crappy 1.5.4

Command and Real-time Acquisition Parallelized in Python

CRAPPY is an acronym and stands for Command and Real-time Acquisition in Parallelized PYthon.

Crappy is developed at the “Laboratoire de Mécanique de Lille”, a mechanical research laboratory based in Lille, France to provide a powerful and easy-to-use framework for materials testing.

In order to understand the mechanical behaviour of materials, we tend to perform tests with more and more sensors and actuators from various suppliers. There’s thus an increasing need to drive these devices in a synchronized way while managing the high complexity of the setups.

As we are one step ahead of industrials, the commercially available testing solutions may also not be well-suited to our objectives. Custom software solutions thus need to be developed in order to further improve our tests.

These are the original purposes of Crappy : providing a framework for controlling tests and driving hardware in a synchronized and supplier-independent software environment.

Key features of Crappy

To this end, choices were made that are now keys to our framework:

• open-source : It is important for us that everyone can use our work, and bring its own code to the world.

• modular : We provide a software basis that can easily be extended to drive new hardware and perform custom operation on data.

• simple : Python has been chosen for its high level. We are not developers, and neither are our users, so we cannot afford to use a low level programming language. We work with typical loop time of more than 1 millisecond (10ms most of the time), and Python is enough for that. It is also pretty easy to add a small piece of C/C++ to the Python code if a speedup is needed.

• performance : A great deal of work is made to ensure the performance of the framework. Most tests require a good repeatability and stability, and may become hazardous in case of non-handled issue.

• parallelization : The key to a good test is the synchronisation between the different sensors. This is why we chose to massively parallelize our framework, ensuring every device can run simultaneously in a same time basis. This is also one of the major difficulties we have to deal with in Python.

Is Crappy for me ?

Although it was originally designed for driving mechanical tests, Crappy has acquired the flexibility to adapt to other domains as well. Pretty much any device communicating over USB, serial, SPI or I2C can be integrated within the framework, making it suitable for many fields !

So Crappy is the right solution for you if :

• You want to drive sensors and actuators in a synchronized and parallelized way.

• You want a modular solution in which you can easily add new hardware, functions and write your own test protocols.

• You don’t want to bother coding in a low-level language.

• You want to remain independent from commercial software environments.

As Crappy’s scope is well-defined, there are also situations in which Crappy won’t be able to help you. So Crappy is NOT for you if :

• You need to acquire data or drive actuators at frequencies greater than 200Hz.

• You cannot drive your devices over USB, serial, SPI or I2C.

• You don’t want to code in Python (although you should give it a try, it’s great and easy to learn :) )