====== Control a Single Motor ======

This tutorial will show you how to control a single motor using EEROS. This example is located in a separate repository [[https://github.com/eeros-project/simple-motor-control.git]]. 
=====Theoretical Background=====

A motor position is measured by an encoder. After differentiating this signal we obtain the velocity. The input of the velocity controller is the difference between reference and measured velocity. Additionally, the feed forward velocity is added. The output of this controller is an acceleration. This value is then multiplied by the inertia and divided by the motor constant, in order to obtain a current reference value to control the motor.

[{{ oneAxis_controlLoop.jpg?688 | //Control loop//}}]

For a good dynamical stiffness we choose //f<sub>0</sub> = f<sub>s</sub> / 20// where //f<sub>s</sub>// is the sampling frequency. With //f<sub>s</sub> = 1kHz// we get //f<sub>0</sub> = 50Hz//. With //ω<sub>0</sub> = 2·π·f<sub>0</sub>// the parameters for the position and velocity controller, kp and kv respectively, will be as follows: 

// k<sub>p</sub> = ω<sub>0</sub> / 2·D // and // k<sub>v</sub> = 2·D·ω<sub>0</sub> //

D is the damping factor and we choose it as 0.9.

=====Experimental Setup=====
The motor we use has the following properties:

|  **Properties**              ^  Value            ^  Unit         ^
^  Inertia    |  9.49          |  kgm<sup>2</sup>        |
^  Motor Constant    |  16.3 10<sup>-3</sup>  |  Nm/A                  |
^  Encoder Pulses    |  500          |        |

We use three different platforms for running the Simple Motor Controller.
  * [[oneaxis_comedi|]]
  * [[oneaxis_bbb|]]  
  * [[oneaxis_cb20|]]

=====Build Application=====

  - Proceed with [[getting_started:write_app|]] and select the right target. Scroll down to ''Use Existing Project''.
  - After cloning the project, navigate to the directory ''simple-motor-control'' where you can find the code of the application.
  - [[getting_started:deploy|]] to the target system if necessary.

=====Test Application=====

You will find different hardware configuration files depending on the hardware platform.
  * HwConfigComedi.json
  * HwConfigFlink.json
  * HwConfigBBB.json

Start our application by choosing the appropriate configuration file, e.g.:
<code>
$ sudo ./simpleMotorControl -c HwConfigBBB.json
</code>
The application logs the motor position once per second. By activating the emergency button, the safety system will immediately switch to an emergency state. Deactivating this button causes the system to switch back to running mode.

===== Develop your own Application Further =====
For further development we recommend to use an integrated development environment as described in [[getting_started:kdevelop|]]. You do not have to create a new project, because you already have downloaded and built the simple motor controller project. Import the project together with the EEROS and wrapper libraries into KDevelop.


=====Implementation=====
==== Control System ====
The control system declares in ''ControlSystem.hpp'' all the necessary blocks as given in the picture at the top of this page. Those blocks are then defined in ''ControlSystem.cpp'', connected together, and added to a time domain. At last the time domain is added to the executor. \\

==== Safety System ====
Safety levels and events are declared in ''SMCSafetyProperties.hpp''. ''SMCSafetyProperties.cpp'' initializes these objects, defines critical inputs and outputs, defines level actions, and adds the levels to the safety system. The levels and events causing transitions between those levels are shown in the next figure.
[{{ :getting_started:tutorials:safetysystemoneaxis.jpg?700 |//Safety levels and events//}}]

Two critical inputs are defined: "emergency" and "readySig1". "enable" is a critical output. Critical inputs and outputs are checked and set by each safety level. For example "enable" is set to ''true'' as soon as the safety level is equal or higher than ''powerOn''. "emergency" is unchecked for the two lowest levels and leads to level change to level ''emergency'' for higher levels. 

==== Sequencer ====
The sequencer runs a sequence which turns the motor each second a tenth of a full turn.