Hello Leyla, Repeatability is the holy grail of all robotics! Motor rotation counts, run time etc have potential to be inaccurate. Wheel slippage, inertia and drive line lash are the main factors for these type of errors. Using sensors can solve many of these issues. However learning to use them is a steep curve. Takes time and effort and many kids have the mindset to just get it done quickly using motor rotations, LoL. Furthermore many kids come with tablets for programming, which have limited support for using sensors and especially math blocks. There sure is a lot to learn. With the tournament dates looming large, my (mostly) rookie team is also struggling with repeatability. Without going into too much detail, I suggest you look at YouTube for solutions to these issues, there are a ton of tutorials out there: Gyro straight line Gyro turns Line following Ultrasonic sensors to determine position Touch sensor / limit switch Sincerely, Rajeev Mehra Coach: Ultimate Onions FLL team # 47864 ________________________________ From: First Lego League in Virginia and DC <[log in to unmask]> on behalf of Leyla Nazhand-Ali <[log in to unmask]> Sent: Saturday, November 9, 2019 10:12 PM To: [log in to unmask] <[log in to unmask]> Subject: [VADCFLL-L] Improving reliability and repeatability Good evening, As a rookie coach, I have a general question for the community: what is the most reliable and repeatable way to go from point A to point B using Ev3 (FLL robot)? I know there is a method to use actual motor rotation counts. I also know we can use a gyro sensor. Any advantages or disadvantages for each of these methods? We have two related problems: 1) our navigation program doesn’t behave similarly a few days later or on a different table. 2) a backup robot we built doesn’t run the same programs in a similar way to our original robot even on the same table and almost the same time. In other words, our solutions are not robust. I know this is a very broad question that probably touches upon various topics. However, I appreciate if the other coaches point me to good resources or share their wisdom with me. Thanks, Leyla -- Sent from my iPhone ________________________________ To UNSUBSCRIBE or CHANGE your settings, please visit https://listserv.jmu.edu/archives/vadcfll-l.html and select "Join or leave the list". VADCFLL administrative announcements are sent via VADCFLL-ANNOUNCEMENTS-L. Visit https://listserv.jmu.edu/archives/vadcfll-announcements-l.html to subscribe. -- To UNSUBSCRIBE or CHANGE your settings, please visit https://listserv.jmu.edu/archives/vadcfll-l.html and select "Join or leave the list". -- VADCFLL administrative announcements are sent via VADCFLL-ANNOUNCEMENTS-L. Visit https://listserv.jmu.edu/archives/vadcfll-ANNOUNCEMENTS-l.html to subscribe.