Nellie the Weeding Robot

Tutorial by MikeTheMaker(@EngineerRigsby) on Instructables.

Mike's book, A BEGINNERS GUIDE TO 3D PRINTING: 14 SIMPLE TOY DESIGNS TO GET YOU STARTED is now available. He is also the author of "Doable Renewables," "Haywired," "Amazing Rubber Band Cars" and "The Flea and the Bee." He have published articles in Popular Science, Circuit Cellar and Robotics Age.
 
Pigweed, which can grow 3 inches per day, has become resistant to the dominant weed killer, glyphosate, sold by Monsanto as Roundup. This super weed threatens the nation's soybean and corn crops. U.S. Farmers spent 13.7 billion dollars in 2012 on agricultural chemicals, 70% higher than in 2002. In soybean fields, weed killer costs have increased $20. per acre over the last five years. Hand weeding—using a hoe—can cost $150. per acre.

Enter Nellie, the weed picking prototype robot. She sees weeds and plucks them the old fashioned mechanical way, one at a time. Since she's a prototype, she plucks a prototype weed.

She runs on carpet, finds a fake plastic weed, picks it and drops it—ready to find another.

This is an entry in Make's "Pitch Your Prototype" competition.

Step 1

This requires three Arduino Uno's and two Arduino motor shields. A Pixy camera is used for detection of the fake weed and a Ping ultrasonic detector determines closeness of the weed. The base is a Canakit 4 wheel drive robot base. Eleven NiMh AA batteries are used for power. A Jameco servo gripper and a high torque servo are used for gripping. The gear mechanism which holds the gripper was 3d printed (files available at
https://www.thingiverse.com/thing:704484)

Step 2

Control of the robot is a distributed process using three modules. The Pixy camera feeds data to an Arduino processor and that processor sends "nothing, target left, target right, target center" commands to the motor controller module.

The motor controller module receives commands from the Pixy and from the Ping/grabber platform. This Arduino and motor shield causes the robot to go forward, left, right or stop.

The Ping/grabber platform uses an Arduino and a motor shield. When the Ping ultrasonic detector senses something close, it sends a "stop" command to the motor controller, then it extends the grabber, closes the pincer--releases the pincer at the end of travel, retracts the arm, then releases the "stop" command.

pixy_vision
pixy_motor
weed_claw
 

Step 3

       
Breaking the tasks into discrete functions greatly simplifies the programming and troubleshooting process (at the expense of more hardware cost and greater power drain).