Lab 06: AEV System Analysis 2

AEV Project Objective
(Problem Definition)
INITIAL CONCEPTS
(Brainstorming)
EXPERIMENTAL RESEARCH
(Programming) (System Analysis)
PT 1
PT 2
PT 3
PT 4
FINAL DESIGN
Present AEV Design

 Download data from the automatic control system.
 Convert EEProm Arduino data readouts to physical engineering parameters such as distance traveled and velocity.
 Calculate the performance characteristics of the
AEV.

 In System Analysis 1, we downloaded data from the automatic control system to calculate:
 Time
 Current
 Voltage
Input Power,
Incremental Energy,
Total Energy,
P in

V

I
E i

P i

P i

1
2
E
T
 sum ( E i
)

 t i

1
 t i


 Now we’re going to make use of the wheel counts recorded by the AEV and compute the following:
• Distance s

0 .
0124 * Marks s = distance (meters)
• Velocity v i


 s i t i

 t s i i

1

1

 v = velocity (meters/seconds) s = distance (meters) t = time (seconds)
• Kinetic Energy
KE

1
2 mv
2
KE = Kinetic Energy (joules) m = Mass (kilograms) v = velocity(meters/second)

 The system efficiency (denoted by ) is composed of both the propeller and the electric motor:
 sys
  propeller
 motor
 The efficiency of the propulsion system is a function ( 𝑓 ) of the
AEV’s velocity ( 𝑣 ) and the propeller speed ( 𝑅𝑃𝑀 ):
 sys
 f ( v , RPM )

 AEV velocity can be easily computed.
 The propeller RPM is a function of the current being supplied to the motor by the command inputs.
 The following are sample equations for RPM* :
RPM
3 inch
 
64 .
59 I
2 
1927 .
25 I

84 .
58
RPM
2 .
5 inch
 
17 .
64 I
2 
690 .
375 I

99 .
77
*We will revisit the RPM curves in System Analysis 3 and update the equations above.

 T he function inputs ( 𝑣, 𝑅𝑃𝑀 ) can be reduced from two variables to one variable denoted by 𝐽 :
 sys
 f ( v , RPM )
 f ( J )
 𝐽 above is known as the Propeller Advance Ratio which is given by:
J

( RPM v
60 )

D
RPM = Revolutions per Minute v = velocity(meters/second)
D = Propeller Diameter (meters)

 The advance ratio is used in Aerospace Engineering.
 It is the ratio of forward speed to the speed of the propeller.
• i.e., The distance traveled per revolution of the propeller.
 Typical range of 𝐽 for AEV: ~(0.15 - 0.40).
 A larger the value of 𝐽 can mean the vehicle is requiring little work from the motor thus operating well with low input power.

 At low motor speeds (~10% or lower) the propeller RPM becomes difficult to measure. To filter out bad data, constraints are used when computing the Advance Ratio.
 First, compute advance ratio:
J

( RPM v
60 )

D
 Second, apply constraints:
J


0

 0 .
for
15
J for

J
0 .
15

0 with
.
15 no with power power

 Now that we’ve learned what 𝐽 is, we need to determine what the function 𝑓(𝐽) is. This requires wind tunnel testing! (Next weeks lab)
 For now, you are provided a sample propeller efficiency equation* :
  
1205 J
3 
1033 J
2 
179 .
4 J

17 .
91
* We will revisit the propeller efficiency in System Analysis 3 and update the equation above.