Initial Optimization:
In the first optimization steps for our ornithopter design, the intent was to reduce the build time and minimize the support structure. The original design consisted of three pieces, with many cut-out sections in the center piece. To reduce the build and assembly time on this design, the center piece and right wing were combined into one piece. Additionally, the cut-out sections were removed, which eliminated the need for support structure in the area. The resulting design can be seen in Figure 1.
Figure 1. Ornithopter design after initial optimization.
Testing the design:
The first design was printed on the Ultimaker machine with a layer thickness of 0.1 mm. The parts were oriented in a position that minimized the z height and support material, thus reducing the overall build time. The design printed without error, and was ready to be tested for function and durability. Some sanding was required for the mating components to fit properly, and the hole designed for the paper clip had to widened so that the paperclip would fit. A video of the first test can be seen in the last blog post. Although the ornithopter remained in the air for a reasonable distance, there were some design issues that needed to be addressed. First of all, the ornithopter was smaller than we would like it to be. The small size made it hard to work with and introduced a higher possibility of component damage. Second, the rubber band (which is intended to power the wing movement) could not function properly due to a high amount of resistance in the shaft (paperclip) near the front of the ornithopter. Lastly, the component to which the shaft attaches was damaged when we tried to initiate wing motion. There was not enough structural support in this area in the original design.
Second Optimization:
To address the problems that we faced during the testing of our ornithopter, we made some additional design changes. First, we increase the overall size and thickness of the ornithopter components in order to improve strength and stability. The thickness of the wing base near the wing joint was increased from 3 mm to 4 mm, and the diameter of the wing joint itself was increased by 30% (from 1 mm to 1.3 mm). Second, the anterior post of the ornithopter that the paper clip is attached to was strengthened by adding a fillet, increasing the width from 2 mm to 3mm, and increasing the thickness from 3 mm to 4 mm. In addition, the diameter of the hole for the paperclip was increased by 40% (from 1 mm to 1.4mm) to better fit the paper clip and account for some shrinkage noticed in the previous print. Third, the drive slot that the paper clip slides in to create the flapping motion was lengthened from 25 mm to 30 mm to allow for increased range of motion. To further improve the rotational capability of the paperclip crank arm, the distance from the anterior post mount to the drive slot was significantly increased from 1 mm to 2.75 mm. These changes can be seen in figures 2-4 below.
Figure 2. Ornithopter design after the second optimization.
Print of Optimized Design:
The optimized design was printed on the Ultimaker machine with a layer thickness of 0.1 mm, as shown below in Figures 3 and 4. The parts were oriented horizontally on the build platform so that z height and support structure were minimized. After removing the support structure, the contact surfaces of the joint were smoothed over with sandpaper. In contrast to the first iteration the effort was reduced drastically.
Figure 3. Separated components of the second design iteration.
Figure 4. Assembled ornithopter after the second design iteration.
Figure 5. Assembled ornithopter with added wing film and crank arm.
Testing the Optimized Design
The optimized design was tested first by attempting to let it glide:
The design was then lubricated with WD-40 and tested with powered flapping:
The design modifications greatly helped the performance of the ornithopter. The first print was able to glide; however, it could not flap by rubber-band power and the anterior post broke due to the force of the rubber band. With this second print, the ornithopter was able to flap its wings at a relatively high frequency while under rubber band power. The adjusted components allowed for better range of motion and sturdier construction which allowed it to work more efficiently, and there were no signs of damage or broken components after numerous tests. The design will next be scaled up and altered to prevent the crank arm from wobbling, as well as making stability enhancements and bat aesthetics.