Making a 29mm Motor Mount.

I was going to build a rocket capable of handling F & G motors. However, the site that I normally use does not have seem to have the parts I would need. They do have an engine hook (I prefer this retention system for smaller rockets), they do sell the engines as well, I found a motor tube on another site, but I am not sure where I could get some centering rings from. The rocket would have a tube size of BT-60 or BT-80. Any ideas? Or does the hobbylinc motor mount for D+E motors hold Fs?

Don't use an engine hook. It will only limit your motor choices. BMS, giant leap, all these guys will have centering rings for that. Just ask.

I found some at Apogee, for a 29mm to a BT-80 tube. I am thinking up buying most of the rocket from there. Then what do you suggest I uses as a retention system? This is a just a design, but I want to have an idea of a cost to see if I should go with it.

Agree, no hook. I would recommend using the Estes retainers that are available from many places (including Hobbylinc.com for around $5-6 IIRC). You can get the rings (as mentioned) from most places including https://www.kandsrockets.com/rings.htm https://www.apogeerockets.com/Building_Supplies/Centering_Rings/High_Power_Centering_Rings https://performancehobbies.com/secure/store.aspx?groupid=28

Forgot to mention, you can also build your own 29mm retention system. I used to build them this way using a 1 1/4" PVC slip joint and an e-clip. Now however (as I mentioned before) I use the Estes retainers because they are so cheap.

Thanks. I have been looking at apogee, and all of the parts are there, I think I will stick with buying them from apogee (to save on shipping costs). Where might I find these Estes Retainers?

EDIT: I am starting to like Apogee components... They have everything I need. Its going to put me back about 45$. With nosecones, centering rings, 29mm motor tube, estes retainer, and Bt-80 tube.

Orion14ed said:

Thanks. I have been looking at apogee, and all of the parts are there, I think I will stick with buying them from apogee (to save on shipping costs). Where might I find these Estes Retainers?

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Here you go... Includes 2 per package. https://www.apogeerockets.com/Build.../Screw-On_Retainers/Estes_29mm_Motor_Retainer

Note: Apogee is far from the least expensive place to buy stuff but they do have super fast shipping and awesome service.

The prices are more than I expected... But I do like having all the parts bought at once. I designed a rocket with these specs, flying on a F motor, reaching 1,400 feet! I think this will have to be my next project. I can not wait!

One other note, in the event that it needs to be said, do not purchase / install a thrust ring. While you may plan on using single use F loads in it right now, leave it open so that you can fly reloads in the future.

I see... I do plan on having it fly some Gs as well. I like this design. Its really simple, and I feel I could have fun adding a cool paint job. what is a good stability? I changed it to be around 1.3, just was wondering.

I have to agree that Apogee is the way to go if you want fast turn around time. I placed a small order on tues. and it arrived today. I was figuring it would be next week - so that means I should be able to get something done this weekend:clap:

Orion14ed said:

I see... I do plan on having it fly some Gs as well. I like this design. Its really simple, and I feel I could have fun adding a cool paint job. View attachment 90998 what is a good stability? I changed it to be around 1.3, just was wondering.

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Your stability margin is good. You want to keep it around 1. Be careful when you fly bigger reloads in there. The CG will move back.

Hobbylinc has LOC tubing, C-rings, parachutes and nose cones for decent prices, they also have Estes motor retainers as well as epoxy, paint, plywood, motors etc. Pretty much everything you need to build, finish and launch a rocket.

For what it is worth, except for the Estes retainers (which can be purchased from many suppliers) you can get all the parts you need for a BT-80 29mm motor mount rocket from BMS. And, like Apogee, BMS has awesome service. In fact, he also has 3" body tube like that used for the Big Daddy from Estes. BMS will also turn custom nose cones and cut custom fins as well from either balsa or ply.

Fitting a 29mm mount into a BT-60? Yeah, we can handle that.

Well, isn't a BT60 38mm across?

blackbrandt said:

Well, isn't a BT60 38mm across?

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BT-60 has an OD of 41 or 42mm depending on maker.

ID. Not OD

blackbrandt said:

Well, isn't a BT60 38mm across?

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blackbrandt said:

ID. Not OD

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No, it is not 38mm.

blackbrandt said:

Your stability margin is good. You want to keep it around 1. Be careful when you fly bigger reloads in there. The CG will move back.

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His screen shot shows 0.75 caliber stability. Don't you want at least 1.0 caliber with the motor installed? His fins look too small to me.

Orion14ed said:

I see... I do plan on having it fly some Gs as well. I like this design. Its really simple, and I feel I could have fun adding a cool paint job. View attachment 90998 what is a good stability? I changed it to be around 1.3, just was wondering.

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Do you have the Open Rocket file?

blackbrandt said:

Well, isn't a BT60 38mm across?

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Just TRY to fit inexpensive clips-and-blind nuts-style motor retention onto the 4.8mm space between the outer and inner diameters of that centering ring. It can be done, but it ain't easy. I was too poor for an Aero-Pack, and the aft end wasn't wide enough for a PVC cap.

MarkII said:

Just TRY to fit inexpensive clips-and-blind nuts-style motor retention onto the 4.8mm space between the outer and inner diameters of that centering ring. It can be done, but it ain't easy. I was too poor for an Aero-Pack, and the aft end wasn't wide enough for a PVC cap.

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Not to mention that the OD of the 29mm AeroPack is 40mm. I ran into the same issue with my Darkstar Mini (29mm motor tube in 38mm airframe) since I didn't end up with enough motor tube overhanging the aft end. I still need to order a slimline from GLR for it because short of something like you did, it is the only alternative I can find to friction fitting.

If you build the rocket with a protruding motor tube, you can use masking tape around the beck end of the motor and the motor mount tube. It has worked for me pretty well over the years without ejecting any motors.

Just wanted to share something I just found and hadn't seen it anywhere else. the tops of Nesquick chocolate milk fit snugly over 29mm loc motor tube. The gatorade top solution is still pretty loose but this seems to be much more secure.

I have just picked up some estes retainers as well, they seem to be similarly sized...

p_g

29mm scratch... friction-fitting is still an option. Depends, I suppose on your NC attachment--planning on shear pins? If so, yes, some kind of mechanical retainer. If not... something to consider, at any rate.


I think it was my Sumo which included a hook that had a reverse bend at the end--did not go through the MMT, but rather hooked in behind a CR, if memory serves. This may be worth looking into as well, if you're going to go with a hook. I'd imagine Aerotech would sell these individually.

Screw-on retainers are nice, though. Estes, Aeropack, Tru-Value... all would work. I rather like the Aeropacks for bigger motors, and know they make them down to 24mm...



Later!

--Coop