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and factors such as your track's length, traction and
composition; tight or open track; and your truck's rear tire
diameter. A basic 24° stock motor would start around at the
low end (9.83:1; spur 87/pinion 23) of the scale while a 36°
to 40° short stack stock motor would start at the high end
(11.91:1; spur 87/pinion 19) of the gearing scale.
MODIFIED. For modified motors we have included a
starting gear ratio chart for the truck. This chart is based on
using seven cells and four inch diameter tires. If you are
running a six cell pack, then you will normally add one or two
teeth to the recommended pinion size for your setup. The
formulas that follow can help you gear correctly for your motor
and help you match a recommended gear ratio given to you.
We recommend starting with a 14 turn modified motor.
Recommended starting modified gear ratios:
spur/pinion
17 turn
87/21
10.77:1
16 turn
87/20
11.31:1
15 turn
87/19
11.91:1
14 turn
87/18
12.56:1
13 turn
87/17
13.30:1
12 turn
87/16
14.13:1
11 turn
87/15
15.08:1
Examples:
Converting a buggy gear ratio to truck ratio. If you have a
recommended gear ratio for a particular motor, but the setup
given was for a buggy, you can convert the final drive numbers
to correct for the differences in tire diameter so that the motor
will see the same load in the truck as it would see in the buggy.
The average difference between buggy and truck tires is an
increase in 33%. Your formula is as follows:
9.5 x 133% = 12.635 = 12.64:1
How to determine the final drive ratio based on actual spur
gear and pinion size. Spur gear = 87, pinion = 20
(87 / 20) = 4.35 x 2.60 = 11.31 = 11.31:1
How to determine starting pinion size based on recommended
final drive ratio and chosen spur gear size. Spur gear = 87,
final drive ratio = 13.50:1
(87 / 13.5) = 6.444 x 2.6 = 16.754 = 16.75 = 17
(always round
to nearest whole number)
BATTERY CHARGING
It is important to understand the characteristics of
the battery pack in your truck. How you charge and use it will
greatly affect both its performance and its life. With proper
care your pack will perform well for many hundreds of cycles.
The ROAR legal battery for use with your truck is
composed of six or seven “sub-C” size cells with a rated
capacity of between 1.2-1.8 amperes for one hour, or 2.4
amperes for 1/2 hour, etc. This charge capacity is the same
regardless of the number of cells in the pack because the
cells are connected in series and the same current passes
through each one.
CHARGER. A good quality automatic charger will
last longer than an economy unit, so please do not cut
yourself short here by trying to save a couple of dollars. Any
good name brand charger will do the job correctly. Associ-
ated recommends a peak detection charger as opposed
to the timer charger. Timer chargers increase the chance of
making a mistake when charging the battery. This also
increases the chance of damaging the battery pack. Peak
detection chargers have an internal circuit that monitors the
voltage and charge rate of the battery pack. When the pack
is fully charged, the voltage will begin to decrease and a peak
charger will detect this and either turn the charger off, or down
to a trickle charge. Some chargers have even more sophis-
ticated features that make charging less time-consuming.
The better chargers like this can easily handle the abuse of
heavy back-to-back type charging that is common when
racing or playing for a long time. The choice of a DC only or
an AC/DC charger should be based on personal needs
(where you will be using your truck, etc.) and usage.
OVERCHARGE. There is no way to make a Ni-Cd
cell accept more charge than it is designed to hold. This
means that as the cell approaches a fully charged condition,
the portion of charging current not being stored becomes
heat and pressure. If charging continues after the cell is fully
charged, all of the current is converted to heat and pres-
sure—about40 watts worth, or the equivalent of the heat
produced by an average soldering iron. High temperature
and pressure is damaging to the cells, so overcharging must
be avoided.
Ni-Cd cells have a built-in process for recombining
the accumulated gas (actually oxygen) produced by over-
charge, but the process produces heat and takes a lot of time.
If you overcharge your battery and it seems to take a long
time to cool down, it’s because this pressure reducing reac-
tion is taking place. Once the gas is recombined the tempera-
ture drops.
HOW TO TELL WHEN YOUR
CELLS ARE CHARGED
One of the problems with Ni-Cds is their inherent
voltage stability; the voltage of a fully charged cell is not much
different from one that’s just about dead. For that reason
several indicators, along with some common sense, are
needed in order to get the most out of your battery. The
following is a list of indicators you can use to detect full
charge.
SLOW CHARGE METHOD. Slow or “overnight”
charging is a method you are not likely to use often, but it is
a good way to bring the pack to absolutely full charge.
However, the output voltage of a slow charged pack is slightly
lower.