X-T3RRA (2014)

IMG_7078X-T3RRA Cropped

Hello! I’m back with X-T3RRA, the second version of X-TERRA. For those of you who are unfamiliar with X-TERRA, the name is an acronym for eXtra Terrestrial Exploration Robot and Rock Analyzer. The name carries over, but now the “E” is a “3” for “EV3.” I usually just refer to him as “Terry,” though. X-T3RRA’s main goal in life is to explore distant planets and collect mineral samples.

See a video of X-T3RRA here: https://www.youtube.com/watch?v=fQG12E8eINU

Motors and Sensors


Thanks to the newfound freedom with EV3, X-T3RRA has four motors. Motors A+B are the two large motors in his feet that drive his caterpillar tracks using skid-steer (tank style). Motor C is a Medium size motor in his right arm. It can open and close his claw using a worm gear mechanism and two 24z gears, one on each finger. The front of the worm gear housing has been reinforced so the worm gear can’t “worm” its way out (pun intended). Motor D is another Medium motor in Terry’s left arm. It is responsible for rotating the shoulder joint on his right arm up or down, via gear reduction and a turntable. X-T3RRA also has four sensors. They are as follows: an IR sensor in his left arm, a Gyro sensor in his right shoulder, a Color sensor in his right claw and an Ultrasonic sensor that forms his head.

Program 1: X-T3RRA RC

This is a rather simple RC program. In the beginning of every one of Terry’s programs, Motors C+D reset. Motor C opens the claw until the EV3 senses the motor’s power drop (stall), then returns the claw to the desired position. Motor D raises Terry’s arm until the Gyro sensor detects the Rate of Change of the arm’s angle drop. At this point the arm should be almost perpendicular to the ground. The Gyro then resets itself, and the arm returns to the desired position. In the program X-T3RRA RC, you use the IR Remote that comes with the EV3 to control Terry’s movement, tank style. If you press the top button, he’s supposed to grab the mineral in front of his claw, but a bad case of Gyro drift is keeping him from doing so. (Gyro drift is when the Gyro sensor’s readings increase or decrease rapidly, giving the robot a false reading and messing up the program. One time, the Gyro was reading -11,600 degrees with no sign of slowing down, even though I didn’t touch Terry once. Any suggestions to fix this problem would be greatly appreciated.)

Program 2: X-T3RRA Autonomous


At the beginning of this program, Terry resets Motors C+D and his Gyro, as explained above. Then, Terry sets out to search for minerals. He drives forward until his Ultrasonic sensor detects a wall. When this happens, he backs up, does a 90 degree turn and repeats the process. However, if Terry’s Color sensor sees a mineral (any color other than black), he will grab it with his claw, exclaim “Foreign mineral sample collected,” lift it up and examine it. Next, he will shout the name of the mineral, depending on the color. White=Quartz, Yellow=Gold, Blue=Aquamarine, Green=Emerald, Red=Iron Oxide (the stuff that makes Martian rocks red) and Brown=Gneiss. After that, Terry says, “Relaying data to Huston Aerospace Base… Resuming search for minerals,” places the mineral back where he found it, then repeats the process.

Program 3: T3RRY


After Motors C+D and the Gyro reset, the program begins. “T3RRY” is a sort of simple artificial intelligence program where X-T3RRA becomes your robotic friend. If he sees you with his Ultrasonic sensor, he says, “Hello, friend!” If you place your hand in his claw and his Color sensor sees it there, Terry will say, “Hello, I’m Terry!” and he will shake your hand. Lastly, if you’re feeling particularly malevolent, you can “beat him up.” If you push Terry backwards, his Gyro will detect his fall. Terry will drive reverse to save himself, flash his brick lights red and exclaim, “Hey! That was mean!” Remember, you can always apologize with a handshake.


I hope you enjoyed reading about X-T3RRA. Honestly, I haven’t had this much fun building a robot since the Timmyton 5. Unfortunately, though, Gyro drift spoiled some of the programs’ features. I’m still searching for a solution to that; any help would be greatly appreciated! From now on, you can expect more EV3 robots to come. Thanks for reading and see you next time!

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