Rookie stupid question

[cobra1336]

My Callisto has arrived. Read all of the instructions and have a question. Retainers ? I searched PML FAQ and it says to use friction fit.......not comfortable with that. Searched this forum and saw a bunch of great ideas about retainers. All seemed to be ejection retainers. Here comes the stupid question...what keeps the motor from pushing thru the body? Want to use different motors that come in different lengths. I have a 29/38 adapter so I can fly localy before I get my L1. Pics would be great. Pizza is here, I'll check back in a while.

 

[cjl]

The motors (the reloadables at least, which is pretty much all you use at this size) have thrust rings on the back of the motors. The back end of the motor is actually larger in diameter than the rest of the motor, so that hits against the end of the motor mount tube and stops it.

 

[cobra1336]

Thanks cjl, found some pics that show what you mean. I feel a bit safer. Time to build.

 

[cjl]

Great

The advantage of this system is that you can leave the motor mount open on the front, without a motor block of any kind, and it will take a motor of any length without any need for spacers or adapters. It makes it a lot easier.

Post pics of the build

 

[dgreenapple]

Two kinds of retainers available from PML. Pretty much similar to what else is out there.

1 - A flat plate with a hole in its center which presses against the end of the motor and takes three screws going into threaded inserts in the bottom Centering Ring. The key here is it is best to plan ahead and mount the threaded inserts in the Centering Ring before you build. Fill them with silicone grease before you epoxy them in place.

If you want to save $15, make it yourself out of 1/8" G10. Cut to size with jigsaw and then grind down to precision sizing using a dremel tool.

2 - A retainer ring and cap. Aeropack, Giant Leap, and now, PML make them. Threaded collar with "well" is epoxied (JB Weld best) to the Motor Tube. Thrust ring sits in the "well" and the cap screws on over it.

Easiest to use in the field. Less "screwing" around, so to speak...

 

[SpartaChris]

FRIENDS DON'T LET FRIENDS FRICTION FIT!!!

Do a search for Kaplow Clips. Super cheap and reliable. That, or a simple washer/wood screw will work fine and save you some cash.

 

[cjl]

FRIENDS DON'T LET FRIENDS FRICTION FIT!!!

I disagree

Friction fitting can be quite reliable when done right. It is the best choice for something like a minimum diameter screamer. It is a lot more of a pain than positive retention though, especially when you have to get the case that is wedged in there back out...

 

[Chicagonative17]

Friction fitting is REALLY beneficial. Less weight and you can use it on any motor sizes where as forward motor retention and aft motor retention you are limited on certain size motors and/or manufacturer of motor. If you can do it where you can't get it out with your own ONE hand, your ready to GO GO GO.

 

[SpartaChris]

Originally posted by chicagonative17
Friction fitting is REALLY beneficial. Less weight and you can use it on any motor sizes where as forward motor retention and aft motor retention you are limited on certain size motors and/or manufacturer of motor. If you can do it where you can't get it out with your own ONE hand, your ready to GO GO GO.

Ummm, I'm not so sure about that..

With forward retention, sure, there is a limit. But with aft positive retention, like an Aeropack or some Kaplow Clips or something, where is the limit on motor length? You can retain any motor with aft positive retention that you can by friction fitting, provided you plan the retention properly.

I strongly dislike friction fitting mainly for the reason that it can be a PITA to get the motor out after the launch if you forget some kind of enforcer, like a broom stick or something to knock it out from the inside with. Not a problem if you only plan on flying the rocket once that day, but if you want to fly more than that, you better have a way to get the motor out.

The other is the risk of not using enough of a friction fit and losing my expensive casing.

Plus, I just sleep better knowing I have a positive way to retain the motors. It makes it easier to get in and out and I'm fully confident taht my motor will stay put.

 

[dgreenapple]

re: Friction Fitting....


I'm very much in agreement that Friction Fitting is a last choice.

I have recently flown 11 flights with my TARC team friction fitting F and G motors. It is time consuming, unpredictable and the motor gets stuck in the tube on occassion after the flight.

If you want to save money, make retention out of the clips mentioned above (Giant Leap sells them) or out of a handmade G10 plate with 2 screw holes in it.

And when you are flying anything above an H motor, please don't friction fit...

 

[Fore Check]

I lost one of the sweetest rockets I've ever made (lawn dart) because it kicked the friction fit motors. GRR!

 

[Chicagonative17]

When I say certain motors won't fit, I mean if you use slimline or aeropac because only aerotech and Pro motors fit it (and I think one more, don't remember). Kaplow clips work with anything yes, but what about minimum diameter rockets? I know it is a pain to get them out but I have friction fitted I's before and gotten them out to launch the rocket 3 more times that day. The trick is to let it cool a little first, even if its 30 minutes, usually it will easily pop out with a broom stick. And even if it does kick the motor out at ejection, I tie my shock cord to the forward end of the motor case, its not going anywhere. I have witnessed K motors friction fitted that use motor ejection, it works when done right.

 

[Handeman]

Cobra,

Here's what I did with my 29MM Calisto.

I epoxied a nut on the inside of the centering ring. Cut a short piece of aluminum angle and drilled it to fit a machine screw. I use the aluminum and machine screw to clamp the motor in the tube.

Sitting next to the rocket is a single use motor. I use lots of masking tape to give it a good ridge to sit against the MMT. Make sure the screw is tight. The tape will compress some during burn and you don't want the clamp coming loose during flight, although I'm not sure it would really be much of a problem.

I've had 15 or 16 flights with the Calisto and have never had a problem with the motors.

 

[cobra1336]

Another great idea. Pictures always help. I have a 38 mm but I'm sure I can use that idea on the adapter.

 

[blackjack2564]

Friction fit is a very misunderstood subject to most, and if done right, extremely reliable. ONLY bottom third of motor is taped, and done in a spiral fashion, like threads on a screw. You spiral tape around the case at a 45degree angle and overlap the tape by1/3. Then screw the motor in and unscrew out.Most friction fits I've seen, amount to little more than tape on a motor forced in, then after the burn, forced out. THe problem with that method is heat turns the tape adhesive sticky and you end up "glueing' the motor to the mount, causing the extraction problems. You have to wait till the motor has cooled off some, the un screw it while just warm. That being said, I still think a mechanical method is EASIER, but we have all seen failures with this also! I have personally done up to 54mm and the gentleman who showed me the correct way does it on 75mm. You also can leave about a 1/2 in. of motor tube stick out of the centering ring and tape your motor to the tube on the outside, this method is easy , foolproof, and definitely reliable for anyone without the skills to friction fit correctly

 

[cjl]

I do a similar method, except that I tend to spiral wrap the top third of the motor, and screw it in. This way, if it somehow does kick halfway (though it would take a LOT of force to do it), it still has something holding it in.

 

[blackjack2564]

Very reliable and works well, doesn't it? Friction fit is a skill worth learning, because there is always the time when you can't find all your parts or murphy's been working overtime on your mechanical method.

 

[cjl]

Absolutely. I've never had a motor kick with friction fit. I still prefer Aeropacks though - not for reliability as much as convenience (it's a lot faster to screw on an aeropack than it is to friction fit properly). Interestingly, while I've never had a well friction fit motor fail (actually, come to think of it, the motor in my Amraam in the drag race at LDRS was friction fit like that), I have had a motor kick past kaplow clips before.

 

[MarkM]

Originally posted by chicagonative17
When I say certain motors won't fit, I mean if you use slimline or aeropac because only aerotech and Pro motors fit it (and I think one more, don't remember).

Part of this is incorrect. Slimlines have some compatibility problems - especially Animal - in the larger sizes. But Aeropacks work with EVERY commercial motor casing available: Aerotech, CTI, Loki and Animal. AND they have adapters to work with the 63mm Hybrids. Aeropack may even work with Kosdon cases.

I use Aeropacks exclusively and love the ease of use and the piece of mind my motor is securely retained.

 

[Chicagonative17]

Now that I looked at my slimline and aeropac retainers, I realized that you are right. I never noticed the difference in what motors you can fit.

as to friction fitting an O motor!!!!!! click the first link on this page that is an O skidmark and read the caption next to the link.https://www.mbrocketry.com/media/balls03.html

 

[heada]

I don't think Aeropack retainers work with SkyRipper motors. Slimlines do though, so there is always an option.

-Aaron

 

[cjl]

Aeropack claims compatibility with skyripper...

Here's the compatibility list off their site:

# Compatible with the following solid fuel rocket motors: AeroTech (TM) / AMW (TM) / APS (TM) / Cesaroni Pro XX (TM) / Dr. Rocket (TM) / Kosdon (TM) / Loki (TM)

# Compatible with the following hybrid fuel rocket motors: AeroTech (TM) / Hypertek (TM) / Propulsion Polymers (TM) / RATTworks (TM) / Sky Ripper (TM) / West Coast Hybrids (TM)

I've never tried them with the skyrippers, but I see no reason to doubt the claims...

 

[heada]

I have the Skyripper 29mm hybrids and several Aeropack 29mm retainers and they do not fit. The thrust ring on the SkyRipper is maybe a few hundredths too wide. I have the 38mm motor set on order and once I have them, I'll check with those (they might fit)

-Aaron

 

[irishwebber01]

Cobra, I hope this dosen't get to you late and hope you find it useful, I have a PML Callisto and I have a 38mm Slimline retainer on it from GLR the kind with the quickclip. just leave enough of the MMT tube extending out so it can adhere and use JB weld to attach it.

Irish

 

[dave carver]

I cut 4 slots in the end of the motor tube and put a screw clamp on, wrap enough masking tape around the end of the motor to slightly expand the slotted section and screw the clamp down. The crush applied is enough to prevent movement forward or back.

This system worked for the 500 pound thrust M2240 Kosdon motor I used in my 3rd level rocket.

Screw clamps also have the advantage of not needing to be glued onto the rocket thus able to be moved to a different rocket.