NIGHTSIGHT Pan and Tilt
NIGHTSIGHT Pan and Tilt
6.0 Design Process
7.0 Design AlternativesDuring the Design phase of our design cycle, we began by prototyping the most feasible of the designs generated through the "How-Why" and brainstorming methodologies and embodied in the Morphological Analysis. Eight designs were developed using rapid prototyping techniques. The U-Joint, Single Mirror, and Two Mirror designs were discarded early in the design process because of the cost involved in integrating them with the current NIGHTSIGHT camera. These designs are listed in Appendix 11.2, Additional Design Alternatives, with full explanations as to why they were not pursued. Five final design alternatives were considered more closely and are included in this section. These designs are the Cradle, Generic, Bevel, Plunger, and Dove Mirror alternatives.
The ability to rapidly prototype designs is an important tool for both testing current concepts and generating new ideas. The materials for our rapid prototyping process ranged from Legos, foamcore, and wood to precision gear trains and off the shelf motors. As functional representations of the concept designs, the prototypes were intended to test both the physical properties and the kinematics of the systems under realistic conditions.
7.1 Cradle DesignThe Cradle Design was developed based mainly on the desire to maintain the aesthetics of the existing NightSight. However, as the concept was developed, the design proved to be a very strong solution. A DC motor fixed to the base rotates the housing by transmitting torque to a ring gear. Another DC motor is fixed to the housing and tilts the sight in its cradle. Power to the tilt motor is transmitted through a slip ring.
FIGURE 13. Cradle Design
TABLE 8. Cradle Design Advantages:
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Advantage Reason
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Low Cost Because there are no tilt arms, the device
will be lighter, require less power to pan,
and will have decreased shaft and bearing
requirements
Low Profile The sight is sitting on the cradle. There is
no need for the greater height that designs
with arms need to allow the sight to clear
the pan base while tilting.
Accentuates Because there are no tilt arms, this design
Aesthetics does not block the profile of the NightSight.
Sight Design Hughes' design for the sight is not final.
Independent The Cradle design is very flexible and can
be used with any design.
Minimizes most difficult Norman Stiepel, Sensormatic Electronics,
aspects of designing pan is the designer of a pan & tilt mechanism
and tilt mechanisms for surveillance cameras that have many
of the same requirements as our project.
He states that the hardest part is tilting and
panning about the center of gravity. Also,
the first parts to fail will be the bearings or
the gears that are connected to the tilt
staff. The Cradle design tilts about the
center of gravity and there is no tilt staff.
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TABLE 9. Cradle Design Disadvantages
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Disadvantage Reason
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Weatherproofing The cradle is exposed to the elements and
water and debris can easily get into the
friction surfaces and interior of the mechanism
Slider Joints The design may necessitate slider joints
between the cradle and the housing to
allow the tilt pinion access to the tilt rack.
Slider joints are not only difficult to
manufacture but are subject to large
frictional forces.
Large Friction The contact surface between the cradle
Surface and the housing may be large. The friction
between the two surfaces will have to be
overcome by additional power from the
motors.
Vertical Stability In order to attach the cradle to the housing,
the design may either have rollers opposite
the tilt pinion to fix the cradle in the
vertical direction. It will be difficult to
eliminate play between the two components.
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7.2 Generic DesignThe second design option under consideration for the Pan and Tilt mechanism is the "classic" double axis gimbal mechanism. Similar to the designs commonly used to manipulate security cameras, this design consists of a horizontal joint mounted on top of a vertical pan joint. The advantages and disadvantages of this system are tabulated below.
FIGURE 14. Field Test
FIGURE 15. Generic Design
TABLE 10. Generic Design Advantages
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Advantage Reason
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Proven This is the standard design for giving two
degrees of motion to a camera. Problem
areas are known.
Robust This design is rugged and is easily
weatherproofed
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TABLE 11. Generic Design Disadvantages
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Disadvantage Reason
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Greater Pan The pan motor would need to be stronger
Rotational Inertia because the tilt motor and arms would be
farther from the center of gravity.
Hughes Design Team is A team at Hughes is designing a
Pursuing This Design mechanism similar to this. We did
not want to duplicate their effort.
Aesthetics Hughes has invested time and money into
a sleek sight housing. The arms on this
design would detract from the housing's
profile.
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7.3 Bevel DesignThe bevel design was based on a concept of providing unlimited pan rotation without the need for a slip ring. To perform this task, both the pan and tilt motors are located in the base and torque is transmitted through a driveshaft coincident with the axis of (pan) rotation. Panning can be controlled via either a separate drivetrain or by differential braking of the tilt mechanism.
FIGURE 16. Bevel Design
TABLE 12. Bevel Design Advantages
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Advantages Reason
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Possible One The motors for this design would both be
Motor Solution in the base. One motor could drive both
functions but a transmission would be
required.
Low Rotational There would be less weight above the pan
Inertia base because the tilt arms would enclose
no motors.
No Slip Ring Required There is no need to transmit power above
the pan base.
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TABLE 13. Bevel Design Disadvantages
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Disadvantage Reason
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Pan and Tilt As the base pans, the bevels must turn,
Functional and the sight tilts. The user will not
Dependence be able to pan without tilting.
Cost The gear train and necessity for a
transmission would make this a very
expensive alternative.
Complexity Complicated gear train and need for a
transmission to decouple the pan and
tilt function.
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7.4 Plunger DesignSimilar to the concept which drove the bevel design, the plunger represents another attempt to attain unlimited pan rotation without the need for a slip ring. The primary advantage of this system, however, is its simplicity as well as the axiomatic division of the pan and tilt functions.
FIGURE 17. Plunger Design
TABLE 14. Plunger Design Advantages
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Advantage Reason
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No Slip Ring Required Both the pan and tilt motor are located in
the pan base. There is no need for a slip
ring because the tilt is powered by a linear
actuator.
Low Cost There is no need for a gear train and the
weight above the pan base is very low.
Great Efficiency The sight is tilted without gears. Links are
more efficient.
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TABLE 15. Plunger Design Disadvantages
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Disadvantage Reason
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High Profile In order to tilt the sight through the
required angle, the lever arm has to be at
least 3 inches long. It will be difficult to
design a mechanism that meets the height
requirement.
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8.0 Design Analysis