Operation Repo
Design and build of a Slide-in Tow Unit
current design
Submitted to
Professor Richard L. Roberts
March 5, 2010
Brian Melo
Rick Piermarini
Tuan Tran
Matt Skillin
WENTWORTH INSTITUTE OF TECHNOLOGY
Mech578
Table of Contents
Title PagePage 1
Table of ContentsPage 2
IntroductionPage 3
DataPage 4
Sample CalculationsPage 5-7
Diagrams Page 8-9
Results Page10-11
Discussion of ResultsPage 12
Conclusion Page 12
Reference Page 13
Introduction
Have you ever had your car towed and when you got it back you found there was damage to your car? Have you ever towed a car using your truck and realized the car was doing damage to your truck? If so we are pleased to introduce Operation Repo, the new line of slide-in towing units that is going to change the way towing is done. Operation Repo is a plan to redesign the current slide-in unit and replace it with a design that has proper weight distribution; it will be safer for both your truck and the cars that you’re towing.
Operation Repo is a vehicle used to transport any vehicles to a different location. It was invented by Ernest Holmes, Sr. in 1916. He was inspired to engineer the tow truck because he was forced to pull a car out of a creek using blocks, ropes, and 6 men. Operation Repo is integrated with a boom and wheel-left system, which it is the latest evolution in tow truck technology. It can be controlled inside the truck and deployed with hydraulic power. The theory that lies behind hydraulic equipment is fluid pressure. A force that acts on a small area can create a bigger force by acting on a larger area by hydrostatic pressure. The large amount of energy can be carried by a small flow of highly pressurized fluid. It uses the system of fluids and cylinders to generate a force to lift the vehicle up. The stinger is a bracket that cradles the tires on both sides of the wheel to lift the vehicle up to prevent any unnecessary damages. Furthermore, it is quick and easy to tow a vehicle away.
Currently the design of the slide-in towing units is flawed because of the placement of the piston and the weight distribution on the piston and the truck. The current design revolves around a piston that pushes off the rear of your truck; our design is going to be placed over the axel of the car so it can easily absorb the weight. Also the unit causes damage on the cars that is being towed. We plan to re-design the unit so that the weight distribution is better suited for the car and the piston and so that the unit doesn’t cause damage to the car as it is being towed. We hope that with a new design of this unit, it can become a more structurally sound unit.
Data
Dimensions and Data taken from the current unit
Sample Calculations
Normal Forces
@ 20 degree
@ 45 degree
Shear Stress:
Beam = 5x5
Pin C Radius = .4”, Diameter = .8”
Pin B Radius = .4”, Diameter = .8”
Pin A Diameter = 1.5”
At 5 degree
At 40 degree
Diagrams
Microsoft Project
Solidworks drawings
Results
Shears
Discussion of Results
While in the process of the figuring out the calculations the team would need to derive for varies portion of the unit, our group decide to use the force at the end of the Snitch unit to be at 3,500 pounds which is typically the weight of an average size vehicle. Our group had to take into consideration of angles to the unit to figure out maximum forces. Our group figure out the maximum forces occurred at the highest boom angle which was 40o and at its lowest which was 5o. From there our group derived stress of the components which is sigma as the force over the surface area of the part and shear of the pins which is tau as the force over the shear area, and in this case since we have a two members sharing one pin at a specific junction, that means the area of shear must be doubled so our equation is . And since point A is where the base plate attaches to the main boom, our group discussed that it is a hinge and their our calculation, the group found out the force where equaled in the x and y direction.
Conclusion
At this point in time our group has come a far way in project operation repo. The team’s final design is a single angle piston placed of over the rear axle of the truck which was based on our design matrix. This design is the best one out of the other three designs that our group considered since it was the most efficient, best durability due to its weight reduction over its predecessor, and feasibility of the tow unit itself. Right now, as a group, calculations are be formulated for varies portions of the unit like for instance the normal forces at the piston, the shear forces at the pins where two members are held together, and other physical attributes that we take into consideration.
References
Askeland, Donald R., and Pradeep P. Fulay. Essentials of Materials Science & Engineering. Detroit: CENGAGE-Engineering, 2008. Print.
Beckwith, Thomas G., Roy D. Marangoni, and John H. Lienhard V. Mechanical Measurements (6th Edition). Upper Saddle River: Prentice Hall, 2006. Print.
How Repo Trucks Work. How Stuff Works. Web. <
Mott, Robert L. Applied Fluid Mechanics (6th Edition). Upper Saddle River: Prentice Hall, 2005. Print.
Mott, Robert L. Machine elements in mechanical design. Upper Saddle River, N.J: Pearson/Prentice Hall, 2004. Print.
A Primer On Hydraulic Machinery. Best Hydraulic Equipments. Web. <
Swokowski, Earl William. Calculus. Boston: PWS-KENT Pub., 1991. Print.
Tow truck. Wikipedia. Web. <
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