Destiny
Destiny is a 3D printed model rocket that has active stabilization.
Goal
The goal of this rocket is to achieve active stabilization of a model rocket by adjusting the angles of fins located at the aft of the rocket. This will be done to keep the rocket as vertically straight as possible even if at launch the launch rod is not perfectly pointed up.
Main Design
Like both of my previous rockets, OpenRocket and Inventor were used to design the rocket. The main difference with the design this time is that each software was used in conjunction to make the final design instead of using OpenRocket first and then finalizing every in Inventor.
This is the case because the design must take in consideration the placement of the servo motors that are used as actuators for the fins. The servo placement dictated a part of the length and it was the main factor determining the diameter of the rocket.
This rocket has no recovery system. This design decision was taken because it simplifies the rocket design and increases performance. While this causes the risk of loss of vehicle and increases the risk factor during the descent, ideal handling of the rocket was seen as a greater priority than proper recovery. Furthermore, after seeing the result of the unsuccessful deployment of the recovery system of some of the past rockets, it was determined that even without a recovery system, the vehicle could still be recovered mostly intact.
Since this rocket was going to test out our design of active stabilization, the focus was proper maneuverability. To maximize control, it was decided that the control surfaces will be located at the aft of the vehicle. The fins could also be installed at the top of the rocket, but in doing so, it would also require fixed fins at the aft of the vehicle. This could cause interference that could harm the stabilization system’s performance. An alternative design that was modeled and almost chosen to be produced of this rocket has the fins at the top of the rocket and this greatly simplifies the design. It also allowed for a recovery system. Ultimately, the control issues that could arise from that design was the factor that ruled out that design.
A system of push rods is used to transmit the rotation motion of the servos to the fins. These rods are installed outside of the airframe of the rocket in the airstream. It was done so to keep the rocket’s diameter to a minimum. No wind tunnel or computational fluid dynamics simulations were done on the rocket as a whole to determine how bad the impact of this would be. This is due to budget and time constraints.
The rockets static margin is roughly 1.4 (this does not include the push rod mechanism). I found that flying model rockets of similar size with a static margin of close to 2 provided the flight path that is closest to vertical. Since the greater the static margin, the less the maneuverability, a static margin that was lower than what was usually used, but still high was chosen as a fail-safe in case the fins did not work properly. The servo’s and electronics’ placement put the center of gravity much higher than simple traditional model rockets that only have an airframe and a motor. Since a large enough control surface was desired, this also played a role into why the static margin is a little elevated.
Since there is no recovery system and this rocket was designed for an Estes C11-0 (an unplugged booster stage rocket motor), there had to be a piece separating the top of the rocket motor and the inside of the main airframe in order to not let any gases into the main airframe and as well as redirecting the gases backwards for potentially a little extra thrust that otherwise would have had to be vented to the side. By redirecting it backwards, it also avoids the hot gases having to be vented to the sides where they could damage the potentially damage the fins or the push rods because they are so thin.
Electronics and software
The flight controller is the exact same one as with Sightseer, with additional wires coming from the servos connected to it.
The software has changed a little. In Sightseer II’s flight, the gyroscope did not use any fusion algorithm which resulted in extremely inaccurate values during launch. To remedy this issue, Kris Winer’s MPU9250’s code was used which incorporates a Madgwick filter. This seems to eliminate most of the gyroscope drift while on the ground, but this algorithm has not flown yet.
In order to control the servos that will keep the rocket upright, a PID algorithm is used. As of writing, the PID algorithm only has a P gain and potentially a D gain. Since this has not been tested yet, we are omitting the I gain for the first launch and will accept that the rocket might not fully recover to a perfectly vertical attitude.
Yorumlar