CUB CADET ZERO TURN LAWNMOWER REDESIGN

 
Cub Cadet Zero Radius Riding Lawnmower
Cub Cadet Zero Radius Riding Lawnmower

The original lawnmower

Comparative changes

PTO Switch Location
PTO Switch Location

PTO switch moved from below seat to next to seat.

Cub Cadet Zero Radius Riding Lawnmower
Cub Cadet Zero Radius Riding Lawnmower

The original lawnmower

 

Introduction:

In this project, my group (Luke Sturgeon and Zhihao Zhao) and I redesigned a riding lawnmower used at Luke’s family’s farm, the Cub Cadet Zero Radius model. The mower is two-wheel drive, self-propelled by a gasoline engine, and utilizes a zero-turn radius steering system, which allows the mower to turn without the unit moving forward first.


Front-End Analysis:

We began the project by analyzing the controls and displays of the mower, as well as considered the anthropometry and ergonomics of its users (handle and steering wheel size, seat height and adjustability, accessible controls, cab size). We also did a small literature review of past articles on lawnmower safety.

We then conducted a front end analysis, where we started brainstorming and coming up with a set of qualitative interview questions that we presented to Luke’s family in a focus group (when he went in person), asking about how the mower is used, special features, and any issues or concerns about the usage of the lawnmower. We then completed a task analysis where the members of the group walked us through how they start, run, shut down, and maintain the lawnmower. We also conducted an environmental analysis where we looked at the conditions the product was typically used in to inform our evaluation and redesign later. From the focus group we realized that they designed their garden around the mower’s width, as well as told us that foliage and branches tend to catch the throttle of the machine, randomly slowing it down. Older users also reported fatigue after using it for more than one hour.

Requirements:

  • Cuts grass evenly at varying heights

  • Comfortably ridden for 2+ hours

  • Adjusts to primary users’ dimensions

  • Provide easy means of maintenance

  • Allow meaningful monitoring of system

  • Intuitive use of controls (steering, stop, and go)

  • Haul yard trimmings up to 100 lbs

  • Safety features that prevent bodily and property harm

First Phase of Prototyping:

The second phase of the project involved the actual redesign of the mower. While the mower had strengths (control markings being embedded into the plastic, so that they can still be visible without wearing off, holes cut into flat surfaces of the machine to increase foot grip, preventing falls, easy-adjust blade deck design, and steering wheel adjustment), the mower also had many weaknesses, which were corrected in our final design.

As we made changes to the 3-D model of the lawnmower, we used an iterative design process and showed his family and our cohort the results and asked for feedback.

A major change to our design is that we changed the steering wheel into an intuitive zero-turn steering system using two handles/levers instead. The original way to activate zero turn steering using the steering wheel was unintuitive, so we redesigned the mower to have a forward/reverse function on each handle (moving the right handle forward would turn the body to the left), and holding a neutral position on the handles is the brake. These handles have adjusting knobs and levers for height and width adjustment. The grips on the handles were also designed with average grip span and hand length in mind, while the tilt and angles of the handles were redesigned with recommendations of handle tilt and rotation from a previous study conducted on commercial lawnmower handles.

     

Second Phase of Prototyping:

In our second phase of iterative design, an issue of operator visibility arose, where users could not see over the mower’s body. Our solution was to remove the bulkheads, controls, and displays, which occluded the visibility of all cutting edges, and moved them to more accessible places. For example, the gas level display was not optimal because it was out of the operator’s visual field (both peripheral and foveal), so we replaced it with a series of three, operator-facing, sawtooth shaped (to help mitigate dirt accumulation) lights at the footboard indicating fuel level. These lights change color depending on the gas remaining (green=full-1/2 capacity, yellow=1/2-1/4 capacity, red=less than 1/4 capacity). The PTO button and throttle were moved from a position under the seat on the floorboard, to the side of the seat, behind the steering handles to prevent awkward reaches or twists to make a non-emergency stop. This also prevents the problem of branches and foliage being driven over hitting the throttle unintentionally.


There were also many miscellaneous changes to the mower, including changing the blade drive method to reduce the chance of fire on the blade deck and to reduce yearly bearing maintenance, changing the seat adjustment to be more easily reached, and adding a basic suspension system for increased operator comfort while running over smaller, deep holes. We also included a ballast under the seat to lower the center of gravity to prevent tipping and increased the motor size to have more towing capacity.