Cartridge - Custom Transformer

Cartridge was a joint project between a classmate and I for a design project in our engineering course. I have always been a long-time fan of the Transformers and wanted to try my hand at creating my own via CAD and 3D printing. I believe it turned out fairly well, though there were some problems we had with tolerancing and joint rotation.

1. Yellow PLA
2. Grey ABS
3. Black TPU
4. 100ct Jumbo Paperclips - Target
5. Gorilla Glue Tube - Target
6. Pliers (for straightening)
7. Sidecuts (for cutting the paperclips)

Color is completely optional here, but we decided on a yellow/black/grey color scheme to give a "construction" vibe. TPU is used for the wheels, to give them the stretch to fit over the pegs on the torso and legs. It will not work without the wheels being TPU or similar.

CAD files can be found here.

At the outset of our project, we created some basic ideas for our first draft. Pictured is a decision matrix we used to decide what vehicle we wanted the robot to have. We settled on a mobile crane for the alternate mode, and got to work on brainstorming what pieces of the crane would become what joints and where arms and legs would fold into. This is the drawing of the crane seen above. Eventually we settled on the legs being the front half/cab area and the arms being the crane assembly itself, with the back half creating the torso. We then did some research on how to create joints from plastic, and learned how to create ball joints in a CAD environment. The ball joints were printed and tested multiple times before a good fit was reached. We went through multiple design iterations, where we got feedback from our classmates on what we could improve. Most of our feedback stated the design was too complex, so we took steps to make it simpler, such as reducing the size and lowering joint count. Then it was off to the CAD and printing.

As with any 3D printed project, the first step is to print the pieces. All pieces in the images were printed using PrusaSlicer on a Prusa Mini, and a 0.4mm nozzle. The prints took 15 total hours with a few reprints on easily damaged or incorrectly toleranced pieces that we broke during testing. Most parts you will only need one of, excepting the thigh assemblies, shoulder connector pieces, and the wheels. You need 2, 2, and 8 respectively.

Once our pieces our printed, we need to remove all the support material. The one very important step is to clear all of the holes for the paperclips. Every part that has a joint has 0.05in holes to put the "pins" into, so it is important that they be cleared before you start assembly. We cleared them by shoving the paperclips/thumbtacks through the holes to remove the supports or pulling out the supports with pliers when we could.

Find all of the leg pieces, take them and line up the holes. Then, take the paperclips, straighten them, and push them into the holes (This will require some major effort!). Once the paperclip has gone all the way through, cut off both ends and dab some glue on either side. Repeat this process for every hole, and then slide the pegs into the hip joint block to connect both legs to each other.

The arms are a bit more complicated. The shoulder itself is 2 interlocking joints, which attach to the rotation gear with pins and the arms with pins. As with the legs, we slot paperclips into the holes where they interlock, and then dab them with some glue to seal them in. The hands attach via ball joint and are a little loose, so be careful with them.

The head attaches onto the ball joint at the end of the torso, and folds into the torso during transformation. The open gap in the ball joint lets it fold down onto the peg and is intentional. Make sure to fully clear the slot of all support material.

The crane rotation gear clips into the circle in the back of the torso. It is intentionally loose (to mimic a real crane's rotation) and should be able to spin with minimal force.

Next, slot the hip joint peg on the legs into the torso to attach the leg and body assemblies.

Congratulations! You now have your very own 3D printed transformer! Have Fun!