To be able to manipulate radioactive substances, Otto Octavius created a device with four tentacle-like, mechanical arms. I've not read the original comic books, but I've seen Spider-Man 2. The Marvel Wikia page on Otto Octavius doesn't fully agree with the film, but both involve accidents. Considering the risk involved, why did he not use remote controlled robots instead? The device itself is not responsible for what happened, but using robots, he could have overseen from a safer location, and since he's depicted as a genius, he surely would have been able to create robot-like machines (though he might have called them something else), even in 1963 (when, according to the wiki, he first appeared).
The out-of-universe reason is most likely that without the tentacles, he wouldn't be Doctor Octopus.
I'm looking for an in-universe explanation. Preferably an explanation given in a published story, but in-universe explanations given by Stan Lee or Steve Ditko or Marvel Comics in interviews or published without being part of a specific story plot are also welcome. If there are different explanations over retcons and reboots, all of them are of interest, but mostly I'm looking for what happened originally.