Adding a Motor Retention System (Example on a LOC Graduator)

Featured Tip:   All  Previous  Next

By Kyle Yawn

I just recently purchased a LOC Precision Graduator kit as I move on into mid power and then on to high power rocketry. I found this kit to be a good choice to fill that need. It didn’t come with the easy to follow detailed instructions that I’d been used to like those of Estes and Aerotech though. I began looking over them and found that the suggested motor retention was to use masking tape to friction fit the motors into the motor mount tube. I knew that this method was not going to hold up to even some of the smallest engines that this kit can fly on, let alone a G or H. I knew that I was going to have to come up with some other method to do this with. I have read a lot of material on mid and high power rocket construction and decided on the following plans to add a good, solid motor retention system to my new LOC Precision Graduator.

• To do this you are going to need the aft centering ring from the Graduator kit, one or two 8-32 ¼ t-nuts, a pen or pencil, a drill press, a hammer, some epoxy, one or two screws to fit the T-nuts.

• After gathering all your materials make two marks directly across from each other on the outsides of the centering ring in the middle of the wood. This should be enough room for the T-nut(s) to fit without any overlap off of the ring.
• Next use the drill press to drill out the wholes in the ring that the T-nut(s) will fit into.

• Place the T-nut(s) into the wholes in the ring and using the hammer; gently hammer the tacks of the T-nut(s) into the wood of the centering ring. This will help them stay in place before you add the epoxy and it will greatly increase their strength.
• Using a tooth pick or straight pin, mix up a small amount of epoxy. Then use the tooth pick or pin to apply it around the base of the T-nut where it contacts the centering ring. Be very careful when doing so that you do not apply any epoxy into the threads of the T-nut or else the screws will not go into them.

• Once the epoxy sets you can place the screws into the T-nuts.

• After this is done you can experiment with different types of metal clips that will hold you motor in place using one or two or even three T-nuts. These are a few examples I found:

GUEST's OPINION:
"3/06 - SAFETY ALERT!!! Never attempt to hand hold parts when using a drill press (as shown in the accompaning photo). Always use a drill vise or clamp the part to the base. Be sure to use safety goggles as well." (B.C.)

GUEST's OPINION:
"3/06 - For a more secure mounting, put the flange portion of the T-Nut on the inner surface of the centering ring. With that configuration, the epoxy and tangs only need to hold the t-nut in place while attaching the retention clips. The screws and clips serve to pull the t-nut flange tighter against the centering ring. Ejection forces are countered by the flange against the upper surface of the centering ring, rather than relying on the tangs and epoxy to withstand the forces of repeated liftoff, ejection, and (not always soft) landing." (S.E.T.)

1. Motors
   Retention: for use with blind t-nuts, I cut some lengths of small brass bar stock. I've since heard that aluminum window screen clips work very well. - from RMR
2. Motors
   Featured Tip: Make Wire Retainers for Motor Retention - I use wire retainers with #6 screws and t-nuts for motor retention. The wire retainer is easy to make, and it only cost a few pennies per retainer. I make my wire... more
3. Motors
   Retention: for use with blind t-nuts, use clothes hanger wire. Make a loop in one end, and a hook out of the other. Easy to do with a coupler pairs of needle-nose pliers.
4. Motors
   Retention: for use with blind t-nuts, the aluminum clips for screen windows work well, I often use aluminum 'standoff' spacers to 'jacket' the screw and give a bit more stability to the clip. You can get the kind of clips with a slot instead of just a screw hole, I use these when the mount is 38mm but I intend to also use a 29mm adapter. when you do this you have to pay attention to the placement of the blind nuts...so the clip will reach the closure 'lip' for both size engines. This is also how you retain the adapter at the same time! - from RMR
5. Motors
   Retention: What I use is found in the electrical section. Electrical conduit in homes are often "tied" down to studs using a metal strap. I offten use the 3/8 inch size for 14-2 to 12-2 cables. Menards sells this product made by Gampak # 44919, ISBN #0-31857-44919-3 - from RMR