Ratchet and Undertone's relationship

**It was'nt really clear on how Ratchet and Undertone have met in Transformers Robots in disguise.**

It was stated by Ratchet that he was ordered to arrest criminals and that Undertone became his partner. But how? I assume that Ratchet found Undertone at some point on Cybertron,knowing that he got lost and has nowhere to go. It was during when the High Council blacklisted the Autobots. Undertone was apparently a supporter of Optimus Prime. When suddenly,a wanted criminal appear. That criminal would have been Tankor. Ratchet followed him on Earth with Undertone and capture him. Undertone then decided it would be best to become his partner.
Later on,he found Clampdown and chase him until he meet up with Bumblebee and his team. 
Ratchet and Undertone helped the Autobots to defeat the Decepticons from Decepticon Island and returned to Cybertron. Somehow,Ratchet found a home for the fellow minicon without being targeted by any Cybertronian. That may be the reason why Undertone was not with Ratchet in Combiner Force.