DIY 38mm Minimum Diameter Motor Retainer

[Mason T]

Hello everyone!

I am in the process of building a 38mm minimum diameter rocket and I was stuck for a while trying to figure out how I was going to retain the motor. I was doing some reading on here a while ago and someone mentioned using pipe expansion plugs but I couldn't find the thread again when it was time to actually get to it. All of this to say I can't take full credit but I don't know who to give credit to.

I used the following

OATEY 33400 X2
5/16 x 3.25" Eye bolt X1
5/16 Washers X2

I dismantled the two plugs and reassembled on the eyebolt using only the two smaller plastic disks and the rubber expansion seal. I added the two washers to set the distance to allow for enough thread to expand when the motor is twisted.

It works quite well in what I have. I can just slide it in and twist the motor and it locks into place. This also allows for using any length of motor case and stuck because you don't have a retainer epoxied in the airframe. This is the solution I've been looking for a while to find.

I made a video about this and have it posted on YouTube

 

[pugachu]

I have a similar setup for my min diameter rockets (54mm version attached)

I would suggest you find a forged eyebolt, not a bent one, as they can unbend with the shock of the parachutes opening.

 

[kjhambrick]

@Mason T --

Here is a post by @manixFan here on TRF: Minimum diameter motor retention - Post #7 where he shows a similar implementation.

I know I also saw this on one of @Adrian A's rockets too.

I love it !

HTH !

-- kjh

 

[cwbullet]

Yup. It is a good refresher on a technique that has been used before.

 

[Mason T]

@Mason T --

Here is a post by @manixFan here on TRF: Minimum diameter motor retention - Post #7 where he shows a similar implementation.

I know I also saw this on one of @Adrian A's rockets too.

I love it !

HTH !

-- kjh

I believe that was the post! Thanks for tracking that down.

 

[Mason T]

I have a similar setup for my min diameter rockets (54mm version attached)

I would suggest you find a forged eyebolt, not a bent one, as they can unbend with the shock of the parachutes opening.

I love the setup. I will defiantly be making one for 54mm as well. I have ordered one of the forged ones once I validated this was going to work with the standard eyebolt. Though I guarantee that the 950lb shock cord I am using is going to snap before it unbends the eyebolt on this ~3.5lb rocket.

 

[manixFan]

Thanks for the kudos, but the original credit does indeed go to @Adrian A of Featherweight fame who originally posted the technique. There are a variety of ways of attaching recovery gear, but for sure using an eyebolt is the way to go over an 'eye hook'. I'll be using that method quite a bit this year with a couple of MD 38mm rockets I'll be flying.

Good luck with your flights – let us know how they work out.


Tony

 

[kjhambrick]

Thanks for the kudos, but the original credit does indeed go to @Adrian A of Featherweight fame who originally posted the technique. There are a variety of ways of attaching recovery gear, but for sure using an eyebolt is the way to go over an 'eye hook'. I'll be using that method quite a bit this year with a couple of MD 38mm rockets I'll be flying.

Good luck with your flights – let us know how they work out.


Tony

Tony --

Yes, I saw that you gave @Adrian A credit for the idea in your post.

And I know I saw a picture of his rig either here or maybe it was in a Rocketry Planet reprint from long ago.

Post #14 in Adrian's 2019 thread: Violent Agreement: Two Stage 38mm to 33,290 feet is the only reference by Adrian that I could find here on TRF but he does provide a handy link to the part at Home Depot.

I bought a pair last year so I could build one maybe someday when I figure out HED

-- kjh

 

[kjhambrick]

I love the setup. I will defiantly be making one for 54mm as well. I have ordered one of the forged ones once I validated this was going to work with the standard eyebolt. Though I guarantee that the 950lb shock cord I am using is going to snap before it unbends the eyebolt on this ~3.5lb rocket.

@Mason T --

Are you talking about a forged version of the Oatley Test Plug or a forged eye bolt ?

If it is a forged Test Plug, I MIGHT WANT THAT

Thanks and good luck with your rocket and flight !

-- kjh

 

[SolarYellow]

You can also weld the bent eye bolt loop.