A few weeks ago, we received a nice new acrylic display stand for DYNAMIXEL servos from our Headquarters in Korea.
I thought the display looked quite nice, but after a little bit of admiration I started to feel that maybe this display was missing something. I quickly realized that the best way to spice up a servo display was to give the servos something to do!
At first I was racking my brain trying to think of a cool project that would show off as much of the actuators as possible. Then inspiration struck!
I had personally been wanting to build a Nixie Tube clock like that one for some time, as they are relatively simple projects that look great and make good conversation pieces. I decided that a similar clock based project would be great to have displayed here in the office, and that it would be the perfect first project to share my build process with the ROBOTIS community!
The first step in any project is deciding what exactly you’re going to be doing. In this case, I need to decide how I want this clock to look and function.
In this case, for ease of use and to get this project put together as quickly as possible I decided that the simplest way to turn DYNAMXIELs into a clock is to attach a clock face to the horn. I plan to use two 540 size servos, two 430 size servos and two 330 size servos in my clock. The horns on the 540 and 430 size servos have some matching mounting holes, and the servo sizes are roughly similar so I figured that I could use the same model for both. This means I should only need to create two models for this project. With that in mind, I got to modeling what I wanted in OpenSCAD.
Starting with a simple cylinder I quickly modeled up a horn design with numbers on the face. At first I started modeling a standard clock face.
I pretty quickly realized that a clock face like that wasn’t going to work with the design I had in mind. I wanted a similar display to the Nixie Tube clock I was using as my inspiration. Three separate two digit display sections, one each for hours, minutes, and seconds. To achieve that, I needed to create a horn attachment that had 10 digits, from 0 to 9 arranged around it’s face.
This was my first time using OpenSCAD, and I had heard that it was much more difficult to acclimate to than most CAD software, so I was pleasantly surprised how quickly I took to it. Programmatic design and scripting feels much more intuitive to me than sculpting or other design programs do, so I’m pretty glad that I decided to make the switch.
While I was modeling, I decided it would be best to try and test fit the mounting screws and center hole for the horn bolt. After temporarily disabling the digits in the model, I printed out the flat disk with the holes for attaching it to the horn.
I got pretty close with the measurements on my first try. The 430 sized horn fit easily in the center, but I was about 2MM off of lining up all four mounting points for attaching the disk. I adjusted a bit and my second print was perfect!
When I was test fitting this on 540 size horns to make sure that I could use the same model for both, I realized that the mounting holes matching the 430 horn aren’t threaded on the 540 horn! I’m glad I noticed now, while I was still in the middle of modeling and fitting the clock faces. I decided it would be easiest to just make 3 different sized clock faces.
After seeing how the size of the clock face allows the DYNAMIXEL model badge to be seen, I decided to keep this scale on the different sized faces for the 540s and 330s.
After doing the remaining modeling, I did a test print with a few faces laid out together.
The 330 and 540 size faces ended up very thick… I didn’t modify the depth when changing the other sizes. For the 330 it actually ended up a good thing, since the screws that I will be using to mount them are pretty long, and they ended up being almost exactly the right size. On the 540 horn the mounting holes are a little bit too big and far apart anyway.
I went back to the model and edited the placement and size of the holes, as well as making the whole thing half as thick. I felt pretty confident that I had gotten all the sizing right this time around, so I set up a long batch print with all the faces I needed and started waiting.
Once everything was all printed up, I was pretty pleased with how it came out. I filled in the relief on the letters with black marker to add contrast. Unfortunately, the letters on the 330s are too small for that, but they came out very legible anyway. The SCAD and STL files that I created are attached to this post, in case you want to make your own!
Now that I’ve got the clock faces assembled, I can get to programming the actual clock in my next post!