Problem with "arcadeControl" in RobotC

Why the robot moves slowly when I use “arcadeControl” function in robotC? For example,when I use “arcadeControl” function,the robot moves slowly;but when I use “tankControl” function,the robot moves quickly.what’s the problem?

There is a duplicate post found at the link below; I would like to keep the discussion centered there to ensure that there is no confusion caused by multiple discussions on the same topic. Thank you!

http://www.vexiqforum.com/forum/main-category/technical-discussion/10030-where-can-i-download-robotc-for-vexiq-version-4-27-i-don-t-need-other-version