I am not certain whether this is the right area to post in but no doubt someone will move it to the right place if necessary.
I am a photographer and working on building a Mendel for RP (See RepRapWiki) but need to design in additional features.
Photography has traditionally been used to represent our 3 dimensional world using 2 dimensional media. My objective is to be able to create 3 dimension photographic works and would appreciate help from those familiar with design and control of robotic devices.
What I need is a small 6 axis robotic arm which could be fixed to the Mendel's carriage to hold either a laser or a tiny spray gun. The arm has to be able to reach into the nooks and crannies of a model once it has been built. I have no idea how to go about either designing or building such a device nor how to control it.
Models will be built in the mendel. The tiny spray gun will be used to apply baryta coatings & light sensitive photographic emulsions so will need to handle a range of viscosities. The laser will be used to expose the emulsions to light and the model will subsequently be processed using traditional chemicals.
The mendel will be installed in a darkroom.
Please ask question
That is a huge challenge you are talking about. However, the type of tool you are using is rotational symmetric (the laser is, if your spray nozzle is round then the sprayer is too.) So that removes one degree of freedom from your arm- no point in being able to rotate your laser pointer pen on its long axis- the effect is the same.
The Mendel already has three degrees of freedom, so if you find a way to use those you only need to build a device with 2 degrees of freedom. However, you mention reaching "in" to the model, so you might need a redundant degree of freedom totaling 3. Your control issues reach an entire new level of difficulty with redundant degrees of freedom in that case. And this is assuming you mount the device to the same carriage as the print head- nothing you can build cheaply will likely fit there.
I suggest obtaining a book on robotic manipulation and mastering the material.
There exist many hobbyist or educator level plastic robot arm kits with 3 or 4 degrees of freedom for very reasonable prices. Your project might turn into a feedback or stepper modification of the axes of the robot arm, or you can splurge for one with a software program/ computer interface built in (your best bang for the buck). If you obtain a kit with 4 degrees of freedom and mount hanging above the Mendel in the same reference frame as the Mendel and use the additional degree of freedom in the sliding build table you will have all 5 degrees required.
I would investigate the kinematics control package EMC2 for controlling the whole thing. The material in a graduate level text on robotic manipulation will let you know or point the way to defining your device so that EMC2 can control it all.