This is my first delta robot. It isn't perfect yet, but it works. I tried to use different tools in the end-effector. A vacuum pump made with a syringe and a pen for drawing. Other details, the code and pictures here: http://robottini.altervista.org/delta-robot-with-arduino
This just goes to prove that a basic delta robot is fairly cheap to make.
The robot is a bit imprecise, most likely due to play in the joints. It would still work great for a pick and place task, such as sorting a bucket of nuts/bolts/washers by size/material. Actually, I should build that, I always have bags of random stuff that need sorting.
For me the difficult is to find good ball joints, cheap, with 3mm hole for the arms. I think the problem is the hardware, not the software. That do you think?