Embedding Hardware in 3D-Printed Objects
Usually here on “Engineers Rule”, I write CAD tutorials, articles on new CAD features or stories about how companies use CAD to create interesting and cool new products.
3D-printed drones are not new. However, printing a drone with the electronics embedded inside, using a high-temperature thermoplastic (ULTEM 9085), is a first.
And naturally, my CAD software of choice was SOLIDWORKS. So in this article, I will be talking about how I utilized various features of this software to realize our product, starting from the predesign phase through to simulation and renders and finally in generating the STL files for 3D printing.
A common theme in my articles is how CAD software can save time and increase productivity, and this was apparent from the very start of this project.
The project was born out of a class project at my university and a collaboration with Stratasys Asia. Stratasys was interested to see if we could print a drone that was ready to fly out of the printer, and my class project required some preliminary designs for academic credit. So I decided to merge the two projects and kill two birds with one stone. The class project resulted in a basic flight hardware list, as well as a preliminary design. That design changed significantly as the project moved from paper into reality, as you will see later in the article.
Commercial drones come in a number of sizes, with the most common being in the 200- to 400-mm class. This dimension measures the diagonal length from rotor to rotor. The 3D printer that I used at the Stratasys office here in Singapore was the Fortus 450mc. The 450 here is the dimension of the print bed length. So with the maximum print dimension being 450mm, we opted for a 400-mm class drone, because bigger drones can lift a larger payload and can have a longer flight time.
So, with the class of drone decided, we next wanted to determine which size of propeller we should use. As a rule of thumb, bigger propellers can move more air and generate more lift. So we wanted as large a diameter propeller as possible for the 400-mm class, while leaving enough clearance so the props don’t smash into each other. At first, I started this task the old-fashioned way (with pencil and paper). After a couple of iterations and a bit of wasted paper, it dawned on me that this would be a lot easier if I just switched my laptop on and sketched it out in SOLIDWORKS. It has the advantage of point-and-click dimensioning, so there is absolutely no need to use a ruler.
So with the maximum propeller diameter found, we looked online to find a suitable propeller that would fit our envelope, allowing an extra bit of clearance for good luck. We opted for the Graupner eProp, with a 254-mm (10-in) diameter. Plugging those values into the basic sketch yielded a propeller tip clearance of exactly 28.84mm. Good enough. And doing this most basic of tasks in the CAD software was much more efficient in terms of both time saved and accuracy of measurement.
With the basic geometric constraints being set, it was time to get creative and start some modeling.
But before we go into detail about the design process, I should highlight the constraints that dictated the final shape of the design.
The requirement to have the drone fly out of the printer meant that it should undergo as little post-processing as possible. This meant that we should use zero internal support structure, be it soluble or breakaway. Not only is it inadvisable to submerge electronic components inside a warm bath (to dissolve soluble supports) but given the compact cavity inside the drone, it would have been time consuming (if not impossible) to remove breakaway structures without damaging the electronics inside. So, we opted to have zero internal supports. This introduced some interesting issues.
Rather than having removable supports, we had to design the structure so that it was self-supporting, and this meant that any overhangs needed to be at a 45-degree angle. However, having everything at 45 degrees results in a rather angular, boxy-looking drone. If we wanted to maintain a curved and organic product, we would need to keep the 45 degrees internally, while covering the exterior angles with curved surfaces. In other words, we would need to cover the whole thing in layers of deadweight in order to keep it looking pretty. Deadweight is the enemy of aerospace product design.
After measuring the electronic components and incorporating them into the basic design, our optimized drone would have looked like this:
However, after taking into account the 45-degree angle rule, the final design ended up looking like the image below. Fans of comedy sci-fi series Red Dwarf may notice similarities with the show’s Star Bug spacecraft. Others may see more than a passing resemblance to the body of a frozen chicken.
After entering the ULTEM 9085 material properties into SOLIDWORKS, it was easy to do a mass analysis of the CAD model. The mass of plastic would come in at around 520g. That is very heavy for a quadcopter frame. Thankfully, the Stratasys Insight software allowed us to employ some honeycomb filling into the deadweight areas, reducing that mass by a few grams.
After getting the basic shape and dimension correct, it was time to design some housings for the modified electronic components. This was to allow the electronics to fit flush within the drone body and to allow us to print directly over a flat surface. Also, the housings had a secondary benefit of protecting the components from the heat of the freshly extruded plastic.
Three housings were preprinted in ULTEM 9085 material. The first was a flat plate to allow us to print a battery cavity, the second was a flight controller adapter, and the third was for the radio receiver. Due to the sensitivity of the receiver to temperature, this part was embedded last, reducing the time needed to remain in the printer chamber.
When embedding hardware in a print job, it is important to leave a little clearance to allow for any shrinkage. We left 0.5mm per side, and that seemed to work just fine. Creating the adapter housing slots within the main body was easily achieved. First I located the center of mass with the SOLIDWORKS mass analysis tool, and using that as my datum, I positioned the flight controller and receiver housing within the main body.
With all the design work and electronic modification complete, it was time to print the drone. The SLDPRT files were all saved as individual files and then exported via SOLIDWORKS as STL files, ready for printing.
We began the print and made the first pause after 5 hours and 11 minutes, at which time the battery plate was installed. Printing was resumed, encasing the plate and creating a cavity internally.
After 9 hours and 10 minutes, the printer was paused again, allowing us to embed the flight controller in the housing, the speed controllers and the custom wiring harness. Printing was again resumed.
The final pause was at 13 hours and 20 minutes, allowing the receiver to be connected to the flight controller and the receiver to be slotted into its position. The printer was resumed for a final time and the entire job was finished after 14 hours in total.
After removing the drone from the printer chamber and allowing it to cool sufficiently for handling, the final touches were added. The motors and props were connected, the battery was added, and we powered the drone up to check that everything had survived. We were happy to see that it had and that everything was powering up as it was supposed to. So we stripped the motors off and sent it to a third party for painting. The blue finish that you can see in the final picture is the result of that painting process.
After receiving the drone back from the paint shop, it was time for a proper flight test outdoors.
All was functioning as it should be, with the drone being capable of some 20 minutes of flight time off a single charge.
It was fairly sluggish to respond to vertical changes, but this was to be expected, as it was a little overweight. This is something to work on in the future. All in all though, the project was a success, and we are looking forward to improving the design in future.
Tips and Tricks
If you are considering embedding hardware to a 3D print, be it mechanical or electrical, then we would recommend a few guidelines to help you achieve your goals. There are as follows:
- Allow clearance for parts to be embedded (around 0.5mm per side).
- Ensure hardware surfaces to be printed over are clean and free from obstruction (flat).
- If necessary, print adapters to ensure a good fit and flat surface.
- A coating of acrylic paint applied to the hardware can assist with layer adhesion on the top.
- Designing clips into the body can help retain the hardware while printing is continued on top.
- If using a heated chamber, the most sensitive electronics should be embedded at the top of the item to be printed, reducing the time exposed to high temperature.
- Under no circumstances should you print over a battery pack—install the battery after the print.
Additionally, if you would like to read the Stratasys guidelines on embedding static mechanical items, please read this.