Problem Definition Phase

Home

Project Overview

Research Phase

Proposal Phase

Detailed Design Phase

Integration/Test Phase

Team Page

Problem Definition

It is during this define phase that the project is being fleshed out by the team. That is to say that as a group, in conjunction with our client, we must decide upon what the project will be about. A detailed list of these needs, wants, and specifications can be seen in the Project Overview Page.

The most important aspects of The Child Mobility Project are exemplefied in the requirements set forth by our client. It is import that the structure of the vehicle fit the child and safetly support their weight. In regards to the vehicle its motion must be controlled by the child and be capable of zero degree turns. The battery life of the vehicle must last at least one therapy session and be rechargeable.

The project is further delineated by the constraints of the project. First and foremost the control scheme must be intuitive for the child and furthermore must be input via joystick. Overall the vehicle must cost less that $500 and be easily transportable.

Research Survey
Early Power Mobility: An article presented by Debra Field and Roslyn Livingstone, illustrates the need for powered mobility devices tailored towards children 12 months and up. Children who are not moving under their own volition by twelve months-of-age are at an increased risk for developmental delays. “The brain’s ability to develop and form connections in the sensory and motor areas peaks at two years-of age, therefore it is very important that children who are not moving independently by 12 months of-age have opportunity for independent mobility experience using power mobility”. Early research on the effects of powered mobility solutions for children shows a positive impact on child development, and an increased level of independence for the child. No evidence of negative impacts to the child’s development has been found. Powered mobility also has a positive impact on a child’s ability to develop more traditional peer relationships.	Early Intervention: Current research shows a direct correlation between a child’s ability to control its own locomotion and positive development in a variety of areas. Children who use powered mobility have seen increased development similar to children without disabilities. These developments include increased alertness, increased understanding of cause and effect, and in some cases increased use of their arms. These improvements were even seen in children who were not able to achieve independence using power wheelchairs. These results indicate the need for powered mobility solutions with simple control schemes. The success seen by children using powered wheelchairs has led some researchers to firmly recommend powered mobility for non-ambulatory children. Another avenue to improve powered mobility integration is to have the children practice in familiar environments; such as at home with family. Powered mobility can be used and practiced when the child is participating in meaningful activities and familiar routines.
Babies Driving Robots: One major concern was the ability of children ages zero to three to be able to operate a moving device. The control scheme, especially, would have to be designed for the target age range. This article describes a study that was done to see if infants would “use their ability to reach and grasp to achieve self-generated locomotion via a mobile robot before they could independently locomote via crawling or walking”. The study called for the infants to be placed in a mobile robot controlled by a joystick. The handler would point to and verbally encourage the infant to use the joystick, but would not show them what it did. Several of the infants expressed positive behavior toward the joystick and increased usage over several sessions. This study shows that infants are able to learn and use joysticks to move a mobility device.	The Dangers of Electric Toys: The United States Government has a committee dedicated to protecting consumers on products sold within the United States called the Consumer Product Safety Commission (CPSC). The CPSC issued an alert specifically focused on electric toys for children outlining the mandatory regulations and standards enforced by the United States Government. The alert outlines standards for both mechanical and electrical construction when constructing electric toys. Some mechanical standards include: having a rigid construction to preserve components when subjected to abuse, guarding moving parts, and positioning pressure relief valves safest possible direction. Some electrical standards include: mounting all electrical components securely to prevent movement, having electrical plugs with grasping areas, and enclosing all live electronics securely.
Segway Inc.’s Human Transport: Segway revolutionized transportation for humans by creating a fast, compact, and innovatively controlled “vehicle.” The Segway has many features including a display that shows the amount of battery left as well as the estimated distance that it may travel. The Segway’s complex computer system, including sensors that calculate the riders lean and weight distribution, are compactly assembled in an aluminum cast platform under the rider. Further, the two Lithium Ion batteries that support the electric motor are also inserted into flat pockets of the cast aluminum platform. While the Segway is turned by the rider leaning to either side, the Segway is also capable of zero point turns. This is achieved by rotating the two wheels in opposite direction simultaneously at the same speed. Miniaturizing and combining design features from the Segway will help shape a functional child mobility platform.	Power Wheels: Although there are several home-made mobility devices, one large scale company, Fischer Price, produces a widely available mobile toy called Power Wheels. Power Wheels come in various styles and models which typically use four plastic wheels and a 12 volt, 9.5 amp-hour battery. Some variations of Power Wheels use a 6 volt, 9.5 amp-hour battery instead. They operate how a car would by accelerating into motion with a pedal at the child’s feet. This site includes safety alerts and regulations for Power Wheels as well as other Fischer Price toys. However, most of these toys are for children ages three and up.
High Power Electronics: Power electronics systems are a system of components that drive high powered outputs, such as a motor, with a low powered control signal. The existing technology are the “brain” systems for current power wheelchairs. These systems have a current delivery from 40-90A, which is meant for use by an adult up to 600 lbs. Even though the current rating is high for use in a product for children, the basic circuitry behind it is the same. The technologies are the same in terms of operation, but they differ in terms of power output and the number of motors that can be powered. The problem with existing power electronics is that they require a high amount of power when driving high torque motors, but again, these values are scaled for adults. A cost effective solution entails a lower power solution. As the price of these controllers scale with power requirements, lowering power demands in the device lowers cost. Overall, getting or making a power controller for this platform will be cost effective for this scale of project.	Microcontroller: Computing technologies have become widely varied in power, speed, and size. Microcontrollers try to incorporate the best of these attributes into a nice form factor. Texas Instruments (TI) has a well-known and popular microcontroller line called the MSP430. There are many MSP430 microcontrollers with each being targeted towards a specific function or specification. For this project there are a wide array of MSP430 microcontrollers to choose from including: Ultra-Low-Power, Low Power & Performance, Security & Communications, Real-time Control, Control & Automation, and Safety centered models. Programming any of these microcontrollers is doable because the curriculum at NAU uses the MSP430 as an educational tool. Cost may be an issue as some microcontrollers are expensive and this project’s design was meant to be low cost. Based on the needs of this project a microcontroller suited to the specifications can be selected.
Speed Control: Motor Control is often difficult to program. It is of great importance to this project that the motors have precise control for the safety and education of the child. This will be hard to accomplish without the use of a motor control methodology called fuzzy logic. Oftentimes programming is discrete, with harsh breakpoints between functionalities of the system. Fuzzy logic moves to represent the system in terms of verbal language instead of mathematical equations. This allows for a more understandable advanced system that can be specifically programmed for the needs of this project. Functionalities such as lower start up torque and slow deceleration should be fairly simple to program with fuzzy logic. There are other references available at TI’s website that give more details on using fuzzy logic for motor control.	Zero Turn Radius: A vehicle or device that has a “zero-point turn radius” has the ability to turn 360 degrees without traveling any distance. Having a zero point turn is important to the platform’s ability to perform in a home environment. One method to perform a zero point turn is to have two electrically powered back wheels and free-moving casters in front. This method functions well if the driver already knows how to operate the vehicle. Another form of a zero point turn radius is having four powered wheels that are all able to turn at a 45 degree angle. This method is more difficult to achieve, but can be more accurate. Using this solution is expensive, and requires costly motors to move a larger weight. Another solution could use less expensive motors with smarter programming to replicate the smooth motions of a zero turn radius. Market conditions make these products very difficult to get a hold of as many of them only distribute through insurance companies. Getting a zero point turn radius mobility option “off-the-shelf” is an unlikely option for most families without insurance.
Batteries: To make motorization possible, a power supply is needed. For the purposes of the Human Mobility Project, the power supply would ideally be portable. A possible method for this is the use of rechargeable batteries. However, with battery usage come concerns of longevity as well as capacitance decay, or the batteries ability to hold a charge over time. This decay is caused by the amount of current density being drawn by the system that is powered by the battery. For the purposes of this project, the power supply as well as the regulated supply will need to be able to withstand the high current impulse draw caused by the motor when initially moving. Increasingly popular batteries, such as Lithium Ion batteries, may also be a great advantage due to their light weight and a low self-discharge weight.	PMDC Motors: For a design revolving around moving a child weighing up to forty pounds, a powerful motor with a high torque output will be needed. Some motors like a pulse modulated alternating current (PMAC) could be used if the vehicle was moving at higher top speeds. For the Human Mobility Project the opposite will be needed, a pulse modulated direct current (PMDC) motor will instead be used for its ability to provide high torque output. The problem with these motors is the high current draw while providing max torque. This also directly affects the power consumption that is placed on the battery. Since there is not a need for high speed, the current draw from the motor may be limited by the use of discrete componentry. This would in turn aid in the longevity of the power supply system as well as wear and tear on the battery in terms of decay and usage time.