Tag: dcrlmtm

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Just a Gear

Imperial Gear

I find it interesting the way we address problems. Take for instance, this simple gear. For the Prusa i3 printers we are building at school we realized we didn’t have 8mm bolts, so we got a bunch of 5/16″ bolts, and then we realized we needed to print new gears…

Calvin started to edit the STL file we had, and I asked if he looked around for an existing 5/16″ compatible gear on Thingiverse. He said he didn’t even think of doing that, and got right to modeling. Sadly, Calvin’s new gear was slightly too small. The next day I mentioned it to Fred, and Fred decided to fix the gear. I told Fred that it might be helpful to just model the new bolt-head part and print it to see if it would fit. This has the advantage of printing much faster than the entire model. He took that advice, but it still didn’t fit.

Meanwhile, I found a gear generator library for OpenSCAD and tried to model a new gear, but that failed as it wasn’t fully parametric in regards to the number of teeth.

After all that, Fons came along and said “I’ll just put the hex head of the bolt on the grinder until it fits the gear that Calvin made.” Duh! A great hack to make it work!

While I loved the hack, I also wanted to make sure that others could easily have a gear that worked with a 5/16″ bolt and did not require grinding down the head. I’m also preparing for the future when a part fails, and someone needs to replace it, and doesn’t realize the bolt was altered, or heated with a torch to get it into place.

So I followed my own rapid-rapid prototyping advice, printed a few versions of just the hex head part until it fit perfectly, then dropped it onto the model of the gear, and printed a few. And they worked.

And then I uploaded the gear to Thingiverse and Youmagine in the hope that someone else who has the same problem in the future can just grab the one I created and get on with their day.

Sharing, it’s a thing.

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Turntable Lathe(ing!)

Lathe

Just a quick follow-up to the previous shaft post… I cut the shaft to length on the horizontal band saw, and then chucked it in the lathe (and had Frankie do a quick check before I started) and then cut down the other end so the bearing would fit. It’s not perfect, but close enough. I’ve still got some of the shaft left if I need to make another one. The main thing is, I got some good experience using the lathe, which will come in handy if I end up turning my own knobs to fit on the potentiometers.

Shaft

One bad thing… we had thought the shaft was steel and would work well for the magnets I plan to use, but… it’s not magnetic! I’ll probably end up drilling (er, lathing) a hole in the shaft to thread a steel bolt into so I’ve got some material I can stick the magnet to.

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Turntable Electronics

Electronics

I finally got the electronics for my Turntable Drawing Machine working. It wasn’t easy…

I decided to use a DC gearmotor controlled by an Arduino and potentiometer for the speed. I did a quick test of this with a Leonardo and a DRV8835 Dual Motor Driver Shield for Arduino. It worked fine for controlling the speed of the motor, but I didn’t really want to use the shield, so I used a DRV8835 Dual Motor Driver Carrier I had on hand. (Since I’m only using one DC motor, I probably could have used a DRV8838 Single Brushed DC Motor Driver Carrier.)

Pololu has an easy-to-use Arduino library for the DRV8835 Dual Motor Driver Shield which worked fine for the shield, but doesn’t (I mean didn’t) work with the DRV8835 Dual Motor Driver Carrier. I ended up hacking the library a bit to make it work. All was well until I added a servo. Since the Arduino library for the shield is hard-coded to use pins 7, 8, 9 and 10 there’s an issue because the default Arduino servo library disables PWM control on pins 9 and 10. I then changed the library to not use pins 9 and 10, but that still didn’t quite work… Seems that the servo library and the motor control library both need to use timers, so there’s some weirdness there…

I ended up digging through the forums and eventually found some useful posts and a link to ServoTimer2.zip. (It’s worth noting that there are a number of ServoTimer2 libraries, but I tried this one and it worked.)

Once I had the ServoTimer2 library in place, getting it to work with the my hacked ‘DRV8835DualDriver’ library was simple. (I’m saying “simple” but it took a few hours of screwing around with things that should have worked but didn’t) If I had used one of the Arduino Megas I had lying around, I probably could have avoided some of the issues the Servo library causes.

Alright, well… electronics seem good! Next step is to build things, and get the turntable portion constructed to test if the DC gearbox will work out. I think it will, as it’s got plenty of torque, and there shouldn’t be much resistance.

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Turntable Shaft

Platter System

For my turntable drawing machine I’ll need the platter to spin. In a “real” turntable (the kind used for vinyl albums) there are three methods, idler-wheel, direct drive, and belt-drive. The illustration above shows my original idea for direct-drive, which I quickly abandoned in favor of belt-drive, on the bottom.

Rod & Bearing

Typically I use 8mm rod for things because, well, I have it handy, and lots of 608 bearings as well. For this turntable shaft, Frankie gave me some 6003Z bearings, which have an inside diameter of 17mm. I found some 17mm steel rod from McMaster-Carr, but I didn’t need very much, so I asked Chad about making a piece on the lathe. He said it should be easy if we had some stock just a bit larger, and well… Frankie did indeed have something! (Oh, if I used 17mm rod I would have added shaft collars… luckily by machining the part, we won’t need them.)

Frankie gave me a crash course in the metal lathe. (I last use a lathe back in the 1980s, and it was a wood lathe!) I learned how to face off the material, and then he showed me how to narrow it down to size. We got it to a perfect fit for the bearing!

Plastic pulley

I also had some plastic pulleys on hand from when MakerBot sold off all their old Cupcake CNC parts… I knew they’d come in handy someday! We managed to drill out the center on the lathe so it fits tight over the steel shaft. I may need to add a set screw or some locking collars, but it’s a nice tight fit right now.

Parts

Here’s the shaft, bearing, and pulley all properly sized. Once I determine the length of the shaft we’ll put it on the lathe, cut it down, and then get the other side to the right size. I’ll make some pieces that hold the bearings by either laser cutting some material, or 3D printing something, or maybe via the CNC router.

Perfect Fit!

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Hammer Ring

Sketch

We had a quick side project in our “Machines that Make” class which involved designing a piece of jewelry in Rhino. The piece was to be 3 dimensional, and entered into the “Rapid Jewelry 3D Printing Design Competition” put on by the Design Museum Foundation.

I’ve never really designed or made any jewelry before, but Frankie suggested I look at cosplay and wearable things for inspiration. Since I seem to have an (unhealthy?) obsession with hammers lately, I went right in that direction.

Prototypes

The hammer, like so many tools we use, is an extension of the human body, allowing us to do thing we couldn’t do with our bare hands. I wanted to celebrate the hammer as a tool and an object, and what better way than by wearing it on your finger?

Of course this hammer becomes somewhat non-functional, at least as a hammer. You can still move your fingers around to simulate the movement, but don’t expect to pound any nails with it. (There’s also a joke here about fingernails, but I’m still working on it.)

Paper Prototypes

Paper Prototypes

I did a quick sketch and then went to work doing some paper prototypes. The prototype fits well as a “mid ring” (a new term I learned) or as a pinky ring. The actual 3D modeled one should fit on my index finger.

Paper Prototypes

Imagine if you will, a whole bunch of these on one hand. Too many hammers to handle? I think not!

STL File

I learned a few new techniques in Rhino, which should come in handy. I really wish I had more time to dig into it this semester, especially the command line features. Here’s what the plain old STL file looks like. We’ve seen this view a million times before, but I also did some renderings using Keyshot which look rather nice… Check them out below!

Rendering

Rendering

Rendering

Rendering

Rendering

Obviously the 3D printed pieces won’t exactly look like this, but it was great to experiment with different materials and lighting in the rendering software. (Of course now I’m tempted to look at the open source 3D rendering applications out there!)