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Cut hole into AT ejection charge cap?

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billdz

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The instructions for some of my AT DMS and RMS motors say that, after the red cap is pushed into the ejection charge chamber, we should cut a small hole in the cap with a hobby knife to release the air. The instructions for other similar motors don't say anything about cutting a hole. So, to cut or not to cut a hole?
 

tfish

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29-54mm DMS


You only cut the nozzle cap on DMS motors. See Buckeye's post for LMS motor instructions

2. Installing the Ejection Charge and Ejection Cap
2.1 Open the supplied igniter and ejection charge kit and remove the contents.
2.2 Place the ejection charge baffle washer into the ejection charge well of the motor bulkhead.
2.3. WARNING: Do not smoke and ensure that there are no open flames or heat sources nearby when installing the ejection charge. Open the ejection charge vial and dispense the desired amount of black powder ejection charge into the ejection charge well of the motor bulkhead. Use
about ½ of the contents of the vial for 2.6” diameter rockets and smaller, and the entire vial for 3” and larger rockets. Note: additional ejection charge may be required for rockets exceeding 4” in diameter.
2.4 Insert the rounded end of the ejection charge cap into the ejection charge well of the bulkhead and press in completely with the end of the igniter tube or similar object.


3. Igniter Installation and Preparation for Flight

3.4 Using a hobby knife or scissors, cut a corner off the end of the nozzle cap (if supplied) to produce a vent hole in the cap about 1/16”-1/8” wide.


Tony


See Buckeye's post below for LMS instructions....Thanks for the heads up Buckeye!
 
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rstaff3

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It's been a long time since I've read those instructions, but I thought the hole was supposed to go on the cap that holds the igniter in. Anyway, if you cut the top cap you risk the powder escaping before ejection. I have never done so :) But I have had non ejection events. But those are other stories.
 

Steve Shannon

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That would seem a recipe to dump ones ejection charge.
Well, it appears it's just an extremely tiny slit, not really a hole, to let captured air out. Now all of us who didn't read those instructions are slightly [emoji30] red faced. At least I am.




Steve Shannon
 

crossfire

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I have flew a fair amount of DMS motors and I just put some masking tape over ejection well for extra added security
 

billdz

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Thanks for the replies. I was asking about the red cap on the ejection charge well, not the cap on the nozzle. I flew today without puncturing the ejection charge cap, no problem. Not sure why DMS and LMS would be different, but I think it was LMS where I read about puncturing the cap.
 

crossfire

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What DMS motor did you use today?
 

jnelson

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Correct... LMS instructions mention venting the ejection cap. And DMS instructions do not. Seeing as both use the exact same cap, I'm not sure why there's a difference.

Speaking from persona experience, I'm in favor of venting the cap. I have seen un-vented caps pop right out of the ejection well. You are only making a tiny slit, nothing large enough to cause BP to fall out. I poke mine with an xacto, then flip the knife over and use the blunt end to push the cap the rest of the way into the well.
 

billdz

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@crossfire - I used an H550 DMS.
@TheTehk17 - What you say makes sense, I take it you poke holes even in DMS motors?
 

rstaff3

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That's good to know. I obviously never read the LMS instructions closely enough. I haven't used a lot of LMS or DMS, but haven't poked any holes and, luckily, never had a problem with them.
 

jnelson

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I take it you poke holes even in DMS motors?
Yes, but mostly just for consistency. Perhaps there is a reason why the DMS instructions don't mention the venting... maybe they really don't require it, who knows. It'd be interesting to hear from AT on why there is a difference between that and the LMS instructions.
 

crossfire

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billdz

The H550ST is a great motor. The last flight was on a 5 lb WM 3" Punisher to around 1600'. I have used 3 of them and all worked out well. I add a little extra powder and don't put any holes in well cap but like I said I wrap masking tape over well hole and use the ejection red cap/plug.
 

billdz

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@crossfire - Agreed, I used an H135 for my L1 test last month and this was the first time I used anything bigger. The H550 was way louder and stronger than the H135. Even with 2 cameras taped to the airframe, height was 2731', speed Mach 0.5, on a 4 lb Darkstar Jr. I will buy more H550s.

graph of flight of Pavel 3 on H550.jpg
 

Buckeye

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@crossfire - Agreed, I used an H135 for my L1 test last month and this was the first time I used anything bigger. The H550 was way louder and stronger than the H135. Even with 2 cameras taped to the airframe, height was 2731', speed Mach 0.5, on a 4 lb Darkstar Jr. I will buy more H550s.
That is a good looking set of acceleration/velocity data. What is the altimeter?
 

billdz

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Yes, Telemetrum on the rocket and an Android phone connected to a TeleBT on a homebrew yagi on the ground (see pic). Provides lots of data audibly and graphically.

yagi antenna.jpg
 

timbucktoo

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I have used a simple flexible scanner antenna with the TeleBT on flights up to 12k with no problems or loss of signal at all.

teleBT.jpg
 

billdz

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Thanks Tim, that's good to know, looks like my yagi is overkill, I can just use the rubber duck from my HT.
 

Walldiver7

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I have used a simple flexible scanner antenna with the TeleBT on flights up to 12k with no problems or loss of signal at all.

View attachment 318868
May 2016, I flew a 4" fg rocket to 22k + with a Telegps (10mw output... I think). I was tracking it with a 5 el yagi, and my friend was tracking it with a 3 el yagi. The trajectory of the rocket was bad; It was moving at above Mach at a 20 degree angle from vertical (landed 2.8 miles away). I had a signal on it all the way down to... less than 400'. He lost it somewhere after apogee. I am very surprised to here your scanner antenna did so well!
 

timbucktoo

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May 2016, I flew a 4" fg rocket to 22k + with a Telegps (10mw output... I think). I was tracking it with a 5 el yagi, and my friend was tracking it with a 3 el yagi. The trajectory of the rocket was bad; It was moving at above Mach at a 20 degree angle from vertical (landed 2.8 miles away). I had a signal on it all the way down to... less than 400'. He lost it somewhere after apogee. I am very surprised to here your scanner antenna did so well!
Two flights to 12k & one to 9k, never lost track at apogee and was able to track all the way down. Farthest recovery was 0.8 miles, never lost signal. Another guy I fly with uses same and has had same results.
 

billdz

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Note the thread about the updated TeleMini, which does everything the Telemetrum does except GPS for half the price:
https://www.rocketryforum.com/showt...tus-Metrum-releases-TeleMini-v3-and-AltOS-1-7

The graph I posted above does not show all the available data from Telemetrum/TeleMini, you can also graph pressure, range, distance, battery voltage, temperature, GPS satellites in view, etc. You can also get a text readout and a map of the flight, as shown below. Telemetrum has 40mw output, not sure about TeleMini.

GPS map.jpg


Flight stats.jpg
 
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