From Sonic Retro
Orbinaut is a badnik that appears in more than one game. It's a hovering sphere surrounded by four spiked balls which rotate slowly and are used for both attack and defence, and is apparently based on a sea urchin (the Japanese word for sea urchin is "uni"). A redesigned Orbinaut appears in the 3D games, where it is called E-32 Unidus. Also there is a badnik similar to Orbinaut in the Sonic the Hedgehog 2 called Sol.
Sonic the Hedgehog
In the Mega Drive version of Sonic the Hedgehog, there are two types of orbinaut. The first appears in Labyrinth Zone, and is referred to as "Unidus" (ウニダス) in the Japanese manual. "Unidus" is red in colour and launches its spikeballs along a horizontal line when Sonic approaches. The second type is found in Star Light Zone, and is known as "Uni-uni" (ウニウニ) in the Japanese manual. It is green in colour and doesn't launch its spikeballs, making it less threatening but harder to destroy. An orange "Uni-uni" also appears in the 8-bit version of Sonic the Hedgehog in Sky Base Zone. If you run away from the Unidus after it throws the first spike ball until it leaves from the screen, when you back to Unidus, all the other spike balls will disappear.
Sonic the Hedgehog 3
A third Orbinaut appears in Sonic the Hedgehog 3's Launch Base Zone and is referenced as Pola (ポーラ) in the Japanese manual. This version is silver-grey and spins faster when Sonic is moving, but doesn't launch its spikeballs. It is similar to Uni-Uni in this regard. Orbinauts can now be quickly defeated with Sonic's new ability, the Insta-Shield
A similar enemy in IceCap Zone, Star Pointer, does launch its spikeballs, like Unidus, so both types of Orbinaut are covered in Sonic 3. Said spikeballs will be destroyed if they touch a lightning shield.
The fourth Orbinaut model, known as Unidus, appears in Sonic Adventure. This version is most close in design with the Orbinaut appearing in Sonic 3. It attacks in two ways, either throwing their spike balls at its enemy or by sending them in arcs for a wide radius attack.
Sonic Adventure 2
The Sonic Adventure 2 model, again known as Unidus, is almost identical to the one in Sonic Adventure, the main difference being that it will not throw its spikes.
Sonic the Hedgehog 4
Both types from the first Sonic game return in Sonic the Hedgehog 4. The Unidus behaves and looks the same as it does in the original game. The Uni-Uni, however, can expand its circle of spikeballs, making it easier to attack.
The badnik returns in Sonic Colours.