Ask HN: Is it practical to create a software-controlled model rocket?

Post by pvarangot » Sun, Feb 17, 2019, 5:36 AM UTC

ccleve wrote: post #22

It's likely to be difficult. I heard a good analogy once: imagine balancing a broom, handle pointed straight down, on one fingertip. It's not that hard. Now imagine balancing a toothpick. Impossible. Scale matters. Bigger things are more stable.

Post by dsl » Sun, Feb 17, 2019, 7:04 AM UTC

Animats wrote: post #61

mplewis wrote: post #5

Be really careful. Adding guidance to a hobby rocket may classify it as a missile, and you will need to start looking into ITAR.

This is a common rumor but appears not be be based in reality. Lots of hobby rockets have guidance now. It's fairly common to have enough guidance that the thing will go straight up.

  (1) Flight control and guidance systems (including guidance sets) specially designed for articles enumerated in paragraph 
  (a) of this category (MT for those articles enumerated in paragraphs (a)(1) and (a)(2) of this category);

  Note to paragraph (h)(1): A guidance set integrates the process of measuring and computing a vehicle's position and 
  velocity (i.e., navigation) with that of computing and sending commands to the vehicle's flight control systems
  to correct the trajectory.

Post by dogma1138 » Sun, Feb 17, 2019, 11:25 AM UTC

gibybo wrote: post #71

dogma1138 wrote: post #4

I’m pretty sure that your problem isn’t going to be the software but rather the engine and the rocket itself. Hobby rockets use simple solid fuel engines you’ll need to build an actual liquid rocket engine with controlled thrust that can be reignited the rocket it self also need to be large enough to be aerodynamically controlled and hobby rockets tend to be too light so they’ll simply tumble in the wind. While you d…

Couldn't you develop some sort of servo-controlled thrust deflector that allowed you to effectively reduce the net thrust without throttling the engine itself? It would be similar to thrust reversal on jet engines, but you would only do it partially since you're aiming for thrust reduction instead of reversal.

Post by twtw » Sun, Feb 17, 2019, 5:45 PM UTC

colechristensen wrote: post #75

twtw wrote: post #66

Earlier quoted context omitted.

It's also quite a challenging control problem, which at the end of the day turns into a software problem. You can see what spacex (probably) does to turn it into a tractable problem for real time control in http://www.larsblackmore.com/iee_tcst13.pdf (Blackmore leads entry, descent, and landing at spacex).

My point being that the design of the control system is the hard part and the software implementation while not trivial isn't the problem being solved. And the design of the control system for a small model rocket and whatever control authority can be created for it in hardware are super hard compared to however it is implemented.