Xrain
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Correct me if I'm wrong but it depends on the board's orientation. If it's measuring acceleration only in the Y direction, the acceleration before arcing over in relation to the board will be negative. However, once it arcs over the rocket will continue to have the same negative acceleration but because the board's orientation is reversed, the board will read it as positive. During that arc as the board's perceived acceleration changes from negative to positive. At some point it should hit 0 acceleration in the Y direction. Deployment can be triggered at that point. Of course this won't work if there is backsliding because the board's orientation will always be the same.
Alex
As soon as the motor burns out, and it is sufficiently far out of the thick part of the atmosphere the rocket will be in freefall. Meaning any gyroscope Accelerometer (oops) will be measuring 0 g's of acceleration for the entire period. Yes gravity is still acting upon the rocket of course, but as far as the internal reference frame of the rocket it will see no acceleration. It is very similar as to why you experience zero gravity on the vomit comet. So he is right you will not be able to get orientation from acceleration. You would need a gyroscope, horizon sensor, or perhaps magnetometer for that.
There is another issue as well, the rocket might not actually turn around until well into its return. So its very possible it could be going several mach before it actually turns around. It isn't the most probable case, but it can definitely happen. At 200k ft the rocket is in almost high vacuum. There are not going to be much aerodynamic forces until the rocket gets back to ~100k feet. I'd say the most likely case with out roll stabilization is the rocket will start to tumble on ascent at about 150k ft. If you don't want spin stabilization because it will make everyone sick watching your video, put 3-4 gopros on board, one in each direction. Then you can stitch portions of the frames together afterwards to eliminate the roll from the video.
Titanium can be had pretty cheaply from titaniumjoe.com I used a fair bit off it from there. Also surface grinding large thin titanium plates would be difficult since it won't hold to a magnetic chuck. I spend a lot of my time at work simplifying parts for low volume manufacturability and I agree that you'll want to simplify your parts to remove multiple machining setups, speed roughing, and avoid complex cnc programming. In small quantity runs these things will make an order of magnitude or more impact on costs.
I was taking a total shot in the dark on the surface grinding. I haven't actually personally done any surface grinding; but I know it has been used for similar kinds of cuts, holding it down will definitely be a challenge. I cant honestly think of that easy of method to make those large bevels on the fins without making a fairly complicated work holder.
I've looked at titaniumjoe's website quite a bit, but I haven't really had a need for much titanium yet. That will probably be changing in the not too distant future so I'll definitely check them out when I do finally bite the bullet.
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