The Anti-Gravity Machine
ME 3311 Project 1
Term B-90

Assigned 11/2/90 ----- Due 11/16/90 (15 days!)

   NASA has contracted with us to design a special purpose machine for their astronauts to use in training for space flight. They want a device which will subject the astronaut to as close to a negative one G force for as long a time as possible in order to simulate orbital flight. It may also provide larger accelerations to the rider for short durations during the cycle as long as these accelerations are physiologically tolerable. These higher accelerations can also serve as a simulation of the takeoff portion of the launch vehicle flight. They have further complicated the problem by requiring that this device be "knock-down portable", and compact enough when assembled to fit into a conventional motel room for "on the road" interviews of prospective astronauts. Even more importantly, the dynamic forces generated by this device must not compromise the operation by imparting reaction forces to the motel floor or walls which might damage the property or disturb the couple on their lunch hour in the next room. The links may be made of any reasonable materials, but the materials and their dimensions must be specified, and the links and pivot pins must be capable of surviving the dynamic loads imposed.

    Your mission (should you decide to accept it) is to design a Fourbar Grashof Crank-Rocker mechanism which will provide dynamic forces according to the above constraints, and to arrange the shapes and sizes and materials of the links such that the shaking forces applied to the structure of the motel are appropriate. The driving torque fluctuations are also of concern as they will rob energy from the drive mechanism and thus should be minimized.

    Luckily for you, NASA has loaned us two Top Secret computer programs developed for Star Wars research called FOURBAR and DYNAFOUR (available in the Aptlab and MicroCad Lab). You will need to have the latest versions which are V5.1. These programs will calculate all the accelerations, forces and torques on a fourbar linkage for multiple positions. You must supply to both programs FOURBAR and DYNAFOUR the link dimensions, coupler point location and the crank input angular velocity. DYNAFOUR also requires the masses, CG locations and moments of inertia for your design's elements, and also any external forces or torques. Note that these programs impose a constant angular velocity on the driving crank, which assumes that the motor used has sufficient torque available at all speeds. You also have to specify what horsepower and RPM will be required of this motor, and specify the required diameter of the link pivot pins based on the dynamic pin forces in your linkage and the material strength. You will first need to research the human factors aspects of the effects of accelerations on the human body to decide on a suitable linkage design. Part of the design problem is to decide how to orient and "attach" the person to your linkage so as to help minimize the resultant dynamic forces and torques. 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 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 previously 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!

      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 human factors involved

    3. Mr. Hrones and Mr. Nelson might 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!

IT IS CRUCIAL THAT YOU START THIS PROJECT RIGHT AWAY! Do not kid yourself that you can knock this off over the weekend before it is due! You cannot! This type of problem requires incubation periods. Work on it until stumped, then put it aside and do other coursework. Then come back to this problem after your subconscious has had a chance to work on it. You'll be surprised how effective this 'time-sharing' of your tasks can be. Read The Design Process in Chapter 1 for more information on this phenomenon. Incubation really does work. You should plan to have all the design work done at least 2 days before the due date, and use that time to write it up. It will take about three times longer to write up the report than you think it will. Allow at least two days for the write-up.

    The report must be word processed and spell checked! WordPerfect (with built-in spell checker) is available in the new Word Processing Lab in Fuller Laboratories. If you have your own PC and word processor, that's fine too. Letter quality output is NOT required, but DARK type is. Use a good printer ribbon, or better yet, take your disk to CCC and laser print the final draft.

Regarding cooperation between students: This is a very gray area. I do not object to your discussing the problem with your classmates or others. Much learning can take place by 'bouncing' ideas off other technically competent people (including your instructors). So you do not need to work on these projects in a vacuum. BUT, and this is a very large BUT, the final result must be your own. Any duplication of results or designs in the final reports will be quite obvious and will result in a very tense confrontation between you and me. So, brainstorm ideas among yourselves if that helps, but make sure that the final result is your own and that you fully explain its intricacies in your report. This is NOT a group project.

    Now please re-read this document to ensure you understand what is being requested. If you are the least bit confused, ASK QUESTIONS IN CLASS OR SECTION MEETING. Above all, Have Fun!

Final Report is due on Tuesday Nov. 16,1990 at 4:00 PM in HL204.

R. L. Norton, 10/31/90