Lightweight PLA 3D printed honey bee kinetic sculpture.
This is a prototype 3D printed honeybee sculpture. I’ll describe the design process and the various components. Several improvements are needed before a final version is built.
The honeybee is roughly 8” or ~20cm from head to the tip of the abdomen. It contains servos, batteries, and a wireless receiver. The wings flap a full 180°. The legs articulate and the abdomen conceals the battery and receiver. After reviewing slow motion video of the wing flapping motion, I discovered the natural harmonics of the wings vibrate in an unrealistic way. I’d prefer to see a larger scoop motion in time with the wing flapping frequency. The parts are mostly printed from light weight PLA. The bee uses very compact, high-quality servos, and the 3D printed body is as accurate to real honey bees as I can achieve right now.
Line art render of the wing mechanism containing four servos coupled to four herringbone gear sets.
The design process starts by creating scale copies of the servos and hardware. Components I know I will need to use. Once those are modeled, I add the structural forms around them and design various linkages and attachment points. During this process, I start 3D printing these parts and assembling them to verify their design and strength. After several iterations, I settled on compact, strong, and fairly easy to assemble parts.
Mesh of honeybee exoskeleton used to create a 2D template.
Previously, I had modeled a honeybee exoskeleton and used to it to create 2D templates from the UV maps. I copied this model and scaled it to fit the servo mechanism. I used several modifiers in Blender to smooth and round the exoskeleton components. These smoother components work better for 3D printing. I printed the honeybee exoskeleton and assembled it by gluing small tabs of craft foam between the sclerites. The articulated legs have small axles of monofilament and give the bee a lot of life. The LW PLA material is quite weak and the legs snap near the joint. The abdomen is somewhat articulated as well because each tergum and sternum are attached inside with flexible craft foam.
While finally assembling this prototype, I discovered a variety of problem areas that will need to be addressed:
The wing motion doesn’t sell the realism.
3D printed PLA is too weak for the leg joints.
The mechanism, batteries, and other peripherals take more space than anticipated.
The head is currently dead weight.
I think I could address each of these issues by updating the model and improving the compactness and strength. If I find a really solid design, I may invest in ABS or Nylon printing either at home or through a manufacturer.
Line art render of wing stroke mechanism embedded into honeybee model.
The servos are a steep investment in these prototypes. It is best practice to allow easy disassembly. The option to reuse the servos is more cost effective. Prices of servos range from $2 per servo to over $200 per servo. Having examined the $2 - $60 range myself, I can agree that you get what you pay for. The more expensive servos have considerably higher torque, they are faster, use precise gears, and have reliable feed back electronics. The housings are accurate, the cabling is decent, and the motors draw more current. Cheap servos are often very inconsistent, vibrate or oscillate due to errors in the feedback circuitry, and can jam on themselves due to poor gear and housing accuracy. However, I still recommend purchasing a bulk order of cheap servos, because they are a low risk way of testing very early design ideas. As the mechanism being designed evolves, nicer and pricier servos can be introduced, to verify the design is working as expected.
Continuing on the topic of costs, what surprised me is the cost of hardware. Several hundred M2-M3, and 0-80 size screws with nuts, washers, threaded inserts, and more added up to over a $100. McMaster has a large inventory and ships quickly, but even the tiniest of screws costs some money. It may be a good idea to avoid using hardware as much as possible.
One future project that I’m interested in exploring is designing parts that could be cut from flat even thickness materials. Several of the frame components are 4mm thick and could be laser or CNC cut. I have also previously used my honeybee model UVs to create foam templates to be glued together into 3D objects. Perhaps in the future, I may find it more economical to order these parts precut. Additionally, if I can borrow some design ideas that reduce the use of hardware, these flat materials may be able to snap or lock together without screws, further saving costs and weight.
Overall, this prototype was exciting to design and build, but I was disappointed by the resulting wing motion. As I reflect on the areas for improvement, I realize that my solutions may work better using a different model organism. I think a large beetle would offer more flexibility with component space, wing stiffness, and including robotics in the legs and head. Finally, this is the sculptural piece of this project, but there is an electronics piece that comes with a lot of complexity. I’d still like to design sensors and an analog computer to accompany this sculpture, so it is an autonomous robot of sorts.