Still having fun with the 3D print projects...so Tom sustained a fin strike to his flyaway rail guide from a commercial vendor. He gave it to me and asked to "fix" it. I saw some inherent design details that I would not have utilized, and decided to redesign a new fly-away that should incorporate some engineering into the package.
If you have used one, you know that you can struggle with keeping them from snapping apart during installation and mounting on a rail. Also, the "hinges" can be notoriously weak (nature of plastic). Lastly, the spring loaded arms tend to be problematic too. So without adding too much plastic what are the solutions? Physics! impulse & momentum, I increased the sudden slam open distance thus the delta change in momentum is increased over distance (and time) (*think a crush zone on a car). I also added a "safety" that holds the fly-away together and automatically disengages upon insertion on the rail (so you don't accidentally take your "fly-away" with you on your flight!). Additionally the hinging mech utilizes the strong carbon fibre rod as it's pivot, instead of printing a separate and weak pin (or out of round pin). Lastly, the spring or elastic loading is accomplished with a smaller (and completely symmetric and interchangeable) separate part that is quicker to reprint incase of accidental breakage.
The one I did is for 80mm (3.16" airframes) because that was the need, however, I will be making these for smaller rockets too.
I would be more than happy to share print files and discuss design considerations. This one is a prototype, I can see areas where even more changes (improvements) are capable.
Edit: You can even see from the photos, that I changed design during the initial printing. Realizing that I didn't need the nuts to hold the bolts in, I just threaded the holes and the plastic is sufficiently strong enough to hold. I also will be reducing the bolts from 2 per rod end to just 1. That will eliminate plastic and weight and bolts. I have some other ideas I am toying with too, but those will be left out for now.
This looks great! I broke my fly-away guide launching on Lake Winnipesaukee in March. I assume the cold weather made the printed parts more brittle. I'd be interested in a smaller version for my 38 mm minimum diameter rocket.
tlainhart wrote: ....Looking at the structure - my first impression is that it might be too much build to be adapted to smaller airframes, like BT-50/55/60/80. Is that true?
I do plan to make smaller...I just haven't gotten there yet. The smaller ones will most likely be just 3 rods of a smaller diameter to reduce inertia. This one would scale larger, but probably only slightly smaller. This particular one was to fulfill a particular rocket that is a 75mm min-diameter, so the added couple of grams was less of a concern.
Certainly would be open to suggestions for lighter airframes. These are really intended for HPR. With low or mid power, certainly the amount of plastic could easily be reduced.