SP753 Projects


Rotary Orbital Shaker

Misty Benham
Shastri Sandy
Wendy Cheng


Background

The rotary orbital shaker has been designed to be used in romote areas of third world countries that do not have the facilities necessary to maintain a typical electric rotary orbital shaker. The clinics in these countries often lack electricity, sterile environments, as well as trained medical professionals. Therefore, our task has been to create a shaker which could be used in these environments to test for specific sexually transmitted diseases (STD). The particular STD we have designed our shaker to test for is syphillis. The primary means of identifying syphillis is through the use of the Rapid Plasma Regain (RPR) test. The RPR test requires that a particular solution and the patient's blood be mixed together at a certain orbital speed for a duration of 8 minutes. After the 8 minute RPR test is done, the blood reactants are examined under a microscope to see if the test was positive or negative.


Project Design

The orbital rotary shaker was designed during the 1998 Spring semister at MIT.During the first two weeks of the semister the group was acquainted with the conditions in the Third world countries where the orbital rotary shaker was intended to be used. Lectures were given by members of the Edgerton Centre,{I should link this} and Mr. Ben Leader, an affiliate of the Mechanical Science department at MIT.


After the group became aware of the working conditions in the developing countries, and other limitations such as the number of tests which would have to be performed daily and the possible sources of power, the group came up with a list of feasible powers sources and methods of moving the top plate. A pro-cons table was created for each item on the list. After discussions with Professor Carmicheal, a professor at the Ocean Engineering department, and Professor King, head of the experimental Physics department at MIT, the group decided to have the orbital rotary shaker powered by a clock spring and move the plates in an orbital manner using a off-centred crankshaft.

In order to determine the dimension of the spring needed to drive the crankshaft, a prototype of the orbital rotary shaker was first constructed. This 'shaker' would be moved manually. This prototype consisted of two plates. The bottom plate was kept stationary while the motion of the crankshaft turned the top plate. To minimize frictional forces, the top plate moved over three ball bearins. These ball bearings were placed in a V-shaped circular grove of radius 1cm. The centres of these three circles formed an equilateral triangle.As the motion of the ball bearing was constrained, so to did the top plate have to move in a circular orbit.


Recommendations

At the end of the semister, the group had built a working prototype of a non-electric orbital rotary shaker. While this prototype was powered by droping a weight, the actually orbital rotary shaker can have its crankshaft powered by clocksprings. By measuring the mass of the weight, the height which it dropped, the group was able to calculate the power needed to have the prototype move at anrpm of 100. From this calculation, the type (lenght, thickness, diameter) of clockspring which could supply this power for eight to ten minuetes can be obtained. With the clockspring, all the user has to do is wind the spring.

When the spring unwinds it will turn the crankshaft and this in turn will make the top plate move at the desired rpm. If the spring can store this energy for ten minutes the orbital rotary shaker can be used to test for the following STD's : monospot (2 min), RH factor (2 min), rubella (5 min), syphillis (8 min) and Vz scan (10 min).

A frame is needed to house the orbital rotary shaker. This frame should be made of light-weight yet protective material such as aluminium.The top plate should be made of stainless steel. This will make it easier to sterilize the shaker.A clear cover, made perhaps from plastics, is needed to create an air-tight covering for the serum mixture.


Water Treatment System
TB Drug Sensitivity Testing Kit
SP753 Projects
SP753 Home Page

This page is maintained by Amy Smith,
mmadinot@mit.edu