Motorized Cube Gears
by dougc314, published
A motorized version of Emmetts' Cube Gears. I built it (Emmett's that is) and was showing it around work. One of my favorite collaborators (Brian C.) and I were discussing motorizing it. I had visions of a tiny motor in the center, and was fussing over battery size, etc. when Brian suggested blowing a hole through one of the big corners and connecting a drive shaft to the center to an external motor. A quick look on Ebay found a motor, and when it came in the mail I started in on the design. I designed the parts in Alibre, sorry, OpenSCAD is a very impressive tool, but I am too CAD oriented). I did import the stl of the gear into Alibre. The zip file has the Alibre files and STEP AP203 exports as well.
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Due to motor availability, the first thing to do is figure out what motor you are going to use. The motor affects all three parts that I designed. The link I provided shows motors with flats, but the motor I found on Ebay has a 4-40 threaded shaft. The main concept is to morph the big corner gear into a gear that attaches to the motor. Design a drive shaft that attaches to the motor shaft and the center part of the cube. In my design I epoxied the drive shaft into the original center hole. The other end takes a epoxied 4-40 "large pattern" nut (0.25 inches across the flats) I liked the threads as it stops the cube from climbing/pulling off the shaft. (if it turns the right direction, CCW when viewed from the top).
My exact assembly process was: print Emmetts parts, thing #10483 print my three parts. (not motorflange2.stl) remove one of the big corners and pin, and the three associated small corners and pins. glue the nuts into the motor-gear flange and drive shaft(4-40 large pattern) and let set. attach the motor to the gear flange (bgear1motorflange2.stl) screw the drive shaft onto the motor shaft and then glue other end of the drive shaft into the center hole where the removed corner was. I used a thick piece of paper to gap the center. Be sure to align the center correctly (mine is wrong, although it doesn't matter too much) Wait for the epoxy to cure, and reattach the three smaller corners. I then cut a USB extension cable to the desired length, stripped the cut end and epoxied the cable into the base. I had to attach the red, or positive USB voltage to the motor NEG terminal to get it to turn in the correct direction. Epoxy the motor into the base. With the motor I used USB power barely makes it go, I assume if I polish all the pins a bit to remove friction it would run more smoothly. Video at http://www.youtube.com/watch?v=TjBAd8S2Yms
I guess I don't know how to add parts properly, so while I figure that out I'll add the url here http://www.hmimotors.com/New_Pages/3440.htm
1/19/11: Due to a builders issue I have added a redesigned drive shaft that captures the nut, so that it isn't just glue holding the cube onto the motor shaft.