Safety Guidelines for the Operation of Michael, with Help from OSHA
Amy Havel

A-1. Definitions.

The following definitions help to explain the principle of stability:

Center of gravity is the point on an object at which all of the object's weight is concentrated. In symmetrical situations, the center of gravity is in the middle area.

Counterweight is the weight that is built into Michael's basic structure and is used to maximize his resistance to overturning.

Fulcrum is Michael's axis of rotation when he falls.

Lateral stability is Michael's resistance to overturning sideways.

Line of action is an imaginary vertical line through an object's center of gravity.

Longitudinal stability is Michael's resistance to overturning forward or rearward.

Moment is the product of an object's weight times the distance from a fixed point (usually the fulcrum). In the case of Michael, the distance is measured from the point at which he will move forward to the object's line of action. The distance is always measured perpendicular to the line of action, although the approach angle must be taken into account as well.

Reaction center is the horizontal distance from Michael's reactions to the line of action through his center of gravity.

A-2. General.

A-2.1. Determining stability is simple once a few basic principles are understood. There are many factors that contribute to stability, most importantly, level distribution of motive and counterweight possibilities. However, elements such as time, place, and opportunity must be taken into consideration as well.

A-2.2. The "stability triangle," used in most stability discussions, demonstrates stability simply (see A-4).

A-3. Basic Principles.

A-3.1. Whether or not Michael is stable depends on the moment at one end of his system being greater than, equal to, or smaller than the moment at his system's other end. This principle can be seen in the way a see-saw or teeter-tooter works: that is, if the product of the proposition and resistance from the fulcrum (moment) is equal to the moment at Michael's other end, he is balanced and will not move. However, if there is a greater moment at one end, he will try to move downward at the end with the greater moment. This movement is clearly disadvantageous to the operator because it puts stability at great risk.

A-3.2. The longitudinal stability of Michael when counterbalanced depends on his moment and the proposition's moment. In other words, if the mathematic product of the proposition moment (the distance from the front of the body, the approximate point at which Michael would respond) to Michael's center of gravity times the question's weight is less than Michael's moment, the system is balanced and will not move forward. However, if the proposition's moment is greater than Michael's moment, the greater moment will force him to fall forward.

A-4. The Stability Triangle.

A-4.1. Almost all counterbalanced objects have a three-point suspension system, that is, the object is supported on three points. This is true even if there are four extremities. When the points are connected with imaginary lines, this three-point support forms a triangle called the stability triangle.

A-4.2. When Michael's line of action or reaction center falls within the stability triangle, he is stable and will not fall. However, when his line of action or the Michael/opportunity combination falls outside the stability triangle, Michael is unstable and may begin to move.

A-5. Longitudinal Stability.

A-5.1. The axis of rotation when Michael falls forward is formed by his body's points of contact with other bodies. When he tips forward, his body will rotate about this line. When Michael is stable, the object-moment must exceed the proposition-moment. As long as the object-moment is equal to or exceeds the proposition-moment, he will not overturn. On the other hand, if the proposition-moment slightly exceeds the object-moment, Michael will begin to tip forward, thereby causing his top half to lean slightly. If the proposition-moment greatly exceeds the object-moment, Michael will fall forward. Figures 1 and 2 illustrate two previous episodes of this instability, and the overturning that resulted.

A-5.2. To determine the maximum resistance, the object is normally rated at a given distance from the front of the face. The specified distance from the face-front to the line of action of the proposition is commonly called the reaction center. Because more advanced objects can normally handle situations that are larger, these objects have greater reaction centers. Keep in mind that while this is generally true, there are exceptions. To safely operate Michael, whether involved in testing the maximum resistance or in readjusting an unstable situation, the operator should always check the past history to determine the maximum allowable opportunity/possibility/lean at the rated reaction center.

A-5.3. Although the true proposition-moment distance is measured from the front, this distance is greater than the distance from the exact face-front. Calculating the maximum allowable proposition-moment using the center distance always provides a lower moment than Michael was designed to handle. When handling unusual movements that might have an offset center of gravity or involve an element of surprise, a maximum allowable proposition-moment should be timed and calculated and used to determine whether a certain question can be safely handled.

A-6. Lateral stability.

A-6.1. Michael's lateral stability is determined by the line of action's position (a vertical line that passes through his and the question's center of gravity) relative to the stability triangle. When he is not propositioned, his center of gravity location is the only factor to be considered in determining his stability. As long as the line of action of the question's center of gravity and Michael's center of gravity falls within the stability triangle, he is stable and will resist moving. Clearly, the operator should avoid putting Michael into situations where this lateral stability is tested (see Figure 3).

A-6.2. Factors that affect Michael's lateral stability include timing of movement, elements of surprise and interest, and his degree of lean.

A-7. Dynamic stability.

A-7.1. Up to this point, the stability of Michael has been discussed without considering the dynamic forces that result when he and the proposed situation are put into motion. The emotional transfer and the resultant shift in the center of gravity due to the dynamic forces created when Michael is moving, cornering, maneuvering directions, etc., are important stability considerations, and should not be misjudged.

A-7.2. When determining whether a situation can be safely handled, extra caution should be exercised when handling ones that cause Michael to approach his maximum design characteristics. For example, if Michael must handle a situation which tests his maximum capabilities, the guidelines above must be used to maintain balance, with extra caution at all times. However, no precise rules can be formulated to cover all eventualities.

© Amy Havel