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Best Practices for Reliable Electronic Deployment
#1
Its been kind of quiet here so I will fill the silence with series of posts on how to maximize reliability of your rocketry electronics.

It will be based on current industry best practices, some personal experiences, and observations from failures of others (because I have not had any personal failures in this area in my memory, however my memory is short.....).

Lets set of goal of NO electronic deployment failures this season.  It is possible.

We will cover all sorts of topics including, wiring, ematches, redundancy, batteries, switches and of course, electronics.
John Derimiggio
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#2
Can you add in diagnosis of cause post "failure" ?  I know you don't have any experience with this, but maybe just guess?

N
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#3
One of the largest opportunities for error and bad practice is the way we wire up our electronics.

1. Wire size.  Our electronics use very little power. Even when firing an ematch, the match will usually burn after a few tens of milliseconds at 500ma or so. Also the length of runs are very short.  A few inches from the battery to the altimeter is very common.  So don't obsess about wire size, 20 to even 28 gage wire will be fine.

2. Solid or stranded?.  This one is argued often.  The issue is not which construction is better but rather how we use the choice that we made. 

Stranded wire: 

Pros: Its flexibility. Finer wires are stronger than wires of the same material at larger diameters.
Cons: This is a big one.  Stranded wires are the worst choice for the common screw down terminals that are used on our electronics.  In fact, in Germany, (German's are really big on standards), using stranded wire in a terminal block is verboten!

Solid wire:

Pros: Best choice for terminal blocks.  Your house is full of solid core wire and screw down terminals.
Cons: Its stiff and easily weakened if nicked.

Most common wire treatment mistake. Tinning the ends of stranded wire with solder and using that in terminal blocks.
This is very bad, don't do it.
Tinning stranded wire actually makes it very weak and fatigue prone.  It WILL break there.

Secondly the contact in the terminal block will be bad.  Why? Because when you screw down on the soldered wire it will flow and relieve the contact pressure between the terminal and tinned wire.  (A lead bb doesn't bounce).

Solid copper wire is superior in this application because copper is relatively strong.  When copper wire is compressed in the terminal block it deforms elastically when means it is always pushing back against the terminals ensuring electrical contact and holding force.

So the question is how can we get the flexibility of stranded wire and be compatible with our terminal blocks?

The answer will be discussed in the next installment of the thread.  Use stranded wire with wire ferrules.
John Derimiggio
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#4
Great topic JD!
I am guilty of soldering my stranded ends.

May I add a good practice?
Having had to do so for my L 3 flight-
Bench testing my whole A/V bay with led lights for charges.
This practice for every flight will help work out the "bugs" of your deployment system. I have found several instances of needed improvements ( like loose wires).

This easy practice leads to greatly increase your succes rate. Not to mention the peace of mind that comes with the confidence of knowing your A/V bay will perform properly upon launching.
You never know if your alt was damaged in some way during the previous flight or not! How many of us actually run our electronics through it's test phase each time prior to use... or ever???
Chris Prinzi
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#5
The best practice, guaranteed reliable wire to electronics connection is stranded wire to wire ferrule to your terminal block.

Here are what these ferrules look like for 22ga wire.


[Image: AW05006_250px.jpg]

Here where you buy them.
http://www.ferrulesdirect.com/terminal/I...W05006.htm

You take your carefully stripped stranded wire, insert into the ferrule and crimp (not solder) the barrel of the ferrule around the wire.  Use this connection at your terminal block and you will have a no short robust electrical connection.

The crimping must be done very well, don't use pliers.  Either borrow or buy a good crimper. There is one on this site for $64 (FD2810HX).  Sounds like a lot of money but how much is your rocket and electronics worth?
John Derimiggio
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#6
John, those look great, thanks for the link!
I used 20 gauge stranded in my ebay, so going to their site, and looking at the specs for 20 gauge ferrules, the pins' OD would be 1.5mm (vs 1.3 for the 22 gauge), and measuring the MARSA4 and Pefect Flight connectors, from what I can see 1.3mm would work fine, but it appears 1.5mm is just a wee bit too large, so I guess I am stuck with the older way...
The other option I suppose would be to cut strands out of the ends of the 20 gauge wiring, before crimping, but I don't like the idea of doing that..
Any suggestions?
Greg
Greg Young - L3
NAR #42065
TRA #00234
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#7
(03-18-2013, 05:58 PM)gyoung link Wrote:John, those look great, thanks for the link!
I used 20 gauge stranded in my ebay, so going to their site, and looking at the specs for 20 gauge ferrules, the pins' OD would be 1.5mm (vs 1.3 for the 22 gauge), and measuring the MARSA4 and Pefect Flight connectors, from what I can see 1.3mm would work fine, but it appears 1.5mm is just a wee bit too large, so I guess I am stuck with the older way...
The other option I suppose would be to cut strands out of the ends of the 20 gauge wiring, before crimping, but I don't like the idea of doing that..
Any suggestions?
Greg

I would go with the thinning of the strands option, you are doing more abuse to those strands when you clamp them in the connector.

1.3mm is marginal for the MARSA connector.  I am counting on a little loss of diameter when it is crimped.  I have some on order to see.  May need to go to 24ga for a proper fit.

Phoenix Data sheet here
http://catalog.phoenixcontact.net/phoeni...neral=enen

Note the range between min and max tightening torque (typical for screw down terminals).  It is difficult to hold that range with stranded wire.  You have a better shot with solid core or a ferrule.
John Derimiggio
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#8
Very true John, but for things I move around a bit, I prefer stranded, as I have had too many solid wires break with repeat movement.
Since I plan to pull out the dual altimeter sled and use it for my L3 project, I will need to remove and replace the leads several times going between the 2 rockets.
I am thinking of installing some quick connects to make it easier... not to mention faster!  Smile
Greg Young - L3
NAR #42065
TRA #00234
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#9
(03-18-2013, 08:39 PM)gyoung link Wrote:Very true John, but for things I move around a bit, I prefer stranded, as I have had too many solid wires break with repeat movement.
Since I plan to pull out the dual altimeter sled and use it for my L3 project, I will need to remove and replace the leads several times going between the 2 rockets.
I am thinking of installing some quick connects to make it easier... not to mention faster!  Smile

Greg, I suggest Dean's connectors for those ones you have to pull apart. They have a very tight fit when connected and are very reliable. They are used in R/C everywhere ( I use them on my altimeter bays :-) )

David
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#10
Thanks for the suggestion David!
Can you help me out a bit, as I am not familiar with Dean's connectors??
If they are also designed for smaller gauge wiring, I may just have to bite the bullet and pull the 20 gauge wiring and go smaller, especially given the ferrules John suggested are designed to work with 22 gauge!
Greg
Greg Young - L3
NAR #42065
TRA #00234
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