EZ-Load Pneumatic Trailer

Case Born Advisor: Dr. Junkun Ma

ET 494 – Senior Design II Final Report May 8, 2015

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TABLE OF CONTENTS:

Abstract ………………………………………………………………………….……..…..………… 2

Introduction …………………………………………………………………….…………………… 2

Objectives ……………………………………………….………………………...………………… 2

Final Design ……………………….……………………………………………..………….……… 3

Overall …………………….…….……………………………….………………….……… 3

Trailing Arm Components ……………………………..……….………….……… 4

Calculations …………………….…….……………….…….………………….……… 6

Pneumatic/Electric System …………..….………………..….………….……… 8

Fabrication ……………………………………………………………………………… 9

Wireless Monitoring …………………………………………………………..…… 10

Timeline …………………………………………………………………………………...………… 13

Intellectual property created, made, or originated by Case Born shall be the sole and exclusive property of Case Born, except as he may voluntarily choose to

transfer such property, in full, or in part. PATENT PENDING - 62111635

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ABSTRACT

The focus of this project is to design and construct a utility trailer with a height adjustable main

deck that is easier and more convenient to load and unload for the end user and is also safer to travel

with. The product consists of a utility trailer that uses no ramps for the loading process and eliminates

the fear that is experienced when riding utility equipment or motorcycles up a ramp (fear of heights).

The main deck of the trailer will lower to the ground when the operator wants to load or unload the

trailer making the process easier. This trailer will operate on a fully pneumatic system that will all be

contained within itself. Once the trailer is loaded, it will be set to a ride height that will match that of the

hitch of the tow vehicle. Matching the height of the trailer to the hitch will provide for a level load that

will not cause vehicle sway or loss of traction during heavy braking, strong winds, or turning.

INTRODUCTION

To achieve the design goal of this project, a pneumatic trailing arm system will be incorporated

in a trailer that has a main deck that will lower and rest on the ground. This will allow any equipment,

four-wheeler, or motorcycle to be driven straight onto the trailer with no ramps and without losing foot

contact with the ground.

By using air bags to raise and lower the deck of the trailer, the trailer will be able to adapt to any

tow vehicle. Since the bags will be inflated to a level deck position, the trailer will stay level with the

horizon while in motion. This will eliminate the need for drop hitches and provide for a safer trailer.

Because the trailer will remain horizontal at all times, the trailer will not want to sway or push the tow

vehicle up or down when the tow vehicle applies the brakes.

FIGURE 1: Improper towing conditions

OBJECTIVES

The trailer frame will need to be compact, lightweight, and have a slim profile. This will ensure

that the trailer deck can be as low as possible to the ground, yet still have a high capacity rate (around

2,000 lbs). To ensure that this unit is versatile and easy to use on any tow vehicle, it will have a

complete onboard system. This includes air compressor, air tank, moisture trap, electric air valves,

properly rated air bags, pressure switches, and all safety equipment. A monitoring system that can be

mounted in the vehicle can also be produced that allows the driver to keep an eye on the trailer system

at all times (tank pressure, bag pressure, compressor status, etc.).

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FINAL DESIGNS

OVERALL

The final trailer dimensions have been set and the bed of the trailer is 5’-8” by 8’. This will allow

two full size motorcycle cruisers, ATVs, UTVs, or other items to be loaded on to the trailer easily. The

main trailer frame will be constructed with 3.25” by 1.50” c-channel. Internal bracing will be added with

standard u-channel steel.

While setting up the trailer layout, it was deemed unsafe for the deck to have a max height over

17 inches when loaded. This would create a huge amount of weight over the center of gravity and the

top of the tires. This would cause the trailer to become top heavy and have a tendency to roll over.

FIGURE 2: Original Maximum Ride Height

To overcome this, the final design will have a max deck height of 17 inches. In order to have the trailer

still adaptable to higher truck hitches, a 3in drop tongue will be used. This will lower the trailer 3inches

from the point of contact, keeping the center of gravity low. To further help reduce the body roll due to

a high load and while turning, each air bag will have its own set of fill and dump electric air valves. This

will separate each air bag and not allow the air to transfer from one to another.

FIGURE 3: New Maximum Ride Height

This trailer has a rough estimated weight of 600 lbs. 3,500lb components have been used which

gives the trailer a total carrying capacity of 2,900lbs. Through investigation, it has be found that

Louisiana requires all trailers with a total weight of 3,000 pounds or greater to have trailer brake;

therefore, trailer brake components have been ordered and implemented into this design.

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TRAILING ARM COMPONENTS

For the trailing arm, a cantilever system is used for the lifting mechanism. This will allow for

more lift to be achieved out of the airbag then if the bag was on the trailing arm itself. Doing this also

allows for some adjusting to be done by the end user for optimal ride height for a particular tow vehicle.

The trailing arm is made from one piece of machined rectangular tube with two off the self spindles

welded to each end and some bracing added for strength. The cantilever arm is laser cut from flat stock.

All bushings will be purchased machined 2” OD pipe with nylon inserts. The main bearing housing on the

frame for the trailing arm will be a standard trailer hub.

FIGURE 4: Suspension Setup Components

Initially, the airbag mounting plate was going to be a piece of flat sheet metal welded to the end

of the trailing arms. By doing this, the air bag will experience a lot of bending as it travels through its

stroke; therefore, putting a lot of stress and wear on one side of the bag. To prevent this, the air bag top

mounting plate will be mounted to a bushing allowing it to pivot. To keep the airbag vertical, a threaded

rod with two ball joint style rod ends at each end will be mounted to the frame from the mounting plate

bushing.

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In order to find the optimal geometry of the cantilever body, the trailing arm, and the best

placement of the dog bone that would link the trailing arm and cantilever body together, a lot of different

factors had to be taken into consideration. I was able to set the trailing arm length to 25 inches. From FEA

test and other calculations, I knew that this would be a safe length for the total trailer weight. This length

would also give me the distance I needed to proper place the center line of the wheels in relation to the

deck to ensure a proper tongue weight to trailer weight ratio.

The air bags that are being used have a minimum height of 2.80 inches and maximum height of

12.50 inches; however, they have an optimal working height of 7 to 8 inches. Now that the trailing arm

length and the amount of lift that is available are known, the cantilever arm can then be properly

designed. Using the average hitch height of trucks currently on the market, I was able to make the

following Excel sheet that would calculate the bag extension based on the trailing arm length and the

distance from the fulcrum of the cantilever body to the point where the dog bone attached.

FIGURE 5: Excel Calculator used to Determine Trailing Arm Length to Cantilever Fulcrum length Ratio

Since the dog bone allows for some adjustment, these values can change to better suit a

vehicles hitch height, or the total weight of the load on the trailer. By adjusting the dog bones, the

operator can make sure that the bags are in their optimal working range no matter what the loading

conditions may be.

FIGURE 6: Trailer Layout

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CALCULATIONS

Strength evaluation based on stress analysis using COMSOL finite element analysis (FEA) and

Solidworks have been run for the trailing arm, hub hosing, cantilever arm, and other structural parts. All

of the components where made in Solidworks and then imported into COMSOL using the COMSOL-

Solidworks Live Link feature. There was some stress spikes located in the joining corners of the

weldment assemblies. These stress spikes can be ignored since these parts will be welded together and

there will not be a sharp transition between them. The smallest safety factor was found to be in the

cantilever arm at 1.7. This is an acceptable safety factor for this application. Since the suspension has a

wide range of travel and this greatly affects the stress that is experienced, it was assumed that the

highest stress concentration in the trailing arm would be when it is perfectly horizontal and the greatest

stress in the cantilever arm would be at maximum lift.

FIGURE 7-8: Trailing Arm Simulation Results

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FIGURE 9-11: Hub Housing and Cantilever body Simulation Results

By using the Live-Link feature between COMSOL and Solidworks, it was easy to see how the part

geometry affected the stress concentrations. At first, the cantilever arm was weak and had high stress

concentrations along its top ridge. I was able to slowly increase its overall height and at the same time

monitor how this height change effected the stress concentrations. This greatly sped up design time and

eliminated a lot of back tracking.

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PNEUMATIC/ELECTRIC SYSTEM

Since this trailer will be using trailer brakes and external power from the tow vehicle to run the

air compressor, a 7-pin trailer connecter will be used. The 7-pin connector allows for standard light

operation, brake signal, and a +12v signal from the tow vehicle battery to run accessories. The air

compressor that was used is a Viair 480C. This is a 12 volt compressor that can operate from 0 PSI to 200

PSI with 100% duty cycle at 100 PSI, and 50% duty cycle at 200PSI. This unit has a max amp draw of

23amps.

It is recommended to only run this compressor while the vehicle is running so that the amp

draw does not completely kill the battery. Calculations where ran to determine the proper gauge wire

that needed to be ran from the vehicle battery to the trailer connector to ensure that the compressor

was able to obtain the proper voltage. Automotive electrical systems run on about 13.8 volts while

running and for most applications a 5% drop in voltage is acceptable. The wire needed to run from the

tow vehicle for this trailer to the compressor was determined to be about 22 feet. The following

calculations where ran to determine the proper wire gauge to use:

FIGURE 12: Compressor Supply Line Size Calculations

After reviewing these calculations, 8 gauge wire was chosen. This was also the same gauge wire that

Viair recommends. This compressor required a 40 amp relay and a 40 amp circuit breaker at the positive

battery connection which came from the +12v line of the 7-pin trailer connector. To ensure that the

compressor only comes on when the vehicle is running, a positive feed was taken from the parking light

circuit and then wired into the pressure switch. The 40 amp relay was then wired to the other pressure

switch lead. This ensures that the compressor only runs when the vehicle is running and when the

pressure switch is activated (see diagram).

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FIGURE 13: Wiring Diagram for Compressor and Arduino Sensor using Voltage Divider

FIGURE 14: Typical Trailing Wiring and Color Diagram

Two digital pressure sensor gauges are used to monitor the pressure in both the air bags and the

air tank. These gauges work from 0-200PSI and increase resistance from 10-180 Ohm’s as the pressure

increases. See Wireless Monitoring section for more details.

FABRICATION

All metal components were arc (stick) welded by me. Since the main frame of the trailer was

constructed using galvanized carbon steel, 6011 electrodes where used. The reason these electrodes were

used is because they preform extremely well on “dirty steel” and work well while welding in any position.

These rods provide a yield strength up to 66,100 PSI which will ensure a strong weld joint. Some parts of

the trailer required 304/316 stainless steel to be welded to carbon steel and was done using 316L stainless

electrodes. If regular steel electrodes where used for the stainless to carbon steel, the stainless material in

the weld would become contaminated and eventually rust resulting in a weak weld joint.

Fabrication of the trailer was finished around the first week of April. The trailer was brought to

Louisiana State Police Troop L for inspection and also received a VIN number. After a VIN number was

received, a title was applied for and a license plate was issued the same day. The trailer passed all state

and local inspections.

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WIRELESS MONITORING

Two Arduino Uno’s will be incorporated into the trailer design. One will contain an LCD screen

that will read out the air pressures in the air bags and the tank, and also read out whether or not the air

compressor is on. The other Arduino will be placed on the trailer and wired into both air pressure sensors

and the air compressor. The two Arduinos will communicate wirelessly with the use of two xBee modules.

Since the Arduino inputs can take a maximum of 5 volts and the air compressor runs on 12v, a voltage

converter was constructed in order to convert the 12v from the compressor to the proper 5v for the

Arduino input.

FIGURE 15: Wiring Diagram for Pressure Sensors to Arduino

The monitoring Arduino will supply the pressure sensors with 3.3 volts and using a voltage

divider setup, measure the resistance of the pressure sensor. Since the pressure sensor has a linear

resistance, 12-180 Ohm for 0-200 PSI, its value can be converted into a pressure reading using a formula.

Since the 5 volt power supply on the Arduino is used to power the whole board, it is 'noisy' and can

cause issues when reading the resistance of these sensors. The Arduino has a separate 3.3 volt power

line that goes through a secondary filter/regulator stage that the 5 volt supply does not; therefore,

creating a ‘clean’ voltage supply. By connecting this ‘clean’ 3.3 volts into the analog reference pin

(AREF), we can provide a stable reference point for the analog pins to compare readings to. To further

ensure the readings are accurate, 5 readings will be taken off the pressure sensor and then the average

off these readings will be recorded.

By setting this system up with a voltage divider, we can easily calculate the resistance of the

pressure sensor. Since we know the equation for a voltage divider is:

𝑉𝑂𝑈𝑇 = (𝑅1

𝑅1 + 𝑅2) 𝑉𝐶𝐶

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And we know when we read a voltage on a microcontroller; we get a number based off of:

𝐴𝐷𝐶 𝑉𝑎𝑙𝑢𝑒 = (𝑉𝐼𝑁 ∗ 1023)

𝑉𝑐𝑐

If we combine the two equations, we get:

𝑉𝑂𝑈𝑇 = 𝑉𝐼𝑁

𝐴𝐷𝐶 𝑉𝑎𝑙𝑢𝑒 = (𝑅1

(𝑅1 + 𝑅2)) (𝑉𝐶𝐶) (

1023

𝑉𝐶𝐶)

𝐴𝐷𝐶 𝑉𝑎𝑙𝑢𝑒 = (1023 ∗ 𝑅1 ∗ 𝑉𝐶𝐶

(𝑅1 + 𝑅2) ∗ 𝑉𝐶𝐶)

𝐴𝐷𝐶 𝑉𝑎𝑙𝑢𝑒 = 1023 ∗ 𝑅1

(𝑅1 + 𝑅2)

Solve for R2:

𝑅2 =𝑅1

1023/𝐴𝐷𝐶 − 1

Since we set R1 to 330 Ohm’s, once we obtain a value from Arduino, we can input this into ADC. From

there we are given the resistance value of R2. The following data also shows the linear relationship that I

found when calibrating the pressure sensors. The equation of the line is solved for the unknown

resistance and then Arduino can convert this into the proper pressure reading.

FIGURE 16: Pressure Sensor Readings

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𝑅2 =330

1023/𝐴𝐷𝐶 − 1

The monitoring Arduino on the trailer gathers all input data and sends it through the xBee

module to the receiver Arduino as one long number stream. The main issue when sending this data is

how to determine when the data stream begins and when it ends; if this is not correct, the wrong values

will be displayed. To overcome this, start and end “tokens,” or indicators, where used and the number

stream then looked like the following:

< 80,80,196,100 >

Where </> is a number stream starting/ending indicator, the first number is the left airbag pressure, the

second number is the right airbag pressure, the third number is the tank pressure, and the last number

is a compressor status indication (100 = ON, 000 = OFF).

The receiver Arduino is constantly looking for input data from the xBee. Once it sees the starting

indicator, it breaks this data down into the appropriate variables and displays it on the LCD screen.

FIGURE 17: Receiving Unit Set up

FIGURE 18: Sending Unit Set up

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TIMELINE

Completed Trailer Frame - February 28, 2015

Completed Fabrication Weldments - March 7, 2015

Completed Trailer Assembly - March 28, 2015

Run Testing/Trailer Registration - April 1, 2015 to April 18, 2015

Implement Any Design Changes - April 25, 2015

Final Trailer Assembly - May 2, 2015

*Strikethrough items are completed

FIGURE 18: Final Trailer

FIGURE 19: Final Trailer

Intellectual property created, made, or originated by Case Born shall be the sole and exclusive property of Case Born, except as he may voluntarily choose to

transfer such property, in full, or in part. PATENT PENDING - 62111635