minimal supportive ematch hardware for chute deployment

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FMarvinS
Posts: 9
Joined: Tue Nov 17, 2015 11:24 am

minimal supportive ematch hardware for chute deployment

Postby FMarvinS » Wed Dec 30, 2015 5:11 pm

Hi,

I have always wanted to minimize the size of the hardware required for ematch support, especially on 38 mm to 2.56 inch diameter e-bays. I have "played" with several approaches including terminal blocks and the direct connection of the ematch (through the bulkhead) to the altimeter. I believe the following method may work well with minimal wasted space. One uses a female JST connector (I get mine from rail-buttons.com) which is placed outside the bulkhead and the leads are passed through a drilled bulkhead hole to be connected to the altimeter. Then the ematch lead ends are shortened to expose only 1/2 inch of bare copper lengths. Each bare copper tip is then folded in half. Subsequently each end is fitted into the appropriate JST receptacle with a modicum of pressure (see the first photo, JST-A). This leads to a moderately tight joint. Once completed, I suggest that overlapping or encirclement of the ematch leads around the base of the ematch be done. By this latter move, you ensure that the JST-ematch lead connections are strengthened and an inherent strain relief exists (see 2nd photo, JST-B). The pictures are of the set up with a 2.56 inch ebay and I mostly use the glove-finger tip ejection method. A small piece of heat resistant tape can also encircle the set up for further protection. I haven't field tested this yet; however, during the "ground testing" of my next several builds (to determine the required BP amount needed for parachute ejection), I'll definitely test out this approach. What are your thoughts & comments? I'd be interested in feedback.

Regards,
Fred (L2, TRA# 15606, ROSCO member)
Attachments
JST-B.docx
(324.41 KiB) Downloaded 323 times
JST-A.docx
(293.83 KiB) Downloaded 326 times

FMarvinS
Posts: 9
Joined: Tue Nov 17, 2015 11:24 am

Re: minimal supportive ematch hardware for chute deployment

Postby FMarvinS » Sun Mar 13, 2016 10:03 pm

Addendum:

The use of the female JST has worked well through multiple ground testing events. The use of 3M high temp Flu tape (viable to 600 degrees F) wrapped around the juncture of the JST & ematch and also to cover the drilled holes in the bulkhead have worked well with no deterioration from the BP charges. The 3M Flu tape is about $8 (15 yards) and available from walmart online.

Regards,
Fred

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patelldp
Posts: 160
Joined: Thu Nov 05, 2015 5:07 pm
Location: New York

Re: minimal supportive ematch hardware for chute deployment

Postby patelldp » Mon Mar 14, 2016 7:57 am

It's certainly a unique approach. I like that it's very streamlined and small, but obviously have the same concerns as you regarding how secure it is.

Adept has offered something alone these lines for a long time: http://www.adeptrocketry.com/HAR22cart.htm

"The ends of the two wire pairs that connect to the two deployment charges include a box connector. The ends of the deployment charge leads plug into these box connectors directly, so an additional terminal block or other connection gimmick is not necessary. The box connectors typically are brought out through holes in the two end bulkheads of the Altimeter Chamber. (Seal the holes where the wires pass through the bulkheads with putty or epoxy.) The ends of the deployment charge leads can easily be plugged into the box connectors. Strip the ends of the wires back about a half inch."

Image

If one can source the same box connectors (preferably with pre-installed leads) for less than the $10/3 that Adept is charging...sign me up. I'm guessing that the box connectors have some sort of positive retention method, but I could be wrong.
Dan Patell
TRA 10904 L3

Alexander
Posts: 46
Joined: Tue Nov 24, 2015 9:45 am

Re: minimal supportive ematch hardware for chute deployment

Postby Alexander » Mon Mar 14, 2016 6:23 pm

These look interesting, I already asked if they can disconnect too and they do. I think I will buy these later on in the future and give them a try.

http://www.amazon.com/gp/product/B018VY ... o_pC_S_ttl
Alexander Solis

FMarvinS
Posts: 9
Joined: Tue Nov 17, 2015 11:24 am

Re: minimal supportive ematch hardware for chute deployment

Postby FMarvinS » Tue Mar 15, 2016 11:55 am

Hi Dan,

I appreciate your response. The Adept products are very good (Tommy does a great job) -they are molex devices. The required tool & connectors are not inexpensive. The JSTs on railbutton.com are only $1.00 per pair. After several testing events, if attached as pictured in the initial post, I have found the connections are secure. The benefits are: 1. prep time for repeat flights is minimal since the e-match is connected outside the AV bay; 2. For smaller diameter rockets (e.g. 38 mm to 2.5 inches) there would be no need to install space consuming terminal blocks; 3. With only 2 connections (at altimeter & at JST-ematch juncture) there are fewer potential "failure" points.
Regards,
Fred

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Rich Holmes
Posts: 7
Joined: Fri Nov 06, 2015 3:06 pm

Re: minimal supportive ematch hardware for chute deployment

Postby Rich Holmes » Wed Mar 16, 2016 8:29 am

For convenience here are Fred's pictures without the DOCX wrappers.
Attachments
JST-A.jpg
JST-A.jpg (45.55 KiB) Viewed 3735 times
JST-B.jpg
JST-B.jpg (50.93 KiB) Viewed 3735 times
Rich Holmes
Camillus, NY
Syracuse Rocket Club newsletter editor

http://richsrockets.wordpress.com


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