"ExPAC - EXperimental Platform for Advanced Concepts" design/build thread

I have come up with a long list of pie in the sky project ideas that merge some of my interests in robotics with my new passion for rocketry, to allow my to test them I need a decent diameter rocket that I can reliably send to 1500-2000 ft on inexpensive motors. My father offered to let me rework his 4" quantum tube scratch build he used for his level two cert. The rocket is 4" diameter and currently stands about 7ft tall, it weighs 7lbs and has a 54mm motor mount though I will likely adapt it to 38mm for early test flights.

I plan to take this development slowly with lots of intermediate testing, but I want to rebuild the rocket with all of the space allocated for the eventual final configuration. I will be keeping the motor section and lower section mostly stock, the upper section will require rework due to a bulkhead approximately half way down the tube. The plan right now is to use the existing rear compartment for a traditional backup chute and rework the upper tube for my av-bay and main chute(s).

Here is the rocket in it's current state:



On my list of ideas for this rocket:
1) Arduino based Altimeter / GPS with live telemetry
2) Wireless deployment to allow seperation of the altimeters and charges
3) Remote deployment of backup chutes
4) Active stabilization / attitude control
5) Controlled reefing of a main parachute for use as a drogue replacement
6) Steerable GPS guided parachute recovery with remote control override

As I have mentioned the project will be completed in steps with each phase building on the last. I will begin by completely the physical build. I will then test launch the rocket with traditional electronics and chutes in a standard-ish dual deploy configuration. The altimeters will be stored in the area that will eventually house the wireless deployment board. All launches will also carry the flight computer that will eventually run the project to allow me to start understanding the data collection capabilities and test my programming as I go and to use it's GPS telemetry for tracking. Next, I will develop and test the remote deployment electronics and move the commercial altimeters to the primary av-bay. I should also be able to test triggering the backup chute via ground remote at this stage. Hopefully by this point I will have had enough test flights on my altimeter software to switch to using my altimeter to run the actual deployment. I could then move on to the stabilization and controlled recovery parts of the project.

I have decided to base this project around the proven APM 2.6 uav/drone controller package with my own branch of the standard firmware and potentially my own PC software or ground control unit.  I have ordered a APM mini and high performance GPS/compass unit and a 915 MHz telemetry unit based on the same module as the eggfinders use. This package will give me an accelerometer (up to 16Gs), gyro, GPS, compass, and precision barometer. The unit also 8 inputs and 8 outputs for pwm R/C servo channels and auxilary analog and digital inputs and outputs, and current and voltage sensing. This package should be able to handle all of my project plans without much additional hardware work. I will have to design something for the wireless deployment.

I will post more about the specifics of the design plans a little later.

I didn’t realize it had been so long since I started this thread, it’s time for an update. I have been very busy designing the various systems at the heart of this project. The hardware has evolved into a planned commercial/opensource flight computer which has its own thread here: . I am building the test rocket to eventually handle all of the planned functionality of that build.

For the first flight, planned for the April 18^th Michiana launch, I have two goals. I am hoping to test the flight computer electronics with near stock firmware. I will be able to pull a complete data log of the flight and evaluate the accuracy of the system against a proven rocket altimeter. I will also use the telemetry link and GPS for tracking, though it shouldn't be needed with the low altitude, and I can verify the link quality. I also plan to do a basic mechanical test of my somewhat unorthodox deployment and my controlled parachute reefing setup. This test will not be automated, but controlled via remote from the ground.

To this end I have acquired all of the necessary parts and begun assembly. I have received the flight computer board, GPS unit, telemetry unit, and power board. As well as a metal gear winch servo and battery. They have been fitted into my unconventional av-bay. The flight will also fly a Raven for actual deployment which will deploy the reefed chute at apogee and a backup chute at a lower altitude if the decent rate is above 25 fps. Upon deployment the entire bay will be pushed out of the rocket by a piston and the bay will hang horizontally between the parachute and rocket, hopefully this will prevent twisting of the parachute lines.



I have also acquired a completely custom 72” Spherachute. This chute has two 4 line risers, one will attach to each end of the Av-Bay. It also has reefing rings sewn around the canopy which are threaded with a reefing line. I want to thank Julie from Spherachutes for the excellent customer service. She was very easy to work with and once the order was placed on a Sunday morning she completed and shipped the chute by Monday afternoon.



As mentioned, the av-bay will be pushed out be a piston which will also house the main chute. Because the av-bay can’t be sealed from the charges (opposite the piston) due to the reefing lines exiting the ends, the piston has to be sealed to the tube. I have built a piston with a nicely sliding x-ring seal to accomplish this, hopefully it works. I’m still debating if I can use grease to help seal the o-ring, but I am worried the grease will degrade the phenolic piston.



The next step will be to finish the various body and internal components that are left and to assemble the rocket, hopefully by this weekend. Once the av-bay is competed I also plan to do a ground test of the reefing system and measure the pull of the chute and reefing line. I will post video of this test once it is done.