Bistable Dragon

a bistable toggle indicator toy

Stanford University, ME102: Introduction to Product Realization, 4 week team project

Challenge

In a team of two, create a bistable indicator using springs and hard stops.

My Role

Designer, engineer

Skills

CAD (Solidworks)
Rapid prototyping
3D printing, laser cutting
teamwork

Ideation

We started this project by researching different mechanisms. From the beginning, we were looking to make something that was fun and interesting. Rather than doing a typical indicator, we decided that a switch that caused visual movement would be much more engaging for the user. Eventually, we landed on a dragon that flapped its wings. Targeted toward children, this toy could be both visually engaging and also mechanically interesting so that the child could have fun and learn at the same time.

After lots of brainstorming, we decided on a wing mechanism

The original drawing of a dragon with flapping wings and a moving tail

Rapid Prototyping

We decided to prototype a compression spring system that would create vertical motion. By switching the lever up, a string is pulled and the wings are opened using rotation around a joint. The lever itself is bistable due to a compression spring. Using mainly cardboard, we made a quick prototype to test out if the system worked. The most obvious issue we found was the spring, which would bend rather than compress.

Originally, we had planned to have springs to bring the wings down to the closed position. However, the rubber bands that we used to model the springs were too strong for the lever, making it impossible to flip the switch. In the end, we realized that the wings would close due to gravity if the friction was reduced, so we redesigned the wings with that in mind.

More Prototyping

Our next prototype focused on 3D printing the necessary components. We created a spring insert that would keep the spring straight, and also made a beta version of the wings. The rest of the lever was laser cut, and the whole assembly was drilled into a scrap piece of backing.

After printing, we quickly realized that by slightly altering the design of the wings, they could be laser cut rather than printed. However, the string still needed a slot to run through, so we decided to create 3D printed tubes for the next prototype. We also decided to 3D print the lever arm to reduce motion outside of the plane of rotation.

The third prototype worked well, but the lever was still wobbly and got stuck in the middle. We changed some dimensions in the screw insert and added lock-nuts, and the final lever was finished.

prototype #2: 3D printed wings and spring insert, laser cut lever. The lever was too wobbly and would get stuck in the middle

prototype #3: 3D printed lever arm and a thicker spring insert to reduce motion

prototype #3: newly designed laser cut wings. We originally tried wire instead of string but it was too stiff

prototype #3: SolidWorks file for the 3D printed tubes for the string to run through

Final Assembly

To finish off the dragon, we needed to design a back board for the mechanics to sit on and a front facade with the dragon. We made SolidWorks mockups for the entire assembly, cut out the parts, and then it was just a matter of putting it all together. We added hard stops for the lever and some front decor, and it was finished!

SolidWorks exploded assembly drawing with a bill of materials