UKRoC Rocketry

Status: Past Project (2019)

Rocket Systems

This is the rocket that me and five other friends designed a built for the 2019 UKRoC (UK Youth Rocketry Challenge). I lead the team as the engineering lead and decided to implement several innovative solutions including active fin stabilization, a radial parachute deployment mechanism and custom lugless launch rail clamps.

Sensors and fins of the avionics bundle. Power LED on. Small lipo battery on the back. Mini boost converter to convert lipo voltage to 5V for electronics.

Fin Stabilization

At the heart of the avionics was an Arduino Nano attached to the modules below:

This was all powered by a small 5V boost converter which fed from a small 200mAH lipo. A mandatory power led and power switch was included on the back.

Not shown is the fifth servo which was housed down below that controlled the parachute deployment.

Avionics performing roll control.

Firmware

The firmware had the role of datalogging and ensuring that the rocket was pointed straight up. This was achieved by reading the sensors, calculating appropriate angles for the fins and then saving the data to an SD card. It also monitors for apogee and then deploys the parachute.

No fancy control algorithms were used other than just ensuring the fins were pointed parallel with gravity plus any roll correction. The entire code can be seen in my github [1] however it is certainly not the bes coding and did not work perfectly (discussed in the aftermath section).

Strengthening cage for parachute compartment. Also notice the rectangular cut-out on the top for the parachute servo.

Radial parachute stowed in place. Also see the cover with strengthening ribs that I made after I almost broke the cover.

Radial Parachute Deployment

Due to the presence of avionics, the common problem for model rockets is where to place the parachutes in order for the hot ejection gasses to push out the parachute and not damage the electronics. The typical solution was to place the avionics inside the nosecone and have the rocket split in two however this years rules required the bottom half and the top half of the rocket to separate completely and have their own parachutes.

I had seen an innovative solution on YouTube [2] (embedded below) which had the parachute deploy from the side of the rocket (radial deployment).

The principle was to use an elastic band that went around the rocket, holding the cover in place which would then hook onto the aforementioned parachute servo. When the servo releases the elastic band, it whips around the rocket and tears the cover off. With the cover falling away from the rocket, it catches the wind and also pulls the parachute out along with it causing it to deploy.

Two parachutes sewn by George who was in charge of the recovery systems!

Aforementioned YouTube video.

Lugless Launch System

Launch lugs are protrusions which allow a rocket to be attached to a launch rail. This guides the rocket initially to allow the rocket to accelerate to speed at which point its fins will be the only stabilization. The main reason I decided to use a lugless launch system was due to the large diameter of the avionics bay. This would not allow small lugs to be used since they would have to extend much further out to accommodate the bay. This makes them very aerodynamically inefficient as well as being a structural weak point.

My solution inspired by an item on the Apogee Rockets store [3]. Their solution to the problem was to have a set of elastically loaded clamps that would separate from the rocket after the launch rail. The lugs would be locked in place, held together by a groove in the launch rail. Once past the launch rail, the elastic bands would lever the clamp open, falling off and letting the rocket shoot past.

Benefits:

Disadvantages:

I believed the benefits very much outweighed the disadvantages. The custom clamp and launch rail were not too much of a challenge as I found it fun to design and assemble. To combat the falling debris problem, the clamps were made of 3mm laser cut plywood as to make them as light as possible and to reduce the environmental impact as much as possible if we were not able to recover them.

Rocket body structure.

Rocket with launch clamps on body.

Aluminium extrusion custom launch rail.

Close up of launch clamps made of 3mm lasercut plywood.

Elastic bands eject clamps once free of rail.

Misc Sections

Propulsion bottom with securing screw slid into bottom of rocket body. 

Baffles with alternating hole pattern.

Propulsion

We designed the rocket to use three class D Klima rocket motors, together with a combined impulse of 60Ns. These slotted into laser cut bulkheads and were secured via a screw on the bottom.

This screw also ensured that the motors were firmly located up against the main bulkhead.

Instead of using wadding to prevent the hot ejection particles from burning the parachute, I decided to use a system of baffles to only allow the ejection gas to find its way to the parachute.

Foam housing for egg.

Egg inside nosecone.

Payload

The competition required us to carry an egg passenger and for it to land safely. We achieved this by creating a custom foam housing for it in the nosecone.

To prevent the foam from falling out. I also laser cut a lock that screws into the nosecone. Unfortunately not pictured.

Huge. (Believe it or not, but red button is actually a 3D print that I sanded and polished).

Inside is an electronics rat nest.

3D printed button.

Ground Station Launch Button

On a whim I decided to also create a huge launch button. The original plan was for it to act as a charger for the rocket as well as the launch button that would set off the igniters.

Unfortunately due to time constraints, I was not able to finish it.

It currently acts as a one button keyboard and is a nice desk ornament.

First layer of primer to make paint adhere better.

Waiting to dry.

Painting

To make our rocket look semi-professional, I used my airbrush to paint all the parts.

Before even painting, I sanded down all the parts. A layer of epoxy resin was then added, sanded and buffed again. A layer of primer was then sprayed on following with layers of colour.

Aftermath/Reflection

Rocket broke halfway up the avionics bay.

On the launch day, a multitude of factors lead to us losing the bottom half of our rocket as well as overshooting our target altitude by 119 meters. (Target apogee was 261m, we achieved 380m).

The major factor in losing the bottom half was me misreading the rules. This lead us to having to change our recovery system on the day of the launch. This resulted in the bottom half of the rocket drifting too far away to recover. The other factor was our supervisor suggesting we use four motors instead of the planned three after witnessing multiple competitors' rockets using four and not making it high enough.

Another mishap was no data was logged into the SD card. I believe this was due to incorrect file naming system however it was probably something else since I also rushed the code and had not fully tested it.

Also, using black fabric to manufacture the parachutes was probably not a good idea as well as painting the entire rocket green when it landed in a lush green field and was a pain to recover. 

On the bright side, the flight stabilization code worked perfectly, the radial parachutes deployed at apogee and the clamps released just as planned. Our egg passenger also survived!

Overall I thoroughly enjoyed leading my first team in a technical competition!

Misc Media

Openrocket model of the rocket. (.ork file in my github [1]).

Disassembled rocket parts.