PerfectFlite Pnut Bedienungsanleitung
Pnut Users Manual
PO Box 29
Andover, NH 03216 URL: www.perfectflite.com
A miniature, high accuracy, data-logging altimeter
for advanced model rocketry research.
Pnut Users Manual
Contents
Introduction................................................................................................. 1
Parts Identification Diagram.............................................................. 3
Installation
Payload Bay Construction........................................................................................... 4
Static Pressure Sampling Ports................................................................................. 6
Operation
Charging Battery............................................................................................................. 7
Power Switches............................................................................................................... 7
Numerical Reporting..................................................................................................... 8
Powerup Sequence........................................................................................................ 9
Downloading Data.......................................................................................................... 9
Changeable Settings....................................................................................................... 9
Tips for Achieving Optimal Accuracy.................................................................. 14
Telemetry Information.............................................................................................. 16
Testing............................................................................................................................... 18
Cautions............................................................................................................................ 19
Specifications............................................................................................ 20
Warranty.................................................................................... Back Cover
1
Introduction
The Pnut is a high-quality, high-precision, full-featured rocket
altimeter that acquires flight data continuously during your
rocket’s flight for later download and inspection. A large
onboard memory stores altitude, temperature, and battery
voltage data sampled 20 times per second for up to 9 minutes
per flight, for the last 31 flights. It also provides immediate
post-flight reporting of peak altitude and maximum velocity
without the need for a computer. It is ideal for intermediate to
advanced rocket education, advanced science fair projects, and
contest use.
The Pnut is installed inside your rocket and activated prior to
launch. When you retrieve your rocket, the Pnut will report
the apogee altitude (how high your rocket went, up to 100,000
feet above ground) and the maximum velocity (how fast your
rocket went, in miles per hour). It uses a convenient, easy to
understand audio reporting method that is audible from
outside your rocket, so removal or inspection of the altimeter
is not necessary. The reported altitude and velocity are
alternated with a 10 second siren sound that helps to locate
your rocket even if it is hidden in tall grass or a tree.
Using the optional USB Data Transfer kit, the full flight data
(altitude, temperature, voltage) can be downloaded to a
computer for storage, graphing, and additional manipulation.
Because of the generous memory size, it is not necessary to
bring the download equipment to the launch – 31 flights can be
made before download of the data is necessary.
If you want to step up to electronic parachute deployment, you
may want to consider the PerfectFlite StratoLogger, which has
the Pnut’s flight data download features and adds two event
2
electronic parachute deployment for advanced users.
Electronic deployment provides the ultimate in control over
when your parachute is ejected – no more guessing about
which ejection delay length to use, the altimeter will always
fire precisely at apogee.
The Pnut utilizes a precision pressure sensor and 24 bit delta
sigma analog to digital converter to obtain an extremely
accurate measurement of the air pressure surrounding your
rocket. When turned on, the altimeter “tracks” the ambient
pressure surrounding your rocket to get an up-to-the-second
reading of the barometric pressure at ground level. As the
rocket rises, the pressure decreases, and the altimeter converts
the pressure differential to a precise measurement of altitude
above launch point according to the US Standard Atmosphere
model. All of the calculations are done inside the altimeter,
with the results reported simply as “altitude above ground
level”. No conversion or adjustment is necessary.
3
Parts Identification
Refer to the top of the altimeter to locate the following items:
A) Beeper: Audibly reports altitude and velocity after flight.
B) Battery: Built-in rechargeable Lithium Polymer battery.
C) Power Pins and Jumper Shunt. Shunt shown in storage (“off”) position.
Place shunt across both pins to turn altimeter “on”.
D) Charge Connector: Supplied charging cable connects here.
E) Data Connector: Connect to optional data transfer kit and computer for
post-flight download of flight data. Can also be used for access to in-
flight telemetry data.
F) Charge LED: Lights during charging, goes out when charge is complete.
4
You should perform initial testing on your rocket without the
altimeter installed. Make sure that the parachute is ejected
and opens properly so that you have a slow and safe landing. If
Installation
For best results, your altimeter should be installed in a
separate payload compartment, sealed from the pressure and
heat of the ejection charge gasses. While other alternatives are
possible, isolating the altimeter in a protected compartment
will provide the most precise readings and will keep high
temperature and pressure from affecting the long-term
accuracy of the instrument.
A typical payload compartment consists of a section of body
tube behind the nosecone with a sealed tube coupler
connecting it to the main body tube (see illustration below).
Some rockets (e.g. Estes “Nova Payloader”, Quest “Zenith II”)
already have such a payload section, and one can be added
easily if yours does not. Use pieces of foam rubber in front of
and behind the altimeter to prevent it from shifting under
acceleration and deceleration and to protect it in the event of a
crash. The altimeter will slide into 18mm/BT20 size body
tubes, and a “sleeve” made out of standard foam pipe
insulation can be used for larger size tubes. Your payload
section should close securely so that the altimeter is not
“ejected” upon motor burnout deceleration or chute
deployment shock.
5
you conduct your preliminary tests with the altimeter installed
and the chute doesn’t eject, the resulting high speed ballistic
descent will likely damage the altimeter (and your rocket!).
When installing the Pnut in larger rockets it may be easier to
add a short (~3” long) section of BT20 tube with padded end
plugs for the altimeter to ride in. The short BT20 tube could be
glued to the inside of the larger airframe or to a plywood
mounting plate. A static pressure sampling hole can be drilled
through the main airframe and into the inner tube to allow
external air pressure to get to the altimeter.
As a last resort, if accuracy isn’t of paramount importance, you
can simply tie the altimeter to the rocket’s shock cord and pack
it in along with the chute. If you must do this, observe the
following precautions:
1. Use plenty of wadding between the ejection charge and the
parachute.
2. Position the parachute between the wadding and the
altimeter to provide additional protection from the hot
ejection charge gasses.
3. Make sure the altimeter is securely tied to the shock cord
so that it doesn’t separate and free-fall.
4. Add a wrap of tape around the jumper shunt so it doesn’t
get dislodged at ejection. Note: Make sure the tape doesn’t
cover the pressure sensor (small white rectangle marked
“U3”) on the bottom of the altimeter.
6
Static Pressure Sampling Holes
You must drill one or more clean-edged holes in the payload
compartment to allow outside air pressure to be sampled by
the altimeter (see table below for recommended sizes). These
holes should be as far away from the nosecone shoulder and
other body tube irregularities as possible (at least 3 times the
body tube diameter or more) to minimize pressure
disturbances being created by turbulent airflow over the body
tube. Sand the area around the hole as necessary to eliminate
flashing or raised edges.
Best performance and greatest accuracy will be achieved by
using four smaller holes distributed at 90 degree intervals
around the body tube’s circumference instead of a single larger
hole. When using four holes, each hole should be ½ the size of
a single hole as noted in the table. This will minimize the
pressure variations due to wind currents perpendicular to the
rocket’s direction of travel.
Payload Payload Single Four
Diameter Length Hole Size Hole Size
<1.5” 6” .024” .012” (small pinholes)
1.6” 6” .024” .012” (small pinholes)
2.1” 6” .042” .021”
3.0” 8” .113” .057”
3.0” 12” .170” .085”
3.9” 8” .202” .101”
3.9” 12” .302” .151”
Other sizes:
Single hole size = Diameter * Diameter * Length * 0.0016
Four holes, each hole = Diameter * Diameter * Length * 0.0008
7
Operation
Battery
The altimeter is powered by a built-in Lithium Polymer
rechargeable battery that should never need replacement. The
battery is charged using the supplied charging cable and a
standard 9V rectangular battery. When the cable is connected
to the altimeter and a 9V battery, the “charge” LED on top of
the altimeter will light. When the charge is complete the LED
will go out. A full charge takes 2-3 hours if the onboard battery
is fully depleted. As long as the altimeter is turned off between
uses, a full charge can easily last for a year’s worth of typical
rocket launches. A single fresh 9V alkaline battery can provide
up to 6 full charges to the Pnut’s battery.
Tip: You can also use partially depleted batteries (e.g. old smoke
detector batteries) and the Pnut’s charger will extract any
remaining life out of them.
Power Switch
The jumper shunt shown in the picture on page 3 is used to
turn the altimeter on and off. Install the jumper shunt across
the two pins on the altimeter’s circuit board to turn the
altimeter on, and remove the shunt to turn it off. When the
altimeter is not in use, you can place the jumper shunt on just
one of the pins for storage.
For added convenience, you can use the optional power switch
cable to connect an externally-accessible on/off switch to the
altimeter. The cable plugs onto the two pins on the circuit
board in place of the jumper shunt, and your switch is
connected to the loose ends of the cable.
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