LESSON ONE: Constructing the motor mount 

We are going to start our first lesson by constructing the motor mount assembly. With the strength of the phenolic tubing we are going to use for the motor mount, we are really going to be increasing the rigidity and strength of this kit.

Below is a photo showing the two centering rings I made, the 29mm phenolic motor mount tube, the fin canister halves we will modify to fit the motor mount tube, and the upper centering ring from the kit we will retain. The one with the "X" over it will not be used, but is a good point of reference for the diameter of the two centering rings needed for the project.

Part of our assembly process will require enlarging the hole in the styrene fin canister to allow the 29mm motor mount tube to fit. To get an idea of how much plastic you'll have to remove, look at the photograph below that has the two centering rings sitting in one half of the styrene fin canister. You can see looking down at the opposite end that there is a pretty good bit of plastic that will have to be removed.

To begin your modifications, you need to mark the proper locations on the styrene fin can halves to remove excess plastic to allow the 29mm tube to fit. Take your fin canister halves and fit them together by hand. We are no where near gluing anything so don't even think about touching glue yet. Use masking tape to hold the two shell halves together in necessary.

Hold one of your centering rings over the aft end of the styrene fin canister centering it over the opening. The two notches are where the original twist-lock engine retainer would have locked in. These notches are the perfect dimension for a 29mm motor mount tube, so center your ring over them and draw a line with a pencil marking a circle such as seen in the photo above. This amount will be removed to allow the 29mm motor mount tube to fit at the rear of the rocket.

At the front end, take your 29mm motor mount tube and place it over the lip that extends from the forward edge. The 29mm motor mount tube will snuggly fit over the lip. As indicated in the photo above by the red arrow, draw a line around the motor mount tube with a pencil to indicate the plastic material that will be removed from this end to allow the motor mount tube to fit.

When you get it marked, it should look like the photo above. This project is just made for the Dremel Moto-Tool. No rocketry hobbyist should be without one, but that doesn't mean you can do this without one. I used my Dremel to slowly remove the plastic as marked from both ends of the two fin canister shell halves.

TAKE YOUR TIME! Go slow. It's easier to sand again and again than it is to add material back, right?

When you are finished, your motor mount tube should fit as nicely as the one in the photo above. Patience really is a good friend when doing stuff like this as it make your work easier to complete when things fit like they are supposed to.

Now that your motor mount tube will fit in the fin canister, it's time to start laying out the placement of components on the motor mount tube. If you are using a motor retainer, start by placing it over one end of the 29mm motor mount tube and marking the proper location of where the retainer ends as shown in the photo above.

When you are done, place a centering ring over that end of the tube and move it down about 1/8" to 3/16" below the mark you just made. We are trying to determine the correct placement of aft centering ring in this process, so using one of the fin canister shell halves, lay the motor mount tube and centering ring into the shell half and line up the pencil mark with the back side of the styrene fin shell half by moving the centering ring around to get a perfect alignment. As indicated in the photo above, you want the centering ring as far forward as it can go and still fit snuggly while keeping the motor retainer line up mark flush with the back edge of the fin canister. Take your time here if you want things to fit as designed and make your look like the photo above.

When you get the aft centering ring in the proper position, repeat the same process at the forward end without disturbing the aft centering ring. When you are done, both centering rings should fit snuggly, with the motor retainer positioning mark properly aligned with the aft end of the fin canister. Test with both halves of the fin canister in place.

When you are certain it all lines up correctly, draw pencil marks on both sides of both centering rings to accurately mark their position on the motor mount tube. The yellow shaded sections in the photo above indicate these lines and where epoxy will be placed.

To assemble the centering rings/motor mount tube assembly, take some 80 grit sandpaper and roughen up the areas noted in the photo above. The nice thing about good marks in pencil and using 80 grit sandpaper, you can sand right over your marks and still see 50% of them when you are done, making alignment a breeze.

Mix up some of the 12-15 minute epoxy and attach the forward centering ring, placing a fillet on the back side but not the front side. A fillet on the front side would interfere with the fit in the fin canister. Make sure you get your centering ring lined up correctly and that it is square with the tube. After it has set up, repeat the process again with the aft centering ring, except place the fillet on the front side.

After the centering rings have dried, you can check their fit into the fin canister shell halves. Mine was so precise the thing practically snapped into place in the styrene shell halves. If need be, clean up your's to fit by sanding until it fits snuggly but with clearance. It's time to turn our attention to the recovery mount.

The photo above shows the forward end of the motor mount tube where the recovery mount will be attached. The forward styrene centering ring has been slid inside the motor mount tube and the dotted line shows how far down the lip of the styrene part extends. You should mark your tube showing the distance your styrene part's lip extends for proper placement of the recovery attachment point.

Here is mine marked, and the "X" marks the spot where I will drill a hole through both sides to slip a 1-3/4" length of carbon fiber arrow shaft through as my recovery attachment point. You can substitute some other suitably strong item here such as a 1/4" diameter bolt or even a hardwood dowel. I like carbon fiber arrow shafts because they are very strong and very light. Check your yellow pages for a local archery shop.

After you drill the properly sized hole, insert your recovery attachment point and apply a liberal amount of 12-15 minute epoxy to the outside, forming a nice fillet all around as indicated in the photo above. Allow to dry.

Next, take your upper styrene centering ring and your trusty Dremel or Dremel-wannabe tool and notch the lower lip extension to clear the recovery attachment point. Personally I think you would hard pressed to yank this recovery attachment point out.

Do not attach the upper styrene centering ring yet. That will come in the next class when we continue the airframe assembly.