2007 Moon Buggy Modification Project
Chris Kitchen*, Tiffany Kerr*, Dr. Ahmed ElSawy**
*Senior Students and **Faculty Advisor
Department of Manufacturing and Industrial Technology
Tennessee Technological University
Cookeville, TN 38505-0001
Abstract
The objective for the moon buggy project was to analyze the current buggy's design to find defects and weak points to enable the student to implement new and improved designs to the buggy to make it more effective in competition.
In our research, we found that the current design did not meet the 4x4x4 race regulations; there was severe deflection in the plate, which joins the two halves together, there were no brakes, and the current wheels were not designed to handle race conditions.
After defining the problems, we had to prioritize them and decide how to correct the problems while still meeting the race restrictions. To do so, we did extensive research on previous buggies and searched the current Great Moon Buggy Race regulations and rulebook.
When all of the research and design is complete, we moved on to the manufacturing stages of the project, which consisted of implementing our new ideas by modifying the buggy.
Introduction
NASA holds the annual Great Moon Buggy Race (Fig. 1), which allows universities and high schools across the country to compete against one another in search for the most elite engineers in the U.S.
Fig. 1 - Great Moonbuggy Race Course
TTU's team has participated in the race for the past 10 years, and our job was to find the problems of the current moon buggy and redesign them to make for better race results at next years race.
Last seasons, the 2007 moon buggy suffered from several design and structural defects (see Fig. 2). These defects include improper wheel selection, weak material selection and placement of the joint plate, and illegal dimensions, which did not meet race requirements. This team job was to seek simple, inexpensive and effective solutions for these problems.
Fig. 2 - 2007 TTU's Moonbuggy
Problems
The main defects of the buggy consisted of improper wheel selection, illegal dimensions, weak joint plates and no brakes. The wheels that were used suffered a structural failure during the race. This was due to weak lateral strength of the wheels. The wheels were originally used for a garden cart, which is not designed to take the abuse of fast vigorous terrain. The overall dimensions of the buggy just missed the 4' cube requirement. This was caused by excess material hanging over the front of the buggy and the cranks stuck out by one-to-two inches. The two plates that joint the two halves of the buggy were deflecting due to weak material and also, from a lack of joining the top- side of the two plates together.
Solutions
The biggest concern was the wheels and the lack of brakes, so question was to decide whether or not to purchase or manufacture new sturdy wheels. After some thought; it was decided that it would be more cost and time effective to purchase the wheels. The team searched for various types of wheels over the Internet and concluded that an extreme downhill mountain bike wheel, would serve as a lightweight, strong solution to our problem (see Fig. 3).
Fig. 3 – Suggested Mountain Bike Wheels
Now, it is necessary just to purchase and mount them to the chassis. These wheels are made of a carbon fiber composite material that is very rigid and strong while remaining extremely lightweight. The rim is constructed of a hollow tubular design, which is engineered to handle extremely large payloads in vertical and lateral directions. An example of this design is represented below in Fig.4. Take notice to the hollow section and the bead along the inner rim. This will allow us to run tubeless tires, which will also cut down on the weight.
It was also decided that the brakes are another component that would be best if purchased. So, it was found two front-mount hydraulic brake kits for a reasonable price (Fig.4).
Fig. 4 – Suggested Hydraulic Brake Kit
They are also off of a free ride mountain bike. The mountain bike parts will keep the weight down while keeping the strength needed to compete. The brakes are lightweight and will provide more than enough stopping power for the operators.
The dimension problem was a difficult and very tedious task to overcome (Fig.5). After countless ideas, we found that the most effective, would be to remove approximately two-to-three inches off of the front of the buggy and to shift the crank set and the seats backwards an additional two-to-three inches. This shifted the cranks and all of the linkage toward the apex of the bend when the buggy is in the folded position, thus creating a tighter and much smaller tuck, which helps to meet the size requirement.
Fig. 5 – Suggested Dimensions for the 2008 Moonbuggy
An additional feature to help us meet the requirement was removing some obstructions that were preventing the buggy to fold up all the way. The team found a simple solution, which can give a total of two additional inches of folding room. This was done by down sizing the wheels from a 26” diameter-to- a 24” diameter wheel. This should not affect the buggies ride height nor its ability to crawl over obstacles.
The joint plate deflection was due to improper design. The two plates were not properly joined at the top of the two plates; which was causing the two halves to separate and bend during operation. The suggested solution was to create a hinge like joint with a removable pin on the top of the plates (Figs. 6 & 7). This would allow for fast removal and replacement during the race, while creating a strong joint to defeat deflection.
Fig. 6 – Suggested Joint Plate Deflection
Fig. 7 – Suggested Joint Plate Assembly
During the fabrication stages of this project the team faced few problems. One of which was the rear wheels. The 2007 team had welded the rear wheels to the axle. This disfigured the axle and made repairs or wheel changes impossible. It was not possible to salvage the axle, so next year's team will have to purchase and install a new rear axle with a serviceable wheel assembly. Also, another problem was the team ran out money and there was no funding for the buggy during the summer semester. So the new wheels and brakes must also be purchased by future buggy teams. And lastly was a lack of time. There was not enough time to implement all of the new design features the team had planned. This will also have to be left up to the future team.
Conclusion
In working on the moon buggy the team have gained a broader understanding of reengineering. This is a very difficult task and it was felt that these innovations and improvements will help future buggy teams grab the gold at next year's race. Overall, this team started by just looking at the buggy, driving it around and talking to past team members to find out what needed to be improved on. It was found many problems and room for improvement; unfortunately, the team did not have enough time, or money to correct them all. So, this team pricked what it was felt would be most beneficial to the team and decided to tackle as much as possible within these limitations. Before working on the buggy it was bending wheels, had deflection problems, had no brakes, did not meet the race requirements, and had permanent rear wheels. After working on the buggy, we feel that Tennessee Tech stands a little bit better chance at obtaining the gold at this year's race.
References