Rail Buttons With Pml Piston? (amraam 4")

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Well-Known Member
Mar 24, 2004
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This may be a stupid question for my first post so please bear with me...I'm currently building my 4" PML AMRAAM with the Quantum tubing. I would like to use 2 (?) rail buttons. Can this be done and keep piston ejection or should I dispose of the piston altogether and use trusty dog barf. It appears as if the piston does travel out of the booster during ejection. If so, would'nt the top rail button bolt interfear with piston travel?
This is my first PML piston kit and I will eventually try dual deployment with a Alt Acc2C for a level II atempt (no CPR).
Thanks in advance for your help!
The piston does come all the way out on ejection. You could probably put the button low enough down to not interfere with the piston or just use a kevlar shock cord and 'chute pad from someone like Giant Leap and leave out the piston and skip the dog barf altogethar.
Like Zippy said, you should be able to place to top button low enough to allow the piston to work just fine.
or make a stand-off out of popsicle sticks (or equivalent) so the rail button dosen't actually extend into the tube. you can read other usefull tips at www.railbuttons.com
hope this helps, and welcome to the forum!:)

If you want to keep the piston, it might be a good idea to use 3 rail buttons. Put 1 down at the botton of the rocket in the lower centering ring, the second one at the centering ring above the fins, and then the 3rd one much higher at the coupler between the booster section and the payload section. The only real gotcha here is that the booster and payload have to be perfectly aligned every time upon assembly, so it helps to design in some easy way to make sure the booster and payload section are perfectly aligned. This design gets all buttons out of the way of the piston.

If you do it this way, the two down at the bottom really do most of the guidance during the flight. The upper one (3rd) serves to support the higher weight of this rocket and for initial stability on the pad.

Always remember with rail buttons: as soon there is only 1 button engaged with the rail, they no longer provide guidance to the rocket.

You could also use surface mounted standoffs as described on the www.railbuttons.com web-site, but they might look funny on an Amraam, I think.

HTH, --Lance.
First, welcome to TRF!!

I put buttons on my Tiny Pterodactyl, which has the quantum tube with piston ejection. The key is to put one button into the aft centering ring, then keep the other low enough so you will have room above the piston for the shock cord, and chute. Just remember, when you put the button on, the piston should be out of the rocket :)
Or you could use the acme conformal guides. Another way would be to sand the bottom rail disk until it conforms to your tube, then glue it on, but I would just go with putting them low.
Rail buttons in line with the lower and upper centering rings on the MMT.

Drill slightly smaller hole than threads on the button, add one drop of CA to threads, use screwgun (or drill motor equivilant) to screw the railbuttons into the quantum, they will cut their own threads. Launch after 5 minutes. Have one with thirtly launches on it, when necessary I can still unscrew the button once I break the bond.
Wow, Thanks to everyone for taking the time to reply. I really do appreciate it guys. Now I can proceed. I'm sure I'll have more questions and look forward to helping other TRF'ers as I can.
- Peter