Manual

Feedback
Kangaroo x2 requires a sensor telling the controller where the device is and how fast it is going.
This sensor signal is called feedback. Kangaroo supports two different kinds of sensors, quadrature
encoders and potentiometers.
Quadrature Encoder
Quadrature encoders are used to determine the position,
speed and direction of a system. The biggest advantage of
encoders is they can rotate continuously: the same sensor can
position to within less than a degree in one rotation or five
thousand rotations. The optical, magnetic and capacitive types of
encoders have essentially infinite lifespan and can turn quickly.
Motors can often be purchased with quadrature encoders already
installed. They sense in discrete counts. The number of counts is
often printed on the encoder or motor. Values from 16 counts per
revolution to over 1000 are common. The downside to
quadrature encoders is they are relative sensors – they only know where they are relative to where they
have been. Some sort of startup routine is necessary to find their position when first powered on.
Kangaroo x2 provides a variety of automatic startup routines for encoders, such as limit switches, index
pulses and mechanical stops. They can also be somewhat expensive – depending on the specifications.
Quadrature encoders usually have four or five wires. Mobile robots and CNC machines are examples of
devices that would use encoders.
Potentiometer
Potentiometers are analog feedback devices. They
typically turn only about 3/4ths of a rotation, though there are
also multiple rotation types. The biggest appeal of using
potentiometers for feedback is they can be very inexpensive –
only a few dollars in single quantities. If you are designing a
mechanism that only moves half a rotation or so, this is a big
advantage. Also, potentiometers are absolute position sensors –
they always know exactly where they are. As a result, they are
ready to work as soon as they’re powered on, with no homing or
startup necessary. The main downside to using potentiometers for feedback is they are limited in their
rotational range, so they are only appropriate for some systems. Inexpensive potentiometers only have
rotational lives of 50,000 or less turns, and even expensive sensor grade models are usually limited to a
few million. Because they are analog sensors, they may have slight noise on their signals, so the control
is sometimes not as smooth. Radio control hobby type servos and robot arms often use potentiometers
for feedback.
A quadrature encoder
A sensor grade potentiometer