1

Shigley Hauler EME 150B Final Report

Team Castor

March 20, 2014

Sean Raley

Josh Aguilar

Rocco Hollaway

Zachary March

Bryce Yee

2

Table of Contents

1. Introduction ............................................................................................................................. 3

2. Analysis ................................................................................................................................... 4

3. Figures ..................................................................................................................................... 6

4. Results ................................................................................................................................... 10

5. Discussion .............................................................................................................................. 10

6. Conclusion ............................................................................................................................. 11

7. Poem ...................................................................................................................................... 12

3

1. Introduction

The purpose of the project was to exercise our mechanical ingenuity through design, analysis,

fabrication, and testing of a gearbox. Competing teams were provided with two sets of nylon

spur gears and a Mabuchi RE280 DC electric motor to be powered by two AA batteries. Teams

were then tasked with designing and manufacturing a gear train system utilizing the provided

materials. However, the provided materials alone would not be enough requiring the acquisition

of other resources to bring the design to fruition. The Shigley Hauler, as it’s called, was to haul a

number of “Shigley’s Mechanical Engineering Design” books up various pre-determined

inclined slopes. To accomplish this, a gearbox and accompanying cart were designed and built in

the EFL throughout the quarter.

A competition was held at the end of the quarter where the teams competed to move the

Shigley’s up the incline provided. The hauler had to move a number of books up a pre-

determined angled incline from a stand-still. Required runs included a single book at 20 degrees,

two books at 30 degrees, four books at 40 degrees, and five books at 60 degrees! Teams were

scored based on the time to complete each run. Of the nine teams that completed all four events,

team Castor placed seventh.

To exercise and demonstrate the well-roundedness of the engineers produced at UC Davis, a

great poetry recitation was held the day before the official Shigley Hauler competition. This not

only displayed the great talents of the engineers, but provided theme songs and an increase in

morale for the competition the following day. Team Castor pulled out all of the stops by

performing a Mission Impossible theme song trombone and tuba duet accompanied by matching

poem, presented later in this report.

4

2. Analysis

For this project, 10 nylon spur gears were provided. Two gears each of ten, twenty, thirty, forty

and fifty tooth gears. After some quick calculations, it became apparent that the highest gear

reduction that could be achieved with the provided set of gears was 100:1. This final ratio could

be achieved several ways, but after additional calculations that can be seen in Figure 3, the team

decided to run a series of compound ratios with three output shafts at three different ratios. The

first ratio was a 5:1 using a 10 tooth gear attached to the motor output shaft driving a 50 tooth on

an idler shaft. The 50 tooth gear was attached to the same shaft as another 10 tooth gear which

drove another 50 tooth gear on the first output shaft at the same 5:1 ratio. The first output shaft

thus had a 5 * 5 = 25:1 reduction ratio with respect to the motor output. Continuing on, a 20

tooth gear on the first output shaft meshed with a 40 tooth gear on the second output shaft

resulting in a 2 * 25 = 50:1 reduction ratio. And last but not least, the same 2:1 ratio was used

between the second and third output shafts with 20 and 40 tooth gears again to achieve the final

output of 100:1. This sequencing of the gears was strategically chosen so that the small 10 tooth

gears were placed at the beginning of the compound sequence where the forces between the

gears were the least. This also allowed the use of a smaller diameter shaft size where the 10 tooth

gear was positioned, reducing the amount of boring necessary to mount the gear while still

maintaining structural integrity of the gear.

Team Castor’s hauler was designed to be small, light, cheap and easy to manufacture. To obtain

these goals, the typical aluminum plating was scrapped in favor of lighter and cheaper plastic

plating. Taking into account the weight of the required Shigley book loads, it became apparent

that a strong plastic that was also machineable able was necessary. Through some online

research, the team ultimately decided on Delrin as the material of choice. Not only was Delrin

very strong and easily machinable, but it was also cheap and had a sleek shiny black finish. An

added bonus with using Delrin was its low coefficient of friction properties, allowing it to be

used as bearing material. Since Team Castor was operating on the mantra “keep it simple”, we

opted to not use any roller bearings. Instead we rolled on plastic plating.

One square foot of ⅛” Delrin Sheet was purchased for this project. This was more than adequate

material intended to provided extra in case of manufacture errors. Three 4” squares were cut out

to form the main structure and set up parallel to form a 4”x4”x4” cube. The gear train was placed

between the middle and left plates, and between the right and middle plates were the replaceable

delrin spools. The delrin cube was then attached to a slightly larger aluminum plate using

aluminum angle pieces. Although the aluminum plate was light weight, it was available for free

and formed a strong and stable platform which was used to mount the hauler to the top of the

incline.

One major strength concerns for the hauler was the bending of the shafts. The sideplates

experienced no bending loads, which typically produce the largest stresses. This is why a side

plate that was thinner and weaker than many common metals used by the competition was

chosen. The supporting shafts for the gears and spools experience both bending and torsional

stresses. To withstand these stresses we chose steel for our shafts. The size of our shafts were

constrained by the size of the gears riding on them, specifically the ten toothed gear. The first

shaft was downsized to ⅛” because it was only a 5 fold increase over the motors torque and had

5

a small gear on it. The following three shafts the 25:1, 50:1, and 100:1 gear reductions were

chosen to be 3/16”. This shaft diameter was chosen because it fit in all of the gears with only a

slight bore to the gears necessary, and would only experience a slight deflection under high

loads. The calculation is shown in Figure 2.

A dynamic analysis was used to select spool sizes. A design with removable spools was chosen

so that the design could be perfected in real world conditions. Although the output shaft speeds

were limited to fixed numbers, a variable spool size on the driven shafts allowed for a range of

possible final torque multiplication. The excel spreadsheet (Figure 3) below shows analysis with

what we believed, before testing, to be the best spool sizes. A desirable spool would be large

enough to provide a decent line speed, yet small enough that enough torque would be provided to

achieve that line speed. Both friction and the time that it would take the motor to achieve the

predicted steady-state speed were neglected in this analysis. Although we expected times slightly

slower than the predicted times, we were prepared for the unexpected. Our strategy for this was

to machine a variety of spool sizes that would be easily replaceable on any of the final three

shafts.

6

3. Figures

Figure 1: Calculations for gear spacing to ensure the gears are properly placed relative to one another in gear train.

7

Figure 2: Simple strength analysis calculation to determine the approximate deflection of the 3/16” diameter A36

Steel shafts. The analysis was performed with more than the maximum possible load that would encountered during

operation.

8

Figure 3: Excel spreadsheet showing ideal and final gear train calculations. It was

formulated to allow for adjustability of the spools sizes at the various runs that would be

required in the competition.

9

Figure 4: A Solidworks model of the Shigley Hauler full assembly.

Figure 5: A Solidworks model of the Shigley Hauler cart and Shigley books.

10

4. Results

Middle of the pack! Woohoo!

Overall, team Castor placed 7th out of the 9 teams that completed all four events based on

combined total time. There were 15 teams total in the competition.

5. Discussion

The overarching lesson we learned from this project was: don’t design to constraints that don’t

exist. We did a lot of things very well, and some of them worked out for us; but some other

decisions were not necessarily the best for reaching our performance goals in the Hauler

Competition. For instance, one decision we made early on was to build the gearbox as compact

and lightweight as possible. While this would be desirable in many applications (such as a

lightweight vehicle, especially an airborne vehicle), it was completely unnecessary for us. To

achieve this goal, we used thin Delrin plates to support the gear shafts. Though the material did

allow for quick machining, it posed other problems we did not anticipate. The plating flexed in

11

the vice during machining, which made drilling precision holes a challenge. Yield strength was a

major source of concern as well, but the Delrin held up very well during competition.

Because we used Delrin for the plates (a known low load bearing material), we also decided

early on not to use bearings. We were well aware that this was a bold move since the use of

bearings seems to be the standard throughout the years of Shigley Haulers. However, Delrin is a

bearing material, so we ran with it. Unfortunately, in the week before the event, our Hauler was

not performing even close to the level we desired. The only plausible reason we could come up

with for the huge disparity between theoretical performance and actual results was friction

between the Delrin plates and steel shafts. A potential solution to this would have been polishing

the holes in the plates as well as the shafts at the points of contact. In fact, we probably should

have done that in the initial round of machining. This solution did not occur to us, so we

panicked and installed bearings on the shaft that would undergo the highest load (5 Shigley’s at

60 degrees). As it turned out, our best run was when the end bearing slipped out of the plate,

causing the spool to become a cantilever! Luckily, our shafts had a high factor of safety, and a

disaster was averted. Clearly, our bearings were not installed as well as they should have been.

This brings us to another lesson: never rush a machining job!! In the interest of time, we

attempted to perform the hole expansions for the bearings using a drill press. One of the plates

came out fine, but on the other one the bearing hole ended up about a quarter inch off. Because

of this, we had to completely remake that plate. When making the original plates, the entire

process was carried out with all three plates clamped together, allowing very precise hole

placement. Making a new plate separately proved very difficult, and though all the shafts ended

up fitting through the holes, the precision was not nearly as high as it had been before, which

definitely caused some friction on the shafts. A lot of time was wasted when we could have taken

a little extra time to find a way to machine the part on the mill without it flexing or flying out of

the vice.

6. Conclusion

Despite some risks and missteps, a few last-minute tweaks in combination with some good initial

design decisions allowed our Hauler to rise to the occasion on competition day (pun intended).

Our JB Weld “hubs” held together, our gears aligned properly, and the Hauler looked pretty cool

while doing its job! Given the chance, there are definitely some things we would do differently;

but as it stands, we are all proud of our compact accomplishment.

12

7. Poem

A tuba and trombone duet to the tune of the Mission Impossible theme song.

Shigley hauler, full of gears.

Shigley hauler, full of fears.

Will it bend?

Will it break?

Undoing all we’ve worked to make?

Not content with block aluminum,

We’ve pushed materials to the minimum.

Hoping that the plastic plating

Won’t cause lockups, shearing, grating.

Don’t be stupid, keep it simple!

Every detail, to the spindle.

Who needs bearings?

Not team Castor!

Who needs gear hubs?

Still not Castor!

Se we put all our faith in this little black cube,

And in Farouki, who says “Don’t use lube!’

We tie down our Shigley’s with fishing line tether

Then all cross our fingers, and hope it stays together!