From DDWiki

Contents 1 Executive summary 2 Customer needs 2.1 Durability 2.2 Realism 2.3 Ease of Use 2.4 User Research 2.5 Target Audience 3 Stakeholders 4 Function 4.1 Forward Locomotion 4.2 Leg Movement 4.3 Turning 4.4 Power Train Mechanical Analysis 5 Components 6 Design for manufacturing and assembly 6.1 Disassembly and opportunities for improvement 6.2 Theories on unique parts 7 Failure mode effects analysis 8 Design for environment 9 EIOLCA 10 Toxic Releases 11 Redesign

Executive summary

The purpose for this documentation of a Remote-Controlled Tarantula is ultimately to improve or expand upon the existing product. By studying the environmental and economic impact of the product, as well as accessing customer needs, areas for improvement can be best considered.

The purpose of this product is to provide entertainment to the customer in a novel manner. The aesthetic appeal and unique locomotive properties of the product are key points that fulfill particular customer needs. Providing a sense of realism, both in form and in motion, is a primary functional requirement of the Tarantula. Also, ease in controlling the Tarantula is important. By expanding the range of ages that can enjoy the product, more units can ultimately be sold. Durability is also a factor to be considered, since the product is a kind of toy that must withstand an appreciable amount of wear and tear.

For this documentation of the product, a thorough dissection of the Tarantula was done. An assessment of the functions of the product was taken, as well as a catalogue of the individual components involved in the assembly. A customer study was conducted, as well as a Failure Mode Effects Analysis (FMEA), and a Design Analysis. The Design Analysis incorporated determining design features for both manufacture and assembly (DFMA), as well as for environmental effects (DFE). Finally, a mechanical analysis of the motor was taken to determine any improvements that could be made to increase the functionality of the product.

After conducting analysis of the product, it was concluded that there are key factors that may be addressed to improve it. The DFM analysis revealed that many small unique parts were used in the production of the Tarantula. This creates additional complications in the manufacturing process, as it requires more attention to detail in order to ensure the proper installation of each piece individually. Also, the need for additional tools in order to open the battery slot, or even to take the tarantula apart, was a complication faced during the analysis. Overall, the FMEA for the product revealed that it is constructed without a substantial amount of risk of failure. When conducting an EIO-LCA analysis of the product, it was determined that the primary source of environmental complications arise from the consumption of batteries over the lifetime of the product. As such, it is a recommendation of our team that the focus of the project be on reducing the consumption of batteries as well as simplifying the necessary components for manufacture.

Customer needs

The Tarantula is designed primarily as a form of entertainment for its user, and to a lesser degree, as an educational tool.

Users of this product seek out the novelty of a seemingly ‘alive’, self-contained creature, that they in turn are able to manipulate and direct, remotely. They may use it to observe the walking behavior of a simulated tarantula; more likely, they may use it to scare other people.

To this end, the user would require that the tarantula be durable, realistic, and easy to operate.

Durability

Ideally, the tarantula would be able to durable enough to function in different environments: indoors, outdoors, and on a variety of surfaces, including carpets and tile. The tarantula may be placed in an elevated location and then drop; therefore, the tarantula should be able to survive falls. The tarantula would also be frequently exposed to a younger audience, so it would need to survive pulling, tugging, tosses, and possibly even being struck or chewed on.

Realism

In order to convince other people that the tarantula is alive – even momentarily – the user requires a certain degree of realism. The user would want the tarantula to appear physically realistic, therefore it should be of the same size, color and texture as a generic ‘tarantula,’ or specifically, what the general population believes a tarantula to resemble. The user would also want the tarantula to have a realistic motion – its individual legs should move in a similar fashion to a real arachnid. The user would want the arachnid to not make a lot of noise – mechanical whirring would be a clear giveaway. Because a typical human being can easily cross a room in several seconds, the tarantula should be somewhat fast in its mobility. The goal would not be to outrun a person, necessarily, but to be able to encroach a person very quickly.

Ease of Use

Finally, the tarantula should be easy to operate. The user expects it to operate in a similar fashion to motor vehicles or other RC cars – in that navigating should be easy. The remote control’s buttons should be few and clearly labeled. The user would not expect to be required to articulate each individual leg, for example. Supervising adults would require that the tarantula not pose a threat, whether a choking hazard, or getting fingers, hair, jewelry, etc, caught in its moving parts, or being struck by the tarantula if it ran too fast. The user would also expect the tarantula to use standard-size batteries, preferably inexpensive, as well as have a long battery life, for multiple or extended use. The batteries should be secure, yet easy to replace if frequency was required.

User Research

In talking to users and allowing users to interact with the tarantula, the above three tenets were commonly raised in some form. Users frequently asked if the tarantula could survive a fall from a table, what directions it could move in, how fast it could run, and how far or how well concealed could the remote be, while still allowing the tarantula to operate.

Target Audience

It is clear from the packaging that scaring other people is the primary function. The ‘creepy’ aspects of the product are focused on. The ‘realism’ of the product is also heavily advertised, although the educational value of the product is dubious. The product is largely targeted to a youth demographic, as it falls under the purvey of ‘toy,’ however, all ages appear to enjoy the product, due to its novelty.

The following table summarizes the highest ranking customer needs, and product requirements.

Rank	Customer Needs	Product Requirements
1	Realism	Durability
2	Ease of Use	Realism
3	Durability	Ease of Use

Stakeholders

The stakeholders for this product are defined as entities that are involved at any of the stages of the product life cycle. All of these entities have an economic investment in the product. This includes the end user, as well as the suppliers of the raw material and components necessary to manufacture the finished product.

• Users
• Designers
• Suppliers (Plastic components, electrical assemblies)
• Manufacturers (Toy production/assembly)
• Distributors (Retailers, novelty specialty stores)

Function

The Tarantula is a variant of commonly seen remote controlled toys. The user holds a controller which sends radio signals to the Tarantula and controls its movement. The appeal of this toy is the novelty of a large moving spider as a remote controlled vehicle. Also, the realism of the device adds to the user’s enjoyment by allowing him or her to scare others with it.

Forward Locomotion

The controller only has two outputs, forward and back. During “forward” the motor runs in a clockwise direction engaging the drive wheels through a gear system. The drive wheels are under the head of the spider, and pivot to steer. A second set of wheels attached to the battery cover support the abdomen of the spider, but do not contribute to steering or propulsion. The drive wheels are vertically offset from each other to mimic a “crawling” motion and add to the realism. Due to the high gear ratio, the movement is slower than most RC toys, similar to what one would expect of an actual spider. However, the toy only functions well on very flat surfaces, and will become stuck on carpet or small obstacles.

Leg Movement

When the motor is engaged, a turn table in the head of the spider also spins. This table is cam shaped which causes it to asymmetrically engage 8 levers which are connected to the 8 legs of the spider. As the turn table engages the legs they are lifted up, but pulled back down by gravity as the turn table disengages them. This up and down motion of the legs mimics the crawling of a spider and it is central to the realism and novelty of the product.

Turning

The spider has no specific steering input form the remote control; rather it turns when the motor is running counterclockwise or receiving a “backwards” input. The drive wheels are setup such that depending on the direction the motor is running, the wheels will align to a certain orientation. The drive shaft for the wheels descends vertically from the head of the spider and connects to the drive wheels at a 90° angle. The bracket which holds the axle sits in two slots which allow it to rotate along the axis of the drive shaft. When the motor runs there is a net torque on the drive wheel axle, causing the bracket and axle to rotate if they are able. The wheels turn 45° relative to the centerline of the Tarantula if the motor is running backwards, and point straight ahead if the motor is running forwards. This causes the spider to turn while it is moving backwards, allowing the user to control the eventual destination of the device.

Power Train Mechanical Analysis

The spider is powered by two AAA batteries connected in series. This powers the small motor and electronics (circuit board, LED eyes). The motor is connected to a gearing system with a large gearing ratio by a worm gear. This results in a slower movement, but higher torque on the drive wheels.

Following the above diagram, the calculation for the gear ratio is as follows:

The coefficients for the gears were determined by counting the teeth on the gears. Gears C and D share a single axle, as well as gears G and F. Therefore the coefficients for their respective velocity ratios are 1.

Components

Part #	Part name	QTY	Function	Materials	Manufacturing Process	Picture
001	Cover Screws	13	Holds bottom cover in place	Steel	Cold headed, Thread Rolled
002	Inner Flat-headed screw	2	Holds circuit board and LED eye in place on interior of machine	Steel	Cold headed, Thread rolled
003	Battery Cover	1	Covers, protects bottom of tarantula	Plastic	Injection Molded, hand modified
004	Back Wheel housing	1	Covers rear wheels Holds rear wheels in place	Plastic	Injection Molded
005	Back Wheel	2	Holds weight of majority of tarantula, allows it to roll on ground	Plastic	Injection Molded, smoothed
006	Small Leg	4	Aesthetic legs that move asymmetrically as tarantula rolls Covered in fake "fur"	Plastic	Injection Molded
007	Medium Leg	2	Aesthetic legs that move asymmetrically as tarantula rolls Covered in fake "fur"	Plastic	Injection Molded
008	Large leg	2	Aesthetic legs that move asymmetrically as tarantula rolls Covered in fake "fur"	Plastic	Injection Molded
009	Feelers	2	Aesthetic feelers that are in a fixed, forward-facing position to mimic a spider Covered in fake "fur"	Plastic	Injection Molded
010	Driving Wheel 1	1	Takes torque of motor, drives the front axle Off-center axle hole	Plastic	Injection Molded, smoothed
011	Driving Wheel 2	1	Shares axle with Driving wheel 1 Off-center axle hole	Plastic	Injection Molded, smoothed
012	Plastic Protection housing	1	Holds motor and gearing in place on interior of robot Provides internal support for robot	Plastic	Injection Molded
013	Back Wheel Axle	2	Each axle has a Back wheel fitted on it, allows back wheels to roll	Steel	Cut wire, smoothed
014	Battery Cover Washer	1	Washer for battery cover screw	Plastic	Punched
015	Gear 1	2	Short and fat gear, used for power transmission	Plastic	Injection Molded
016	Gear 2	1	Medium gear, wide, used for power transmission	Plastic	Injection Molded
017	Gear 3	2	Thin, tall gear, used for power transmission	Plastic	Injection Molded
018	Gear 4	1	Large gear with cam, used to actuate tarantula leg movement	Plastic	Injection Molded
019	Axle 1	1	Smooth, long axle used to hold Drive wheels (both of them) on the exterior of tarantula	Steel	Cut wire, smoothed
020	Axle 2	1	Smooth, medium axle Used on interior to hold Gear 1	Steel	Cut wire, smoothed
021	Axle 3	1	Smooth, short, and wide axle Used on interior to hold another Gear 1	Steel	Cut wire, smoothed
022	Axle 4	1	Long, double-roughed axle Used on interior to hold gear 3 (both of them)	Steel	Cut wire, smoothed, stamped rough areas
023	Axle 5	1	Short, double-roughed axle, used with gear 2 and gear 4	Steel	Cut wire, smoothed, stamped rough areas
024	Axle Cap	1	Axle endcap	Plastic	Injection Molded
025	Switch Assembly	1	Electronic Off/On switch with 2 wires and small circuit	Circuit Board (silicon), metal wires, plastic switch	Assembly
026	Switch Cover	1	Covers switch, protects it	Plastic	Injection Molded
027	Motor Assembly	1	Motor that powers tarantula Worm-geared output shaft	Metal wiring, magnets, Metal casing, plastic gearing	Assembly
028	Circuit Board Assembly	1	Remote receiver has attached antenna controls motor function	Circuit Board (silicon), metal wires	Assembly
029	LED Assembly	1	Aesthetic assembly to make eyes of tarantula glow as it moves	Circuit (silicon), metal wires, LED	Assembly
030	Tarantula exterior bottom	1	outer shell of tarantula	Plastic	Injection Molded, hand modified
031	Tarantula exterior top	1	outer shell of tarantula covered in fake "fur"	Plastic	Injection Molded, hand modified
032	Battery Connector	1	Small flat metal piece that connects + end of one battery to - end of the other	Steel	Cut sheet metal
033	Battery + connector	1	connects to + end of batteries in series, connects to wire which runs to motor	Steel	Cut sheet metal
034	Battery - connector	1	connects to - end of batteries in series, connects to wire which runs to motor	Steel	Cut sheet metal
035	Metal screw receiver	1	threaded cylinder of steel to receive a screw mounted inside bottom plastic exterior to stop screw from tearing into plastic	Steel	threaded cylinder
036	Drive Wheel Mount	1	Holds drive axle in place	Plastic	Injection Molded

Design for manufacturing and assembly

The Design for manufacturing and assembly refers to ways the process of manufacturing and assembling of a product can be optimized, reducing complexities and overall cost of production. These are some notes about the current design of the remote control tarantula:

• The product is constructed mainly of injection-molded plastics
• Exterior molds show evidence of modification by hand (scratched texturing, extra melted-on pieces of plastic to cover certain components)
• Many fasteners are used in the product, including 13 of just one type of screw for the exterior pieces
• Mostly unique gears are used throughout the product - out of all the gears used in the interior, only two are identical
• Mostly unique axles are used throughout the product - only 2 axles are identical in the robot, and they are two separate axles for each back wheel
• Some axles show machine-added grooves to give friction to gears situated on the axles
• Design has three separate circuit boards that require being screwed to the frame - the LED fixture, switch fixture, and control circuit board
• Soldered wires connect the circuit boards together

Disassembly and opportunities for improvement

The group found out after taking apart the tarantula that it definitely was not made with the idea of disassembling in mind. One of the soldered wires broke off at its connection while the robot was apart. The gearing was tightly packed and covered in grease. The gears themselves took a lot of effort to be taken off their axles, and in a couple cases the removal stripped the gears of teeth. While looking over the contents of the tarantula shell, we noticed first the complexity of the construction along with the necessity of human involvement, along with the many unique parts that were inside. Many axles, while similar to each other in the robot, were slightly different, such that each had to be cut to different lengths and one had to be made with thicker metal. The case used lots of screws to fasten itself together. In one specific spot, there was also a inversely-threaded cylinder of metal that had been placed in the shell of the robot and covered with a melted piece of plastic. This was most likely put in place to keep metal screws from ripping apart the softer plastic shell, but the work done to keep this from happening seemed time-intensive.

Ideas for improvement:

• Make the outer shell snap together, removing the need for 5-7 screws and the screw-receiving piece of metal mentioned above.
• Design the gearing to utilize more similar gears, or just fewer gears, to minimize unique part counts. As an addendum to this, redesign the parts to use the same sized axles, so there are fewer unique parts.
• Make stronger soldering points with wires, or use fewer electric components, or put more of the electric components next to each other so wiring isn't required.
• Combine the back two wheels so that they share an axle.
• remove some of the hand-done etching to the outer shell of the robot, make certain designs with stickers or paint instead.
• increase the size of the shell of the robot so that it is easier to work on parts on the interior.

Theories on unique parts

The group, after seeing so many small and unique gears and axles, had a theory that these pieces of the tarantula could have been purchased from an outside supplier. If so, this supplier could have supplied all of these different unique parts at a flat fee, meaning that even if redundant parts had been utilized, they would have been the same cost. Since the supplier would be making these unique parts anyways, it would save the company no money to change the design unless they produced all of the parts in-house.

Failure mode effects analysis

Most of the failure modes have low Risk Priority Numbers (RPN), the most significant concern is an internal disconnect of a wire, leading to complete loss of functionality. In this system the electronics are far more vulnerable than the mechanical components, and are the primary concern for possible failure modes. In the process of disassembly on the team’s part, wiring was inadvertently disconnected. While improper disassembly by the user is not something that can be easily protected against, it is possible that relative motion of the internal components could eventually cause a failure. It is recommended that solder joints be reinforced. Other possible failure modes are listed below.

Item & Function	Potential failure mode	Potential failure effects	SEV	Potential causes	OCC	Design controls	DET	RPN	Actions recommended	Respons ibility	Actions Taken	New SEV	New OCC	New DET	New RPN
Internal Electronics Components	Wiring Disconnect	Complete loss of function Diminished control of toy Unreliable operation.	8	Temperature Cycling Jarring of internal components causing disconnect Disassembly by user	4	Close fitting parts allowing for minimal movement Connection check post-assembly.	6	192	Increased solder for vulnerable connections More chassis/electronics connection points Warning to user of possible consequences of disassembly	N/A	N/A	6	2	6	72
Power Train	Wearing of gears or motor. Loose mounting allowing for vibration.	Increased noise during operation causing: loss of realism noise irritation to user reduction in "startling" ability	4	Wear on motor and gears Misalignment causing additional wear Insufficient or loss of lubrication.	5	Standardized lubrication application Quality control of gears and mounting.	6	120	Improved gear quality Running motor at lower speeds.	N/A	N/A	4	3	6	72
Gears	Gear slip	Toy may stop working entirely Lose functions such as turning, leg movement or forward movement	6	Gear misalignment Unexpected load on drive train	4	Textured axles Quality controls of gear supply and positioning	5	120	Higher density gears Adhesive applied to axles.	N/A	N/A	6	2	5	60
Motor	Overheating resulting in seize	Temporary or permanent failure of motor Loss of functionality during motor malfunction.	7	Prolonged use environmental conditions moisture heat particulates)	3	Some protection from environment by body Low capacity batteries preventing prolonged use.	5	105	Better use of internal space to improve heat dissipation Further sealing of body from environment.	N/A	N/A	7	2	5	70
Internal Electronics Components	Short circuit	Complete loss of function Diminished control of toy Unreliable operation	7	Exposure to moist environment immersion in water	5	Limited routes of exposure from internal components to environment Warning to user of potential effects of moisture on device	3	105	Minimize number of chassis openings to environment Seal joints with moisture-resistant adhesives or seal sensitive electronic components	N/A	N/A	6	2	3	36
Drive Wheel Mount	Mount is unable to pivot	Inability to either turn or go straight consistently User is unable to control movement of Tarantula to reasonable expectations.	6	Clogging of slots that mount slides in Misalignment of parts caused by jarring Off specification parts causing jamming	4	Recessed slots Lubricated parts.	4	96	Sealing of slots to outside environment	N/A	N/A	6	2	4	48
Hair Covering	Flaking of hair off of body	Decreased realism Hair shedding onto environment	3	Wear from handling/usage Low resilience adhesive	10	Lack of hair on parts frequently in contact with other surfaces	3	90	Improved adhesive or hair quality to limit shedding Use of textile-type cover to achieve similar realism with more durability	N/A	N/A	3	5	3	45
Remote Control	Interference with other RC devices	Inability to independently control other Tarantulas nearby Decreased control of Tarantula depending on nearby radio-emitters	5	Same frequency use by other devices Single frequency use across all Tarantulas	8	Use of frequency that is uncommon in other devices	2	80	Cycle tarantula frequencies among toys.	N/A	N/A	5	2	2	20
Legs	Legs become fixed in a single position	Legs no longer move as Tarantula does Novelty of toy diminished Realism of toy (and thus "startling" effect) diminished	4	Low tolerance on hinge Environmental conditions causing jamming.	5	Simplified leg mechanism Simple maintenance by user.	3	60	Enclosed leg joints	N/A	N/A	4	3	3	36
LED Eyes	LED eyes become dim, asymmetrical or unlit	Reduction of novelty or "startling" aspects Inability to visually recognize when the toy is "on" resulting in excess power consumption	3	Dirt or other particles blocking eye holes LED defect Disconnect from power source Internal shifting of LED.	6	Bright LED's Multiple enclosed eye holes LED quality control Cleaning by user	3	54	More secure fasteners for LED	N/A	N/A	3	4	3	36

Design for environment

The environmental impact caused by the Tarantula is attributable to separate stages of its life-cycle. In order to produce the Tarantula, several factors are required prior to and during the manufacturing process. Energy is required to produce the materials necessary for the components, which also involve the generation of waste byproducts.

Over the lifetime of the Tarantula, the factor with the most environmental impact is its need for batteries. In order to operate the product, a supply of batteries is necessary. With this in mind, the production, use, and disposal of batteries must also be considered.

The amount of environmental impact attributable to a single Tarantula is relatively negligible. But when the large volume of numbers produced is taken into account, the amount of pollutant emissions, economic demands, and energy needs become a larger factor to consider. The apparently environmentally harmless product becomes more a larger problem when considered in the grander scale of manufacturing and production.

EIOLCA

The method used to calculate the environmental and economic impact of the Tarantula involves the use of data provided through the Economic Input-Output Life Cycle Assessment (EIO-LCA) database. In order to get a proper appreciation of the impact of the product, all calculations and measurements are done in terms of millions of dollars of economic activity. The database compiles information pertaining to the economic demands, pollutants emitted, energy demands, even the labor needs for certain sectors of different industries. Once a sector’s impact is calculated, the information pertaining to the contributing factors for each million dollars of activity can be accessed and compared.

Production of the Tarantula pertains primarily to sector 33930 - Dolls, Toys, and Game Manufacturing. However, over the lifetime of the product’s use, multiple purchases of batteries are required. As a result, the economic and environmental impact of the product is also linked to sector 335912 - Primary Battery Manufacturing. The focus of this analysis is to observe the main sources of emissions and demand for energy. The types of emissions observed are greenhouse gases, conventional air pollutants, and toxic releases.

For sector 33930, the primary consumer of energy is power generation itself. It consumes nearly three times the energy as the next two sectors, which are toy manufacturing and paperboard mills. These three sectors combined contribute for approximately half of the total energy required, amounting to 3.99 TJ/$1 Million for Production. The non-toxic emissions produced are also primarily attributable to power generation.

Use of the Tarantula requires the consumption of multiple batteries. During operation, two AAA batteries are used in the Tarantula, with an additional three AA batteries in the remote control. During our analysis, an hour of constant use would deplete and require a change of AAA batteries in the tarantula. The AA batteries in the controller, however, would drain at a quarter of that rate. Thus, after four hours of constant use, the consumer would have gone through eight AAA and three AA batteries. The lifetime of the product was gauged at 48 hours of constant use over a calendar year, which would require a total of 96 AAA and 36 AA batteries.

For the LCA analysis, it was assumed that the production cost of each tarantula was approximately $8.00. Also, it was assumed that each battery, either AAA or AA, would cost about $0.08 to produce. So, for an equivalent $1 Million for Tarantula production, approximately $1.32 Million would be spent on Primary Battery Manufacturing.

Over the lifetime of the products use, the consumption of batteries is the dominant factor in the environmental footprint of the product. For battery production, a total of 56.2kg of toxic emissions are produced in comparison to 46.4kg necessary for toy manufacturing. Additionally, the air pollutants associated with battery production is overall higher than that of toy manufacturing. A comparison of the SO2 and CO emissions between the two show that battery production has a 21% and 45% increase over toy manufacturing, respectively.

Due to the nature of battery production, inorganic chemical manufacturing is required. Inorganic chemical manufacturing contributes a significant portion of the total toxic emissions caused by battery production. With this in mind, a possible course of action for product improvement would be to decrease the amount of batteries consumed over the product life cycle.

Toxic Releases

The contributing sectors primarily to Toxic Releases for sector 33930 Doll, Toy and Game Manufacturing are:

• 325211 Plastics material and resin manufacturing
• 331112 Ferroalloy and related product manufacturing
• 325190 Other basic organic chemical manufacturing
• 325110 Petrochemical manufacturing

When factoring in the reliance on battery usage over the lifetime of the product, considerations must be made. The end-life status of the batteries is the main concern for our study. The corresponding sectors that contribute to sector 335912 Toxic Releases are:

• 325180 Other basic inorganic chemical manufacturing
• 326290 Other rubber product manufacturing
• 331492 Secondary processing of other nonferrous
• 325190 Other basic organic chemical manufacturing

Redesign

Redesign can be found at: Remote control tarantula redesign.