MEGR 3256 - Senior Design

Motorcycle Luggage Trailer - Senior Design

Senior Design, a year long class that allows students to work for companies on a project; or, if the student wishes, he/she may come up with their own project to complete upon the approval of the faculty. 

For my project I decided to work alone in designing and building a single wheeled trailer to be pulled my Yamaha FZ6. The single wheel design will allow the trailer to lean with the motorcycle so that it will not hinder the lean angle of the motorcycle. The trailer will be connected via universal joint, which will allow the trailer to move in the X and Y planes only. This will allow it to move up and down, and side to side for sudden grade changes and tight turning. However the u-joint will be fixed to the hitch and trailer to prevent rotation.

The first semester was devoted to the basic design of the trailer. This included all the drawings, calculations and budget planning.  The second semester was devoted to the build and testing of the trailer.

Calculations for the trailer included finding the center of gravity of the motorcycle with and without luggage, rider and passenger and comparing it to the theoretical CG of the trailer in various loading conditions based upon the conceptual drawings. The goal of this was to keep the mass moment of inertia of the trailer, in the rotational direction, less than 10% of the motorcycle's. There was no significance in having it be less that 10%, my professor and I felt that this was a good value to to shoot for in designing as we wanted to minimize the trailers input to the motorcycle.

Another design of this trailer that made it unique from other single wheel designs on the market at the time, was a working, fully adjustable suspension on the trailer. Most designs that were out at the time were rigid, which left all the spring/damping up to the tire on the trailer. In turn this lead to having the trailer bounce while going down the highway when the road surface is poor or an obstacle was encountered. With a working suspension, the "bounce" that is often seen from other trailers, was eliminated. 

Using a motorcycle dynamics book, I modeled a simple swing arm design that was similar to the set up on my motorcycle. After a basic model was composed in Solidworks, I began playing with swing arm lengths, mounting locations and wheel size to optimize the suspension design and maintain a ride height that would not hinder the bikes lean angle.

To fully understand the dynamics of the suspension, the CG of the motorcycle and trailer was needed. Using the mass properties in Solidworks, the weight of the trailer was determined to be roughly 70 lbs and the gear that was considered to be carried in the trailer weighed approximately 100 lbs. With this in mind, I was able to run an Ohlin's rear shock that was designed for a youth motorcycle. This shock had been modified to support the weight of an adult on the motorcycle for pit bike racing. In addition, this shock was adjustable in compression, rebound as well as pre-load. These adjustments allowed changes in ride quality of the trailer when other loading conditions are encountered.

The wheel of the trailer, along with the axle, came from the front of a Yamaha Zuma, a 250cc scooter. The wheel size was 12" and after making some spacers, it was easily fitted to the swing arm that was designed. This scooter was equipped with disk brakes from the factory. (Currently, there are no brakes of the trailer, but the mounts are still on the wheel so the option is there for later up grades.)

Using an engine hoist and a bath room scale, the CG of the motorcycle was found.

Measuring the height of the rear wheel to determine the angle of lift while measuring the weight on the front tire.

Luggage rack mounted to the motorcycle. The hitch of the trailer will be bolted to the luggage rack around its mounting points to the motorcycle.

The motorcycles stock stator. Due to the extra electrical load of the trailer (lights) I felt that the output of the stator needed to be increased as I am currently using most of its available power with gadgets that are currently on the motorcycle.

For the concept design review in December, I wanted to have something for guests to see so that they may better understand my design. This is a rapid prototype of the hitch design.

RP of the trailer chassis design.

After the design review in December, it was time to start building the trailer. However, in order to make it safe to pull the trailer, some modifications needed to be made to the motorcycle. This included upgrading the suspension on the motorcycle as well as a plug-in for the trailer lights and the stator needed to be rewound for more out put.

After winter exams were over, I took the bike home for and immediately began tearing the bike down to complete the modifications. Aside from the modifications for the trailer, it was time to do some winter maintenance as well.

The new Ohlin's fully adjustable shock with 150 N/mm spring installed sitting next to factory shock. (Factory spring rate is 140 N/mm)

Race Tech emulators. These valves are added to the forks of the motorcycle to control damping and rebound.

Gear indicator and voltage meter installed to monitor voltage level on the battery.

The internals of forks.

Front end removed from motorcycle to work on forks and replace head bearings.

To make the emulators work, the factory damping holes in the damping rod needing to be made ineffective. This was done by drilling them out with a 5/16" drill bit.

Emulator rests on top of the damping rod and is secured in place once the spring is placed on top.

Stator after being rewound.

Soldering the connections of the factory tail light harness. Making room for the trailer light harness to be added.

Trailer light harness complete and ready to be connected to the motorcycle.

Harness added and secured with wires loomed. Plug is secured to the license plate bracket.

Rear end of the motorcycle torn down. In addition to the new shock, the swing arm bearings were cleaned and re greased.

New shock mounted!

Test fitting the oil reservoir. Making sure there was enough clearance for body work. The reservoir was later secured with a metal hose clamp. (Zip tie was temporary.)

During the first part of the spring semester I spent considerable time double checking my calculations and verifying the amount of material that would be needed for this project. During spring break I made the purchases needed to begin the construction of the trailer. Fortunately a family friend, Doug, owns a bike shop in Salisbury, North Carolina and is known for his aluminum welding abilities. For the next 6 weeks I spent every Friday, from 11am to 7pm in his shop assisting where I could with the welding of the trailer. In between these welding sessions I was spending up to 20 hours a week in the machine shop, cutting the tubes and making the components to be welded to the trailer.

This was my first time working with metal in this manner, so I felt that 1/4" thick aluminum tubing would probably be strong enough for my application. Let's just say it was a bit much...

We had to notch each tube down so that the weld could penetrate, in addition I had to preheat each tube before it was welded.

We were able to build the trailer on Doug's swing arm jig.

Trailer chassis almost completed.

Adding the lower shock tabs to the swing arm for the trailer.

Doug and I had to get creative in welding the hitch. We really needed a jig for this type of set up, however with time running out we had to rely on scrap metal, clamps and Doug's amazing welding abilities to pull this one off.

After the chassis was complete I went to work on cutting the sheet metal to "skin" the trailer. In one long weekend, with the assistance of my father, we were able to cut all the sheet metal and paint it. In addition, we completely painted the trailer, wired it for lights and assembled all the components.

Swing arm and shock added to the trailer.

Latching system for the box that is placed on the trailer. This allows for the cargo box to be easily removed from the trailer when needed.

Hitch secured to the luggage rack of the motorcycle.

Complete!

In order to keep the trailer, I personally funded the project. This forced me to be aware of the money involved and find ways to save money where ever I could. In order to monitor this, I maintained a very elaborate budget. In the end I saved over $1000.00 due to UNC student discounts and working directly with manufactures.

At the end of the semester everyone enrolled in Senior Design had to display their projects in the Student Activity Center. This expo was open to the public as the faculty members judged the projects and the accompanying display. At the end of the expo, prizes were awarded to the top three projects in both departmental and industrial sections. For the Spring 2010 Expo, the Motorcycle Luggage Trailer took top honors in the departmental category and won the Deans Choice Award.