Weed whacker redesign

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Executive Summary

For this phase of our design project, we focused on studying user and shopper interactions with weed whackers and performing market research of current state of the art designs for weed whackers. Along with these studies, we also came up with an expansive list of ideas for innovations in the weed whacker design. This brainstorming process was basically just a good way for us to get any and all ideas out on the table, no matter how illogical they seemed, in order to encourage innovation and "out-of-the-box" thinking. From this list of ideas, we can pick and choose good elements from different ideas and combine them into a more realistic concept.

From these user studies and research findings, we were able to determine the important design factors of a weed whacker that we felt affected users the most. We were then able to come up with a few different concept designs, each one focusing on improving upon one or two of our determined design factors. Utilizing a Pugh Chart, we then compared and contrasted our ideas with the current weed whacker design we analyzed in Phase 1 of our project. By examining how each design accomplishes our chosen design factors, we were able to get a better idea of which design would be optimal to pursue. This idea will be brought into the prototype 1 phase.

We have an idea of which design we would like to prototype; our plan for the next few days is to run some more detailed calculations and construct some initial prototypes in order to ultimately decide if we would like to pursue this design and bring it into the prototype 1 phase of the project.

User Study

Research and Observations


After asking many potential customers who were looking at weed whackers we found that the main concerns of users were:

  • Cost
  • Maintenance
  • Safety
  • Ease of use

Other concerns included:

  • Weight
  • Noise
  • Vibration
  • Power

We noticed that many of them assumed characteristics of the design.

Gas powered:

  • High power
  • Noisy
  • Vibrates
  • Hot

Electric powered:

  • Not enough power
  • Low battery life


After observing a few weed whacker users, we asked them what their main complaints and difficulties of using their particular weed whacker.

Gas Powered:

Awkward holding position: The design of the weed whacker forces the user to hold it in a position that has been reported to be very awkward to the user. The right hand holds the handle where the trigger is located and the right arm is what holds most of the weed whacker's weight. The left hand is located about ten inches down shaft of the trigger hand, and The right arm is mostly kept bent and the left arm mostly kept straight throughout the usage in order to keep the weed whacker angled downwards toward the grass. After a short time of use, the user's right arm would get tired and straighten, thus making the weed whacker hard to maintain over grass.

Weight Distribution: Users complained about the weed whacker being heavy. Also they didn't like how most of the weight was located in the back where the engine is. Users found it unnatural to maneuver, and some muscles, such as biceps and back muscles, were being over used.

Vibrations: The constant vibration of the 2 stroke engine proved to be quite an issue for users. The engine is constantly erratically vibrating while idle and while throttled, which added to the inconvenience of holding the weed whacker for a prolonged amount of time in the holding position. Also, when the trigger is pulled to throttle the engine, the sudden clockwise rotation of the axle creates an opposite reaction of the weed whacker being suddenly thrust in a counter clockwise moment. This twisting of the weed whacker seemed to be small issue with some users.


Awkward holding position: Similar to the gas powered weed whacker, the hand positions are awkward making the left arm completely extend forward and the right arm bent to the user's side. We observed this position made it difficult to sweep the device from side to side.

Weight Distribution: The electric weed whacker design had most of the weight too far forward as the motor was located at the head of the weed whacker. Although it is lighter, users experience that more effort is needed to hold the weight. Over time we observed the user resting the end of the weed whacker on the ground to rest their arms.

Power supply: The particular design used a power cord to supply power. This allowed the motor to spin at optimal speeds so we did not observe a lack of power. Vibration and noise did not seem to be a problem either. However the user constantly pulled and relocated the power cord while usage. This problem was not reported as a problem when asked. We observed that the cord could cause major injury if cut or caught on the user.

Conclusions from User Study

From our user shopping research, we found that appearance made a larger impact than the specifications listed on the box. In order to keep potential customers from overlooking our product, we must explicitly show that it is a weed whacker, and will provide the services needed. We also found that users had a preconceived notion regarding the type of engine which made them overlook the power provided.

Because of this, we decided to keep the string as the blade. The type of power source would determine the main focus of design. However, because battery power and life are extremely difficult to improve, we decided to keep an engine.

From the user study, we were able to define the major areas of improvement. Because we are continuing to use a engine as the power source, our main concerns are:

  • Awkward holding position
  • Weight
    • Weight distribution
  • Vibrations
  • Cost
  • Safety
  • Intuitive use

Existing Designs

Currently there are an exorbitant amounts of weed whacker/string trimmer designs. Most of which regard attachments, blades, wires, or the wire feeding mechanism.

Regarding the entire apparatus, we found a few existing designs that focus on usability rather than novelty or alternatives.

Weed Whacker/Blower/Vacuum

Out of the many novelty patents we found this particular design vaguely relates to one of our concepts. We considered creating a vacuum or blower combination with the weed whacker, but we decided that its usefulness is very limited. Instead we shifted focus on redesigning the weed whacker to be easier to use.

  • Has multiple uses


  • Higher weight/inertia
  • Same handling problems as basic weed whacker

Backpack Weed Whacker

Using a torsional cable, this design can put the majority of the weight on the users back. This is where some of our ideas were formed. However, the direct drive shaft and bevel gear casing are still required adding a substantial weight. We thought that this concept was a great idea, but changed the method of power transfer to pneumatics for reduced weight, and focused on the way the user handles the cutting end.

  • Relieves majority of the weight from arms
  • Lowers inertia


  • Same awkward handling problems as basic weed whacker
  • Weight is shifted too far forward requiring 2 hands or a large force on user's wrist

Height Adjustable Wheeled Design

Using wheels can alleviate the weight issues, as well as keeping a uniform cut length. However the wheels will add friction and inertia making the apparatus more difficult to manuever. The wing nuts require too much adjusting to get the angle and height to desired specifications. Mimics a lawn mower by removing many functions of a weed whacker. We looked at this design, and thought that using wheels may be another way to decrease weight and allow the user to handle the weed whacker more efficiently.

  • Less weight on user
  • Uniform length


  • Same awkward handling problems as basic weed whacker
  • Heavier
  • Too many parts
  • Requires too much adjusting
  • Can't reach hard to reach places
  • Can't edge trim

Note: Other wheeled designs exist, however they all have a similar problem of restricting side to side motion.

Other Design Options


  • Better cutting ability


  • Image
  • Safety
  • Cost/maintenance
  • Loss of edge trimming

Electric Motor

  • Better for the environment


  • Power
  • Battery costs
  • Battery life


  • No battery
  • Much higher power output than on battery


  • Requires outlet
  • Cord gets in way

Motor attached to cutting head

  • Better power transfer


  • Much higher inertia

Concept Designs

Concept 1

This design locates the majority of the weight on the user's back. Doing this lowers the arm strength needed to manuever the cutting end by lowering the weight held, and the inertia.

To improve handling we replaced the drive shaft, bevel gears, bearings, and bevel gear housing with a pneumatic hose to reduce weight and inertia. We also redesigned the handle. Using 2 straps onto the forearm, will alleviate the forces on the user's wrist and elbow. This will also allow the user to manuever the cutting end more intuitively and remove the two hand requirement that current designs implement.

Ease of use would be greatly improved with this design compared to the existing designs on the market. Many of the existing designs overlook the awkward positioning of the handles and weight, and this particular design attempts to solve them. Vibrations will still exist, but they will no longer impede the user's ability to handle the device.

Manufacturing would be similar to the original device, lowering part count, but adding complexity.

Maintenance would be easier, as grease is no longer needed for the gear housing or axles.

Other features that are in the process of acceptance:

  • Adjustable shield/length
  • Exhaust of pneumatics as blower/hover
  • Auto-kill switch if arm strap falls loose

Concept 2

This design removes the majority of the weight that is applied to the user. Doing this allows the user to have more control over the cutting end. However, dragging the engine around on the ground presents many potential problems. Tipping, catching, and interference can all cause potential safety issues.

To improve handling we replaced the drive shaft, bevel gears, bearings, and bevel gear housing with a pneumatic hose to reduce weight and inertia. Without all the weight, handling the cutting end would be easy and require little force.

Compared to existing designs, this is better for weight and handling, but worse for cost and potentially safety.

Manufacturing would be more difficult, as there are more parts, and is slightly more complex as the original design.

Maintenance would be easier, as grease is no longer needed for the gear housing or axles.

Other features that are in the process of acceptance:

  • Adjustable shield/length
  • Exhaust of pneumatics as blower/hover

Concept 3

This design attempts to put all the weight of the weed whacker on the ground. Doing this lowers the arm strength needed, however this design keeps the inertia high potentially making handling difficult for the user. Having two wheels will let the user control the pitch and height of the cut, and letting the wheels free rotate will let the user sweep side to side. The increased inertia and the friction of the wheels will probably cause the weed whacker to be difficult to handle.

Compared to the existing design of a wheeled weed whacker, this concept can manuever better, and can be swept left and right allowing a much greater range of motion.

Manufacturing would be just as easy as the original device.

Maintenance would be slightly harder as we are adding a feature that may fail.

Other features that are in the process of acceptance:

  • Adjustable shield/length

Concept Evaluation

Pugh Chart Analysis

In order to get an idea of how our each of our design concepts compare to the current model that we are trying to improve, we have used a Pugh Chart. A Pugh Chart, or design selection matrix is a useful tool for comparing several design concepts against each other. The key component is to compare several qualities of different concepts against a currently existing design, notated as the datum. This chart allows us to benchmark our concepts against the datum using an established set of criteria. For our Pugh analysis, we determined our benchmarking factors to be:

  • Handling
  • Vibration
  • Weight
  • Affordability
  • Safety
  • Ease of Use

We gave each of these factor a weight, based on how important we felt they were. For instance, we gave Handling and Ease of Use a weight of 3 since we determined these to be most important to improve upon for users. Weight, Safety, and Affordability have a weight of 2, and Vibration has a weight of 1.

Pugh Chart

+ Better
++ Much Better
- Worse
-- Much Worse
Description Standard Weed Whacker Concept 1 Concept 2 Concept 3
Criteria Weight Datum Design 1 Design 2 Design 3
Handling 3 0 ++ + +
Vibration 1 0 + + 0
Weight 2 0 0 + +
Affordability 1 0 - - -
Safety 4 0 0 - 0
Ease Of Use 3 0 + + 0
+ 0 10 9 5
- 0 2 6 5
Net Score 0 8 3 0

Appendix A: Brainstorming Ideas

Weed whacker head

  • Blades instead of wire
  • Plastic Blades
  • Heavier wire
  • Metal wire
  • Non-circular wire (star cross-section wire)
  • Weed “vacuum”
  • Opposing rotation whacker heads
  • Full shield (360 degrees)
  • Adjustable shield
  • Clear shield
  • Automatic line feed
  • Heavier shield
  • Disk shield located higher on shaft
  • Laser cutting
  • Scissor
  • Heat generating blades
  • Adjustable string length
  • Adjustable angle of attack
  • Height reference attached to whacker head to ensure consistent height of grass

Shaft/axle/power transfer

  • Length adjustable
  • Telescoping shaft
  • Hula hoop weed whacker
  • Rotatable shaft
  • Clear plastic shaft
  • Angled shaft
  • Bendable "snake"
  • U shaped weed whacker
  • Locking positions
  • Torsion cable
  • Hydraulic
  • Pneumatic
  • Electric cables
  • Simple Electric Power Switch(better usability)
  • More gears to provide more speed


  • Clamping handle
  • Smaller handle
  • Ergonomic trigger
  • Button or slide instead of trigger
  • Grip trigger
  • Shoulder strap
  • Strap to arm
  • Shoulder mounted weed whacker
  • Arm attachment weed whacker
  • Split weed whacker (dual wielding)
  • Back-Pack like straps
  • Luggage like straps and wheels
  • Push handle forward or backward will angle whacker head forward or backward
  • Button on handle to feed wire

Power Source

  • 4 stroke engine
  • Self-starting engine (no pull cord)
  • Electric motor
  • Power source closer to head of weed whacker
  • Back pack style power source
  • Solar powered
  • Hydrogen powered
  • User powered
  • Corded
  • Hybrid powered


  • Built in safety goggles
  • Safety goggle compartment
  • Safety gloves
  • Safety glove compartment
  • Safety boots


  • Night light
  • Vacuum attached to whacker
  • Blower attached to whacker
  • Wheel on bottom
  • Plastic whacker
  • Tripod whacker
  • Robotic
  • Remote controlled
  • Auto kill-switch
  • Attachments for other lawn care
    • Leaf Blower
    • Mulcher
    • Spray gun
    • Hedge trimmer
  • Hovering weed whacker
  • Magnetic weed whacker
  • Collapsible for easy storage
  • HUD for weed whacker properties
    • Display of amount of the gasoline left
    • Display of amount of the co2 emission
    • Display of amount of the oil
    • Display of the how many hours the fuel will last
  • Pager
  • Intercom
  • Mp3 player
  • Radio
  • Beverage holder
  • A GOAT
  • Advanced mechanics to reduce the sound of the engine
  • Holes in the materials
  • Collapsible for different shape and usage
  • Add key for security
  • Aesthetically pleasing design
  • Two weed whackers at the shoes
  • Use of electric shock to cut the weeds
  • Engine-less device that is pushed and rolled to cut the weeds
  • Contain the co2 by putting co2 absorbing chemicals or bags

Current Trend in Weed Whacker

Fifteen years ago, first metal weed whackers were sold. It was highly dangerous and bystanders were told to stay 30 feet away. The major danger comes when blade get caught up in the thick brush, and cause a "Kick Back", throwing all the energy stored in the blade back to pole. That can cut the head and leg muscle. In early 1998, when high school football star had started the gasoline engine of his weed whacker, plastic hub broke. And flying metals struck his legs. Other blade designs that has been released for weed whacker has not been safe or reliable. And therefore, current trends of the weed whacker is using the plastic strings. Consumer Product Safety Act often realize that the blade based weed whacker contains a defect which could create a substantial hazard or unreasonable risk of injury.

Nowdays, manufactures produce weed whackers with strings. One of the problems that weed whackers have is the string breakage. The term whiplash could be applied here, when the elastic limit is exceeded at a sharp bend in the string, resulting in the initiation of fracture. Care in operation can minimize this kind of breakage.

Pollution from gas-powered equipment is a significant source of air possition, and U.S government limit emission from small engines. However Electric model produce no emissions.

Also the amount of the household that actually has this product is very few. Only about 2 percent of the population has weed whacker.

Future Plan


Member Contribution

Wesley Chu

  • User Studies
    • Usage Study
    • Conclusions
  • Existing Patent Research
  • Concept Design
  • Brainstorming

Mike Menchaca

  • Executive Summary
  • User Studies
    • Shopping Research
  • Existing Designs Research
  • Concept Design
    • Concept Art
  • Pugh Chart
  • Brainstorming

Tim Andersen

  • Existing Designs Research
  • Brainstorming

Koji Ito

  • Current Trend in Weed Whacker
  • Gantt Chart
  • Brainstorming
  • Shopping
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