03-08-2012, 11:45 AM
Hovercraft
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Introduction
We are designing a hovercraft that would maintain a certain altitude. Two
vertical poles are guiding the hovercraft when it’s in motion (see Figure 1). A battery
operated motor and propeller are providing the necessary power to left the hovercraft and
its load.
Manual control can be done by installing a variable resistor over the motor
power leads. The computer control system was done using I/O card.
Abstract
Altitude of the Hovercraft was to be measured and controlled using a feed back
system. Feedback system was designed using a voltmeter and a resistor wire. As the
Hovercraft changes altitude, the internal resistance of the wire changes relatively. The
resistor wire was placed along one of the poles. A linear relationship between altitude and
the internal resistance was established as the guidance for the closed loop system. System
was constructed using wooden plate for the base, wooden poles, voltmeter, motor and
propeller, brass tubes as bearings, and wires. Parts were glued together (see Appendix D
for a picture of the hovercraft).
The system was designed for a one-semester project and is quite fragile. Some
reinforcement could be needed if the system was to last longer, including gluing some
stronger flat surface to the base of the system to avoid the misalignment of the poles
because of bending. Also, some reinforcement could be needed for the poles and some
springs could help avoid the hovercraft to hit the base to hard when the power is reduced
too sharply.
5
Apparatus
The following is a list of all of the part used to construct the hovercraft. The
actual project budget, $63.89, came under the initial estimate, $72.00. The cost of
each part is listed in Appendix B. The input/output computer card and board were not
included in the total budget because the University of Texas at San Antonio supplied
them. Minor supplies, such as glue and lubricant, were not included in the total
budget as well.
Table 1: Equipment List
Part Specifications
Motor Graupner “Speed 400”. Voltage 7.2. Produces
120W
Propeller SlimPROP “Super”. Size 9x5”
Resistor Wire 52cm long
Voltmeter RadioSHACK 22-410. 0-15V
Spinner C.G. 1”
Constant Current
Supply
LKG Industries M-W-122A
Electrical Wire 18 Gage
Brass Tube 7/16 round
Wood Sheet Size 0.25x6x36
Wood Sticks 52cm long
Hardwood Dowel Size 3/8x36
MOSFET Philips ECG2395 (See Appendix G)
Heat Sink 1.5”x1.0”x0.5”
Batteries Sanyo KR-600-AE. 8.4Volts
6
Sensor Mechanism
An altitude-sensing device is needed for this project. It was made from
resistor wire. The resistor wire was attached to the support stick. A voltmeter was be
used as a height gage. One voltmeter lead will be attached to one end of the resistor
wire, while the other lead will be attached to the hovercraft. The higher the
hovercraft goes, the higher the measured resistance will be (see Figure 2).
Figure 2: Sensor Mechanism
The following table is used to determine the location of the hovercraft. The
height in inches is given for selected voltage readouts. Other heights can easily be found
by interpolating between the given values.
Table 2: Voltage Across Variable Resistor
Voltage (V) 0.49 1.09 1.67 2.28 2.99
Height (in) 0 5 10 15 20
7
The following plot shows the relationship between the voltage measured across
the variable resistor and the height of the hovercraft.
Height vs. Voltage
0
5
10
15
20
25
0 0.5 1 1.5 2 2.5 3 3.5
Voltage (V)
Height
By linearizing this relationship, we get the following equation describing the
voltage in terms of height.
V = 0.126H + 0.49
Where V: Voltage in (V)
H: Height in (in)
This equation was used in the control diagram to convert the desired height
into voltage. This step allows for a direct comparison between the voltage readout
across the variable resistor and the desired height.