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Finding the correct gear ratio is a rather delicate subject and needs
some experience and trials. Assuming that the motor has its best
efficiency at a certain, specific speed, it must be your aim to operate
the motor in this specific range. Here efficiency means best energy
economics at best power output. In practice it is not very efficient to
operate a motor at 50% speed with high energy consumption as it
would perform better at 70% speed at even lower consumption.
Let us discuss the following example:
You have a motor with nominal 25,000 rpm . The efficient speed
would be abt. 17,500 rpm being abt. 70%, depending on the motor's
quality.
The target speed of the main rotor is abt. 1,300 rpm so we have to
find the proper gear ratio.
Various pinions are available from your IKARUS dealer. Let us do
some calculation:
17,500
------------ = 13.46
1,300
The 13 t pinion would offer the longer -, the 14 t pinion the shorter
transmission. Select the shorter one in order to compensate possi-
ble deviations on the motor.
Another example. You have a very powerful motor that runs 12,000
rpm only, effective 9,500 rpm. To get the same mainrotor speed, a
pinion of 24 t will do.
There are other factors that may influence your decision: If you go
for hot aerobatics, 1,500 rpm mainrotor speed are interesting. To
obtain 1,500 rpm with the 17,500 rpm motor, the 15 t pinion should
be the best.
It is never easy to estimate the efficient speed of your motor. Con-
sider 70% of the nominal speed as a good value to start with and
select a pinion in the range. If you have doubts, go for the smaller
pinion.
The battery is the second sensible source of energy economics.
NiCad-batteries offer very good efficiency and performance data - if
treated well. The fun with NiCad cells is that they allow high energy
input while charging and very high output if required. In car racing
these cells often have more than 100 A output.
To get a good performance you should have an eye on the charging.
NiCad cells tend to remind certain states of discharging which may
influence the capacity. The so called "Memory Effect" may damage
your cell if not treated correctly. Let us have some first remarks
here:
-
Charge your batteries just before you intend to start.
-
Discharge your batteries correctly after use.
-
Use a suitable charger to improve the batteries lifetime and
performance.
In detail: 6 -12 cell packs are available in any hobby shop. If you
have the choice use selected or matched types. Remove the shrink
folio for better ventilation. Use silicon or cyano glue to keep the cells
together. Use first class gold plated connectors (order no.:631 554)
only and solder the connectors properly.
Various methods of charging are on the market. Let us discuss the
most interesting ones:
DELTA PEAK: The cells are charged until they reach their maximum
voltage. The charger detects a slight drop of voltage in the pack and
cuts the charging automatically. It is the most safe and commonly
used method. Chargers are available at a wide variety in view of
quality and price. We recommend a charger with 5 - 8 A output for
Your experience ...
... that the motor does not run
freely.
... that the motor runs free but
the helicopter seems to be slow
in response.
... that the motor and the
battery are very hot after the
flight.
... that the motor and the
battery are rather cool after the
TOO MUCH HEAT IS A SIGN OF POOR ENERGY ECONOM-
ICS. ENERGY TRANSFERRED TO HEAT WILL NOT BE TRANS-
FERRED TO FLIGHT TIME AND FLIGHT PERFORMANCE!
best performance.
TIME: The charging is done by the formula capacity (mAh) x
1.4/charging current (mAh) = charging time (h). This methods need
some discipline as overcharging can easily be done and destroy the
battery.
The most forgotten feature about NiCad cells is DISCHARGING. In
order to avoid the Memory Effect and increase the lifetime of the
battery pack it is highly recommended to discharge the battery
completely after use.
Use a 30 Ohm/10-15 VA ceramic resistor, available from your
hobby or electronic shop for 6 h on the complete pack or 5 Ohm/1
VA for 24 h on the single cell and discharge until both, the resis-
tor and the battery are back to normal temperature. It may not be
practical to discharge the packs after each use but you should do
so at least after 3 charging periods. Watch the electric model car
racers for their charging and discharging equipment. They
ally have the best stuff.
Watch for the recommendation of the manufacturer. Avoid overcharg-
ing as poisonous gas may escape from the cells. Do not dump NiCad
batteries, do not expose them to hot sunlight or throw them into fire.
Never open the cells. Handle damaged cells with care and wear eye-
protectors and gloves. Damaged and worn cells can be recycled and
should be treated properly.
Help:
Try 2 tooth less on the pinion.
Try 1 teeth more on the pinion.
2 tooth less on the pinion are
possible.
1 tooth more on the pinion is
possible.
usu-
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