I think there should be a way to classify different robot types/body types to distinguish between a few major ones and make searching for them easier.

There's already android which is supposed to cover all anthropomorphic robots. In my opinion there should be a distinction between human and furry-shaped robots, either through adding subtags to android (humanoid_android and furry/anthro_android) or changing the definition of android to apply only to humanoid robots and creating a new term for furry-shaped robots.

Two other body types I feel would be useful to tag would be feral and abstract robots. Even if all human and furry-shaped robots are properly tagged, this still leaves robots that are obviously animal-shaped grouped in with robots that have neither a human or animal body-plan, such as glados, BB-8, and robot tentacles.

As-is there's no real way to search specifically for robots based on what they look like beyond android. This means that a search for 'feral robot' will turn up results like this:
post #986476 post #1132570 post #781787
as well as results like this:
post #968477 post #1102015 post #1091605
without a way to filter them from each other.

Similarly if someone wants to see furry characters interacting with humanoid robots or vice versa, there's no meaningful way to separate this:
post #971766
from this:
post #191251
as both would be tagged with android humanoid anthro.

This isn't a robot-specific issue, by the way. Just like there's no way to separate (humanoid android) anthro from (anthro android) humanoid, there's no way to separate (male wolf) (female cat) from (male cat) (female wolf). That's just how the tag system works.

The reason we don't have a male_wolf tag (or the feral_robot tag you're suggesting) is that it quickly gets out of hand making tagging extremely difficult. male_wolf becomes male_wolf/fox_hybrid becomes black_fur_male_wolf/fox_hybrid and so on.

What you're really asking for, as a general solution, is character-based tagging. Then you can search for (humanoid android) and (feral robot) and (black_fur male wolf) (female cat). But that would require a complete makeover of existing tags and the current post-based tag system. See my answer to a similar request, forum #223421.

Yep, though perhaps there is room for some new robot subtags without going overboard with tag combos.

Sorting them by locomotion type could work. Bipedal is the default for this site, so adding subtags for less common types such as as quadrupedal_robot and hexapod_robot (or just multi-legged_robot?) would improve searchability. ...maybe something like airborne_robot for flying types, and an another subtag for wheeled and threaded ones? Not sure how well any of those would work, I'm just throwing out some ideas.