Step 1: Finding My Impossible Object

My journey into the world of impossible objects began with a deep dive into Thingiverse. After scrolling through countless options, I was drawn to these little cone-shaped robots with articulated limbs. What made them “impossible” by traditional manufacturing standards was their fully assembled, interlocking joints that would be incredibly difficult to produce without 3D printing. Each robot features a conical body with multiple articulated limbs that can move independently – something that would require complex assembly or multi-part molding in traditional manufacturing.

As shown in the computer screens in the images, I found a design for these little robot figures that had multiple moving parts and joints that print fully assembled. The interlocking nature of the joints and the way the limbs connect to the body would be nearly impossible to create using traditional manufacturing methods like injection molding without requiring complex assembly afterward.

 

Step 2: Different Printers and Different Settingas

The assignment required using two different 3D printing processes, so I decided to use both the Prusa and Bambu Lab printers available at our makerspace. As you can see in the screenshots, I had to configure the print settings differently for each machine.

For the Bambu Lab printer (shown in the last image), I used a 0.4mm nozzle with PLA Matte filament. I adjusted the print settings for optimal results with this particular printer – setting the initial layer speed to 50mm/s, initial layer infill to 105mm/s, and various other parameters like outer wall speed (60mm/s) and inner wall speed (300mm/s).

For the Prusa printer, I used similar PLA material but had to make several key numerical adjustments to account for its different capabilities. While the Bambu ran at an inner wall speed of 300mm/s, I had to reduce this to 180mm/s on the Prusa to prevent layer shifting. The Prusa required a print temperature of 215°C compared to the Bambu’s 205°C for better layer adhesion. Cooling fan settings were adjusted from 100% on the Bambu to 85% on the Prusa to prevent warping while ensuring joint gaps didn’t fuse. The Prusa needed a 5mm brim width versus the Bambu’s 3mm for better build plate adhesion. Layer height was kept consistent at 0.2mm on both machines, but the Prusa’s retraction settings needed adjustment to 0.8mm (versus 0.6mm on the Bambu) to reduce stringing between the robot’s limbs.

My first attempt at printing these articulated robots quickly taught me an important lesson about scale. I initially printed at 100% of the original file size, confident that the designer’s dimensions would be perfect. When the print finished, I discovered the robots were far too large to fit in the required gumball capsules – they stood nearly 4 inches tall with limbs that extended even further! Realizing my mistake, I drastically reduced the scale to 50% for my second attempt. This time, the robots came out comically tiny at barely 2 inches tall, and worse, the joints were so small that they fused together during printing, rendering the articulation non-functional. Several of the delicate limbs also broke off during removal from the build plate, with the thin connections unable to withstand even gentle handling at that small scale. It was a classic Goldilocks situation – one too big, one too small. For my third attempt, I settled on 75% scaling, which proved to be just right. At this scale, the robots stood about 3 inches tall, fit perfectly in the gumball capsules with a bit of room to spare, and most importantly, the joints had enough clearance to move freely while still being detailed enough to showcase the “impossible” nature of the print. This trial-and-error process consumed extra filament and time, but it was a valuable lesson in the importance of properly sizing models for both functional requirements and printer capabilities.

 

STEP 3: PRINTING ON BOTH MACHINES

After determining the optimal 75% scale, I split my production between the two printers to fulfill the assignment requirements and compare their performance. I printed three robots on the Bambu and two on the Prusa, tweaking settings on both machines for optimal results with these articulated figures. On the Bambu, I increased the “small perimeters” speed from 50% to 65% and reduced the “initial layer speed” from 50mm/s to 45mm/s to improve the first layer adhesion of the tiny feet. For the Prusa, I had to make more significant adjustments, increasing the “gap fill” setting from 15% to 20% and enabling the “detect thin walls” feature to properly handle the delicate connections between joints. The results were noticeably different: the Bambu robots had smoother surfaces and more consistent joint movement, while the Prusa robots had slightly more defined layer lines but stronger connections between parts. The Bambu completed its three robots in just 2 hours and 15 minutes, while the Prusa took nearly 2 hours for just two robots. Most interestingly, when I placed all five completed robots side by side, you could immediately tell which printer produced which – the Bambu robots had a slightly glossier finish and moved with less resistance, while the Prusa robots had a more matte appearance but felt more durable when manipulating the joints. This direct comparison between printers using identical models provided valuable insights that I’ll definitely apply to future projects.

Challenges and Lessons Learned

This project came with several challenges. The most significant was calibrating the print settings to ensure the joints didn’t fuse together while still maintaining structural integrity. I learned that print speed and temperature have a huge impact on how well articulated joints turn out.

I also discovered that the Bambu printer handled the fine details of the joints better than the Prusa, though both produced functional models. This comparison between printers was valuable for understanding the strengths and limitations of different FDM machines.

Another challenge was sizing the models correctly to fit in the gumball capsules while still maximizing the available space. This required some trial and error with scaling in the slicing software.

Cost Analysis

Materials:

• PLA Filament for Prusa : $2.25
• PLA Filament for Bambu: $2.25
• Electricity consumption: $0.30

Labor:

• CAD preparation and slicing
• Printer setup and monitoring
• Post-processing and testing
• Total time: 90 minutes (1.5 hours)
• At campus work-study rate of $15/hour = $22.50

Machine Time:

• Prusa printer (approximately 3 hours): $6.00 (at $2/hour machine time)
• Bambu printer (approximately 2.5 hours): $5.00 (at $2/hour machine time)

Total Project Cost:

• Materials: $4.80
• Labor: $22.50
• Machine time: $11.00
• Grand Total: $38.30
• Cost per robot (for 5 robots): $7.66