4 lb
• Material: This component contains a lead-acid battery and a plastic casing. The plastic casing contains the battery and protects it from external elements. The plastic casing can be mass produced quickly and at a relatively low price through injection molding. Lead acid batteries are usually cheap for the amount of power that they give off. They are also common and most people have a common knowledge of how to use them. Lead-acid batteries are also rechargeable and easy to recycle.
• Aesthetics Properties: This component does not have an aesthetic purpose, it cannot usually be seen to the user because it is located underneath the hood of the Barbie Dune Buggy. The outside of the battery has a smooth finish and is grey with warning labels on the side. The plastic coating serves to protect the battery. The warning labels are also used for safety purposes.

Manufacturing Method

• The plastic casing was most likely made through injection molding. This would allow parts to be made quickly and cheaply. The battery was added to the casing and then a top was added. There are visible seams on the casing. The lead-acid battery was most like manufactured by cutting lead panels and combining these panels to form cells. The cells are placed in the battery casing and then an electrolytic solution, most like sulfuric acid is added. Some economic factors that influenced these decisions were that plastic is a cheap material and lead-acid batteries are a lower costing battery. Some societal factors that influence these decisions are that there are some safety issues because of the toxicity of lead. All workers involved in the processes must be extremely careful and follow safety standards when working with the lead-acid batteries.

Component Complexity

• Overall the component complexity is around a 3. Even though connecting and using the battery is simple, the reactions that occur within the battery to convert chemical energy to electrical energy are extremely complex. The battery is also able to send power throughout the toy.


Hood

Component Function

• The hood of the Barbie dune buggy power wheels has two main functions. The first function is to enclose the area with the battery is housed. This prevents the young passengers from tampering with the battery and prevents debris from entering the battery housing and effecting the battery function. The second function is an aesthetic function. The hood is present to make the dune buggy resemble a real car. The hood is not associated with any flows. The hood functions in a normal environment, meaning no harsh weather conditions or drastic changes in temperature which would affect the strength of the hood.

Component Form

• Shape: The shape of the hood is semi-parabolic and essentially two dimensional. The components shape makes it a good cover for the battery area as well as the aesthetic function is fulfills.
• Part Geometry/Part Features: The hood is symmetrical about one axis, and that is directly cutting the length in half. The hood has three clips that come off it that lock into the body of the power wheels
• Dimensions: The hood is 23.25 inches long at the top and has a width of 9.25 inches.
• Weight: The hood weights about .25 lb.
• Material: The hood is made from plastic, which makes it a cheap alternative to a metal hood. There is not a specific material for the hood, but plastic is the cheapest option, easiest to shape into the hood shape, and the lightest option. Plastic is also a good material to use in injection molding so the part can be mass produced quickly. A hard plastic is used to protect the battery from outside factors. An economic reason for the material selection, is that plastic is the cheapest option for the mass production of hoods. A global factor in the selection of plastic as the material used is that plastic is an easily accessible material in the United States, which is the primary market for the Barbie dune buggy. As an societal concern, the plastic hood is safe for the children using the product. An environmental concern in the material selection is that plastic is not biodegradable and must be recycled after the lifecycle of the product or it would be bad for the environment.
• Aesthetics Properties: On of the hood’s main functions is aesthetic, meaning the addition of the hood makes the power wheels look like a real car. The component is blue, because that was the plastic color selection of the entire power wheels body. The hood has a fine surface finish due to the manufacturing process used.

Manufacturing Method

• The hood was made through injection molding of blue liquid plastic into a hood shaped mold. This manufacturing method is evidence by the riser marks on the underside of the hood used to push the hood out of the mold. The material choice did not really effect the method of manufacturing, because if a metal was used, it would have been manufactured through die casting which is the metal equivalent of injection molding. The shape did impact the manufacturing method, because the slightly curve parabolic shape is most easily made through injection molding. If it were a simpler shape, bending or shaping could have been used. Injection molding is a cheap method of manufacturing, so that was an economic factor in the manufacturing decision process. A global factor is that injection molding can be performed in any technologically developed region, so it is available in those regions. A society factor is that injection molding is safe after the process is finish, but during the process heating plastic releases toxic fumes so therefore this method of manufacturing is dangerous while the process is occurring. This is also an environmental factor because the heating of plastic releases these toxins into the air and environment.

Component Complexity

• The hood is one of the least complex components in the Barbie dune buggy power wheels, so it gets a complexity rating of 1. There are no part interactions so there is no rating for that aspect. The hood is not complex, it simply snaps into its location on the body of the power wheels.


Motors

Component Function

• The motors’ main function is to convert the electrical energy, which is transferred to it though connecting wires, to rotational energy of motor shaft and connecting motor gear. No other function is performed by the motors. The motors are associated with the flow of energy in the system. The speed of the motor shaft, and therefore the rate of energy transfer is dependent on the signal which controls the speed of the dune buggy. The motors are designed to function at a normal environment, meaning no extreme temperatures or conditions. Grease is required to make the motor gear and gear box gear interactions as efficient as possible.

Component Form

• Shape:The motors are cylindrical in shape. At one end of the cylinder a motor shaft with an attached motor gear is present. This allows for the rotational energy to be transferred. The motors are three-dimensional components.
• Part Geometry/Part Features: The motors appear to be axially symmetrical from the outside, but the inside is not necessarily symmetrical in anyway. There are four holes at the base of each motor that allows the release of hot air as a result of the thermal energy.
• Dimensions:The cylinder part of the motor component is 2.25 inches long with a diameter of 1.5 inches. The motor shaft is 11/16 of an inch. The largest diameter of the motor gear is 10/16 of inch and the height of the gear is ½ inch.
• Weight:1 lb.
• Material:Each motor is made from a steel cylindrical casing which houses copper wires, magnets, and plastic rotating pieces. These material choices were made from the general form and materials of motors which are based on efficiency and strength balanced with weight. These materials are necessary for the motors to function. The motor material was not a decision made by the design team for the Barbie dune buggy power wheels. A global factor in the design of the motors would be that steel, copper, plastic and wires are fairly accessible materials in the United States, which is the primary market for the power wheels. An environmental factor in the design is that steel and copper, which make up much of the motor are materials that are recyclable therefore at the end of the products’ lifecycle, the materials can be recycled. A societal factor would be the safety of the motors. During energy transfer, thermal energy is developed, so the design must account for this, so that the motors do not get too hot to the point where they could burn someone or melt the plastic body or tires. Since the motors will go through many interactions, strong and reliable materials must be used.
• Aesthetics Properties:The motors do not have any aesthetic purposes. Their purpose is solely function. The motors are a silver color, because that is the color of the steel material used. The surface finish is fine, because that is the finish from the manufacturing process There is no aesthetic purpose to the finish.

Manufacturing Method

• The manufacturing method for the steel casing of the motor would be die casting which is evidenced by the fine surface finish and part lines. If the material was not steel, die casting would not have been used. The component shape was not influence by the material choice, because for the most efficient motor, it should be cylindrical. The gear was made through an extrusion process starting with steel. The copper wires would have been drawn out into their thin, essentially one dimensional form. A global factor in the manufacturing of the motors is that these processes can be performed in any developed country with industrial technology; therefore the motor component of the power wheels can be available in those places. Also in regards to the manufacturing on an economic level, this gives the opportunity of importing the motors from a cheap source to lower the cost to the consumer. A societal factor is that the motors are generally made in a safe way, so that the individual components of the motors are not toxic or harmful when used properly. Environmental factors include: the fact that each component is made in a way that is not extremely harmful to the environment.

Component Complexity

• The motors have a complexity rating of 5, which is the highest rating on the scale. This component is one the most complex components present in the Barbie dune buggy power wheels. The motors have only one function, but the internal interactions of the motor components is also a 5 on the complexity scale. The motor evaluated as an individual component of the Barbie dune buggy has many individual parts of its own, including motor gear, motor shaft, and copper wire, spinning magnet, spinning plastic and wire attachments. This makes the motor the most complex component.


Gear Box

Component Function

• This function is associated with energy flows. This piece is used to change the high rpm low torque rotational motion generated by the motor into high torque low rpm motion which is used to move the car. The component functions in a standard environment. It would not be able to function with many external forces or in extreme heat and pressure.

Component Form

• Shape: Oval with modifications; This shape allows all the gears to be held in one place and interact with each other.
• Part Geometry/Part Features:The gear box has a large hole where the rear axle enters along with the wheel guard. The gear box does not have any symmetric qualities. All the gears inside are symmetrical in any way that can be cut horizontally though the center
• Dimensions: While the part is three dimensional to save space its function essentially acts along two distinct two dimensional planes as each gear incrementally reduces the speed of revolution. The exterior case is 9 inches long 3 inches wide and 2 inches deep. The largest gear has a radius of 1.75 inches the second gear has a larger radius of 1.25 inches and a smaller radius of .75 inches the third gear has a larger radius of 1.25 inches and a smaller radius of .5 inches the third gear has a larger radius of 1 inch and a smaller radius of .375 inches.
• Weight:0.5 lb
• Material: The gears and gear box are all made out of plastic. The use of a plastic material allows the components to be manufactured using injection molding. This process allows the components to mass produced quickly and at a relatively low cost. The hard plastic also allows these components to interact with each other without breaking. The poles that the gears ride on are made of metal and the entire interior is coated in some sort of lubricating jelly to let the gears move freely. The lubricating jelly allows the gears to interact more smoothly and decrease the effect of friction on the interactions.
• Aesthetics Properties: This piece has a protective case to keep the lubricant in it but it is not visible to the user so aesthetics was not heavily considered.

Manufacturing Method

• Injection molding was used to make this product one can tell this by looking at the at the part lines and riser marks. The process was chosen since each car has two gear boxes and injection molding is good for making high volumes of a part with relatively good accuracy. The main factor effecting the decisions about manufacturing method and material was an economic one. Since making plastic is relatively cheap and besides initial cost injection molding is inexpensive. It is also possible that Fisher Price can use the same gear layout for multiple models which would help to make the initial cost less of an issue.

Component Complexity

• This was rated as a 4 in terms of complexity. This is because it involves some of the most moving parts in the entire car. It also requires more precision since if any of the gears came loose and slid away or if any of the teeth snapped the motor would greatly decrease in efficiency or stop working completely depending on the degree of the problem.


Wheel

Component Function

• The function of the wheel is to support the rest of the toy. The wheel also functions to utilize the rotational energy from the gearboxes and cause the motion of the Barbie dune Buggy. In conjunction with the steering wheel and steering column the front wheels are also responsible for the direction of motion of the toy. The wheels are connected to the axles and located underneath the chassis. The component can function in various types of environments and should be able to function with changing weather situations and surfaces.

Component Form

• Shape: Cylindrical; This shape allows the rotational energy from the gearboxes to cause motion of the vehicle.
• Part Geometry/Part Features: Axial symmetry, three dimensional
• Dimensions: 12 in diameter, 6 in deep
• Weight: 2 lb
• Material: The material is primarily made of plastic. Manufacturing decisions did impact this material. Plastic is a cheap material. The rigid plastic that is used on the wheels of the car is also fairly durable. An economic factor that may affect the material is the price of the plastic being used. A durable plastic that is also reasonably priced would want to be used. A societal factor about the material is that it must be safe for the use of children. This material is easily accessible to the user (most likely a child) and must be safe (ex. no lead paint). An environmental factor that could affect this material is if the plastics are recyclable or not.
• Aesthetics Properties: This component does have an aesthetic purpose. The wheel is purple and coordinates well with the other colors on the toy. The toy has a Barbie theme and the colors correspond well with said theme. The component had a rough surface which has both an aesthetic and functional purpose. The rough surface gives more traction for the user to go on multiple surfaces and up inclines. It also makes the toy look more like a real car.

Manufacturing Method

• The component was most likely made by injection molding. It was likely made by creating two halves of the wheel and then sealing the two halves of the wheel together. This can be seen by the line that runs throughout the middle of the wheel. The plastic material used for the wheels could have also easily been used in the injection molding process. Economic factors could have influenced this decision because the method allows parts to be created quickly and at a lower cost.

Component Complexity

• The wheel would rate as a 2 on our scale. Even though it helps in both the direction and overall movement of the car, it is a fairly simple component. The motors in the power train system, steering wheel and steering column are more of the complex components in the aforementioned functions.


Steering Wheel

Component Function

• The steering wheel is a key part of the user interface. It allows the user to determine the direction of motion for the toy. The steering wheel is connected to the steering column which ends up directing the front wheels which allows for the direction of motion to be determined. The steering wheel does not have protection from outside elements, so it must be able to function with different external stress such as changing weather.

Component Form

• Shape: Circular
• Part Geometry/Part Features: axial symmetry (for the bottom half of the steering wheel), essentially two dimensional because the depth of the steering wheel doesn’t really affect the overall function.
• Dimensions: 7 in diameter
• Weight: 0.25 lb
• Material: This component is primarily made of plastic. Manufacturing decisions did impact this material. Plastic is a cheap material. The rigid plastic that is used on the wheels of the car is also fairly durable. An economic factor that may affect the material is the price of the plastic being used. A durable plastic that is also reasonably priced would want to be used. A durable plastic must be used since the user is frequently interacting with this component. A societal factor about the material is that it must be safe for the use of children. This material is easily accessible to the user (most likely a child) and must be safe (ex. no lead paint). An environmental factor that could affect this material is if the plastics are recyclable or not.
• Aesthetics Properties: This component has an aesthetic purpose. It is a pink steering wheel so it fits well with the Barbie theme of the toy. The steering wheel also has the Volkswagen branding symbol and other stickers. The steering wheel has a finish that is supposed to resemble leather. This was done for both functional and aesthetic purposes. The finish allows the steering wheel to be easier for the user to grip. The faux-leather finish also alludes to a real vehicle instead of just a toy.

Manufacturing Method

• The steering wheel was most likely made my injection molding. The type of plastic used on the steering wheel is a good material to use during this process. The steering wheel was most likely made by two separate parts which were then connected together. This can be seen because there is a line that travels around the circumference of the steering wheel. There are economic factors which could have been use to make this decision. Injection molding allows parts to be made quickly at a cheap rate.

Component Complexity

• This component received a component complexity rating of 2 on our scale. The component is very user friendly and then used to determine the direction the vehicle will be moving in.

Solid Modeled Assembly

The system of steering components was the subsystem chosen to be modeled digitally with CAD. This system begins with the turing of the steering wheel. From here a rotation is created about the central axis of the steering shaft. This rotation creates a torque about the steering axel which in turn pulls on the end of the steering boot. Directly connected to the wheel by the L-bar, the moment that was created in the steering boot is directly transferred to the steering wheel. Therefore, the turning of the steering wheel creates a similar turning of the wheel.

Figure 3. Exploded Assembly of Steering Components

Autodesk Inventor was chosen as the preferred CAD package. This is due to previous experience with the program and its ease of use. Along with this, Autodesk Inventor also has excellent graphics and renders images to look closely like their actual components.

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Figure 4. 3D Model Parts List

Engineering Analysis

The main function of the Barbie Dune Buggy Power Wheels is to entertain the user by transportation. However, not much entertainment would be achieved by the child operating the product if the battery died before the car could move very far. Thus, it would be a good idea to test how far the product could go before the battery would need to be recharged. One method that could be used to find this distance would be to employ pre-established mathematical and scientific formulas. Knowing the voltage of a fully charged battery, one could calculate how much energy is produced by the battery. Then, taking into account the frictional force applied at the wheels (based upon the combined weight of the vehicle and average-sized rider), and using the concepts of the conservation of energy, the kinetic energy of the car could be found. As this kinetic energy is equal to the product of force and distance, the distance could thus be determined. Another means by which the distance could be calculated would be by the experimental method. Product testers could fully charge the battery, and with a load the weight of an average user, allow the car to run until the battery died. Measuring this distance and performing multiple trials, the average distance per battery charge could be determined.

The official statement of this problem would be:

What is the maximum distance that the Barbie Dune Buggy can travel on one full charge while carrying a single passenger?

The diagrams corresponding to this problem would look similar to the following:

FBD 1
Figure 5. Free-Body-Diagram of Problem

FBD 2
Figure 6. Flow-Diagram of Problem

For these calculations, the following assumptions would need to be made:

  • The Barbie Dune Buggy uses a 12 V battery
  • The mass of the passenger is 20 kg
  • The mass of the Barbie Dune Buggy is 90 lb
  • The battery efficiency remains constant
  • The Barbie Dune Buggy is traveling on a level concrete surface
  • The coefficient of friction between the tires and the concreter surface is 0.4
  • The center of gravity of the car is taken in the center of the car
  • The passenger is riding in the middle of the car and the center of gravity of the passenger can be taken as a single point
  • The acceleration due to gravity is 9.81 m/s2
  • There are no external loads acting on the vehicle


If the mathematical method is to be applied, the following governing equations would be used:

  • E=K+U
  • W=qV
  • W=-∆U
  • W=Fd


Definition of Variables:

  • E = Total Energy
  • K = Kinetic Energy
  • U = Potential Energy
  • W = Work
  • q = Charge
  • V = Potential Difference
  • F = Force
  • d = Distance Traveled in Barbie Dune Buggy

Design Revisions

After evaluating the functions and make-up of the product, various revisions that would make the Barbie Dune Buggy Power Wheels more efficient were devised. They include the following:

Tire Material

A common complaint about power wheels is that the toy slips on surfaces because there is not enough traction between the surface and the tires. Some consumers complain that their children can only use the toy on blacktop or concrete because the toy does not handle well on grass. If a child is playing with the toy on the road, this increases the chance that a child could be injured by oncoming traffic. Currently, the Barbie Dune Buggy has tires that are made of plastic. However, our group would like to propose the idea to use rubber tires on the toy. If rubber tires were used on the toy, the coefficient of friction between the tires and the driving surface would increase. This would allow the toy to be used on more surfaces. Although using rubber tires would increase the cost of producing the product, it would increase consumer satisfaction and the consumer may be willing to pay extra for a higher performing toy. Many consumers already replace the plastic wheels with rubber wheels for prices as low as ten dollars. If this was done with mass production, the price would be even lower.

This change would address many societal concerns. Adding rubber tires would increase the safety of the toy. There would not be as much slipping or skidding while the toy was in use. The new tire material would also allow the toy to be used better on grass so children wouldn’t have to use the toy in the road which could be potentially hazardous. The new tire material would also cause the toy to look more like a real car. This falls back into the idea that children want to imitate their role models and drive cars.

FBD 1
Figure 7. Current Wheel Design

Installation of Kill Switch

Another proposed design revision is the installation of a kill switch in the Barbie Dune Buggy. Right now there is a continuous brake that works on the car, but if the pedal is compressed, the car will continue to move. If the pedal gets stuck, there is no way to stop the car from accelerating. The proposed design revision is for there to be a kill switch installed either in the dashboard console of the car so the user can push the button if they need to automatically stop the car or a button that is outside the car so the parent of the user can control the kill switch. Since the toy is intended to be used with adult supervision, the parent could see if the child was having trouble controlling the car, or directing the car in a hazardous direction and operate the kill switch. There would be a small increase in the price to install a kill switch, but it would increase the safety of the car, and protect the production company in case there were ever any defects with the pedal of the car.

This design revision would address societal concerns. The installation of a kill switch would increase the safety of the Barbie Dune Buggy. There would be an easy way to stop the acceleration of the car in case something went wrong with the controls in the toy and the user would remain safe. This is especially important because Fisher Price has had to recall toys because the toys didn’t stop and users were injured in the past.

FBD 1
Figure 8. Example of an electrical kill switch that could be added to dashboard controls

Adjustable Seat

An additional design revision suggested by Group 23 is to have multiple seat settings for the Barbie Dune Buggy. Right now, the Barbie Dune Buggy seat fits into slots on the chassis and is then screwed in to lock the seat into place. If multiple slots were placed in the chassis the seat could have adjustable settings, and the toy could be used to grow up with the child. The Barbie Dune Buggy is designed to hold a passenger up to 130 pounds, but the space that is available for the user to sit may not coincide well with the height of the user. If there were multiple slots put into the chassis, the seat could move back as the user got taller, and the toy could be used for a longer portion of time. There would be a minimal cost increase to the producer because all the parts would remain the same just with additional slots for the seat on the chassis. The producer would also be able to charge a higher price to make up for this price if they wanted to because the toy would now be marketable to a larger group of consumers.

This design revision would address economic, environmental and societal concerns. If the toy was designed to be used for a greater range of ages, the consumer would be able to purchase one ride on toy instead of a ride on toy for each time the user had a growth spurt. This would decrease the economic burden on the consumer. This would also address environmental concerns, because there would be less ride on toys being thrown away after the child outgrows them. The toys are made primarily of plastic and there are not many known ways of recycling these toys and they usually end up in landfills and dumps.

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Figure 9. View of chassis where extra slots could be added

Clearer Controls

Another design revision suggested by Group 23 is a design with a clearer control system. The control systems for the Barbie Dune Buggy are not always clearly marked. For example the direction shift does not have labels to tell you if the car will be moving in reverse or the forward direction (please note that we are basing this off of a used model and there may have been more stickers for controls when the car was originally purchased). The dashboard controls for the radio system is also vague. The user must test out all of the controls to learn what they do and then memorize what each control does. This could be solved by placing stickers by the controls to say which each control does. This would add a minimal cost to the product and make the product much more user friendly.

This design revision would address societal concerns. Making more direct labels for the control system would make the toy more user friendly and easier to use.

FBD 1
Figure 10. Current User Interface

References

[1] Power wheels race cars with variable speed pedal and rubber tires. (2010). Retrieved from http://www.saltydog.com/powerwheels/
[2] Waterston, Diana. How to stop power wheels tires from slipping (2011). Retrieved from http://www.ehow.com/how_6620819_stop-power-wheels-tires-slipping.html
[3] U.S. Consumer Product Safety Commission. CPSC, Fisher-Price announce recall to repair power wheels ride-on battery-powered vehicles. (1998). Retrieved from http://www.cpsc.gov/cpscpub/prerel/prhtml99/99012.html
[4] Mattel. Barbie dune beetle owner's manual. (2003). Retrieved from http://service.mattel.com/instruction_sheets/B3162a-0920.pdf
[5] Battery tutorial. (2011). Retrieved from http://www.batterystuff.com/tutorial_battery.html