JR R921 Receiver

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9 channels
2 internal receivers
1 or 2 (optional) remote receiver(s)
Patented MultiLink™ technology
Two types of fail-safe—SmartSafe™ and Preprogrammed fail-safe
Flight Log compatible
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Number of channels—9
Modulation—DSM2
Band—2.400 to 2.4835GHz
Dimensions (WxLxH)—.35”x2.06”x0.55”
Weight—Main 15 g/.6 oz; Remote 3 g/.2 oz each
Current—70mA
Voltage range—3.5 to 9.6V
Installing the R921 Receiver
The R921 incorporates dual internal receivers and one or
two remote receivers, offering the security of up to four
simultaneous RF links for the ultimate in multi-path RF security.
Two internal receivers are located on the main PC board, while
a third remote receiver must be plugged into one of the antenna
ports in order for the system to operate. Optionally, a second
remote receiver can be plugged into the remaining remote
antenna port giving a total of four operational receivers. By
locating these receivers in different locations throughout the
aircraft, each receiver is exposed to its own RF environment,
greatly improving path diversity (the ability of the receiver to
see the signal in all conditions).
Using double-sided foam tape (servo tape), mount the remote
receiver(s), keeping the remote antenna(s) at least 2 inches away
from the primary antenna. Ideally, the antennas will be oriented
perpendicular to each other; however, we’ve found this to not
be critical. 6-inch, 9-inch, 12-inch, 24-inch and 36-inch leads
are available and, in sophisticated aircraft, we’ve found it best
to mount the remote receivers in different parts of the aircraft,
keeping the remote antennas as far away as practical from
any conductive materials. A typical installation would include
the main receiver mounted in the conventional location in the
fuselage and the remote antennas in the nose (jets) in the top
turtle deck and even in the tail. The optimum location is as far
away from any conductive materials as practical.
R921 Binding Instructions
Standard Range Testing
The R921 receiver must be bound to the transmitter before it will operate. Binding is the process of teaching the receiver the specific code of the
transmitter or transmitter module so it will connect only to that specific transmitter. Once bound, the receiver will only connect to that specific
transmitter (module) or when used with a Spektrum™ or JR® transmitter that has ModelMatch™, the receiver will only connect when the previously
bound model memory is selected. If another model memory is selected, the receiver will not connect. This feature is called ModelMatch and
prevents flying a model using the wrong model memory.
Before each flying session, and especially with a new model,
it’s important to perform a range check. The X9303 2.4
incorporates a range testing system which, when the bind
button on the transmitter is pressed and held, reduces the
output power, allowing a range check.
QuickConnect
Range Testing the X9303 2.4
In the event of a power interruption, the receiver will reconnect with the transmitter immediately when power is restored. This feature
helps avoid control loss during short interruptions in power. NOTE: If a power loss occurs, the LEDs on the main receiver and remote
receiver rapidly flash indicating a power loss has occurred. If this happens, it is strongly suggested that the cause be determined and
corrected before further flying.
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1. W
ith the system hooked up as shown, insert the bind plug in the charge plug
receptacle. The switch must be a 3-wire type switch (JRPA001 or JRPA004) to enter
the bind mode through the switch. If a 3-wire switch is not available, install the male
bind plug into the charge plug receptacle and power the receiver through any other
open port to enter bind mode.
4. P ress and hold the bind button on the back of the transmitter while turning on the
power switch. The bind button should flash and within a few seconds the system
should connect. The LED’s on the receivers should go solid, indicating the system
has connected.
BIND PLUG
Install the main receiver using the same method you would use
to install a conventional receiver in your aircraft. Typically wrap
the main receiver in protective foam and fasten it in place using
rubber bands or Velcro straps. Alternately, in electric models or
in jets (low vibration), it’s acceptable to use thick double-sided
foam tape to fasten the main receiver in place.
Mounting the remote receiver(s) in a different location(s)
from the primary receiver gives tremendous improvements
in path diversity. Essentially each receiver sees a different RF
environment, and this is the key to maintaining a solid RF link,
even in aircraft that have substantial conductive materials (i.e.
turbine engines with metal tail pipes, carbon fiber, tuned pipes,
etc.) which can attenuate the signal.
3. You should have total control of the model with the button
depressed at 30 paces (90 feet).
4. If control issues exist, call the JR Service Center at
1-877-504-0233 for further assistance.
2. Turn on the receiver switch. Note that the LED’s on both receivers should be flashing,
indicating that the receiver is ready to bind. To program SmartSafe™, leave the bind
plug in the receiver during the entire bind process. To program Preset Failsafe with the
LED’s flashing, remove the bind plug prior to step 4. This will program the receiver in
the Preset Failsafe mode.
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Advanced Range Testing Using a Flight Log
5. Remove the bind plug and store it in a convenient place.
6. After you’ve programmed your model, it’s important to rebind the system so the true
low throttle and neutral control surface positions are programmed.
Note: To bind an aircraft with an electronic speed controller that powers the receiver
through the throttle channel (BEC), insert the bind plug into the battery port and
proceed to Step #2.
While the above Standard Range Testing procedure is
recommended for most sport aircraft, for sophisticated aircraft
that contain significant amounts of conductive/reflective
materials (i.e. turbine-powered jets, some types of scale
aircraft, aircraft with carbon fuselages, etc.) the following
advanced range check will confirm that all internal and remote
receivers are operating optimally and that the installation
(position of the receivers) is optimized for the specific aircraft.
This Advanced Range Check allows the RF performance of
each individual internal and remote receiver to be evaluated
and to optimize the locations of each individual remote receiver.
Advanced Range Testing the X9303 2.4
Note: The R921 requires that at least one remote receiver
be used.
2. Face the model with the transmitter in your normal flying
position and depress and hold the bind button on the back of
the transmitter. This causes reduced power output from the
transmitter.
Note: The R921 features DSM2 technology and is compatible with all Spektrum and JR DSM2 aircraft transmitters. The R921 is not compatible
with the DX6 first-generation DSM® park flyer system. 3. Establish the desired failsafe stick positions: normally low throttle and flight
controls neutral.
In helicopters, there is generally enough room on the servo tray
to achieve the necessary separation. If space is limited, a mount
can be made using clear plastic to mount the external antenna.
1. With the model resting on the ground, stand 30 paces (approx.
90 feet) away from the model.
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The R921 receiver combines two internal with one or two (optional) remote receivers (JRPRR121), offering superior path diversity.
The radio system simultaneously transmits on two frequencies, creating up to four RF paths on two different 2.4GHz channels.
This multi path redundancy, plus the fact that each of the up to 4 receivers are located in different locations throughout the aircraft,
exposes each to a different RF environment creating a superior RF link in all conditions. The JR R921 allows the use of an optional
Flight Log Data Recorder (JRPA145). The Flight Log plugs into the data port and provides quality of RF link data of the previous
flight, allowing the confirmation of the operational performance of the systems.
Specifications
Features
AR900
JR R921 Receiver
The R921 features two types of failsafe: SmartSafe™ and Preset Failsafe
SmartSafe Failsafe
Preset Failsafe
SmartSafe is ideal for most types of electric aircraft and is also recommended for most types
of gas- and glow-powered models. With SmartSafe, when signal is lost the throttle channel
only is driven to its preset failsafe position (normally low throttle) while all other channels
hold last command. Here’s how SmartSafe works:
Receiver power only
When the receiver only is turned on (no transmitter signal is present), all servos except for
throttle are driven to their preset failsafe positions, normally control surfaces at neutral and
the landing gear down. These failsafe positions are stored in the receiver during binding.
At this time the throttle channel has no output, to avoid operating or arming the electronic
speed control. In glow-powered models, the throttle servo has no input signal so it remains
in its current position.
After connection
When the transmitter is turned on and after the receiver connects to the transmitter, normal
control of all channels occurs. After the system makes a connection, if loss of signal occurs
SmartSafe drives the throttle servo only to its preset failsafe position (low throttle) that was
set during binding. All other channels hold their last commanded position. When the signal
is regained, the system immediately (less than 4ms) regains control.
SmartSafe:
• Prevents unintentional electric motor response on start-up.
• Eliminates the possibility of over-driving servos on start-up by storing preset failsafe
positions.
• Establishes low-throttle failsafe and maintains last-commanded control surface position
if the RF signal is lost. Note: Failsafe positions are stored via the stick and switch
positions on the transmitter during binding.
Preset Failsafe is ideal for sailplanes and is preferred by some modelers for their glow- and
gas-powered aircraft. With Preset Failsafe, if the signal is lost all channels are driven to their
preset failsafe positions. Here’s how Preset Failsafe works:
Receiver power only
When the receiver only is turned on (no transmitter signal is present), all servos except for
throttle are driven to their preset failsafe positions, normally control surfaces at neutral and
the landing gear down. These failsafe positions are stored in the receiver during binding.
At this time the throttle channel has no output, to avoid operating or arming the electronic
speed control. In glow-powered models, the throttle servo has no input signal so it remains
in its current position.
After connection
When the transmitter is turned on and after the receiver connects to the transmitter, normal
control of all channels occurs. After the system makes a connection, if loss of signal occurs
Preset Failsafe drives all servos to their preset failsafe positions that were set during binding.
For sailplanes, it’s recommended that the spoilers/flaps deploy to de-thermalize the aircraft,
preventing a flyaway. Some powered modelers prefer to use this failsafe system to program
a slight turn and low throttle to prevent their aircraft from flying away. When the signal is
regained, the system immediately (less than 4ms) regains control.
Preset Failsafe:
• Prevents unintentional electric motor response on start-up.
• Eliminates the possibility of over-driving servos on start-up by storing preset failsafe positions.
• Establishes preset failsafe servo positions for all channels if the signal is lost.
Note: Failsafe positions are stored via the stick and switch positions.
1. Plug a Flight Log (JRPA145, optional) into the data port in
the R921 receiver and turn on the system (transmitter and
receiver).
2. Advance the Flight Log until F- frame losses are displayed,
by pressing the button on the flight log.
3. Have a helper hold your aircraft while he observes the
Flight Log data.
4. Standing 30 paces away from the model, face the model
with the transmitter in your normal flying position and
depress and hold the bind button on the back of the
transmitter. This causes reduced power output from the
transmitter.
5. Have your helper position the model in various
orientations (nose up, nose down, nose toward the
transmitter, nose away from the transmitter, etc.) while your
helper is watching the Flight Log, noting any correlation
between the aircraft’s orientation and Frame Losses. Do
this for 1 minute. The timer on the X9303 can be used
here. For giant-scale aircraft, it’s recommended that the
airplane be tipped up on its nose and rotated 360 degrees
for one minute, then record the data. Next place the
airplane on its wheels and do a second test, rotating the
aircraft in all directions for one minute.
6. After one minute, release the bind button. A successful range
check will have recorded zero frame loses. Scrolling the
Flight Log through the Antenna fades (A, B, L, R) allows
you to evaluate the performance of each receiver. Antenna
fades should be relatively uniform. If a specific antenna is
experiencing a high degree of fades, then that antenna should
be moved to a different location.
7. A successful Advanced test will yield the following:
H- 0 holds
F- 0 frame losses
A, B, R, L- Antenna fades will typically be less than 100
It’s important to compare the relative antenna fades and if a
particular receiver has significantly higher antenna fades (2 to
3X), then the test should be redone, and if the same results
occur, move the offending receiver to a different location.
Flight Log (JRPA145)—Optional for R921 Receiver
Antenna fades—represents the loss of a bit of information on
that specific antenna.
Typically it’s normal to have as many as 50 to 100 antenna fades
during a flight.
If any single antenna experiences over 500 fades in a single
flight, the antenna should be repositioned in the aircraft to
optimize the RF link.
Frame loss—represents simultaneous antenna fades on all
attached receivers. If the RF link is performing optimally, frame
losses per flight should be less that 20.
A hold occurs when 45 continuous (one right after the other)
frame losses occur.
The Flight Log is compatible with R921 receivers. The Flight
Log displays overall RF link performance as well as the
individual internal and external receiver link data. Additionally it
displays receiver voltage.
Using the Flight Log
After a flight and before turning off the receiver or transmitter,
plug the Flight Log into the Data port on the R921 receiver. The
screen will automatically display voltage i.e. 6v2= 6.2 volts.
Note: When the voltage reaches 4.8 volts or less, the
screen will flash indicating low voltage.
Press the button to display the following information:
A - Antenna fades on internal antenna A
B - Antenna fades on internal antenna B
L - Antenna fades on the left external antenna
R - Antenna fades on the right external antenna
F - Frame loss
H - Holds
This takes about one second. If a hold occurs during a flight,
it’s important to re-evaluate the system, moving the antennas
to different locations and/or checking to be sure the transmitter
and receivers are all working correctly.
Note: A servo extension can be used to allow the Flight
Log to more conveniently be plugged in without having to
remove the aircraft’s hatch or canopy. On some models, the
Flight Log can be plugged in, attached and left on the model
using double-sided tape. This is common with helicopters,
mounting the Flight Log conveniently to the side frame.
Receiver Power System Requirements
With all radio installations, it is vital that the onboard power
system provides adequate power without interruption to the
receiver even when the system is fully loaded (servos at
maximum flight loads). This becomes especially critical with
giant-scale models that utilize multiple high torque/ high current
servos. Inadequate power systems that are unable to provide the
necessary minimum voltage to the receiver during flight loads
have become the number one cause of in-flight failures. Some of
the power system components that affect the ability to properly
deliver adequate power include: the selected receiver battery
pack (number of cells, capacity, cell type, state of charge), switch
harness, battery leads, regulator (if used), power bus (if used).
While R921 receivers’ minimum operational voltage is 3.5 volts,
it is highly recommended the system be tested per the guidelines
below to a minimum acceptable voltage of 4.8 volts during
ground testing. This will provide head room to compensate for
battery discharging or if the actual flight loads are greater than
the ground test loads.
Recommended Power System Guidelines
1. When setting up large or complex aircraft with multiple high
torque servos, it’s highly recommended a current and voltmeter (Hangar 9 HAN172) be used. Plug the voltmeter in an
open channel port in the receiver and with the system on,
load the control surfaces (apply pressure with your hand)
while monitoring the voltage at the receiver. The voltage
should remain above 4.8 volts even when all servos are
heavily loaded.
Note: The optional Flight Log has a built in voltmeter and it
can be used to perform this test.
2. With the current meter inline with the receiver battery lead,
load the control surfaces (apply pressure with your hand)
while monitoring the current. The maximum continuous
recommended current for a single heavy-duty servo/
battery lead is three amps while short duration current
spikes of up to five amps are acceptable. Consequently, if
your system draws more than three amps continuous or
five amps for short durations, a single battery pack with a
single switch harness plugged into the receiver for power
will be inadequate. It will be necessary to use multiple
packs of the same capacity with multiple switches and
multiple leads plugged into the receiver.
3. If using a regulator, it’s important that the above tests are
done for an extended period of 5 minutes. When current
passes through a regulator, heat is generated and this heat
causes the regulator to increase resistance, which in turn
causes even more heat to build up (thermal runaway).
While a regulator may provide adequate power for a short
duration, it’s important to test its ability over time as the
regulator may not be able to maintain voltage at significant
power levels.
4. For really large aircraft or complex models (for example
35% and larger or jets), multiple battery packs with
multiple switch harnesses are necessary or, in many cases,
one of the commercially available power boxes/ busses
is recommended. No matter what power systems you
choose, always carry out test #1 above making sure that
the receiver is constantly provided with 4.8 volts or more
under all conditions.
5. The latest generation of Nickel Metal Hydride batteries
incorporate a new chemistry mandated to be more
environmentally friendly. These batteries, when charged
with peak detection fast chargers, have tendencies to false
peak (not fully charge) repeatedly. These include all brands
of Ni-MH batteries. If using Ni-MH packs, be especially
cautious when charging making absolutely sure that the
battery is fully charged. It is recommended to use a
charger that can display total charge capacity. Note the
number of mAh put into a discharged pack to verify it has
been charged to full capacity.
Warranty Period
Inspection or Repairs
Exclusive Warranty- Horizon Hobby, Inc., (Horizon) warranties that the Products purchased (the
“Product”) will be free from defects in materials and workmanship for a period of 3 years from the
date of purchase by the Purchaser.
If this Product needs to be inspected or repaired, please return to Horizon Hobby. Pack the product
securely using a shipping carton. Please note that original boxes may be included, but are not
designed to withstand the rigors of shipping without additional protection. Ship via a carrier that
provides tracking and insurance for lost or damaged parcels, as Horizon is not responsible for
merchandise until it arrives and is accepted at our facility. A Service Repair Request is available at
www.horizonhobby.com on the “Support” tab. If you do not have internet access, please include a
letter with your complete name, street address, email address and phone number where you can be
reached during business days, a list of the included items, method of payment for any non-warranty
expenses and a brief summary of the problem. Your original sales receipt must also be included for
warranty consideration. Be sure your name, address, and phone number are clearly written on the
outside of the shipping carton.
Limited Warranty
(a) This warranty is limited to the original Purchaser (“Purchaser”) and is not transferable. REPAIR
OR REPLACEMENT AS PROVIDED UNDER THIS WARRANTY IS THE EXCLUSIVE REMEDY OF
THE PURCHASER. This warranty covers only those Products purchased from an authorized Horizon
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ABOUT NON-INFRINGEMENT, MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
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THAT THE PRODUCT WILL SUITABLY MEET THE REQUIREMENTS OF THE PURCHASER’S
INTENDED USE.
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(i) repair or (ii) replace, any Product determined by Horizon to be defective. In the event of a defect,
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warranty does not cover damage due to improper installation, operation, maintenance, or attempted
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Damage Limits
Warranty Inspection and Repairs
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replaced free of charge. Repair or replacement decisions are at the sole discretion of Horizon Hobby.
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Should your repair not be covered by warranty the repair will be completed and payment will be
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4105 Fieldstone Road
modification or misuse, no liability shall be assumed nor accepted for any resulting damage or injury.
Champaign, Illinois 61822
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Safety Precautions
Please call 877-504-0233 with any questions or concerns regarding this product or warranty.
This is a sophisticated hobby Product and not a toy. It must be operated with caution and common
sense and requires some basic mechanical ability. Failure to operate this Product in a safe and
responsible manner could result in injury or damage to the Product or other property. This
Product is not intended for use by children without direct adult supervision. The Product manual
contains instructions for safety, operation and maintenance. It is essential to read and follow all the
instructions and warnings in the manual, prior to assembly, setup or use, in order to operate correctly
and avoid damage or injury.
FCC Information
Questions, Assistance, and Repairs
This product contains a radio transmitter with wireless technology which has been tested and found
to be compliant with the applicable regulations governing a radio transmitter in the 2.400GHz to
2.4835GHz frequency range.
Your local hobby store and/or place of purchase cannot provide warranty support or repair. Once
assembly, setup or use of the Product has been started, you must contact Horizon directly. This will
enable Horizon to better answer your questions and service you in the event that you may need any
assistance. For questions or assistance, please direct your email to productsupport@horizonhobby.
com, or call 877.504.0233 toll free to speak to a service technician.
This device complies with part 15 of the FCC rules. Operation is subject to the following two
conditions: (1) This device may not cause harmful interference, and (2) this device must accept any
interference received, including interference that may cause undesired operation.
Caution: Changes or modifications not expressly approved by the party responsible for
compliance could void the user’s authority to operate the equipment.
The associated regulatory agencies of the following countries recognize the noted certifications for
this product as authorized for sale and use:
Instructions for Disposal of WEEE by Users in the European Union
This product must not be disposed of with other waste. Instead, it is the user’s responsibility to
dispose of their waste equipment by handing it over to a designated collection point for the recycling
of waste electrical and electronic equipment. The separate collection and recycling of your waste
equipment at the time of disposal will help to conserve natural resources and ensure that it is
recycled in a manner that protects human health and the environment. For more information about
where you can drop off your waste equipment for recycling, please contact your local city office, your
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10901.2