User blog comment:TheGoodDoctor19/Some questions about the not fully established RWBY universe/@comment-24911350-20140608212718

It's highly unlikely that Penny is a robot, and even if she was, it may not a good idea to emulate something like that in a hunter or huntress. They'd have no aura or semblance, and wouldn't be a big problem for trained, non-Grimm combatants, as well as being highly vulnerable to heat and magnetism. Someone like Pyrhha could just stomp right over them, because magnetism is the only possible non-semblance way that Penny could manipulate her weapons like she does.

They'd also have to be powered by dust, and couldn't last much longer than a few hours, or with a huge margin of error for RWBY-ness, a day before recharging. This is not an ideal situation for someone where a significant part of the job is going into the wilderness to kill monsters.