is that ture, that single-wire encoder has 90 counts per 360degree,
and two-wires encoder has 360 counts per 360degree?
I saw this in the robotc teaching vedio.
Yes, it is true. Also, the two-wire encoder is able to detect which direction it is being turned, whereas the single-wire encoder is unable to do so. Here is a document that explains the difference: http://cdn.robotc.net/pdfs/vex/curriculum/Quadrature+Encoders.pdf
And here is an explanation of how the two-wire encoder works: http://content.vexrobotics.com/docs/instructions/276-2156-instr-0312.pdf
i the past (before IME’s were available in vex) we only had to plug in one.
Since you already know which direction you want the robot to go 