This is a joystick interface to servos and steppers. Basically a pluggable controller for the Pololu Micro Maestro 6-channel servo controller, which I use for a small servo-actuated 6DOF arm, and the Peter Norberg Consulting SD6DX stepper motor controller, which I use with an American Robot MR6200 Merlin 6DOF arm.
There is a Joystick class that is basically a wrapper for pygame and is
fairly specific to a Logitch F310 joystick using only some of the axes and
buttons. It is really easy to extend if someone wanted, pretty handy
set of abstractions. There is a Loop class that is allows scheduling a
repeated task on a fixed interval, used for updates. Fixed interval meaning
fixed time between starting runs, it accommodates the duration of the actual
task, which needs to be less than the desired loop time. There is a
Quantize class that allows for arbitrary returned precision; this is used
to prevent noise on the joysticks from changing the incremental positions
of the controllers. There are the two controller classes, Maestro and
Norberg that accommodate the specifics of the respective controller. Each
of these are subclasses of the Controller class that provides common
initialization and a consisten interface for control (e.g. pos() and
inc() for setting either absolute or incremental positions). Controller
is a subclass of VirtualController, which is in place so that the getters
and setters can be used virtually, meaning without actually controlling
some serial device (used for intermediate values for inverse kinematics). For
the purposes of joystick control only the incremental position is used, though
for other types of control (e.g. inverse kinematics) the direct position
control is used. There is also a Joints class that is basically just a
lookup between English names for the 6DOF robot joints and the index for the
joint used by the controller, as well as a Cartesian class that is a lookup
for traditional Cartesian axis names. The whole of this is wrapped in an
argument parser that delegates the different controller commands. The reason
for this is that it is handy to be able to select what type of coordinate system
the joystick control will be describing as well as which particular physical
controller will be used as an interface.
The Maestro controller must be set up in advance using a utility provided by the manufacturer. Since this must be done, advantage can be taken of configuring the maximum speed, acceleration and stops using the utility rather than implementing them in software here. This controller by default runs in vector mode with all actions on all servos occuring synchronously.
The Norberg controller is a far more advanced controller intended for CNC control. That said, it has a slew of features not used here (e.g. vector control for curve contours, analog-to-digital inputs, etc.). It allows either synchronous (vector) or asynchronous control; here we are using vector control operations. Despite the controller supporting relative position control, this is implemented manually. Reason for that is it is extremely easy to compute manually and simple to rely only on the controllers vector implementation of absolute position.
While this code is an exercise in simple joint controllers that can be used with a joystick, there are a number of other things the controller classes are candidates for use with:
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Actuation for ROS controllers
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Actuation for inverse kinematics