Discuss the design, include pictures from CAD, explain design decisions, things that did/didn't work, things we learned/how we would want to change things for the future. Discussion of friction problems, calculations we made, pictures of real life mechanism.
Air Brakes was a brand new subteam for rocket team. Our goal was to create something that could control the deceleration of the rocket, preventing it from surpassing the designated apogee goal of 30k as needed by Spaceport. We explored multiple concepts of varying difficulty before settling on a sliding plate design. The purpose of this selection over a hinge design was to reduce mass and due to the fact that it be more simple to integrate into the rocket. While the main concern of this sliding mechanism is that less surface area would be achieved compared to a hinge design, the integration of the system was the most crucial in developing the machinery.
To design the airbrakes, we needed to start with calculations (can be found in Engineering Notebook) ranging from projected additional drag to what torque the servo would need to successfully deploy the plates. Possible designs were drawn and once the general figure was agreed upon, 3D modeling began.
With a Solidworks model now existing, proper material simulations could be made to find a good material to use. We settled on Aluminum 6061-T6 for its resistance to deforming, ease of machining and its high strength-to-weight ratio compared to other materials.
Leaves
- Since we decided on a sliding design, we had to modify the leaves of the air brakes in order to maximize the surface area without compromising the structural integrity of the rocket or taking up too much space. After going through multiple iterations of lengths and widths of the leaves, we decided on a 3.5” width x 2.25” extended length to maximize the area. Each leaf of the design has an extended area of 7.88 in^2 for a total surface area of 31.52 in^2 for each air brake system. Our initial design of the leaves had a surface area of 5.49 in^2 for each leaf, so by increasing the area, we’re able to achieve a higher drag capability.
Trays
- To prevent any galling between aluminum surfaces and to reduce the friction on the leaves, we decided to 3D print trays in which the leaves would slide on. These trays would be SLA printed to provide more durability than our PLA printed parts since they would be under more force than the other plastic spacers in the system. Each pair of leaves would sit in one tray that extends the diameter of the air brakes, allowing for a larger contact area and smoother operation. The SLA-printed trays are designed to “guide” the leaves when they’re extending, preventing any lateral misalignment or unintended tilting of the leaves. The guidance ensures the leaves follow their intended path during deployment, minimizing wear and tear on the aluminum and allowing for multiple usage cycles.
- In our initial design, we overlooked the potential of galling in the system, so the trays serve as a crucial improvement to address this oversight. This increased the longevity of the system by preventing abrasive wear between the aluminum components should they slide against each other without any plastic spacer between them. Aluminum on aluminum sliding has a kinetic friction coefficient of ~1.4 so by inserting a tray printed with standard resin, we were able to reduce this to ~0.3-0.5.
Connectors
add photo here (of hex and leaf)
- These were the main cause for concern in the system, since a problem we were facing in the design and calculation process was whether or not the system would actually deploy based on what design choices we had. Based off of our torque calculations and simply observing the way the connectors interacted with the leaves and shaft, we were concerned that not enough force would be applied in the direction the leaves should be deployed in. Due to this, the connectors went through many changes:
- lengths of the hex connector and leaf connector
- width of both connectors
- whether or not the holes were countersunk
- placement of the connection between the leaf connector and leaf itself
- Later on, we saw that there was too much friction between the connectors themselves (hex connector and leaf connector) and the connection between the leaf connectors and the leaf. Due to this, we had to include washers between these interaction points which made the extension of the plates smoother.
The initial system consists of two separate systems, one for the booster and one for the sustainer. Each system would deploy four plates, which extend out at a desired altitude, creating additional drag and slowing the flight vehicle down to apogee. On the booster, the air brake system would cause drag separation. On the sustainer, the system’s primary purpose is to reach the target altitude without overshooting. This, however, was later changed to only having one system on the sustainer, as it was decided that a second one would be unnecessary and would need much more machining than previously anticipated, since our design changed over time.
PDR
This is when we reached PDR and presented our design to rocket team. After good discussions, the design was changed to better accommodate a bigger servo and surrounding components inside the rocket. Based on this change, we saw that the torque required to deploy the system increased significantly, so we had to use a much larger, industrial grade servo instead of the smaller one we had initially used.
CDR
This is the final design of the air brakes system. From PDR, we realized that we had to have additional frames where the trays would sit in and where the system itself would be screwed into the mission package tube. We also added additional spacers between the frames and the servo bulkhead, which acted as "guiding rails" for the leaves and allowed additional room for the connectors to extend.