Q1 2017 Rocket active stabilization system update; Finally have working PID for positional control of a DC motor! New gear, livestreams and the first program sponsor!

After nearly 4 and a half months of late nights, caffeine fueled jam sessions, one livestream(more on that later!) and more frustration than anticipated I FINALLY figured out implementation of PID for positional control of a DC motor with an encoder. More details after the break including a breakdown of problems I ran into, some shiny response graphs and most importantly; SOURCE CODE!?!?!

Motor control testbed using TB6612FNG motor driver

Q3 2016 Rocket active stabilization system update, complete hardware redesign of fin drive system with bonus sketches and a needed disclaimer

The old and new designs, massive improvements to the overall design

Update time has rolled around again now that a good chunk of progress is completed on the Arduino based rocket stabilization system. This has taken a while since I've been busy with not only work but also getting the A+ certification in computer repair and completely reworking my current workstation. After much discussion with several other rocket tinkerers, the conclusion was reached that stresses on the servo spline itself would be quite considerable and may result in damage or inoperability. Based on force distribution I surmised that flanged bearings embedded in the system shroud tube would function as not only supports but also as smooth rotation points. With the challenge of a new fin drive train in mind, I set to brainstorming. My first thought was to use linkages connecting the servo to the actuation shaft, though it would increase the diameter of the system unless the servos were staggered which would also increase the overall height of the system. Stepper motors were considered, however as I was unable to find suitably sized units and the common 28byj-48 had too low precision and torque this too was eliminated from consideration. After those two ideas were discarded, it was relegated to the back burner while I had work. The breakthrough was about a week later, while browsing patents looking at missile fin drives I noticed an old Raytheon control segment used bevel gears to transfer the motion and that became the seed for the new design. 

Q1 2016 Rocket active stabilization system update, now with fins, nose cone and a mockup

With 2016 well underway it's time for the first update on the state of the stabilization system!

First off, apologies for the massive delays this post has had, was originally slated for mid-Jan launch but between job hunting and other stuff I've been hitting delays and trouble at every turn. Since last semester ended on Dec 18th, I'd been going to TechShop pretty much every day until Jan 18th making massive leaps and bounds of progress along the way. The most obvious of progress is the completion of the demonstration mockup airframe which will be gone into more in-depth after the break. 

The system's current state on the demonstration mockup

Hackaday DC event recap

Giving a talk to the packed room

As some of you might have seen, I recently attended the Hackaday DC event and gave a talk on the rocket stabilization system while there in addition to explanations and demonstrations to quite a few people that came by my table. Surprisingly, the Amazon AWS crew that was there took quite an interest in my project and gave advice on code upgrades for the stabilization system, namely dynamic control movement ranges dependent on velocity.

Spring break TechShop progress

Near-final fin with correct blending

Over this recent spring break, I'd decided to forgo the archetypal partying of the Senior year and continue work on my projects. My primary objective was to redesign the fin so it could be used with the round metal servo horns for easier integration and sturdier mounting. The main issue I was having was the splines not printing due to the low resolution of the printer which meant the servos are unable to properly engage with the fin.

February rocket active stabilization system update

Stabilization system miniaturization

Due to school preventing me from spending days at TechShop to use their printers and CAD workstations (my school lacks a technical education program sadly and my computer is on OSX so I can't use Inventor on it until I figure out how to install windows on an external hard drive) I have not made much progress on the system as of late.

Christmas break TechShop Day 1 update

Test fit

First day back at TechShop after 3 months away due to the start of school soaking up the vast majority of my time and preventing me from going into DC every day. After arriving I immediately set to work on the new integration cans as the early prototypes are about ready to be phased out. Halfway through modeling the alpha I realize that I would not be able to slot in the middle segment due to it having the fittings on both the top and bottom, preventing the middle section from being able to slide into place.

Early November active stabilization system [Codename ARGuS] update!

Finally got back on the stabilization system development track! I finished the major school project and the replacement MPU-6050s arrived. The code recently got a MAJOR upgrade thanks to Bogdan Markovik who sent me the modified MPU6050 test code that has PWM drivers in addition to full roll, pitch and yaw control as well as fully configurable degrees of freedom for each axis. Bogdan has been assisting me with everything from code to new sensor possibilities and I hope to continue working with him as the project continues. I will be eventually moving away from the MPU-6050 as it can be kind of iffy with angles sometimes and calibration is rather annoying as I'd rather not risk the very costly high power rocket airframe to loss of structural integrity due to the sensor getting confused and shaking the rocket to bits. Thanksgiving break is coming up soon and that means my probable return to TechShop and further rapid development of the system! In addition to Bogdan helping out with the system, Sagar, the original coder of the very basic code that drove the first prototypes, is a frequenter of the same TechShop and will be working on refining his own system. Video of the new code in action is right after the break.

Fin development

Evolution of fin design

Fin development is one of the hardest parts of designing and building a stabilization system in my experience. It has to be aerodynamically sound, servo compatible and not break when initial liftoff forces kick in.

Preliminary fin printing, lessons learned.

Yesterday I moved the fin into preliminary 3D printing. Initial print was flat on the print bed, apparently the support structure caused it to warp and the layers stacked strangely. Vertical printing worked a heck of a lot better! Also reprinted the baseplates to the correct size and spacing of servos.

Adding on to code for opposite fin pair drive, fixing a MAJOR problem

Today I decided to fix the issue of opposite servo pairs actuating in opposite directions which would result in a uncontrolled spin and subsequent destruction of airframe. It only took a few modifications totaling in 10 additional lines of code. This site was extremely helpful in explaining the servo drive code for opposite servo pairs.

Null1.write(valNull);

Obfuscated = valNull;

Null2.write(180-valNull);

Obfuscated = valNull;

What this does is take the opposite servo and drive it 180 degrees in the opposite direction of the reference servo(1)[Yes I censored the code because this is ITAR regulated, Deal with it. If you really do want to take a look at my code, you will have to prove you are based in the US and sign a waiver that transfers all responsibility for what you may do with my code to you].

Working on the fins

Started work on the servo-actuated fins today, Simple extrudes and lofts based around a standard servo arm, will print these before the end deadline

Finally got rid of the cardboard structure! (size of prints is still wrong :[)

At long last, the horrible cardboard vanishes(except the fins). With the print that was completed today the tolerances came closer than ever before to being perfect but they still are wrong (D:). I had to take an exacto knife and shave the notches slightly wider but for some reason one of the plates was not circular but rather an oval which was nearly imperceptible except when they are stacked on one another(:/).

3D printing plates

Started printing plates to replace the crappy cardboard demo model. First time(black plastic) I had the slots for the servos too small; fixed it and am now printing it again(red plastic)
The initial print had issues with the quality of filament bead as is seen in the partially completed picture

printed revised prototype