4qd VTX-75 Manual de instrucciones - Página 9
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Imprimir páginaSpeed pot.
We suggest a 10K linear pot, although other values
from 4K7 to 20K, linear or log, can be used.
The gain adjustment on the controller alters the
amount of rotation required before full speed is
reached: this enables a simple lever operated control
by means of a lever arm screwed onto a standard
rotary pot.
The simplest speed control is an ordinary rotary pot:
this won't give any 'dead man' control as the pot
won't return to zero when it is released. 4QD can
supply a spring return to zero hand control.
Alternatively 4QD can supply a plunger operated pot
(linear position sensor), suitable for incorporating
into a foot pedal.
The drawing shows the pot supplied by 4QD
front
With this pot you should only solder to the tips of the
tags: the holes shown are not for soldering but as
heat barriers to stop heat travelling up the tag and
melting the plastic body.
¶ Use as voltage follower
Instead of a pot, the input may be fed from a variable
voltage. 0v (common) to pin F, signal input (+ve) to
pin E. A resistor (10k) should be connected from pin
D to pin F to over-ride the internal pot fault detector
circuit.
Zero speed will be for zero voltage input and full
speed voltage may be adjusted (by the pre-set) to be
from 3v to above 20v. Input impedance is 100K.
If pin D is shorted to pin E (and the 10K present) the
gain control may be used as a pre-set speed control.
Ignition and reverse inputs are both high impedance
(voltage controlled). High activates. Thresholds are
around 5v and 7v.
VTX series instructions
side
back
On/Off switch
Circuitry in the controller switches it off (zero
current consumption) unless there is a voltage on pin
B or pin C.
The wiring is shown on page 6.
Beware of changing any switch when the motor is
running: the motor will brake to a halt more or less
quickly, depending on the deceleration ramp setting.
If the switch changed is the reverse, it will then
accelerate up to speed in the other direction. This
process is quite safe (for the controller).
With the ignition off, or even with the battery
disconnected, the relays short out the motor so free-
wheeling is not possible. To freewheel properly the
motor should be disconnected.
Reversing
Reversing switch
Reversing switch connections are shown in the
diagram above. Reversing is 'dual ramp' which
means that, if the vehicle is reversed at speed, it
automatically slows down under control of the
deceleration ramp then reverses and speeds up under
control of the acceleration ramp.
Whenever the vehicle is in reverse, a speed reduction
circuit operates, so that (if the gain adjustment has
been set up sensibly) full reverse speed is half of full
forward speed.
Reverse Speed reduction
¶ If half speed reverse is not required it can be
disabled by moving the header marked 'HSR' on the
board (and shown in the 'features' diagram). This is
a pinstrip with a shorting link which simply unplugs.
As shown (bottom pin free) reverse is at half speed.
Reverse threshold
If you are reversing the controller from, for instance,
a microcontroller, the threshold is around 5v. A
voltage above this selects reverse, below the
threshold selects forward.
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