The Transformers cartoon
Metroplex's cog was damaged in 2005 during the Decepticon siege of Autobot City, which explains why he did not transform to robot mode during the battle. Perceptor built a replacement cog and entrusted its delivery from Cybertron to Autobot City on Earth to Blurr and Wheelie. This proves you can be brilliant but still stupid.
After numerous setbacks, the cog was delivered just in time. As the city was under siege once again, Pipes quickly installed it, allowing Metroplex to fight off Trypticon.
The cog also makes a nice substitute for a football. Apparently, it can also change its shape to look like flat, toothed wheel every time a lazy animator wishes it.
Nitrostreak suffers from a broken transformation cog.
War for Cybertron
In one chapter of the Autobot campaign, Silverbolt, Jetfire, and Air Raid, must destroy Trypticon's transformation cog to revert him to his humanoid mode to prevent him from destroying Optimus Prime. They make it to Trypticons transformation cog and blast the turrets on the cog to let trypticon transform. This leads to the final chapter of the Autobot campaign, and the final chapter in the main campaign mode.
All Transformers contain a transformation cog (referred to as a T-Cog), a biomechanical organ which not only allows them to scan and transform into vehicles but also to activate their energon blasters.
Bumblebee and Bulkhead, at one point, were tracking down an energy beacon. Bumblebee arrived first, but found out that it was a trick by MECH, the decoy used to transmit the beacon knocking him out. MECH then removed Bumblebee's transformation cog before Bulkhead was able to show up and retreated.
Back at their base, MECH installed Bumblebee's cog into their own Transformer. It was able to scan a vehicle, but not to transform. Starscream the entered and told them that Transformers only run on energon.
While attempting another test, this time with energon to power the cog, Bumblebee intruded and was able to rip the cog out of MECH's robot before being knocked out by Starscream. Bumblebee attempted to retrieve the cog from him upon waking, but it was ultimately destroyed. However, upon reinserting the cog into Bumblebee, he was able to transform into his vehicle form and back again.
When Starscream met with Silas, he disappointed the human by stating that the cog was destroyed, but MECH then knocked out Starscream and stole his cog. Nemesis Prime.The cog was later used for the
After destroying his remaining clone, Starscream took the transformation cog from it and was about to surgically implant it in himself, but the Harbinger had located Decepticon activity in the Antarctic before he was able to.