29mm motor - actual outer diameter?

[spudman]

It's thinking it is the 3/4" one they sell at home depot even. You need room for the sand paper.

I misplaced my set of "motor pokin' tools" which we called these Dowels when I traded my truck in for another in 2018. 'Cause if you get a motor stuck in the motor mount tube you need a motor pokin' tool to push it out from the other end; using a rubber mallet gently.

I think it may be closer to 1", since the inside diameter of that tube right now is about 28.5mm, which equates to 1.12". I think a 7/8" dowel would be just perfect to allow for the thickness of the sandpaper. I know I'll find something, as I have a Menards, Home Depot and Hobby Lobby right here in town. Thanks!

 

[lr64]

The sandpaper thickness will vary by grit and type. You might take calipers to the store with you.

 

[SolarYellow]

machining a few thousandths off the outer diameter of the motor casing (possibly less safe?)

The case will not be able to handle the same pressure, and will be a research/experimental motor if you do that, which requires you to have an L2 cert to fly it.

 

[terryg]

Between sanding some on the inside of the motor tube and peeling off the label on the motor it should be doable.

 

[spudman]

Well...one problem solved and another one to be solved soon! I received the AeroTech Economax 29mm motors today. Once I removed the adhesive label from the motor case, they measured about 28.4mm to 28.5mm in diameter (depending on exactly where on the length of the motor I was measuring) and they slid into the motor mount tube snugly. I'll still do a bit of sanding on the inside of that tube, as I'm guessing the motor case may expand a bit after use and I'd hate to have it get "permanently" installed. The new issue is of course the NCR motor retainer ring. Apparently, the fattest part of the Aerotech motor case at the aft end (the "lip") is bigger than the Estes/NCR Dark Star motor fattest part, so the ring won't fit over it in order to snap in place. A slight bit of material removal on the inside of this ring with a Dremel should do the trick. If not, I'll just pick up a new retainer and epoxy it to the motor mount assembly. Thanks again for all of your help and suggestions! I really appreciate it.

 

[dhurstell]

TLDR:

External Dimension Drawings
Onshape CAD library of commercial rocket parts

 

[OzHybrid]

All commercial rocket motors are in fact imperial sizes. Ex motors can me any size....

A 29mm motor is 1 1/8" OD 28.575mm OD The tube this fits into as a motor mount is approximately 29mm.

Metric equivalent sizes to designate motor sizes seem to have been used to allow people to choose the correct tubing size for a motor mount.
29mm motor tube has an approximate size 29mm internally. Even then the exact size varies slightly from tube manufacturers.
This allows you to identify which tubes are motor mount tubes. Their size will be specified in mm and that will be their internal diameter(approximately)

All other tubes have their size specified by their external diameter. ( Usually in inches) All the BT sizes match externally. Their wall thickness may vary from manufacturer so the internal diameter varies slightly.

All motor mount tubes match internally and their outside diameter may vary slightly due to wall thickness.

Hope this clarifies what's going on. And there are of course exceptions as well just to make things less clear.....

 

[SolarYellow]

And one production lot may vary from another, for the same SKU from the same brand.

Some retailers decide to use their own naming conventions for the same tube specs, just to make it more difficult to figure out how to match up their stuff with all the other stuff that's out there, or because they are pedantic aspies and insist on using the metric system for everything, or using the ID to name a product instead of the OD like everybody else does for the exact same tube specs.

The only way to work it out is to start building yourself a spreadsheet and mining websites. If you care that much.