Construction of the first rocket is almost complete. This post will detail the building process of our rocket. We will be launching this rocket February 17th, 2018 in Princeton, Illinois.
- Component Construction for Avionics Bay
- In order to make a removable sled for our altimeter and battery, we had the machine shop make us two wooden end caps that have a lip matching the inner diameter.
- We then drilled two ¼” holes for a U-bolt that will be the tethering point for the kevlar shock cord.
- We purchased two #8 all-thread from Lowe’s and the appropriate nuts.
- We drilled two holes slightly larger than #8 in the top bulkhead to fit the T-nuts. Originally, the T-nuts had three spikes that were meant to be driven into the wood. Since we already had 4 holes and the wood was beginning to chip, we used a belt grinder to flatten the T-nuts so that they sit flat on the bulkhead. This provided a large surface area for the epoxy to hold.
- Next we added the threaded rods and secured them with the epoxy’ed T-nuts.
- Ejection Charge Wiring
- We used two 3 terminal blocks and used a belt grinder to remove one of the terminals. This left us with the two 2 terminal blocks for the ejection charges
- We then attached a terminal block to each bulkhead. We drilled two small holes for the leads of the terminal block and then ran 18 gauge wire through each hole. Once the wires were through the bottom of the bulkhead and out the top, we soldered the wires to the leads on the terminal block. It took some time to get the solder to fit in the 18 gauge hole we drilled. Slightly larger holes would have been easier to work with.
- Once we had the terminal blocks soldered, we used two-part JB Weld to seal them to the bulkhead. The black powder charges will leave behind a corrosive residue, so we were careful to seal the holes completely.
- We used a length of wire roughly equal to one and a half avionics bay tubes. This is because we will need to attach the wires to the altimeter on launch day and it would be nearly impossible to do so with a short wire on the inside of the tube.
- Sled Construction
- To make the avionics bay sled, we cut a piece of ¼” plywood to match the inner diameter of the avionics bay. The snug fit reduces vibration.
- For rail guides we used 4 metal tubes on each corner of the sled
- Typically, these guides are coplanar with the sled (⦁–⦁). We made our sled with raised guides (⦁_⦁). This was done in order to better center the mass of our electronic components.
- Switch Band Installation
- Before we glued, we sanded the location of the switch band on the avionics bay as well as the inside of the switch band with 80 grit sandpaper.
- We used PC Super Epoxy with a 15 min work time from Murdale Hardware to fix the switch band to the avionics bay
- Nose Cone Setup
- First we marked the halfway point of our nose cone coupler. Using 80 grit sandpaper, we roughened the upper half then used PC Super Epoxy (15 min work time) to attach the upper half of nose cone coupler to the nose cone.
- We then drilled two ¼” holes in the metal bulkhead that came with our kit and attached a U-bolt. Next, we epoxy’ed the metal bulkhead to the open end of the nose cone coupler.
- We had a close call while epoxy was drying. We had glued both the bulkhead and the coupler at the same time and had stood the nose cone up to dry. The weight of the metal bulkhead and U-bolt pushed the coupler almost entirely into the nose cone. Luckily, we checked on it as we were about to leave and were able to pull the coupler out. We made sure to let the system finish hardening on a flat surface. The excess epoxy was difficult to remove, but 30 minutes with a razor blade cleaned it up nicely. NOTE: Don’t glue multiple system components at the same time.
- Dry-Fitting and Drilling
- Our rocket recovery system is controlled by a dual deployment altimeter. The first event will occur as soon as the altimeter detects a lack of increasing altitude. This is the highest point of our rocket’s flight and is referred to as the apogee. The first picture shows what the rocket will look like after the apogee event. The back half of the rocket is referred to as the booster, it consists of the body tube, motor mount, and fins. The shock cord that connects the booster section to the exposed U-bolt on our avionics bay will be glued to the exterior of the motor mount. We are still waiting on our motor retainer to be delivered before we fabricate the motor mount and fin sections.
- There is no connection between the booster and the payload sections of our rocket except the friction of the coupler. This does not matter as the dominant forces it will experience are directed upward.
- In order to prevent unwanted separation elsewhere, we drilled two 5/32″ holes 180 degrees from each other, one inch above the bottom of the payload section. We drilled through both the avionics bay and the payload section. Strong plastic rivets will go into these holes to prevent the avionics bay from falling out of the payload section.
- I mentioned earlier that the forces on the booster do not require an attachment other than friction. However, this is not true for our nose cone. The nose cone has a solid aluminum tip, metal bulkhead, and U-bolt, which will give it more momentum than the aft sections of the rocket. When the motor burns out, the nose cone’s momentum may potentially pull it from the rocket. To prevent this, we drilled two holes 180 degrees from each other through the nose cone coupler, one inch below the top of the payload section. We then used a tap to thread the hole. Our nose cone will be held on by a weak nylon screw, called a shear pin, which will be sheared off by the pressure generated by the ejection charge.
- Second Event
- The second event will be triggered when the altimeter reads 700 feet. This event will activate a black powder ejection charge on top of the payload bay and push off the nose cone. It will take some testing to figure out how much force we need to shear the pins holding the nosecone on.
- This where we will put our parachute. The first event will separate the rocket into two tethered halves, preventing a ballistic, vertically downward descent. The second event will release the parachute and carry our rocket safely to the ground.
