RC rock crawler truck redesign

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Executive Summary

This stage of our project required our group to analyze opportunities for improvement. To identify our customer needs and suggest improvements we conducted a through analysis which included novice and professional user studies, a Value Opportunity Analysis and benchmarking against existing products.

Through our market research we identified that most consumers purchase the Wheely King for rock crawling, bashing, or rock crawling competitions. There was a general consensus between consumers that the Wheely King did not meet their desired needs. Consumers felt that the Wheely King needed extensive modifications to be a competition caliber crawler. In comparison to its competitors, the Wheely King is relatively cheaper, easier to maintain, assemble and disassemble. However it fails at one very important criterion, which is rock crawling. Major problems with the stock Wheely King faced by consumers include burned ESC, top heavy, too many cheap plastic parts, wrong tires and poor steering.

From our research and analysis, several components stuck out as parts that played a major role in the satisfaction of the stakeholder needs. Considering a single part for re-design did not seem enough to address the design problem and the needs of the consumer. Therefore, our group has decided to design a Rock Crawling kit that addresses all the major problems identified through our research. The kit will include parts such as link replacements, servo mount, differential locks, new chassis and a skid plate. From our pugh chart, we concluded that the remodeled kit, including all of the components listed, was the best design improvement because it offered the best solution to the most important needs of the stakeholders which include durability, rock crawling performance and ease of assembly and disassembly. We believe that the our product excels over our competitors because it not only addresses the most important needs highlighted by the consumers, but also targets all consumer segments.

Research and Observations

Design Problem

From our market research we identified that the primary reason users buy HPI’s Wheely King is because it is a low cost RC Truck that can be used as a Rock Crawler. However, since it is cheaper than most of its competitors, it fails to satisfy the desired need of the consumer which ranges from bashing, rock crawling for fun and rock crawling as a sport. We identified that the major problems with the Wheely King are its cheap plastic parts that are susceptible to failure, poor weight distribution that makes it difficult to rock crawl, lack of locked differential and inefficient placement of servo motor to obtain maximum traction. In order to understand design problems faced by every user, both novice user test data and expert user opinons were collected.

New User Study

For the novice research, our group set up a simple course that every participant was instructed to use. The course was 10 feet long and consisted of varying sized rocks as well as a slippery incline. The goal was to make it across the course without flipping the car or having to use reverse. Time was not a measured factor. Each participant was given 2 minutes before attempting the course to familiarize themselves with the car. After completing the course the participants were then asked to fill out a questionnaire so we could obtain feedback on the cars performance. Our findings are summarized below:

• The most common problem was the car tipping over. This happened mostly because the users were not familiar with rock climbing
• The second most common problem was the need to reverse because the car could not climb over bigger rocks. This suggests to us that the car needs to have a more flexible chassis in order to keep its balance when going over uneven surfaces.
• Lack of flexibility in suspension resulted in loss of traction
• Low weight at front end diminished steering ability

Expert User Study

For our professional research our group went to an indoor rock crawling facility located in Beaver Falls, Pennsylvania. We were invited by the owner of the hobby shop where we purchased our car. The facility was an empty warehouse that was rented out for the weekend. We spent two hours at the facility watching competitions and talking with numerous professionals. As we had previously thought, everyone in the facility knew of the HPI Wheely King and everyone was quick to offer their opinion of the car. It was the general consensus that it was a good base model to transform into a rock crawler, but had some distinct flaws. Everyone first mentioned its weight imbalance, saying that a car designed to do wheelies is not designed to crawl rocks or go up steep inclines. Second, its flexibility was mentioned, saying that it had decent flexibility for a stock model but needed more axle freedom in order to climb the larger rocks without flipping.

In addition to the physical research conducted, we posted a questionnaire (see appendix) on the RC rock crawling forums. We obtained about 11 responses from professionals and our findings are highlighted below:

• Average age of consumer: 35-45
• Reason for purchasing Wheely King: Rock crawling, bashing, formula off-road i.e rock crawling competitions
• Stock Wheely King did not meet the desired need of the consumer
• Major problems faced with Wheely King include burned ESC, top heavy, too many cheap plastic parts, wrong tires and poor steering
• Consumers felt the Wheely King needed extensive modifications to be a competition caliber crawler
• In comparison to its competitors, the Wheely King is easier to maintain, assemble and disassemble and is relatively cheaper however it is worse from a rock crawling perspective

Overall our research was very beneficial. We were able to identify the needs of both the amateur and the professional, giving us the advantage of designing an improvement kit that can be sold to a very diverse market. As well as being able to identify needs, our research provided us with professional advice that is now directing us to an improved product.

Value Opportunity Analysis

From our Value Opportunity Analysis (VOA), we identified that consumers want a product that is durable and fun. They would also like the Wheely King to have reliable mechanical and electronic components, can be set up independently i.e. without the help of someone else, is visually appealing, and safe.
Image:Rock crawler Voa.JPG


Stakeholder Needs

•Performance - steering, suspension flexibility, stability with tipping
•Ease of assembly
•Ease of disassembly
•Compatibility with other trucks and parts
•Maintenance - replacement or repair if necessary

•Ease of manufacturing - few components and easy machining
•Market compatibility

Design Concepts

Servo Mount

On the stock Wheely King, the servo is mounted to the chassis toward the top, behind the front shock tower. The steering power, is translated to the front differential through a five part linkage. The weight of the servo and linkage components is not necessary to have up top (poor effect on COG) when we can mount the servo elsewhere, lower on the truck. By mounting the servo directly above the steering rod, on the differential, we can lower the COG a great deal. Another disadvantage to having the servo connected through a linkage is that any deformation in the linkage components results in inaccurate steering. Many times in rock crawling, the steering system will have to overcome large load, such as when the trucks weight rests on the side of the front wheels. With the servo connected more directly through a one part linkage as opposed to a five part linkage, the steering system has greater strength. Reducing the part count is a good thing in this case as the added components can only introduce more modes of failure or weaken the steering system.

Redesigned Chassis

Many major component assemblies are attached to the chassis. The center gearbox and battery housing, for example, are two high-mass assemblies whose positions are dictated only by the anchor points to the chassis. By redesigning the chassis and moving these components around as we wish, we can lower the truck's COG without compromising ground clearance. The improved chassis can also facilitate the extension of the wheelbase, further increasing the vehicle's stability. Manufacturing the chassis from machined aluminum plate can be accomplished realistically with either manual milling for prototypes or CNC milling for large batch production. Aluminum has many advantages over plastic in this application. The increased strength of the metal allows much less material to be used while still increasing overall chassis rigidity.

Sway Links

In order to lengthen the wheelbase, the sway bars must be replaced as well. This could be accomplished with machined plate aluminum, but the alternative we'll more likely choose is to design a small adapter component that will allow us to use aluminum rod and ball-pivoting rod ends. These can be the same materials as will be used in the suspension links and steering components. In this case, increasing the part count makes sense because we can reduce the amount of machining required for our components; rod and rod ends will be much easier to implement.

Concept Evaluation

Using a Pugh chart, we were able to asses our design concepts in comparison with existing products. This also showed us the positive and negative points between each characteristic of each design choice. When evaluating each design, we took into account criteria that were important to the manufacturer, and more importanly, the consumer. These criteria are weighted in accordance with our groups opinion as to how important they should weigh in the selection of the proper design. The picture below is our Pugh chart comparing the different products. First seen is our benchmark product, the off-the-shelf Wheeley King. The next product compared is an existing kit provided by HPI made for our truck. This product it mainly plastic components with very few parts made out of durable materials. Next in the chart are our two desgin concepts. The second concpet varies from the first as it has a new chasis and skid plate. Our team then evaluated each of the concepts as if they were in use on the truck. From our evaluations, the chart shows that the our second design concept with the chasis and skid plate offer us the best solution, and therefore this concept will be the one we choose to investigate further.



After conducting a comprehensive market study and analysis we recommend that Initech implement the RC Rock Crawler Conversion Kit because the kit will allow Initech to not only target expert users, that make up most of the market, but also novice users who use the Wheely King to pass time. From our pugh chart, we concluded that the remodeled kit, including all of the components listed, was the best design improvement because it offered the best solution to the most important needs of the stakeholders which include durability, rock crawling performance and ease of assembly and disassembly while still being competitively priced.

Future Plan

After the concept generation and selection stage of the design process, it is important to have a structured time plan so that all tasks can be completed by their deadlines. This is especially important for the design concept which we have chosen because it will take a very long time to create CAD and SolidWorks drawings of our components as well as a fairly large lead time to machine all parts that need to be machined. Also, if something does not come out the way our group had hoped, we need additional scheduled time in order to troubleshoot our problems and re-evaluate what needs to be changed. Below is a Gantt chart that our group has created in order to stay on task and on schedule for the entirety of this project.

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Team Members

  • Mike Ricci: Research, Concept Design, Mechanic
  • Alex Timmons: Research, Executive Summary
  • Zahoor Rahimtoola: VOA, Pugh Chart, Market Analysis
  • Brad Henderson: Future Plans, Pugh Chart, Gantt Chart


  • Michalek, Jeremy. “Design for Manufacturing and Assembly.” Engineering Design II. Carnegie Mellon University.
  • Kalpakjian,Serope. "Manufacturing Processes for Engineering Materials (5th Edition)"
  • www.rccrawler.com
  • www.hpiracing.com


From New User Study

Image:Rc questionnaire.JPG

Posted on Forums

• Have you ever used the Wheely King 4x4 before?
• What age bracket do you fall under (specify age if you want)?
• Why did you buy the Wheely King? (Tick all that apply)
Racing | Rock Crawling | Fun | Annoying family members | Passing time | To perform wheelies | Other
• How does the Wheely King compare with other RC Rock Crawlers? (Rate the following based on the scale below)

1 (The best)
2 (Good)
3 (Average)
4 (Bad)
5 (The worst)

Cost | Racing Performance | Rock Crawling Performance | Speed | Maintenance | Assembly & Disassembly | Ease of Upgrade | Other
• What are the specifications of your original Wheely King?
• What modifications have you made to your car & how has that improved the performance?
• What disadvantages do you see with the original Wheely King?
• When you first used the Wheely King, what problems did you face? How did you resolve them?
• Does the Wheely King perform the function that you bought it to perform? (See Question 2)
• What design modifications would you suggest to improve the overall experience of your Wheely King?

Concept Brainstorming

1. reverse chassis to redistribute weight to front to improve rock crawling ability
2. lengthen wheelbase to increase ground clearance
3. fabricate aluminum sway bars
4. remove rear rod balance for flexibility
5. lock differentials
6. redesign chassis to reduce fasteners and improve handling
7. reverse tires for better traction
8. down gear for improved torque
9. re-fab steering components
10. solid driving axle
11. fabricate aluminum suspension links
12. redesign suspension links (tube shaped) to increase yield stress while maintaining factor of safety
13. Additional body mounts to change body on chassis (aesthetics)
14. better esc
15. mount servos on both front and rear axles for low cg
16. increase tire weight to lower cg
17. change shock spring
18. change shock fluid
19. upgrade motor
20. cast new body
21. convert to tank tracks
22. insert memory foam into tires
23. upgrade bearings
24. upgrade steering servo
25. add solenoid to front suspension for “jumping” onto obstacles/rocks
26. bug metal gears
27. rearrange cells in battery pack for better weight distribution
28. metal wheel rims for lower center of gravity
29. get metal drive shafts
30. increase cells in batter for longer lifespan
31. bend a tube chassis
32. dual motor
33. mount servo to differential: lower COM and less complicated steering linkage
34. build tube frame chassis
35. waterproof electronics
36. remount lower sway bars for increased ground clearance
37. mount servo above knuckle for greater ground clearance and stronger steering
38. increase servo arm length
39. add functional headlights (aesthetics)
40. add spare tire in bed (aesthetics)
41. repaint body for realism (aesthetics)
42. add roof rack (aesthetics)
43. upgrade tires for better tread grip
44. use sheet metal (~1/8 in)to redesign parts (easy manufacture)
45. add sheet metal skid plates
46. substitute delrin for aluminum in places where the weight would raise the COM
47. cast another larger, more proportional body (realism, aesthetics)
48. combine upper suspension links and battery mount into one part (also moves battery) to a more desirable location
49. add rear view mirrors (aesthetics)
50. incorporate skid plate into chassis redesign
51. add ballast in tires
52. design snap fastener body mount
53. make chassis solid plate
54. make chassis of a rigid non-metal (carbon fiber)
55. make suspension and steering components of carbon fiber tubing
56. attach skid plate to front diff for steering protection
57. bend a scale brush guard
58. design adapter to fit between diff and sway bar to allow sway bar to be made of rod and rod end like the suspension links (DFMA+ for us as conversion kit manufacturers)
59. make steering linkages from rod and rod ends (also DFMA+, maybe thinner rod though)
60. zip tie electronics cords to chassis/components to keep them out of the way
61. put additional holes on redesigned chassis to allow for adjustments and to work with a larger range of existing components on the market
62. integrate plastic "windshield" into body
63. change shock spring color for aesthetics
64. design a one piece chassis
65. make wheels larger than body so it can flip over and still maintain traction
66. give a full 180 degrees of rotation between front and rear axle
67. change truck to a ball that can just roll over obstacles
68. less fasteners
69. air freshener in cab
70. missiles
71. american flag
72. missiles AND american flag
73. convert to robotic "spider" legs instead of wheels
74. attached cup holder for beverage retrieval
75. plow or cow catcher mounted to front
76. increase scale and power to provide for sidewalk shoveling in winter
77. controller that is an actual steering wheel
78. "nitrous" button on controller for increased speed
79. change to three wheel ("omniwheel") design that allows travel in any direction
80. increase battery life
81. wheels with cleats
82. tires equipped with chains for better snow traction
83. convert to half track system (two front tires and tank tracks in the back)
84. make components from reused/recycled material (green machine)
85. put a remote camera in the truck to improve performance for rock crawling competitions
86. actuated arms to move obstacles from truck's path
87. launchable cable grabber to drag itself through obstacles
88. functional winch on the front
89. aesthetic muffler or exhaust system
90. novelty "la cuca racha" horn
91. carrying case/storage box
92. cleaning kit
93. oil slick squirter
94. actuated arms on the side so it can right itself if rolled
95. add mud flaps
96. ability to do burnouts
97. place to store antenna
98. adjustable antenna to cover different ranges
99. fixed antenna
100. carbon fiber body (aesthetics)

Existing Related Products

Wheely King + HPI conversion kit

Image:Rock crawler competitor Hpi.JPG

  • 2 1/4in longer wheelbase for better stability
  • Longest wheel base allowed by class rules
  • Diff Lock (Front and Rear) for increased traction
  • Front battery layout moves weight forward for better crawling stability
  • Additional body mounts allow fitment of all Savage bodies
  • Aluminum lower suspension links for extreme durability and good looks
  • High link suspension mount brackets for more ground clearance
  • New Steering servo mount repositions servo to allow battery in front of crawler
  • Optional 17mm hex hub included for fitment of 17mm hex hub wheels. (Savage wheels etc.)

Price: $220 + $80 (for kit) = $300

Losi 1/18th mini rock crawler

Image:Rock crawler competitor Losi.JPG

  • Metal Twin Vertical Plate (TVP) chassis design
  • Multi-link crawler suspension design
  • Heavy duty metal ring and pinion gears, axles and axle shafts
  • Gusseted drive cases for increased strength and durability
  • A true locked-out rear end design, no steering spindles
  • Heavy duty universals with slide-type outdrives and metal yolks
  • Alloy lower suspension links with captured ends
  • Extra long oil filled shocks, front and rear
  • Solid axles with optimized drive shaft angles allow for a freely-rotating driveline throughout the entire suspension travel
  • Telescoping slider driveshafts
  • 3-Gear center transmission with spool and slipper
  • 4WD with locked differentials
  • Ball bearings throughout
  • 1.9 Bead lock style wheels with 12mm wheel hexes
  • New electronic FWD/RWD rock crawling specific speed controller (ESC) with extra drag brake
  • High-torque rock crawler specific motor
  • Mini high-torque rock crawling servo
  • Tuber style body: Scale looks of the full-scale rock crawling machines; 3 colors to choose from: Red, Blue and Black
  • Features Mini-Rock Claw Tires for superior traction (modeled after the National Champion winning 1/10-scale Rock Claw 2.2 Tires)
  • Losi LSR3000 radio system featuring Spektrum™ 2.4GHz DSM® technology for crystal-free operation
  • 7.2V 1100mAh NiMH Battery and Charger
  • 4 AA batteries included for transmitter

Price: $320

Axial Rock Racer 1/10th RTR Rock Crawler

Image:Rock crawler competitor Axial.JPG

  • Complete ready to race/crawl out of the box
  • 4WD
  • 27T Electric Motor: Tear up the terrain in-door or out-doors. Easy Operation: No Tuning, No Fuel, No Loud Exhaust Noise. Just Plug'n'go!
  • 20T pinion paired with an 87T spur gear gives you a quick rock racer ratio, or install the included 14T pinion for a slower rock crawling ratio
  • True Beadlocks: No Messy Glue!
  • Hi-quality Composite Plastic and Metals
  • Durable (ESC) Electronic Speed Controller: Hi-quality durable forward and reverse speed controller
  • Hi-Torque Servo help hold your line when rock crawling
  • Solid Rear Axle lockouts improve ground clearance when crawling
  • Slipper Clutch: Reduces gear wobble for a more efficient drivetrain. Allows a motor to work more efficiently and greatly enhances the durability of the drivetrain
  • Aluminum Chassis plates with a molded nylon skid plate provide a solid and rigid chassis
  • Ultra compact and lightweight transmission
  • Open front diff for smaller turning radius, or install the included front locker for more traction when rock climbing!
  • Rear axle is locked for better traction
  • Full Ball bearings
  • Overall gear ratio range from 15:1 to 74:1
  • Transmission: 2.6:1; center mounted
  • Differentials: Front - gear differential; Rear - locked (spool)
  • Transmission: Single-speed
  • Tires: Axial 2.2 Rock Lizards
  • Wheels: Axial 2.2 8 Hole Beadlocks (Satin Chrome)
  • Suspension: 3 Link
  • Drive Shafts: Universal front and rear

Price: $ 475

Duratrax cliff climber 1/14th scale electric Rock Crawler

Image:Rock crawler competitor Duratrax.JPG

  • Twin 380 motors deliver high turn with low RPM, for massive torque to climb near-vertical inclines and clear the largest obstacles.
  • Oil-filled shocks are adjustable and come with aluminum caps.
  • True full-time 4-wheel drive. A solid spool locks the hardened steel axles. No diffs mean zero slippage, for maximum traction.
  • Gunmetal-colored anodized aluminum chassis sides.
  • Front and rear bumpers that won't hang up on obstacles.
  • 12 mm hex wheel mounting that's compatible with many other wheels.
  • Tires designed specifically for crawling. An extra-soft compound enhances traction, and the foam inserts mold to the tires and *rebound slowly.
  • The RTR comes with the radio, ESC and motors already installed, and the truck body is painted and trimmed in one of six colors.
  • The Prebuilt lets you use your radio and ESC, and its clear body allows for total paint customization.
  • Servos mounted on both the front and rear axles for low CG.
  • Servo savers on both steering servos.
  • Required Parts: 6-cell NiMH batteries, charger

Price: $360

Traxxas Stamplede VXL brushless Monster truck

Image:Rock crawler competitor Traxxas.JPG

  • 65+ mph top speed on 8000mAh 3S Lipo
  • Velineon Extreme Brushless Power System
  • Traxxas High Current Connector
  • Maxx Cable 12 gauge wire
  • Velineon 3500 brushless motor
  • Velineon VXL-3s fwd/rev/brake ESC
  • Precision high-torque digital steering servo
  • Steel internal transmission gears
  • New front steering spindles and rear hubs with 5x11mm rubber-sealed ball bearings
  • Precision metric hex hardware
  • Included 4-position adjustable wheelie bar
  • Veratile,pre-glued Talon 2.8
  • all-terrain tires"
  • Sinister black chrome All-Star 2.8wheels"

Price: $510

Hot Bodies Minizilla RTR Mini 4WD 1/18th Scale Monster Truck

Image:Rock crawler competitor Minizilla.JPG

  • Radio, ESC and steering servo included
  • 7.2v Battery & Wall Charger Included
  • Super Stock 370 motor provides great acceleration and high speeds
  • 4WD Shaft drive system
  • Long travel suspension for excellent handling
  • Full ball bearings provide longer battery life
  • Low-maintenance gear differentials
  • Wide stance for greater control
  • Battery slips inside a protective case
  • Stylish wheels and tires provide excellent traction
  • Includes 3 pinion gears
  • Painted and Trimmed Body Included

Price: $200

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