Pml retainer any good?

[BlueNinja]

I am gonna order my Tethys today, and with that I would like to purchase a motor retainer. The PMR looks cheap and easy, so has anyone used these before? how strong are they?

Blue N150

EDIT 5:30 PM: WAS gonna order the Tethys. Too late now i think. I could email it in, but that would prolly be 24 hours... I think calling would be best.

 

[Justin Horne]

I bought one once, and just could not get it to work.. I almost destroyed the ring. I ended up filling the hole with epoxy and getting a slimline...

 

[BlueNinja]

How could you not get it to work?

 

[Missileman]

I have only used one once with an I195 motor in a scratch build.
Worked just fine.
One advantage to the PML retainer is it can be fitted to a rocket that is already assembled.

 

[solrules]

I use one on multiple rockets. They work pretty well, you just have to be sure exactly where to drill the holes in the centering ring, or you will run into problems. I used a modified system similar to this (same PML ring, but different inserts and screws) at LDRS 23. Rocket came down under chute a bit fast, and I noticed 2 of the screws were bent from landing.

 

[Justin Horne]

My problem was the inserts, instead of screwing in, were just chewing the hole away... oh well, it must have just been me.

 

[solrules]

Originally posted by Justin Horne
My problem was the inserts, instead of screwing in, were just chewing the hole away... oh well, it must have just been me.

You could use CA or Epoxy to strengthen it up a bit once the inserts are set......or use blind T-nuts. Those work a whole lot better, although you can't retrofit them to your rocket.

 

[Ryan S.]

or if you already build the rocket epoxy some threaded inserts

 

[BlueNinja]

I looked for threaded inserts and the best i could find were plastic screw anchors... I think i'm gonna get the PML retainer, it just appears to have a couple of minor problems.

 

[BlueNinja]

How cna you make sure the holes are drilled in the right places? use the ring as a pilot hole gauge?

 

[solrules]

Originally posted by Blue_Ninja_150
How cna you make sure the holes are drilled in the right places? use the ring as a pilot hole gauge?

Yeah. The first rocket I put it in, one hole was in the wrong spot (pencil thickness away....) and ended up having to drill out the ring itself a little bit to accomodate the hole. One great thing about the retainer is that it holds 38mm as well as 29mm.....not many other retainers can boast that. I have found it very useful.

 

[Missileman]

Originally posted by Justin Horne
My problem was the inserts, instead of screwing in, were just chewing the hole away... oh well, it must have just been me.

I had the same problem at first then I realised that PML had me drill the holes too small.
I drilled the holes a bit bigger and everything worked out great.
I did put a drop of CA along the outside of the insert, being careful not to get any on the threads.

 

[BlueNinja]

Another question about alignment for that:

I have a 29/40-120 case that I might have some nozzles for, and I need to fit th ering over the nozzle to align it right. Is the hobbyline RMS nozzle outside dia. the same as hipower nozzles, or is it smaller?

 

[Missileman]

Center the ring on any nozzle. There is plenty of room for about any size nozzle. The ring itself fits close to the outside of the 29mm motor. The PML retainer is 29/38 it fits both size motors.

 

[BlueNinja]

K... I've got an F40 here that I put in a plastic ziploc for some reason when I got it and it got all condensed and stuff inside... I may cut it up and use it for igniters but for now it's gonna be a marking guide for the retainer.

 

[Larry]

Originally posted by solrules
Rocket came down under chute a bit fast, and I noticed 2 of the screws were bent from landing. [/B]

solrules,
Use some nylon spacers under the retainer where the screws go through. This will let you tighten them down good without bending the retainer, and it would keep the screws from getting bent........Larry
p.s. thought I had a picture, but I must have already deleted it, sorry.
blueninja,
The PML retainer works real well. I have one on my Amraam 4. No problems, but when you put in the threaded inserts make the holes just a little bigger than they tell you. I put some grease on my screws and srewed them in and put some epoxy around the inserts. Once the epoxy started to set I took the screws out. I put the screws in the holes just to keep epoxy out of them. Don't slop epoxy all over them

 

[LampertRocketry]

Originally posted by Blue_Ninja_150
I am gonna order my Tethys today, and with that I would like to purchase a motor retainer. The PMR looks cheap and easy, so has anyone used these before? how strong are they?

Blue N150

EDIT 5:30 PM: WAS gonna order the Tethys. Too late now i think. I could email it in, but that would prolly be 24 hours... I think calling would be best.

Two ways to go in my humble opinion. The BEST way is to go with an Aeropak motor retainer. Glue it on and be done with it. Downside is that they are expensive.... that's why I am building fibreglass and carbon rockets these days... I want the rocket to last as long as my motor retainer.

Option No. 2... threaded brass inserts and thumscrews. I picked up a box of both at my local hardware supplier. It was cheaper to buy a box at a real hardware wholesaler than to pick up a plastic pack of a dozen at the local mom and pop hardware. I have a lifetime supply for $20 or so. Oh, pick up an assortment of washers to fit the thumscrews... different diameters. I put three or four threaded brass inserts into the rear thrust plate every time I build anything.... only use two but it's good to have an extra in case a rough landing messes one up. All you need to do is find the appropriate diameter washer and put a couple of thumscrews into the threaded inserts, using the washer to hold in your motor. It's as simple as that.

DO NOT MESS AROUND WITH BENDING CLIPS! I did the clip thing a few times and it worked fine the first couple of times. I have found that the clips will bend under the stress of a motor ejection charge sometimes and you lose the motor casing in the woods. No need to mess about with various clips and so on... just buy an assorment of different diameter washers, thumbscrews and threaded inserts. BTW, I use a dab of epoxy to ensure the threaded inserts stay put. I put a blob of modeling clay or vaseline inside the threaded insert to make sure no epoxy finds it's way in there while gluing.

McMaster-Carr sells all of the above. If you are looking to outfit a few rockets (2 -3) the parts will cost you a total of about $5 - $10 maximum. And you will have stuff left over for the next 2 - 3 projects.

Murray Lampert
www.lampert.ca/Rocketry.html