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I feel quite dumb asking this question...

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el chubbo

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I have just ordered my first set of CTI Pro-38 casings -

I know that the "38" in "pro38" refers to 38mm being the diameter of the casing itself... but I am making my own centering rings and need to know what others have used for motor tubes.....

please advise!
 
A

Austin

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For the 38mm motor mount, you should use either the PML 38mm Bodytube/MMT tube (it's the same stuff, just different lengths), or use LOC's Motor Mount for 38mm. Ross at <a href="http://www.magnumrockets.com">Magnum Rockets</a> carries both at a good price. The difference is the PML is Phenolic (plastic impregnated cardboard) and the LOC are very thick and heavy paper tubes. Giant Leap also used to carry Phenolic...they may be another good source.

Carl
 

eugenefl

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Nah dude...dumb is ordering something without asking first and then having to go through the hassle of returning stuff. Not dumb at all.

If anything else bugs you and you need to ask don't hesitate.
 

el chubbo

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these tubes are a straight 38mm ID? Are they an exact fit to the 38mm casing? Or is the 38mm casing slightly undersized?
 

Rocketmaniac

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Originally posted by el chubbo
Are they an exact fit to the 38mm casing?
Well, there may be a few thousandths difference between the motor tube and the casing, but basically the same size......
 

el chubbo

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with being unable to get the casings out of the tubes after flight?
 

Rocketmaniac

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Originally posted by el chubbo
with being unable to get the casings out of the tubes after flight?
nope...... If you use friction fit for motor retention, the tape "might" get hot and become more sticky, but still shouldn't be a problem at all....... If you another kind of motor retention, the casing will just slide on out!!!!!
 

el chubbo

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it is amazing how I can find the exact answer to any odd question I post....

matt c
 

mikeyd

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For my Crayon Level 2 rocket, on a Pro28 J motor I used a 1.5" mailing tube for the motor mount, with a paper towel tube over it to make the outside diameter meet the hole in the "spindle" of the cable reel ends I cut my centering rings from. Worked great at LDRS22 to about 2,000 ft for my Level 2.

Here is a link to the parts.
http://members.cox.net/shortckt4/Rockets1.html#crayon
 

el chubbo

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I have one other question.... sorry.

I am STUCK on how to build a motor mount that will accomodate both H and I pro38 motors. Both motors have the same diameter but different lengths.

I am new to HP so this may be a really simple question that I am just missing.

Thanks!
 

wwattles

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The answer lies in your retention system. Many folks like to use friction fit to hold the motor in place, with a slightly larger buildup of tape on the last 1/4 inch of motor to act as the thrust ring. That way, you can stick as long a motor as you want into the mount and not have to worry about where you put an Estes-style engine block/hook.

WW
 

flying_silverad

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No such thing as a dumb question? I'll let you be the judge.

When-5 years ago
Where-Work, in my office
Who-myself and a co-worker

I was sending one of my underlings to a maintenance meeting. About 3 hours before the meeting he knocked on my door and said,
"Hey boss, what time is the three o'clock meeting?"
I just stared at him for about 15 seconds and shook my head. He then relized what he had said, closed his eyes and walked away. I have a witness.
:D
 

wwattles

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My wife used to work at one of the Disney parks in Orlando, and she said that at least once a week she was asked, "What time does the 4 o'clock parade start?" And, being a warm, friendly, and always responsible Disney employee, she was never able to reply with the smart-*** remark that she would invariably feel welling up from within...

("Here's your sign...")

WW
 

Rocketmaniac

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Originally posted by flying_silverad
"Hey boss, what time is the three o'clock meeting?"
Very early in my Air Force career (first year or so) a pilot came back from a mission and told me "The cameras worked fine in DAY and NIGHT mode, but didn't work at all in O-F-F mode" (I worked on Recon cameras on spy planes)
 

flying_silverad

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Originally posted by Rocketmaniac
Very early in my Air Force career (first year or so) a pilot came back from a mission and told me "The cameras worked fine in DAY and NIGHT mode, but didn't work at all in O-F-F mode" (I worked on Recon cameras on spy planes)

Well..it must be the Air Force then..casue that's exactly where it happened to me!! :D :D
 

Ryan S.

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Originally posted by Rocketmaniac
Very early in my Air Force career (first year or so) a pilot came back from a mission and told me "The cameras worked fine in DAY and NIGHT mode, but didn't work at all in O-F-F mode" (I worked on Recon cameras on spy planes)
I hope you gave him a dummy smack right away
 

Rocketmaniac

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Originally posted by Ryan S.
I hope you gave him a dummy smack right away
nope.... I just had a "I can't believe he really said that" look on my face and said, "you mean the off mode sir?" He very quickly realized how dumb he was........ I couldn't sau much more, he was the "educated" officer and I was the un-educated enlisted man.......
 

Missileman

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Back to the original questions,
38mm motors are 38mm OD 1.5"
There are many sources for this size tubing.
The pro 38 motor mentioned has a thrust ring built into the aft end of the reload.
I would never friction fit a high power reloadable motor.
First there are some RSOs that will not let you fly without positive retention.
From a personal standpoint I would rather not take the chance of losing an expensive motor casing and possibly the rocket due to kickout for lack of 50 cents worth of hardware.
As far as length, It depends on what you want to do with this rocket in the future and how long the rocket is.
I would make it at least as long as the longest motor you plan on using.
If you want to use a modular ejection baffle add at least 12" to that.
Leave room for your chute and keep an eye on center of gravity.
Sounds a bit confusing but once you get started it will all fall together.
Good Luck and lets see some PICs
 

cls

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for cheap, available 38mm MMTs, I found the heavy cardboard tube, at the center of the roll of produce bags at the Safeway, is the perfect size for Dr Rocket motors. it's long enough to accomodate a 38/600. 38/720 sticks out a bit :)


regarding use of tape, masking tape works just fine for fore-ward and rear-ward motor retention, up to 38mm. in fact it works a little too well, often after flying it's hard to pull the motor out!! for this reason hardware is much preferred for rear-ward retention.
 
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