# DEWBOT VIII Wheel Friction Coefficient Testing

During November and December of 2011, friction coefficient testing was carried out on several different wheel types. These wheels included 4" HiGrip wheels, 4" Plaction wheels with blue nitrile tread, Rover wheels, Omni wheels, and 8" FIRST wheels with rubber tread.

## Procedure

1. Sets of 4 wheels were clamped into the wheel wells of DEWBOT V's frame and fixed in place.

2. The frame, with wheels, was then placed on an inclined carpeted surface along with an angle/pitch measure.

3. The surface's incline was increased gradually until the frame began to slip down the surface, at which point the surface's incline was measured with the angle measure. This was repeated for 3 trials to eliminate error.

4. After the completion of Step 3, a polycarbonate inclined surface was substituted for the carpeted one in order to test the wheels on different types of surfaces.

5. The frame was then rotated 90 degrees and steps 1-4 were repeated with the new orientation.

6. Steps 1-5 were then repeated for each new set of wheels.

## Calculations

In order to find the friction coefficients, the tangent of the angle of incline had to be measured for each test. This was done using Microsoft Office Excel. Below is a sample, blank, spreadsheet for these tests:

Wheel Friction Coefficients 1: New Wheels

___________________________Polycarb ______________ Carpet __________________________

Trial 1: Orientation 1

Trial 2: Orientation 1

Trial 3: Orientation 1

Averages

Coefficients

Trial 1: Orientation 2

Trial 2: Orientation 2

Trial 3: Orientation 2

Averages

Coefficients

## Results

1: 4" HiGrip Wheels

Orientation 1: Carpet Coefficient: 1.755559014

Orientation 2: Carpet Coefficient: 1.709011649

Orientation 1: Polycarb Coefficient: 0.954508314

Orientation 2: Polycarb Coefficient: 0.700207538

2: Plaction Wheels with Blue Nitrile Tread

Orientation 1: Carpet Coefficient: 1.829062775

Orientation 2: Carpet Coefficient: 1.343233111

Orientation 1: Polycarb Coefficient: 0.487732589

Orientation 2: Polycarb Coefficient: 0.502218876

3: Omni Wheels

Orientation 1: Carpet Coefficient: 0.357395613

Orientation 2: Carpet Coefficient: 0.152426157

Orientation 1: Polycarb Coefficient: 0.218644772

Orientation 2: Polycarb Coefficient: 0.058243367

4: Rover Wheels

Orientation 1: Carpet Coefficient: 0.237004354

Orientation 2: Carpet Coefficient: 0.249328003

Orientation 1: Polycarb Coefficient: 0.116883237

Orientation 2: Polycarb Coefficient: 0.128694322

5: FIRST Wheels with Rubber Tread

Orientation 1: Carpet Coefficient: 0.324919696

Orientation 2: Carpet Coefficient: 0.546728091

Orientation 1: Polycarb Coefficient: 0.182331854

Orientation 2: Polycarb Coefficient: 0.261723367

## Conclusions

Although the Plaction wheels had a slightly higher friction coefficient for Orientation 1 on carpet than the HiGrip, the HiGrip wheels not only greatly outstripped the other three sets of wheels in every category but also had higher coefficients than the Plaction wheels in the other three sets of trials.

## Links

Spreadsheet: File:Friction Coefficient Spreadsheet.pdf

Presentation: File:Results of the Friction Coefficient Experiment.pdf