Model Rocket 29mm Motor Mount Tubes

Model: Model Rocket 29mm Motor Mount Tubes

Overview:

These are motor mount tubes for BT60, BT65, BT70, and BT80 Estes body tubes.  While the stock kit MMTs work well enough, there are not many out there that are designed for 29mm motors in these body tube sizes.  This set of files fills that gap.  You simply print, then fit into the body tube of choice.  You may leave ~ ¼-in (6mm) between the end of the tube and aft motor mount.  This will give you enough room to add/remove the retainer cap and add extra fillet of glue for added strength.  

This will allow you to use larger motors in smaller body tubes for experimental designs, and is intended for experienced rocketeers.  The prints are heavier than stock MMTs and will most likely upset the center of gravity of the rocket, making it unstable and dangerous.  If you are unsure what this means, start by building some stock Estes kits and/or check out Apogee Rocket's YouTube channel.  They have over 10 years of rocket-building videos and are an excellent source of information for those starting out.

Disclaimer:

Safety is everyone's responsibility, especially the builder.  I have provided these models for experienced model makers.  I assume no responsibility or liability should these models be used in an irresponsible or unsafe manner.  If you print and use these, you are responsible for any outcomes. 

Included Models:

There are a few variations:

Each STL file contains a MMT with and without the retainer ring, a separate retainer ring, and a retainer cap. For the BT60, the retainer cap is smaller than the others so it will fit within the circumference of the BT60 body tube

The retainer ring is the same size for all models, so you can use the BT60 retainer cap for any other model but the larger cap will only fit on the BT65-80 models as it is wider. 

 MMTs:

Each tube is designed to use a 29mm motor tube as a liner to protect the print from deformation.  I have used variations of this design multiple times with PLA and PLA+ filaments and it works rather well.  I would recommend using epoxy to secure rather than CA glue but either should be fine, just do not use the thin CA because it will grab before you get the tube seated and then you will be sad/mad.  Be sure to rough up the print's surface where glue will be applied.

Shock Cord Anchoring:

To secure a shock cord to the BT70/BT80 models, you can drill a small hole in the forward ring and feed a length of Kevlar cord though and tie it off.  For the BT60/65, I used a file to create a notch on the forward closure and tied my shock cord underneath the forward centering ring, feeding it forward thought the notch.  I may modify the model in the future if there is enough response for this feature. For added protection, you can feed some small heat-shrink tubing over the cord to help protect it.  

Retainers

For the retainer cap, you can coat the throat of the opening with a thin film of epoxy to help protected it.  Make sure not to get any on the threads.   I haven't had enough deformation with mine to warrant reprinting a cap but there may be some, and the epoxy will help some with that.

Each tube size includes a separate model without the retainer so you can either use it without the retainer or install it separately.  I usually test fit the 29mm motor sleave for fitment and placement, leaving enough at the aft to accommodate the retainer ring.  Trim the forward motor sleave to be flush with the forward centering ring or just above it, based on your motor usage.

I have printed this with both PLA + and PETG and both have worked equally well. 

The outer dimensions were taken from the OpenRocket database, so check the STL against your tube.

I hope that this helps you with your rocket journey

Print Suggestions

Print with:

• Resolution: Any - I print mine with higher resolution to help the layers bond
• Infill: 15 - 100% (more infill will make it more heat resistant)
• Perimeters: 2-6 for strength
• Supports: On the bottom of the aft centering ring, with the retainer ring pointing up
• Brim: will make the print more stable and stick to the bed.  I used 5mm
• Infill Pattern: I like 3D honeycomb because its really strong, but its the slowest.  

Final Notes:  

• The fit for the retaining ring and cap is tight.  After printing, gently screw and unscrew the cap, working your way down the threads until it seats.  Don't do too much at first or the cap might get stuck.  Just work it back and forth a few times and it will loosen up.
   
• Test fit everything before you go to glue – you will thank me.
   
• I have spent many hours designing these.  Because I enjoy the sport/hobby, I wish to give back and hope that you find these helpful.  You are welcome to use, modify, alter these in any fashion you see fit so as you do so safely and abide by the Creative Commons License.  

Please follow the NAR Safety Code and have fun.  This is an immensely fun and rewarding hobby when everyone is able to enjoy it.