Simon (Juggler) has explained to you how light tents work (or are claimed to work), but you specifically mention a light CUBE.
A light tent has translucent sides and top, 2 or 3 lights are placed outside the tent and shine through the diffusion material. The results aren't great but are often acceptable to many people.
Light cubes though are different, they are cheaper to make and easier to use, with one or sometimes more LED lights placed inside the cube, and they generally produce even worse results.
So, if it is a light tent then the results may be OK for the pencil drawings but if it's a light cube then you would produce better results, and more easily, just by getting a couple of LED lights, putting your camera on a tripod, fixing each drawing to a vertical surface such as a wall and putting one light each side of the drawing at an angle of around 45 degrees.