The LV-3.1 Electromechanical Recovery System (ERS) is a fully-resettable recovery system for the PSAS Launch Vehicle v 3.1 (LV-3.1). The system uses a geared motor to release the nosecone and drogue chute, and a linear actuator to release the main chute. The ERS expects deployment signals from LV-3.1 avoics and an onboard control board uses optical encoding to determine and confirm deployment states.
note: Solidworks files for all components are found under /mechanicalsystem/cad, and primarily follow the naming convention of "Foo part" --> foo_part.ext (e.g. twist coupling -> twist_coupling_v4.SLDPRT). The complete assembly can be found here; all parts in its parent directory are needed to properly view the assembly.
The ERS main assembly houses all the necessary components for functionality of the system. The upper ring houses the electromechanical components, and is coupled with the upper ring by the twist coupling. The nose cone is fastened to the upper ring using the LV-3.1 arc-clamp system and houses the parachute cups above the main assembly. The keeper ring is fastened near the bottom of the lower ring and serves as a platform for the battery, control board, geared motor, linear actuator, parachute anchors, and the pizza table. Attached to the inner diameter of the upper ring is the tube ring which serves as an attachment point for the surgical tubing used to eject the nose cone from the rocket. The ring components of the main assembly are machined out of 6061 aluminum.
The pizza table elevates the parachute cups above the electromechanical components and supports the weight of the parachutes and cups and the preload force of the surgical tubing. The legs of the pizza table also secure the control board and positions the optical sensors needed for function of the control system. In the current iteration, the pizza table is made of of 3D-printed carbon-fiber reinforced nylon.
// pizza table image
The twist coupling couples the nose cone the rest of the rocket assembly and releases the nose cone by twisting out of a locked state. Once released, the surgical tubing rapidly deploys the nose cone, which then deploys the drogue parachute . The twist coupling has six L-shaped channels that mesh with six pins on the upper ring, and an internal spur gear that meshes with a gear on the motor. Upon receiving the necessary signal, the motor will rotate the twist coupling to release the upper ring and nose cone. The grey code tape necessary for control logic is attached to the inside of a skirt on the twist coupling, and is read my the sensors on the control board. Machined Delrin was used to fabricate the twist coupling to reduce friction between the mating surfaces.
Deployment of the main parachute is accomplished through a 3-ring release system widely used skydivers and military personnel. Three interlocked rings tie two ends of webbing together and are released by pulling on a stiff cord (we use a nylon coated wire). The interlocking rings multiply the mechincal advantage of the release cord and can release of >150 lbs of force with only a 3 lb force. A linear actuator is used to pull the release cord upon receiving signal from the control board. A member of the design team sew the 3-ring release system, but commercial alternatives are available.
The parachute cups separately house the drogue and main parachutes and related webbing cord needed the secure and deploy the parachutes. The cups are stacked upon each other and supported by the pizza table in pizza-table/main-cup/drogue-cup order from bottom to top.
The top of the drogue cup has cone-shaped indent to support the elastic bands for nose cone release and align them to the central axis of the rocket. Upon release of the nose cone, the drogue cup is mechanically flipped upside down through webbing routing, which promotes rapid release of the drogue parachute. The nose cone, drogue chute, drogue cup, and main cup remain attached by webbing for the entire descent of the rocket, and are detached from the main airframe upon release of the main parachute.
The main cup houses the main parachute and 3-ring release system. Upon release of the 3-ring release system, the rocket airframe will enter free fall and the drogue parachute will pull away the main cup to deploy the main parachute. For the rest of the flight, the rocket airframe will descend on the main parachute, and the nose cone, drogue, and parachute cups descend separately.
The ERS attaches to the rocket airframe using the same arc clamp system used to attach the nose cone to the ERS. Two signal wires from the rocket avionics module enter the ERS through the bottom and are used to signal release of the parachutes. On the exterior of the ERS are keys used to turn the system on and to arm the system, for integration into the launch procedure.
The control system is a PCBA with an STM32F0 microcontroller. The PCBA drives a motor and linear actuator which will release the main chute and the nose cone when told to do so by the main avionics. The full requirements are summarized here:
- Receive two incoming signals from main avionics
- Release nose cone
- Release parachute
- All logic controlled by an STM32F0
- Use BPR-301 phototransistor sensors to verify nose cone separation
- RJupyter un off LiPo batteries
The firmware being run by the STM32F0 is written in C/C++. It was written in an IDE provided by STMicroelectronics called STM32CubeIDE, and the firmware folder contains this project. Within this project directory, the /Core subdirectory contains all the control code.
The board was designed in EAGLE to support the requirements of the system. this is in the /eagle subdirectory of the control system.
The ERS system will be tested by dropping it from a helicopter over a field. Many parameters must be considered for this test including wind speed, altitude, field size, parachute drag coefficients, and parachute release timing. Analysis of drop test dispersal patterns based on fixing some parameters and simulating variation in others enables us to choose an appropriate drop site and drop parameters. Analysis notebooks can by found in the /analysis directory.
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