> For the complete documentation index, see [llms.txt](https://docs.andymark.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.andymark.com/robits-build/intermediate-and-expansion-kits/launchers.md). # Launchers Launching scoring objects is a common game objective in FIRST Tech Challenge, RECF Achieve, and RECF Engage involving moving an object from a robot through the air and into a much higher, much further away goal. A launcher can be constructed in many different ways, and it's important to choose what works best for the object, the goal, and your knowledge. The [Robits Launcher Expansion Kit](https://andymark.com/products/robits-launcher-kit) is a supplemental kit to the Robits Core Kit designed to explore projectile launching mechanisms. The kit provides the components needed to construct and experiment with the three main types of launcher; a catapult, hooded flywheel, and double axle flywheel. The kit is intended as a starting point for understanding how mechanical design choices affect projectile motion, or the parts can be integrated with the Robits core kit to build more for tasks that may require launching. ### Catapult
The catapult uses stored elastic energy and a cam-driven mechanism to pull the launch arm backward before releasing it. Catapult mechanisms can provide repeatable launches and can accommodate a variety of scoring object shapes. The launch characteristics can be changed by modifying: * Cradle shape * Arm length * Elastic strength * Release angle * Cam position Changing these variables can alter the amount of stored energy, release timing, and trajectory of the launched object. ### Hooded Flywheel
The hooded flywheel launcher uses a rotating wheel to accelerate an object against a curved hood. As the object passes between the wheel and hood, the wheel transfers energy to the object and launches it. This configuration introduces rotational spin to the object and is recommended only for scoring elements that can roll against a static surface. The object's flight and behavior once it hits the target will be affected by the amount of spin. When prototyping with the hooded flywheel, consider these variables: * Compression * Wheel type * Wheel velocity * Hood wrap * Hood angle The hooded flywheel provides an opportunity to look at how geometry influences launch velocity and trajectory. #### Double Axle Flywheel
The double axle flywheel launcher uses two opposing wheels to accelerate an object as it passes between them. The two wheels are controlled separately and can be operated at the same or different speeds. When both wheels rotate at similar speeds, the launcher can reduce the amount of spin imparted to the object. This is best for elements that are affected by spin or have a specific orientation they must be launched in. When the wheels rotate at different speeds, the amount of spin can be directly controlled by the relative wheel velocity. The system can be used horizontally or vertically. Key variables include: * Compression * Wheel type * Relative wheel velocity This configuration is great for investigating how differences in wheel speed affect object rotation, flight path, and behavior once it reaches the target. *** ### Testing a Launcher Mechanism Use caution when testing a launching mechanism, especially one that is used with high speed motors/wheels. Before powering the mechanism, be sure that all connections are tight. Watch for: * Oreintation of the scoring element through the system * Launch accuracy/precision * Motor speed before and after the shot * Catch points through the system A successful launcher mechanism needs to balance several factors, all of which relate to each other. * Friction within the system - balancing friction of the launch location, compression, and geometry * Speed of the launcher and the distance the object can reach * Torque determines how much friction the system can overcome * Spin on the object can impact how it stays in the goal or bounces out For meaningful comparisons, change one major variable at a time and record the resulting launch behavior multiple times. Measurements such as launch distance, launch angle, repeatability, and projectile spin can help quantify the effects of each design change.