Most special-effects centaurs in films (like the Narnia films) are made this way: The actor is costumed from the waist up (barechested or something modest, depending on gender), plus their makeup, hairstyle, and "horse ears" added. They wear all-green (or all-blue) pants that are edited out later and replaced with a CGI horse body.
In my idea for a Andalite costume, I depart significantly from this. Since Andalite bodies are smaller than horses (closer to the flank height of a deer) this makes it easier. Centaurs are taller than humans, because of their large horse bodies, Andalites, on the whole, are just as tall as humans: five to six feet tall.
First of all, the rear, "horse" part of the Andalite costume would be entirely mechanical. The "butt" area hold a motor and computer that drives the rear legs, which can be operated remotely, but their primary mode of operation is on automatic: The user walks forward, pulling the body, and the rear legs walk automatically. Running, which would require a galloping "animation", is not supported at this time, and CGI is recommended here. The Andalite costume's tail is fully remotely operated, by someone nearby. It cannot move as fast as a real Andalite tail, but it can move fairly quickly, by the way of powerful motors and joints. The blade can be made of metal or plastic.
The majority of the rear Andalite body in this costume is hollow and empty, save for the rear legs motor and tail mechanism. There is an option for the user to disattach their main body costume from the rest of the costume, by way of hidden zippers. If they need to leave their costume for a short break, there is a support stick ("kickstand", though you don't kick it) that slides out of the body cavity on a track and hinges down to touch the ground and hold up the costume while no one is wearing it, in much the same way as the user's legs would hold up the costume while it is being worn.
The user wears shoes that resemble an Andalite's hooves, but due to the different shapes and sizes of human and Andalite feet, some "corners" must be "cut". The pant legs are very tight, like spandex, and colored like an Andalite.
Picture for a moment, if you will, a cast member at a Disney park wearing a Flik or Atta costume, or something physically similar to it. (Flik and Atta are ant characters from Pixar's
A Bug's Life.) The body part they wear is stiff and resides outside their "underclothes". Their legs stick out from holes in the bottom of the "shell", as do their arms (I assume). This is how the majority of the Andalite "human" torso is constructed. The arms are covered in a thin sleeve (like pant legging material) that of course is light blue. The user wears special gloves that have seven fingers each. The sixth and seventh finger are controlled directly by the movement of the fifth finger (the pinky), by way of small sensors in the hand powered by motors attached to the inner side of the chest piece, via small electrical wires.
Retcon here: If you want moveable sixth and seventh fingers, you can't have the really thin sleeves-for-arms. The arms would have to be opaque to allow for small wires powering the extra finger motors. You can't have that much contraptional junk in the hand!
Like most professional costumes where the wearer may get overheated (or like astronauts' suits), the Andalite costume features a cooling system that works by cooled water pumped in small transparent tubes throughout the area where the user's body is. The extra "horse" body that comes as part of the Andalite costume gives an added bonus of having extra space to store the water source for such a system. This water pump can be turned off and disconnected from the pipes if the user wants to separate from the "horse" body for any reason.
Now we get to the head. The nostrils of the nose have holes in the mask, which are used for breathing from the mouth. An optional feature is a small lapel/lavalier microphone like this:
http://www.alpha-music.com/productcart/pc/catalog/654566565656X.jpg, which amplifies the user's voice, as if it were thought-speak, through loudspeakers hidden in the "horse" body.
There are two options for the eyes. One is to be like most masks where there are holes for the eyes, which the user can see out of. This allows for a mask where the eye holes are right up against the user's eyes to simulate real eyes.
The other option calls for a slightly larger mask, and motorized Andalite eyes which look like real Andalite eyes. These eyes are directly in front of the user's eyes, and their motion is controlled by the motion of the user's eyes. The user wears special glasses that have sensors built into them that track eye movement, as well as displaying a 3D view of what the cameras in the Andalite eyes see. These glasses function
only as virtual reality devices, and do not work like regular glasses, sunglasses, or 3D glasses which allow light through. These glasses only work with the eye/camera VR system hookup.
Optional: The ears may be motorized and controlled remotely by someone nearby.
Not optional: The stalk eyes are controlled remotely by somebody else, and fortunately, do not function as visual aids, as this would confuse the viewer if he had a Picture-In-Picture view of what those cameras see in the corners of his vision. (Though I suppose that's a possible option too, though the user wouldn't have control over what he sees, it'd be at the whim of his friend what he makes the stalk eyes look at.)
What am I missing? Uh... obviously (to me), the mask extends down the neck below the "body shell". I guess that's it.
Did I miss something? Do you have other or better ideas to add? How much do you think this would cost? Would you wear one? Am I crazy?
At some undetermined point in the future, I will work on my idea for a Hork-Bajir costume.