Mechanical CAD and Designs

All CAD files were printed on a Bambu Lab Design 3D printer. This greatly reduced the cost of the mechanical portion. The project will be significantly more expensive without access to a 3D printer and different colored filament. The 3D print can be painted but due to its smooth surface, the print will require sanding to hold paint.

Dragon Body

We sourced the Toothless CAD from a Toothless popcorn bucket online that provided the STL files (Figure 1). Because these files were sourced from the internet, the files did require scaling to fit the 3D printer. We had technical difficulties with the STL file as it downloaded extremely large so we scaled down to about 10% of the original size. However, if recreating this project, scale to your desired size.

Figure 1: Full Model of Dragon Head and Body on Bambu Print Plate

Dragon Head

In order to detect the Capacitive Touch Sensor through the PLA, the inside of the nose was cut out using needle nose pliers, a soldering iron (not reccommended), sand paper, and pure will (Figure 2). The Capacitive Touch Sensor was then secured to the inside using hot glue and super glue and frequently tested to be sure it could be detected.

Figure 2: Physical model showing the inside cut out where the Capacitive Touch Sensor lay

Since it was only printed with black PLA, the eyes were painted on with a green acrylic paint pen.

Dragon Body

In order to let the wires pass into the dragon stand box underneath, the body was mechanically modified by drilling into the bottom with a hole saw set (Figure 3).

Figure 3: Set Up with the hole made by the Hole Saw

Jaw Mechanism

In order to open the jaw, we planned for the servo to be held in the head and a lever arm to push against the bottom jaw such that the head opens and closes.

We designed all of the parts based on caliper measurements that we took of the Dragon’s printed body. The lever arm was originally printed to short where the IR proximity sensor would still trigger in it most open position. We ended up increasing the threshold for detection on the software end as well as modifying the mechanical part to be longer. The Bottom Jaw was also modified to contain two cylindrical extensions that extend down to the bottom of the dragon’s body to additionally support it as we were worried about the push back force from the servo motor. The Top Jaw was also modified after discovereding that one corner of the part holding the motor was hitting the inside of the dragon’s head and making it hard to line up nicely.

Bottom Jaw (IR Sensor Holder)

Figure 4: CAD for the bottom jaw. The extrusion below the rectangular opening screws into the lever arm that is manipulated by the servo motor. The raised extrusion with two holes houses the IR LED and the IR-PD for the hand detection sensor. The slant on the outside rim slides into the dragon body

Top Jaw (Servo Holder)

Figure 5: CAD for the top jaw. The rectangular extrusion holds the servo motor with M2 screws. The rectangular extrusion is curved on the end to fit the curved inside of the head.

Lever Arm

Figure 6: CAD for the lever arm that screws into the servo motor and into the bottom jaw. Due to the bottom jaw being screwed on to the heavier dragon body, when the servo pushes the lever arm down, the top jaw opens up.

Dragon Stand

Dragon Stand Left

Dragon Stand Right

Figure 7: CAD for the dragon stand. The three holes in the corner are to hold buttons for the electrical stop and a volume increase and decrease button that are electrically connected to the DFPlayer. The hole in the middle allows for wires to be passed from the head into the body and into the box. The square on the left side holds the speaker whereas the rectangular hole on the right side allows for wires to be passed outside to an external power supply.

The bottom of the dragon and top of the dragon stand also had pieces of velcro attaching the two parts together to make sure it didn’t slide around during demos and break any of the more fragile electrical connections.

Although a very fun part of the project, the mechanical part was unfortuantely what broke on us for demo day. As a user tried to trigger the Capacitive Touch Sensor they pushed down on the head too hard while the Servo Motor was trying to move which meant the hinge connecting the dragon head to the body broke off. We’d like to thank hot glue and elastic hairbands that allowed us to make a quick recovery.