The Donald (Chump) is planning to move his operations to Australia to escape his creditors and start afresh. All that Yvana and Marla have left him with is a battered pickup truck and fare to "down under". He has appealed to our engineering firm to design him a "bucking kangaroo" ride to mount in the bed of his Ford F-150 pickup truck. (Of course his credit is good with us!) His concept is similar to the "wild bull" rides that were common in yuppie bars some years ago. In a brainstorming session with Yvana and Marla (who are anxious to be rid of him) our management came up with a conceptual design for this device which is (what else?) a simple Grashof fourbar linkage. This linkage will be permanently mounted to the bed of the truck. The rider will sit on (or in) the coupler link which is disguised to look like a "roo". A motor running off the truck’s battery will power it at whatever rpm you specify. He would like to give his customers as exciting a ride as possible without injuring them. You can obtain some human factors information on human tolerance of acceleration from the books on reserve for ME3311 in Gordon Library. He also would like this device to NOT destroy his somewhat rusty pickup truck with its shaking forces.

    I told him that the WPI engineering brigade would be able to solve this problem in less than two weeks, So, your assignment is to design a mechanism based on the fourbar Grashof crank-rocker linkage which will provide suitably interesting ride motions, and to arrange the shapes, sizes and materials of the links such that the shaking forces applied to the frame of the vehicle are as small as possible. The driving torque fluctuations are also of concern as they will rob energy from the drive mechanism and thus should be minimized. The pivot pins must be sized against failure, and the dimensions and materials of the links specified.

    Luckily for you, the Donald has loaned us a computer program developed for gambling casino research called "DYNAFOUR" (available in the Aptlab and MicroCad Lab). You will need to upgrade your copy to version 5.1, rev 18, 6/15/91. This program will calculate all the forces and torques on a fourbar linkage for multiple positions. You must supply it the link dimensions, masses and moments of inertia for your design's elements, and also the crank input angular velocity, and any external forces or torques. Note that DYNAFOUR imposes a constant angular velocity on that driving crank, which assumes that the motor used has sufficient torque available at all speeds. You also have to specify what horsepower will be required of this motor, and the required diameter of the pivot pins based on the dynamic pin forces in your linkage and the material strength. TKSolver will be an invaluable aid for calculating masses and moments of inertia of your links.

    As with any design problem, there is an infinity of solutions possible. You are expected to come up with one solution which will work and, most importantly, to understand how it works or, if it doesn’t work, at least be able to explain in good engineering detail why it doesn’t! To do so you will have to try out many alternate designs and iterate to your 'best' solution. You should expect to go through at least ten iterations before arriving at an acceptable solution. You will need to do some paper and pencil (or preferably TKSolver) calculations for masses and moments of inertia of your proposed links before going to the computer to use DYNAFOUR. The entire project including its kinematics can be designed using only DYNAFOUR but the kinematic accelerations can be more quickly done with program FOURBAR. DYNAFOUR can then be used for the force and torque calculations. Note that a Fourbar data file can be read into DYNAFOUR as well.

    You are also required to document your solution in a professional engineering report which adheres to the "Project Report Specifications" document which will be distributed. This report will document the process by which you iterated to your final design as well as the design itself. Do not just describe the final result. Rather show me how you arrived at it, including the failures encountered along the way. This will demonstrate to me that you understand the engineering concepts and the relevant course material. A working cardboard model of at least one plane (one side) of your design is required. Your report should include titled (labeled) plots and tables from program 'DYNAFOUR'. Remember, one purpose of the project report is to convince me that you understand your solution well enough to have been the real designer thereof! You are also required to submit a progress report on Thursday, 11/14 which describes your concepts and the work done to that date. This is limited to three (3) typed pages MAXIMUM plus any number of figures, sketches and computer printouts. This progress report must, at a minimum, contain two animation plots of your linkage showing coupler curves at the rider’s CG and head and also polar plots of the acceleration at those points. If in on time, I will return this to you ASAP but no later than 11/18/91.

Some suggestions to get you started:

1. Do research before trying to solve the problem! Don't 'shoot from the hip'. Avoid BFI (Brute Force and Ignorance). Engineer it.

2. Investigate the dynamic factors involved

3. Mr. Hrones and Mr. Nelson will definately help.

4. Cardboard models make designing much easier.

5. THINK about the theory discussed in class and in your text. It IS applicable to this problem!

IMPORTANT! IMPORTANT!