Recently, we’ve been messing around with motors and gears at Pemtech. Students in one of my classes are building an underwater ROV, and we don’t have any decent propellers. Rather than shop for them, we’re fabbing our own with the laser cutter and MakerBot. Earlier this week, Jett worked out the proper dimensions to fit a plate to a motor shaft. He did this by measuring out a range of holes and then cutting them in quarter inch acrylic. Once they came out of the laser, he tried pushing the motor into each of the holes until he found the “Goldilocks fit.” Now that we had a plate, he used the same process to cut a series of holes into the plate that could be threaded with M3 screws. This setup allows us to attach anything to a motor.
Last week, we were printing motor holders. These were designed in Sketchup, and printed out on the MakerBot. After fine-tuning the design to fit the motor, shaft, and provide bolting holes, we added a bit of height. Ollie and Kyle then set about waterproofing them with a combination of petroleum jelly and candle wax. They used the hot pot and made a double boiler to make the wax. Brad set the motors up with soldered leads that can be connected to the snake. This motor holder allows us to attach a motor to anything.
Among the ways that these breakthroughs will come in handy are by combining motors to gears. The other day, I had a bit of class preparation time, and decided to return to my desire to design my own gears. Recalling a passage on making gears in Dustyn Roberts’ excellent book Making Things Move, I opted to give Inkscape’s gear generating tool a try. There is a very informative version of the tutorial for designing gears on Make: Projects. After cycling through it a few times making cardboard gears for my self and through a few students, I slimmed the instructions down to just a few lines for getting started. It now only takes five minutes or so to design a pair of gears that will work together, fit on an axle and onto a motor.
Chris, one of the students in the Fashioning Tech class, saw the need for a propeller, and suggested modifying a computer fan. We removed the hub motor and found a 1 inch cavity in the center of the propeller. By cutting disks to the right exterior dimension with a hole in the center sized for the motor, it could hold with a compression fit. To make sure it can be secured to the propeller, we cut a set of holes in the disks to accept the M3 screws and nuts. A bit of quick work with the drill and the fan blade can now be attached to the motor, which can in turn be attached to the vehicle.
One of the things that we will be needing next is assemblies to hold gears that can be adjusted to various ratios. Those can be designed out of flat stock with a variety of holes cut at intervals. We’ll work it out in cardboard, then upgrade to acrylic. Another will be a rack and pinion or other system allowing us to convert the rotary motion of the motor to the linear motion needed for manipulators and water testing tools. There are some excellent visualizations of mechanisms over on Robives.
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