The weaponoid is a large generally humanoid shaped robot that is functionally a walking weapon. This isn't to mean that they are capable of deploying themselves, but rather, should they adopt their weapon stance, something else suitably large could pick them up and use them as a weapon.
The Urban Protocols and limitations on paramilitary and security mecha meant that in times of military crisis, many available mecha were unarmed or drastically under-armed. A potential answer for this was floated in the idea of the weaponoid. The prototype weaponoid was a self mobile version of the Wolverine's autocannon. Most of the weaponoid's mass consisted of the gun components, but it could stand and move on it's own. The addition of a humanoid chassis, internal power system, and other components increased the effective weight of the weapon system, but not to a degree more than something like a Wolverine main battle mech or Sentinel security mech couldn't handle.
The original weaponoids were a backburner project that was an attempt to recreate self propelled guns that weren't covered by the anti-tank bans. Replacing tracks with legs, and turrets with arms, the designers made bizarre insect like walking cannons and crawling missile batteries. The machines had two modes, an active mobility mode, and a fixed firing mode. When on the move, the weapon system was typically unavailable. Barrels were segmented, housings were locked down in armor modes, there wasn't enough power to spare for locomotion and firing solutions, and so forth. These programs ultimately failed as powered armor troopers handled the jobs better, and the self propelled systems were prone to breaking down, were often slow, and when moving, very easy to engage and destroy.
The Adventures of CannonMan was a military propaganda adventure series that followed a sentient auton who had the ability to turn himself into a giant cannon. He couldn't shoot himself, and had to be picked up by a robot to keep in the fight. The series was fundamentally identical to the Lone Ranger, with CannonMan being the Lone Ranger, and Turret the giant unarmed mecha was Tonto.
Weaponoids have not successfully been deployed, and currently are nothing more than a weird military project. The desire to have a robot that can run up to a mech and transform into a weapon have been stymied by the fact that the comparable robocized version of a weapon is often twice as heavy as the regular weapon, and much more prone to fouling or being damaged.
Weapon Droids have proven successful, if much less dramatic. A weapon droid is an unmanned kaze type aerial vehicle. Working either solo or in groups of up to eight, these rather small drones have proven able to airlift self contained weapon systems and deliver them to mecha and robot units in the field. While much less incredible, the droids are not performing a new function, as the droids are simply running logistic support flights carrying arms rather than ammunition. The droids are also rather vulnerable to hostile fire and are easily destroyed, requiring either escort, good luck, or a clear corridor of operations. The military has used droids in this capacity for years, moving power armor troopers, supplies, gear for mecha, and even field construction equipment, with little fanfare. The Sikorsky 'Skylord' Kaze can lift a Wolverine by itself. It isn't a popular military use droid as it is large and easily engaged and destroyed. In such hostile areas, the military favors carry-all transports.
Additional Ideas (3)
The Cepha-Droid was a proposed electronics warfare droid similar to the weaponoid. The Cepha-Droid would fly itself into a combat zone where it would literally replace the existing head of a mecha already on the scene. Contrary to popular thought, the mecha pilot doesn't actually sit in the head of the machine, it is already a cramped location, limited in armor capacity, and a natural target. Instead, most head units are used for housing sensors and electronics systems. Removing the head does damage a machine, but unlike humans with their central nervous systems, the machine can have sensors all over the body, not limited to the cranium. Removing the head just takes out the primary units. The Cepha-Droid would 'laser' the head off and using adaptive fittings, take it's place. Then it would deploy advanced targeting and information systems, superior communications, and specialized task equipment.
The few test models made handled poorly, were demonstrated to be be easily intercepted by enemy fire, and were very poorly received by mecha pilots. The general sentiment towards the program was demonstrated when in a live fire test, a test pilot shot down his own cepha-droid rather than letting it decapitate his mech.
The Reactor Droid never made it off of the drawing board, as the notion of having an additional power supply that was self mobile was considered laughable. The core idea was to have a power amplifier that could provide additional support for mecha using energy weapons. Rather than strain their own reactors and capacitors, the reactor droid would serve as a high power discharge unit, allowing for higher and more sustained fire from the mecha. Considering how poorly the cepha-droid performed, having a flying backpack reactor was considered stupid.
The solution was eventually realized in improving the power amplifiers already on energy weapon using mechs as well as better discharge and capacitor systems. Older units could be retrofitted with more robust internal reactors, and units operating in fixed and limited mobility locations could access local power supplies through industrial power umbilicals.
They were all on drugs, I mean that's the only thing that can make sense. Dealing with mecha is already a pain in the ass. They are big and stompy, and they shake everything, and linkages, there are linkages everywhere. These guys come along like this is some sort of game and that you can send out a barely armed, half blind, underpowered war machine and then like a swarm of singing magical birds, all the giant robot parts it needs are going to come effing literally running to it?
That's begging for disaster. Pardon me while I strike the droids assemble pose. Don't shoot at me while this flying head tries to cut off my head and this weird ass backpack centipede tries to crawl up my shiny metal robot's ass because way cool it's 'MER POWR' for the pew pew pew. Oh hang on, my gun seems to have gotten lost, seems it came running through the bad part of the ruins and there is a gang of armor troopers mugging it. It might be a bit late, and probably missing all of it's ammo.
We ask for a better ejection system, better LAI interface, better armor, and what do the boffins try to sell us? Mecha handguns shaped like people.