Model robot, which may alternatively called Gunpla (derived from "Gundam plastic model"), arised from the marketing schemes for Gundam and numerous model anime (Indeed, some hardcore mecha show fans complained modern mecha shows is nothing more than 20 minutes of model commercial) Usually, they are marketed in scales 1:100 and 1:144, like model aircrafts, which seems strange to some westerners as they believe that they are best displayed in scenes crashing against houses, and thus should use natural model railway gauges instead. Still, as there are 1:144 model railways, in Japan itself this does not matter much; and numerous after market accessories for mecha models (as well as scratch building, which is what makes this hobby fun) render this "strange" scaling matter into non-matter.
Currently, Bandai is the main producer of mecha models, commonly called Gunpla, as most of them are models for Gundam. (Wikipedia)
CollectionDX uses this category for ALL model kits.