Log Hauler. Senior Design Project. Department of Mechanical Engineering Trevor Kline 4/19/2011

Transcription

1 Log Hauler Senior Design Project Department of Mechanical Engineering Trevor Kline 4/19/2011

2 Table of Contents BACKGROUND:... 3 INSPIRATION:... 3 PROPOSAL AND REQUIREMENTS:... 4 DESIGN:... 4 LOG SIZE:... 4 MATERIAL:... 5 WHEELS:... 5 FRAME SIZING:... 5 ATTACHING THE WHEEL SPINDLES... 9 HANDLES FACTORS OF SAFETY WEIGHT CALCULATIONS: COST ANALYSIS: TESTING: SUMMARY... 16

3 Background: For a number of years my father ran a tree trimming and removal business. Since then, he s ended the business but has been doing work on the side for over 20 years. Naturally, I ve found myself helping on tree jobs after school or on the weekends for extra money. When I needed an idea for my senior design project, I realized that I wanted to design and build something that I could use. When I approached my dad with the problem, he suggested building a device that we could manually take into suburban areas and remove logs from backyards. Typically, we cut the wood into 16 firewood lengths and remove them from the customer s yard. However, sometimes we encounter an oak or cherry log that would be more valuable to have milled into boards, but do not have the means of retrieving the log from the backyard. The log hauler has the capability of entering into backyards and moving these valuable logs to a better trailer loading location. Inspiration: I realized that this idea was most likely not unique and used the internet to research log movers. I found a company called LogRite which manufactures several types of log arches. Some were built to attach on the back of an ATV, but several models were made to be man powered. These were the devices I took interest in and based my design off of. One model in particular, the Fetching Arch, was man powered and used to move large logs of up to 26 in diameter and 2000 lbs of weight. I recognized an opportunity to reduce the manufacturing cost when I saw the Fetching Arch was listed for $1, I believed that I could manufacture a device with close to the same or better capabilities for a quarter of the cost. Below is a picture and specifications of the LogRite Fetching Arch upon which I based my design. LogRite Fetching Arch

4 LogRite Specifications Pricing Log Capacity: 26" diameter Fetching Arch $1,800 Length Capacity: 16' fully suspended Two Man Handle $121 Weight Capacity: 2000 lbs Total Cost $1,921 Tire Size (OD): 24" Tong Size: 25" Arch Width: 54" Arch Height: 44" Arch Length: 78" Arch Weight: 206 lbs Proposal and Requirements: The Log Hauler is a man powered tool designed to retrieve logs from areas where heavy machinery is unable to go due to lack of space. It also prevents heavy machinery from damaging lawns. The hauler takes on the shape of an arch and is essentially a large lever with two wheels. It is designed to be placed over the center of the log where the skidding tong can be lowered to grasp the side of the desired log. By using mechanical advantage with a prying motion, one or two men depending on the log size can raise the log several inches off the ground and wheel it to the desired location. Its easy grab and release action makes the hauler time efficient and easy to use. A six foot long handle extension provides extra leverage when inserted into the original lever arm. Objective: Reduce the build cost to 25%, ($500), of the LogRite Fetching Arch retail price. Constraints: Design: Must be able to fit in the back of a pickup truck with an 8 bed. Must weigh less than 200 lbs. Able to support the load of a 25 x 8.5 log. (Unseasoned Oak log approx. weight of 1,857 lbs) Log size: The first step in the design process was to determine what size logs I wanted the device to handle. From experience, I know that oak trees that grow very large in diameter tend to rot from the inside, thus making the log worthless. Due to this knowledge, I determined that it would be sufficient to make the maximum log diameter 25. Now that I knew the maximum diameter, I needed to figure out how much weight to design for. I was able to find a green log weight chart on SherrillTree.com, a website that specializes in providing gear for tree care professionals. As expected, it was clear from the chart that the different types of oak would be the heaviest wood to handle. A 25 diameter oak log with

5 an 8.5 foot length would weigh around 1860 pounds. Assuming that we would have the logs milled into eight foot lengths, I would leave an extra six inches for error. Material: With this knowledge, it was now time to consider what would be the best and most cost efficient material to construct the frame out of. Due to the large stresses induced, I knew that a metal would be the best and most economical choice. Aluminum would be too expensive, so I selected to use steel square tubing. The square tubing acts as a shape factor and adds strength to the material. I visited Industrial Tube and Steel s website, (a company based out of Kent, Ohio), and viewed the different standard tubing sizes. I was also able to view the material properties of the steel. The standard A500 series Grade A steel has a yield strength of 33,000 psi and an ultimate strength of 39,000 psi. Through rough calculations, I determined that two inch square tubing would be able to handle the forces created by a 2000 pound log. With this information, I was able to determine the wall thickness of the two inch square tubing to meet factors of safety later in the design process. Wheels: The next step was to figure out what kind of wheels I would be using and how to attach the axles to the frame. I was able to find axle spindles on ebay that were rated for 1375 lbs per wheel and specifically made to slide into two inch square ¼ wall tubing. This further validated my decision to make the frame out of square tubing. The spindles came with a five point lug pattern. At this point I had a stroke of luck when my grandfather happened to have a set of spare trailer tires and rims with the same five inch bolt pattern that he let me use. The tires were 205/75/R15 load range C and rated to 1820 pounds per wheel. I could have easily used smaller wheels; however I could not pass up a set of free tires. I decided to use them and incorporated their radius in my design. This would later be used to help calculate the frame component lengths. Frame Sizing: Figuring out the general shape and length of the different frame members proved to be the most challenging. I investigated many ways of lifting the log with the goal of maximizing the height of the log in the lifted position and minimizing the forces needed to achieve it. Below is a profile diagram of my selected arch shape in the lowered position followed by the raised position. Note that at this point, I am only concerned with the basic shape and not in strengthening the frame yet.

6 The idea behind the design is that lift is achieved by tilting the arch forward, attaching to the log and pulling down on the lever arm, which hoists the log into the air. Before I could make any definite calculations, I needed to figure out how I was going to grasp the log. I decided to use tongs, similar to the LogRite design previously shown, for easy grab and release. After researching, I discovered that there is a difference between lifting tongs and skidding tongs. Skidding tongs are used to lift one end of the log off the ground and then drag. They are not rated to lift any specified weight. On the other hand, lifting tongs look the same as skidding tongs but are rated for overhead lifting and are more than twice the cost. Since no overhead lifting would be done with my design, I determined that the skidding tongs would be sufficient for lifting a log a maximum of six inches off the ground. I found two sizes available from Northern Tool, and selected the larger of the two. The tongs purchased are capable of grasping logs up to 32 in diameter, which I believed would handle smaller logs with ease. However, the skidding tongs presented a new challenge. The height above the ground with which the tongs grasp different size logs varies with the diameter of the log. I found the height of the lifting ring when grasping a 25 diameter log to be 37.5 from the ground, while a log less than 20 in diameter places the lifting ring at 33 above the ground. Below, one can see the difference in height when grasping different log sizes Skidding Tong Pickup Positions

7 Once I knew the dimensions of the skidding tongs and wheels, I was now ready to use Excel to help me find the appropriate frame dimensions. A massive amount of trig was used to determine the forces that would be necessary to pick the log up and then determine the change in height of the log and the positions of the various handle lengths at the varying pickup positions. Below is a diagram of the design in the pickup position. Charts were made for for the following log diameters, 20, 22, 24, and 25 each having a different initial pickup height and a different calculated log weight. The wheel radius was specified as as well as the lengths for the original 8 foot handle and the six foot handle extension. An overhang value was also defined as a constant in the chart. The handle angle from horizontal (A2) was varied from 0-90 degrees. For example, knowing that the pickup height for a log 20 diameter or less was at 33, I was able to calculate the dimension of the arch length, the handle heights and initial force required at both handle lengths. This was done for each of the different log diameters. The chart below shows the various input and output parameters for a 20 log. 20" Diameter Log Input Variable Output Pickup Position Height Position 2 Height Wheel Radius Change in Height Overhang Angle A1 (0-90 ) Handle Height at 8' Force Required at 8' Handle Height at 14' Force Required at 14'

8 Determining the appropriate lengths was challenging because there were many trade offs between the different variables. For example, I could generate enough force to raise a 2000 lb log one foot off the ground; however the height of my handle at the pick up position would be out of reach. I determined that raising my largest log 2-3 inches off the ground would be more achievable. Also, shortening my overhang length would allow me to lower my handle height but also place my load farther away from the wheels once lifted, hence requiring more force to hold the log in the upright position. I determined that having an adjustable overhang height would be the best solution for this. I was able to sort through these tradeoffs with the Excel charts I generated. I made a conditional formatting rule that highlighted each chart s cells requiring less than a 160 pound force at 14 feet. I did this for each of the varying log diameters. It became clear that I would need the height of my raised position to be approximately 40. This then told me the dimensions of the arch I would need. Below are the final dimensions of the frame. Arch Dimensions Frame before paint

9 Attaching the Wheel Spindles As previously stated, the axle spindles were rated for 1375 pounds and specially made to insert into square two inch tubing with ¼ inch wall thickness. The spindles slid into the tubing four inches and a three inch L-Channel seven inches long with 1/8 thickness was used to allow for an easier welding surface. The L-Channel slightly narrowed the diameter of log that would fit between the arch to under 25. The assembly can be seen in the photo below. Wheel Spindle Assembly Attaching the Skidding Tongs Figuring out how to attach the skidding tongs to the lever arm took some creativity. I was able to salvage a piece of 1½ x 1½ bar stock with two previously cut holes and made it into the skidding tong holder. I selected the 1½ x 1½ bar stock due to the fact that it slid nicely into the end of my two inch square tubing. I then welded a thin plate to the bottom of the stock to ensure that it fit tightly inside the tube. I also welded the heads of ½ bolts 1½ apart with a piece of 1/8 sheet metal. Below is a picture of the bar stock and the finished assembly. The bar stock adds strength to the overhang and also makes the overhang length adjustable. This becomes advantageous when picking up smaller logs or chunks, the bar stock can be extended for a higher pickup height. When being used for very heavy logs, the bar stock can be slid in, shortening the overhang and requiring less force to lift the log. Skidding Tong Attachment

10 Handles Two handles were made, one for the original 8 foot lever and one for the 6 foot extension lever. A one inch diameter pipe was welded on the end and used for both. I left a 12 overlap between the joint and drilled holes six inches into the original lever for a pin to join the two together. Below is a picture of the handle. The extension handle can be viewed later in the report. Factors of Safety Handle To make sure the structure I designed would be safe; I used Excel to help calculate the factors of safety for different thicknesses of steel tubing. Once calculated, I could then pick which thickness would give me the factor of safety I desired. I knew that the yield strength of the structural steel was roughly 35,000 psi. To analyze my design structure, I used a simple beam analysis for various members of the frame. The top arch which was 25 in length was modeled as a simply supported beam, and the stress induced by a 2000 pound log was found and compared to the yield strength of the material. I knew that I wanted a factor of safety of two for this member, so I selected quarter inch wall thickness which gave me a FOS of I modeled the 8 foot handle, the 6 foot extension, and the overhang all as cantilever beams. The following table shows the results for each factor of safety. Detailed table calculations can be found in the Excel file. Factors of Safety Component Modeled Type Material Dimensions F.O.S Cross member Arch Simply Supported Beam 2" x 2" x 1/4" Foot Handle Cantilever Beam 2" x 2" x 3/16" Foot Handle Extension Cantilever Beam 1½ x 1½ x 3/16" 1.44 Overhang Cantilever Beam 2" x 2" x 3/16" 2.76

11 I was concerned that the eight foot handle s factor of safety wasn t large enough; however I could not use ¼ wall thickness because my handle extension wouldn t fit inside. So, I instead braced the initial eight foot lever arm with L-channeled braces for extra support. The braces were each 30 in length welded from the lever arm to the middle of the arch. Weight Calculations: My total calculated weight without the 6 foot handle extension was 242 pounds. Unfortunately, this meant that I wasn t able to meet my weight requirement of weighing less than 200 lbs. I could have lowered the weight by reducing the thickness of the two inch square tubing used for the arch to 3/16. That would have lowered my weight by approximately 10 lbs. However, I already had the quarter inch wall thickness material and was able to use it instead of paying for new steel. I also could have reduced the weight substantially by using smaller wheels. Again, I chose to use the large 15 rims because my grandfather let me use his spare trailer tires. Below is a breakdown of the different components and their weights. Note that the handle extension written in red was not included in the total weight. Log Hauler Weight Components Weight (lbs) Wheels (2) 76 Axle Spindles (2) 30 Skidding Tongs " x 2" (1/4" thickness) " x 2" (3/16" thickness) ½ x 1½ (3/16" thickness) " x 1" x 5' L-Channel 1/8" thickness 7 3" x 3" x 14" L-Channel (3/16" thickness) 6 1½ x 1½ Bar Stock 8 Handle 5 Total lbs Cost Analysis: I was surprised to see the total cost of the project. Since I was able get many of the components for free, I totaled what I spent and then what I would have spent buying all the components. I spent a total of $ on the project, which was well under my budget of $500. However, looking up the costs of each component I used in my design, I would have spent $ This made my cost reduction around 27% of the LogRite retail price and slightly over my goal of a 25% cost reduction. However the tires I used on the design were well over the load requirement and retailed for $84.95 each. I could have bought smaller, cheaper tires for much less and incorporated them into my design. Also, I believe that I could have found a better price for the steel I purchased if I had time to get more price quotes. The table below shows what I spent on the project compared to what the actual estimated cost would have been.

12 Expenses Components Cost Actual Cost (2) Wheels 205/75/D15 Load Range C Free (2) Axle Spindles Skidding Tongs " x 2" x 9.5' (1/4" thickness) Free " x 2" x 8.5' (3/16" thickness) 1½ x 1½ x 7' (3/16" thickness) ½ x 1½ x 10" Bar Stock Free 8 1" x 1" x 5' L-Channel 1/8" thickness Free 15 3" x 3" x 14" L-Channel (3/16" thickness) Free 6 Handle Free 6 (2) Rustoleum Protective Spray Paint Free 7.96 Total $ $ Testing: I started by first picking up various chunks of wood that were firewood lengths. The device raised a 25 diameter firewood length chunk of wood with ease to a height of three inches. At this point I realized that the hauler would be useful in moving chunks of wood from a job site as well. Instead of rolling oddly shaped wood, the hauler could make the job much easier. I also realized that the weight of the lever arm lessoned the force required to raise the log. If I had taken this into consideration during design, I may have been able increase my maximum pickup weight. The pictures below show a 22 diameter firewood length piece of wood. As you can see, it takes little to no force for me to balance the wood in the lifted position with the lever arm.

13 20 Diameter Firewood Length Log 20 Diameter Firewood Length Log (side view) After testing the Log Hauler on chunks of wood, it was now time to see how it would work with a large log. Since I did not have an eight and a half foot log that was 25 in diameter to test for the maximum

14 load, I instead used the biggest log available. The log in the picture below is 12.5 foot and has a diameter at the butt end of 20 and a diameter at the far end of 15. With the help of the log weight chart, I estimated the black walnut log weight to be approximately 1,000 lbs. This is around half of the maximum load I designed for. As you can see in the following pictures, I was able to pick the log totally off the ground by myself without the handle extension. Log in the Pickup Position Log in the Raised and Balanced I did find it necessary to use a strap to make sure the log was completely off the ground and balanced. As you can see, there is barely any weight on the lifting strap hence me being able to hold it with two

15 fingers. I also tested out the hauler with the extension handle. It reduced the force needed to raise the log even more and can be seen in the picture below. Lifting with the handle extension Lifting with the handle extension

16 Ideas for improvement for the design would be to construct a hitch attachment that would allow you to trailer the hauler behind an ATV or truck. Adding a pulley directly under the arch with a cable that runs to a hand winch would also allow you to balance the entire weight of the log above the two wheels. Summary Overall, I was very satisfied with the outcome of the project. I believe the hauler has surpassed my initial expectations when I began working on it. I m proud of coming so close to my goals I had from the start of the project. However, there are many improvements that could be made such as reducing weight by using thinner walled material or smaller tires. Also, reducing cost by using smaller tires as well. The hauler cost me $ and I estimated that my hauler would have cost me around $ if I had to purchase all the material myself. This placed me at a 27% of the cost of the LogRite Fetching Arch retail price. The weight of my design was 242 lbs, which also was over my goal of 200 lbs. The finished product did fit in the back of a pickup truck as shown in the picture below. I learned just as much through the building process as I did through design and am happy that it has proven itself useful. I m looking forward to seeing its true capabilities on the next tree job.