G-24
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 the 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.
Receiver Power System Requirements
