Depends on your goals and budget. I've seen a lot of cheap hobby servo based arms. Precision is awful, payload is miniscule. OTOH, you will learn why precisi

Depends on your goals and budget. I've seen a lot of cheap hobby servo based arms. Precision is awful, payload is miniscule. OTOH, you will learn why precision is important :) and you will learn the software of arm motion planning. The next step up in cheap arms is to build around Bioloid/Dynamixel style servos, which will increase the budget significantly, but you will end up with useable but coarse precision. Meaningful payloads will still cause servos to overheat but at least those brands will shut down rather than smoke -- usually. If you want to do serious research you will need a serious budget. Arms are hard. This is not to say you can't have a lot of fun and learn a lot with something less. A friend build a smart task lamp around Bioloids -- the goals was a lamp that would autonomously aim a work light where he was soldering by following the soldering iron tip using CV and a cheap web cam. This is totally within the payload and precision limits of hobby servos, and the software can run on a RasPi.