Keeping It Together

A while back I decided to upgrade the motor retention on my upscaled Star Trek Starter Set rocket. My original setup was a couple of machine bolts that held a braided steel wire across the motor at two points. The idea was that it would be able to handle all three size motors included with the Kwik Switch system (29mm, 38mm, 54mm).

I had used this system years ago on my Maxi Scamp and it had worked well. Of coarse that was just a 29mm motor. I came up with it then because I had the parts to make it just laying about the house. I always go for the "free" answer if I can.

However, scaling it up didn't work as well as I had hoped. The wires were hard to wrap around the motor and they ended up having too much play in them. In fact, on the second flight (when the STSR streamed in) the motor was ejected out the back on impact, right through the wires. I noticed this when I had hiked all the way back to the range head. Bummer. Chas Russell and John Dyer helped me find the casing, however, so all was not lost (literally).

When I rebuilt the rocket I used the same system because I used the same parts. However, after thinking about it, I decided that a better solution was needed. PML has a HAMR system that is designed for the Kwick Switch mount. I went ahead and bit the bullet and ordered it.

The retainer is basically a 54mm screw on retainer with two washers to adapt it to 29mm and 38mm. My main issue was retrofitting it onto the model. Here is how that's done...

This is the original setup. I was going to have to do some work on it for the new retainer to work. Time to grab the trusty Dremmel!

The first thing I needed to do was to remove the paint and epoxy fillet from the motor mount. The machine bolts were in the way, so out they came! I may put them back later. PML says that the retainer should fit loosly so the epoxy can grab better, which makes sense.

Next, I had to counter-sink the plywood ring around the mount. I had just shy of the 3/8 inch lip the retainer required. A little shaping with my router bit fixed it!

Now it was time for the epoxy. PML says that you need to make sure that the epoxy you use is for high temperatures, since regular construction epoxy softens when it gets hot. Not optimal for anything holding in a hot metal motor casing! I used a JB Weld epoxy specifically designed for use on automotive engines, etc. It had about twice the heat rating of their regular epoxy.

And there she is! This epoxy cures SLOWLY (4 to 6 hours) so I had plently of time to wipe away any stray glue before it set...and to write this blog!

So there you have it! Pretty darn easy, really! Hopefully the Star Trek Starter Rocket will be in the air very soon!

Until next time, fly 'em fast and high!