The Duocons, Battletrap and Flywheels, are unique in that they are autocombiners, whose humanoid modes are formed from the combination of two separate vehicles that have no other transformation or individual sentience.
Marvel Comics continuity
The Duocons appeared in some UK comics, where they were more like Triple Changers, rather than the divided altmodes of the toys. Battletrap was featured in some of the final U.S. issues. He was never shown to transform.
Japanese G1 continuity
Dreamwave comics continuity
Shockwave experimented to create a Transformer with more than one alternate mode. While he eventually succeeded with the Triple Changers, an early step in the process resulted in the Duocons—a failure due to their consciousness being split between two vehicles.
The Duocons share a semi-autotransform feature. Transformation begins by lining up the tab and slot on the underside of their aerial component with the corresponding slot and tab on top of the ground component. With the two parts lined up, pushing the aircraft down causes the tabs on both parts to trip a catch in the other, releasing the springs that keep the components folded up. The aircraft essentially folds in half over the "legs" that form from part of the rear of the ground component to form the robot.
Transformation from robot to vehicles lacks any kind of automatic action. The halves of the robot are pulled apart and the nose of the aircraft is realigned with the fuselage and the leg/torso is folded down to the rear of the ground vehicle, with the moving parts being held by the spring-loaded catches.
The Duocons suffer from a complete lack of useful articulation.