Aug 20, 2018
Late last year, four pioneers — Alex Larson, Greg Kent, Kristen Schreck, and Brian Wetzel — proposed the Ultibot-D project. They wanted to create an interactive desktop sized Ultibot and provide creative solutions that spoke to lessons about 3D printing, like documenting solutions for functionally attaching components, using appropriate materials, showing off different software solutions, using the slicer for interesting effects, and more. This post, written by Brian Wetzel, is the first in the series.
To say I was excited to jump aboard this project, as outlined by Pioneers Alex Larson and Greg Kent, would be a huge understatement. The Ultibot-D model has been an iconic mascot of the Ultimaker community for several years now. The original Ultibot, as modeled by Ultimaker founder Siert Wijnia, was split into 5 sections: the head, body, feet, and two arms. For demonstration purposes, the largest section was scaled to its maximum size and the other sections were scaled to match. However, when the pieces are printed, we needed a way to bring the Ultibot back to its modeled form. Many 3D printing experts have had mixed success with fusing printed parts together. Some have tried soldering methods; others have tried different types of glues and epoxies. However, success is reliant on the material type and other factors too numerous to name. Our challenge became “How might we redesign the Ultibot so that these post-processing methods are not necessary?”
This project aims to answer this question. Makers have an extraordinary ability to think of creative solutions to these types of open-ended problems. There are many design choices available to create these solutions, such as Fusion 360, Tinkercad, Inventor, Blender, and many more. Each has their own benefits and drawbacks and all makers have their preference when it comes to design software.
Always willing to experiment, I used a newer program on the market called Onshape. Onshape is primarily web-based, but also offers Android and iOS apps. It conveniently offers educational-based subscription services with the ability to sign up students quickly and easily without the need to request services from your IT department. Onshape works and acts very similar to products that designers may be more familiar with, such as SolidWorks, Autodesk Inventor, or Fusion 360. You can start from scratch, creating your 2D drawings and extruding them into 3D models, or you can start with a given model and add to or subtract from it according to your preferences.
Since this was my first extensive use of Onshape, I decided to create a fairly easy method of securing the four pieces to the body. I decided to go with simple and consistently sized connectors and slots for this attachment. The connector would ideally fit into a hole into the body and then would be able to slide into place, securing the attachment. With previous experience, I thought that it would be best to use a tolerance of 0.5 millimeters to give a little bit of extra space for the male part of the connector to fit into the slots designed on the bodies.
I began by giving myself a tour of the Onshape interface. I like the clean look of Onshape with the common tools above the work plane. Having a fair level of experience with Fusion 360, the OnShape icons and vocabulary were easy to pick up. There was a features tree on the left side of the work area and a view cube on the right to cycle around the model. It was also quite easy to use the mouse with the left button to input commands, the scroll wheel to zoom, and the right button to orbit around the model. The workflow was very similar to Fusion 360 as well. I was able to open the STEP files directly in Onshape and could then begin creating sketches and extrudes as desired on the given planes and faces. After deciding to start with the design of the male connectors, I opened the feet of the model and began designing.
At first, it seemed as if I needed to create a plane in the center of the feet. Reflecting back on this, the plane I created was the same as the Top Plane as pictured above; however, the fact that the planes were not in alignment with the feet threw me off for a bit. On this plane, I thought the T-shaped connector would be created easiest with a revolve, which Onshape conveniently has. I began a 2-dimensional sketch on the plane I created. I quickly found the need to project some of the existing geometry to find the middle of the model. Onshape also offers this capability; however, it took me a minute to find it as they call this functionality “Use”. I then used simple lines to draw an L shape which I would later revolve to create the male connector.
As for sizing, I wanted something that would be proportional in size to the already created attachments. It was at this point, that I noticed that the default units were in inches, which is not my preference, as it doesn’t translate well to our common slicing programs. However, I did not look around much for how to change this. After sketching the rough outline of my connector, I felt that working in quarter inch increments seemed to be best for the model. This would give the base a diameter of 1 inch and the larger sized head of 1.5 inches. I assigned the dimensions accordingly and revolved. In the related image, you can see the sizing and initial design. Replicating this design process was quite easy for the bottom of the head and the two arms as well.
The female counterparts of these connectors were a little trickier. It was here in which I felt the pains of working with inches the most. Having never designed mating pieces in imperial units before, I was completely unsure of the tolerance that would match my desired ±0.5 millimeters. At the time, I was unsure of how (or if) I could change the units in the model. Using a conversion tool, I learned that 0.5 millimeters is roughly equivalent to 0.019685 inches. Knowing that I would need this measurement often, I easily found the tool to create variables in Onshape. This is something that I have never done in Fusion, but will soon try to figure out. With this tool, I could easily create a set value for dimensioning the female cutouts that is based on a string of letters and/or symbols. I decided to create four variables: a long and a short version of my quarter inch and half inch. These variables (expressed in inches) would represent these two measures plus and minus 0.5 mm. The associated image shows one example of these measurements. Below you can see how I dimensioned the cut out using my variable name preceded by a # symbol.
Another tool that came in quite handy is the section view, but I found it a little more difficult to use. Since I was working primarily in the internal geometry to cut out the mating section, I needed to see the actual plane I was drawing on. When looking for this functionality, I was searching for a “slice” view, as that is the box you check in Fusion 360. However, they titled it section view and it was hidden within a context menu under the view cube. I found it much more difficult to slice the section to see the actual plane I was utilizing for my sketches. After a few sketches, revolve cuts, and extrude cuts, I finally had the shape that I was looking to make. As you can see to the right.
Once my cut-out was created, Onshape gives you the ability to mirror features across a plane as most other design programs allow. I mirrored my original across the body to the top for the head. I had to repeat my sketching process for the arm; although I could copy and paste the sketches onto different planes. Doing the arm cut-outs caused a slight redesign on the arm connectors because, at first, I had the connector near the top of the arms. I felt it better to move the connector closer to the center so that gravity would not affect the resting place of the arm when connected.
While not perfectly aligned, you can see a section view of the fittings. I have not had a chance to print this model yet, and I’m sure that in doing so, I will need to adjust some of the tolerances. I thought that this was a great project for me to learn a new design program. Onshape did run very smoothly in my browser for a more advanced CAD tool. Even as a desktop application, Fusion can run slow and choppy at times, even on a MacBook Pro. Onshape is much more cross-platform having iOS and Android apps, and since it primarily runs in a web browser, you can also use it with any operating system, including Chromebooks.
I did not get much into anything beyond the design workflow. While I know it has the capabilities to create them, I would have to experiment with Onshape much more to get a feel for its ability to create joints and assemblies. I found it very easy to create the variables as I discussed, something I have yet to learn in Fusion 360, and learned later how to change the units of a model to millimeters if I would choose to. While there are many things nice things about Onshape, I am not sure that I will be using it in future projects. I guess I am just used to Fusion 360 and still learning how to use it especially its sculpting and rendering functionalities which seemed absent to me from Onshape.
As I mentioned at the start, this writing is just one in a series of posts to be created by Alex Larson (@STEMedTeacher), Greg Kent (@gkkent), and Kristen Schreck (@mongemath). Each will be writing about how to mate these components together with a prospective tool. Furthermore, in the second phase for this series, our next posts will turn the Ultibot into a mix and match component set. I liken this to Mr. Potato Head. We will create our own attachment(s) to be used in conjunction with the Ultibot. We will also encourage readers to submit their own designs and attachments. Be on the lookout for those posts as well!