A Mistake Proofing Technique for Dual Deployment

[Rocketclar]

Mistake proofing is a technique used in production systems. It's a way to minimize errors. (A common mistake proofing example: you can't put your AT car into gear unless you have your foot on the brake. Modern cars use a number of mistake proofing items to help us not make errors.) One of the ways I've applied the concept in rocketry is to use different electrical connectors for the drogue and main charges. The 4 wire connector to attach the 2 mains charges (1+1 for redundancy) uses a male connector whereas the one to attach to the 2 drogue charges uses a 4 wire female connector. My safe switch connections are also set up differently for the redundant altimeters and are of a different connector (2 wire) type, again using female for one and male for the other. With these connectors set up this way, there is only one way to hook them up thereby eliminating the possibility of having an altimeter fire the wrong charge.

 

[rharshberger]

Mistake proofing is a technique used in production systems. It's a way to minimize errors. (A common mistake proofing example: you can't put your AT car into gear unless you have your foot on the brake. Modern cars use a number of mistake proofing items to help us not make errors.) One of the ways I've applied the concept in rocketry is to use different electrical connectors for the drogue and main charges. The 4 wire connector to attach the 2 mains charges (1+1 for redundancy) uses a male connector whereas the one to attach to the 2 drogue charges uses a 4 wire female connector. My safe switch connections are also set up differently for the redundant altimeters and are of a different connector (2 wire) type, again using female for one and male for the other. With these connectors set up this way, there is only one way to hook them up thereby eliminating the possibility of having an altimeter fire the wrong charge.

You can further eliminate issues by wiring the ematch directly to the altimeter terminal blocks so there are no connectors at all between the altimeter and the charge.

 

[Rocketclar]

Here is a picture of my sled with the PerfectFlite Stratologger CF and the redundant MissleWorks RRC2+. This is interchangeable with other bays for different rockets. Using the quick disconnects, allows for easy and fast changing between rockets.

 

[mpitfield]

I have taken this approach as much as possible, I call it ID 10T proofing. On one rocket I had the electrical ID 10T proofed, however in my haste, I inserted the altimeter sled into the bay backwards. So electrically it was connected property and to the correct AV bay bulkheads, however it resulted in a long walk. To ID 10T proof it I keyed the altimeter bulkheads. Now this rocket could literally be properly assembled by a drunk 6 month old blind monkey.

 

[KenRico]

Here is a picture of my sled with the PerfectFlite Stratologger CF and the redundant MissleWorks RRC2+. This is interchangeable with other bays for different rockets. Using the quick disconnects, allows for easy and fast changing between rockets.View attachment 302054

I do this too ..with almost identical 4 pin JST SM connectors for the bulk heads and the 2 pins JST SM for switches mounted in the bands if needed .

Like mpitfield , I can pull the entire thing apart like and put back together again without tracing any wires because the connectors are reversed so they only plug in one way .. I also mount the all threads to the aft lid with nylon nuts and a nut on the other side of the lid so they are locked in tight and wing nuts to secure the forward lid ..now I dont have to write 'main' or drogue on the lids .

On the sled I like to have the wires running on the underside and have holes drilled for the wires to come through and connect .. each hole corresponding to the altimeter terminal blocks . If I pull the altimeter , can remount without tracing the wires .

Previously I used the sled to fill the space with no runners ala CJ ..but have started using the tubes underneath again as they show me where the all threads will pass through and allow me to lock down the wiring without binding with sled insertion or removal , it allows me to use longer relief wires to the lids without them being caught too . I do try to fill the space forward and backwards with the sled - so that when buttoned up it cant shift more than a hair. Guess I wont be buying any 3d sleds anytime soon .

Kenny

 

[K'Tesh]

I think I will have to try some of these... However, I don't think I'll be looking for any 6mo, blind, drunken monkeys.

 

[Nick@JET]

I have taken this approach as much as possible, I call it ID 10T proofing. On one rocket I had the electrical ID 10T proofed, however in my haste, I inserted the altimeter sled into the bay backwards. So electrically it was connected property and to the correct AV bay bulkheads, however it resulted in a long walk. To ID 10T proof it I keyed the altimeter bulkheads. Now this rocket could literally be properly assembled by a drunk 6 month old blind monkey.

This ^^
I'll be doing the same.

For the connectors I also color code and female one side make the other - so it is not possible to install AV Bay, sled or bulkheads backwards, because I resemble the ID 10T remark on occasion

 

[Woody's Workshop]

When you do K'Tesh, I Volunteer! You Buy. And I warn you, it takes at least 2 5ths of Jameson's to even get me to feel it!

I think I will have to try some of these... However, I don't think I'll be looking for any 6mo, blind, drunken monkeys.

 

[OverTheTop]

Poka-yoke is the fancy term they use for it in manufacturing sometimes. A useful thing to use, along with KISS, where appropriate.
https://en.wikipedia.org/wiki/Poka-yoke

 

[les]

Mistake proofing is a technique used in production systems. It's a way to minimize errors. (A common mistake proofing example: you can't put your AT car into gear unless you have your foot on the brake. Modern cars use a number of mistake proofing items to help us not make errors.) One of the ways I've applied the concept in rocketry is to use different electrical connectors for the drogue and main charges. The 4 wire connector to attach the 2 mains charges (1+1 for redundancy) uses a male connector whereas the one to attach to the 2 drogue charges uses a 4 wire female connector. My safe switch connections are also set up differently for the redundant altimeters and are of a different connector (2 wire) type, again using female for one and male for the other. With these connectors set up this way, there is only one way to hook them up thereby eliminating the possibility of having an altimeter fire the wrong charge.

You can further eliminate issues by wiring the ematch directly to the altimeter terminal blocks so there are no connectors at all between the altimeter and the charge.

Great examples of engineering / personal trade offs

Using different connectors helps minimize human error of miss-connecting the main and drogue, but adds another set of connectors that themselves are a failure path
Directly wiring to the altimeter terminal blocks eliminates the potential failure of an additional set of connectors, but allows for human error by miss-connecting the drogue and main wires.

Which is better? You can try to minimize the human error by having check lists and double/triple checking your work, but humans will still find a way to make a mistake. In a hurry, interrupted by people stopping by while assembling, etc.
Conversely, on my job I have determined the area with the highest failure rate are the blinkity-blank connectors......well, maybe relays are worse....

I think the correct answer will come down to personal preference

 

[K'Tesh]

Poka-yoke is the fancy term they use for it in manufacturing sometimes. A useful thing to use, along with KISS, where appropriate.
https://en.wikipedia.org/wiki/Poka-yoke

Thanks for that!

I learned something new tonight... Though I like the term Baka-yoke more than Poka-yoke.

 

[Lowpuller]

Rocketclar,

On Post No. 3 pic, I don't understand what your doing with the 2 pin JST connector. I tried to trace out the wires but they cross over each other and I may be getting on the wrong wire. Can you explain further or send a simple wiring diagram?

Thank you,

 

[cwbullet]

You may reduce mistakes, but eliminating them is never gonna happen.

 

[mpitfield]

You can try to minimize the human error by having check lists and double/triple checking your work, but humans will still find a way to make a mistake.

Ah yes the old checklist. I started to make one but have not finished it yet. I think it is a great idea just as one more prompt before flight...plus it's so NASA. Problem is I keep forgetting to finish the darn thing. :bangpan:

 

[OverTheTop]

Don't forget to add an item to the checklist at several locations: "All previous items on the checklist completed?".

Depending on the project you can add: "pause, breathe", and/or "take photographs"

 

[Rocketclar]

Hi. The 2 pin JST connectors (one male and the other female) go to my external mounted screw switch which has the corresponding mates. There is a separate switch for one of the altimeters. When I turn on the screw switch one altimeter powers up and beeps out its codes. If OK, I pull a "remove before flight brass rod" that activates the other altimeter and listen to its codes. The 4 wire plugs (again, one male the other female) go to their corresponding mates to the bulkheads. The mated set of 4 wires goes thru the bulkhead to attach to 2 sets of terminal blocks. I epoxied the holes the wires pass thru to minimize ejection gases getting to the electronics. I even use different size ejection charge holders for the backups. See attached.
I also use different igniters for 1st and redundant charges.....Quest Q2 for one and JTEK firewires for the backup. I've had great success with the Quests....and OK with the JTEKs once I got their replacement for the bad lot I first got.

 

[Lowpuller]

This is a great help thank you!

Do you have an inside pic of the switch?

Where can I get the switch?

Why do you use different size charges?

 

[Rocketclar]

The switches are available at: https://aeroconsystems.com/cart/switches/ I use the 'Through Mount Slotted Switch'. I've had good luck with them. It takes a small flat screwdriver to turn them. After soldering the JST connectors, I cover the contacts with electrical tape since I don't want to short out the battery(s) when I slide the sled in with the metal all-threads. The pic shows the inside you requested along with a picture of a switch. While the charge containers are different size pipe, they contain the same amount of charge based on calculations and ground testing. [Can't stress the importance of ground testing! I video my ground tests....but that's a whole different topic.] As stated above, I put one type of igniter in one and another type in the other pipe canister. Part of the reason is for space too. Again, I try to use standard parts to go between rockets. With small diameter rockets (2-3"), I use the smaller canisters.

 

[Lowpuller]

So what's wrong with videoing your ground testing😀😀😀😀

https://youtu.be/l7tsDRP2D18

https://youtu.be/eMkJMdoy2Hs

 

[Lowpuller]

Thank you for sharing the additional picture and the switch source.

 

[crossfire]

Jolly Logic chute release. I have 6 flights using one and have work perfect.

 

[rharshberger]

The switches are available at: https://aeroconsystems.com/cart/switches/ I use the 'Through Mount Slotted Switch'. I've had good luck with them. It takes a small flat screwdriver to turn them. After soldering the JST connectors, I cover the contacts with electrical tape since I don't want to short out the battery(s) when I slide the sled in with the metal all-threads. The pic shows the inside you requested along with a picture of a switch. While the charge containers are different size pipe, they contain the same amount of charge based on calculations and ground testing. [Can't stress the importance of ground testing! I video my ground tests....but that's a whole different topic.] As stated above, I put one type of igniter in one and another type in the other pipe canister. Part of the reason is for space too. Again, I try to use standard parts to go between rockets. With small diameter rockets View attachment 302403(2-3"), I use the smaller canisters.

I believe those "through mount slotted switches" are the very same Schurter switches of which one vendor recently posted a problem with, and one of our TRF members has had a failure with, I could be wrong. Here is the thread https://www.rocketryforum.com/showt...ter-switch-notice&highlight=schurter+switches

 

[dshmel]

I use well nuts and pass the e-match wire through the bulkhead for a continuous wire. Very simple.

 

[rharshberger]

I use well nuts and pass the e-match wire through the bulkhead for a continuous wire. Very simple.
View attachment 302493
View attachment 302494

+1, this is my preferred method as well.

 

[cerving]

I use well nuts and pass the e-match wire through the bulkhead for a continuous wire. Very simple.
View attachment 302493
View attachment 302494

I've done the same thing but plugged the hole with tacky putty. I like your technique better... time to go to Ace and get some well nuts.