Curtis PMC 1204X/1205X/1209/1221 Manual
5
HARDWARE INSTALLATION
THROTTLE
0–5kΩ Input
The standard controller throttle input is 0–5kΩ. Curtis PMC potboxes (PB-5,
-6, -9, -10) are designed to match this input. Some of these potboxes have a built-
in microswitch, eliminating the need to install a separate pedal-actuated
microswitch. Curtis PMC also offers a self-contained footpedal unit (FP-2) that
eliminates the need for fabricating and installing a pedal-potbox linkage. Mount-
ing dimensions for the potboxes and for the footpedal unit are shown in Figures
4 and 5.
Any potbox that provides a nominal 0–5kΩ output (controller output
begins at ≈300 ohms, full output is ≈4400 ohms) will work with the standard
throttle input. For other types, contact your Curtis office.
If a Curtis PMC potbox is used, it must be mounted so as to allow
connection between the potbox lever arm and the vehicle accelerator linkage.
The lever arm provides a series of holes so that the accelerator pedal “throw” can
be converted into the correct amount of potentiometer rotation. Use of a second
return spring on the pedal, in addition to the potbox return spring, is required to
prevent an uncontrollable full-on throttle input (which could happen if there was
a single spring, and it broke). If the self-contained potbox spring is insufficient to
return the pedal by itself, two additional pedal return springs must be used.
It is also required that the accelerator pedal hit a mechanical stop at its full-
on position just before (≈1 mm [1/32"–1/16"]) the potbox lever hits its own full-
on stop. This mechanical stop will prevent the potbox lever arm from bending if
undue force is put on the pedal. Protection of the potbox from water and dirt will
help avoid problems of corrosion and electrical leakage.
After the potbox has been mounted, operation of the pot can be tested by
measuring the resistance between the two wires with an ohmmeter. With the
pedal not applied, the resistance should be less than 50 ohms. As the pedal is
applied, the resistance should rise smoothly until it reaches a value between 4500
and 5500 ohms. Values below 4500 ohms may cause a reduction in efficiency
and top speed. Values above 7000 ohms indicate a defective potbox, and will
cause controller shutdown.
5kΩ–0 Input
The 1204X/1205X/1209/1221 controllers are also available with 5kΩ–0 throttle
inputs. Using this throttle type, controller output begins at ≈4400 ohms with full
output at less than 300 ohms.
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