Building First RMS Motor

[markjos]

Any chance that the delay is sitting *against* the o-ring in the forward closure, instead of having the o-ring around the exposed forward end of the delay? Sometimes while fiddling around, the o-ring pops off of the end of the delay. Forgive me if I've repeated something already suggested. As others have indicated, this is trickier with the plugged closure. I wouldn't recommend leaving parts out of this assembly, even if it seems reasonable with the plugged closure. Good luck. And don't let this experience turn you away from RMS reloads - they're worth it, and satisfying to use.

 

[Steve Shannon]

I suggest you contact either Aerotech Customer Service or your motor vendor. Whether it’s their mistake or yours, they are happy to help.

 

[Handeman]

I re-read the delay kit instructions- picture below. When I don’t install the delay o-ring or the forward delay spacer, it fits perfectly. I have a stepped plugged forward closure. So I don’t use the delay o-ring or the forward delay spacer. See pics. Last question- the first note says to ‘fill the opening in the forward delay spacer with grease. I assume note two supersedes note one in the case.

Sounds like problem solved.

I've never used a plugged closure, but following the directions does seem to be the best route.

Good Luck with your flight.

 

[Rob Campbell]

Here is what works for me when assembling an AeroTech motor:

1. Install the delay element in the front closure per the instruction sheet and set the closure aside.
2. Remove the propellant grains from the carboard insulator.
3. Install the cardboard insulator and center it in the case.
4. Slide the propellant grains into the insulator and center them.
5. Ensure all spacers and O-rings are in place and screw the forward closure to the case.
6. Install the aft spacer in the case, place the nozzle in the aft closure and install the aft O-ring.
7. Screw the aft closure into the case. Ensure the nozzle is correctly centered and not canted.
8. Carefully add the ejection charge powder to the charge well. Tap the top of the case so the ejection charge grains fill the area between the delay element and the forward closure.
9. Place the red cap over the ejection charge.
10. Install the motor in the rocket.

 

[Steinerino]

Just heard back from Aerotech on this. Turns out, with a plugged, stepped forward closure, we should not use the delay o-ring OR the forward delay spacer. We also need to grease the forward end of the delay element --- otherwise could cato the motor. They noted that the development and communications around this new closure was not cleanly done.

 

[Antares JS]

Turns out, with a plugged, stepped forward closure, we should not use the delay o-ring OR the forward delay spacer.

That does make sense when I think about it. The delay o-ring is to prevent any hot gas from touching the ejection charge before the delay burns through, and I assume the spacer is to ensure some powder can fill that space in the center and ensure a decent amount of contact beyond just the touch hole for the ejection charge. Both issues are moot if there is no ejection charge.

 

[Zeus-cat]

Glad you got the problem solved. Good luck with the flight.

 

[rcktnut]

What exactly is a stepped forward closure? Plugged end burner, plugged/ tapped? Looks like lots of guys never heard of them as well as myself.

 

[Steinerino]

If you see the picture I posted, there is a step in the forward portion of the closure to accept the delay grain - but not the delay insulator. I believe other forward closures are flat at the top.

 

[rcktnut]

OK, I see the little step now. True that the other plugged forward closures are flat at the top and assemble "normally." Now to go to the Aerotech thread to find out the purpose of the step, design change. One would think it would be much easier to machine the closures without the step. There must be some good reason for the change.
Just thinking about it, it could be to eliminate the " air lock" experienced when using the delay o-ring. The o-ring does compress the air in front of it when inserting the delay element into the closure. Never had a problem doing it, I just insert it very slowly.