I am trying to build a H-BOT motion system based 3D Printer.
I was reading through some forum online where they said that it is important for the belts in core XY system to be straight and not slant when going towards the pulley else triangulation errors occur. What is the triangulation error?
Don't worry about finding the triangulation error. Just design the mechanism so there isn't any. It's not difficult.
The important thing to do is line up pulleys so that the belt segments that vary in length are always parallel to their respective guide rails.
In the image below, a corexy mechanism, segments A-H all vary in length as the extruder moves around. Segments C,D,E, and F have to be parallel to the X axis guide rails and segments A, B, G, and H have to be parallel to the Y axis guide rails. Segments J, K, and M do not vary in length, so they don't have to be parallel to the guide rails. You make the belts parallel to the rails by careful positioning of the pulleys, motors, and belt anchor points on the extruder carriage.