Crayon Car Mechanism

By gzumwalt

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Crayon Car Mechanism A few weeks ago, a video appeared in my recommended video feed from Tim at GrandIllusions ( showing a crayon line following toy car designed forty years ago that had no electronics whatsoever, but no operational details were provided (Tim was perplexed regarding how the car operated). Not long after that, John at RobotHut ( sent me a link to a video of a design he created of a three motor version of the crayon following car. Between the two videos, and always loving to design, 3D print and assemble mechanisms, I designed this single motor crayon following car using a flexible 3D printed TPU axle to transfer rotary motion from the rear wheel to the front wheels. The theory behind the design is elegantly simple. A single rear wheel drives the car forward while the counter rotating front wheels "sense" the crayon line. When the counter rotating front wheels come in contact with the sticky wax crayon line, they are designed to steer the car away from the line. The front wheels in my design spin 1.75 times faster than the rear wheel to allow time for the vehicle to make line following corrections. In this video, I drew the crayon line on two sheets of 8.5" by 11" standard copy paper that I had taped together. It is important to have a heavy crayon line for the vehicle to work (maybe that explains my poor crayon coloring skills?). I thought the mechanism was pretty neat, and our grandson was enthralled by it! Many thanks to both Tim and John! As usual, I probably forgot a file or two or who knows what else, so if you have any questions, please do not hesitate to ask as I do make plenty of mistakes. Designed using Autodesk Fusion 360, sliced using Cura 4.121, and printed in PLA on Ultimaker S5s. One final note, I receive no compensation in any form for the design, parts and/or materials used in this model.
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Joined over 8 years ago My basement in Oklahoma, US
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