Crayon Car Mechanism.
Introduction: Crayon Car Mechanism.
A few weeks ago, a video appeared in my recommended video feed from <PERSON> at GrandIllusions (https://www.youtube.com/c/grandillusions) showing a crayon line following toy car designed forty years ago that had no electronics whatsoever, but no operational details were provided (<PERSON> was perplexed regarding how the car operated).
Not long after that, <PERSON> at RobotHut (https://www.youtube.com/user/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 <PERSON> and <PERSON>!
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 4.12.1, and printed in TPU and 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.
Supplies
Soldering Iron.
Solder.
Thick cyanoacrylate glue.
Double sided sticky tape.
Step 1: Parts.
To assemble this model, I acquired the following parts:
* One 3.7vdc 100ma Lithium Battery (https://www.adafruit.com/product/1570).
* One JST PH 2-Pin Cable (https://www.adafruit.com/product/3814).
* One N20 6VDC 100RPM to 120RPM gear motor.
* One O-Ring, R-18 (22mm ID, 3.5mm section).
And I designed and 3D printed the following parts using PLA (unless otherwise noted) at .15mm layer height, 20% infill:
* One "Axle, Flex.stl", 3D printed using TPU filament on a TPU raft with TPU support.
* One "Axle, Gear, Bevel (1.8m, 8t), Axle, Flex.stl".
* Two "Axle, Wheel, Font.stl".
* One "Axle, Wheel, Rear.stl".
* One "Bushing, Axle, Font, Flex.stl".
* One "Bushing, Axle, Front.stl".
* One "<PERSON>, Axle, Wheel, Rear.stl".
* One "Chassis.stl".
* One "Gear, <PERSON> (1.8m, 8t), Axle, Flex.stl".
* One "Gear, Bevel (1.8m, 14t).stl".
* One "Gear, Motor (1.8m, 12t).stl".
* Two "Wheel, Font.stl".
* One "Wheel, Rear.stl".
This is a high precision print and assembly model using at times very small parts and in very tight spaces. 116
Prior to assembly, test fit and trim, file, sand, etc. all parts as necessary for smooth movement of moving surfaces, and tight fit for non moving surfaces. Depending on you printer, your printer settings and the colors you chose, more or less trimming, filing and/or sanding may be required. Carefully file all edges that contacted the build plate to make absolutely certain that all build plate "ooze" is removed and that all edges are smooth. I used small jewelers files and plenty of patience to perform this step. 632