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4" Electronics Bay Design for my Level 2 Cert Flight

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g.pitts

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I have designed and redesigned my electronics bay many times now. The first implementation was to create a sled using the PCB as the sled itself. I successfully used that on my Level 1 certification flight, so proof of concept was established.

I decided that I was solving a three dimensional problem using two dimensional techniques. Over the next couple of weeks I'll post more as stuff comes together (I hope!), but for now the photo below is what the bulkhead is shaping up to look like.

BTW, props to Nat Kinsey (natkinsey@gmail.com) who did the machining on the bulkheads - awesome guy and he does great work!

IMG_3659.jpg
 

BSNW

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Say, If you want some ideas, check out the Avionics Bay Thread in the Recovery pages/forum. LOTS of cool photos and great ideas on how folks put their bays together.
Andrew
 

g.pitts

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A little more progress on this activity. Here's a photo of the sled design with brass inserts installed. Two Eggtimer Quantum altimeters will be mounted in the area toward the top of the image, and an Eggfinder TX goes in the area toward the bottom of the image. I didn't have the Eggfinder TX in-hand when I designed the sled, but the idea is that the area on the bottom right is to secure (and protect) the antenna. Each of the three "buttes" printed in that area have a through-slot to accept a cable tie that is intended to secure the antenna. Now that I have the Eggfinder TX, I can dial-in the size of those things and remove a little material from the next revision of the sled.

IMG_3665.jpg


The backside of the sled houses three Turnigy 800 mAh 2S 20C LiPo batteries. There are no switches involved, but the batteries are sized to be able to operate the electronics for over five hours. I printed wire traps into the battery area to help manage the extra wire lengths of the power leads, but they're a little tighter than I would like to see. I am going to open them up a little more on the next revision to make them a little more field-friendly. Being able to work them in with your fingers is preferred to having to use a tool to press them in.

IMG_3667.jpg


Opening up the wire traps a bit will help manage the wiring better than what is shown in the photo below.

IMG_3672.jpg


Here's what the back-side looks like when it's all buttoned up:

IMG_3673.jpg


One final detail on the top-side of the assembly. I designed a simple PCB to cleanly route the power to the each device, and to get the altimeter charge outputs to the either end of the sled. The connectors used for power and altimeter charges are JST PCB mount (automotive) connectors. I used this particular connector family in a commercial design that had to endure high shock and vibration, and they worked out quite well. The connectors on either end are a two-piece Phoenix terminal block (only the PCB mount side is shown). This system is good enough to go well beyond any G-force my Level 2 attempt will see. I could change the connector orientation by 90 degrees on the PCB and have a lot more margin, but that would come at the expense of clean wire routing. What's here is "good enough" for this planned usage.

IMG_3669.jpg


That's pretty much where I am as of this morning. An improved sled design in a couple of areas is my next objective. More in another week or two.
 

BDB

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Very interesting. But why three batteries for two altimeters?
 

FMarvinS

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Nice work! You are more festidious than me. The detail work is excellent. I like the use of your lipo lead channels to confine the "clutter." I think I'll incorporate that concept into my future prints. I'm not familiar with all the ports on the surface pcb. Would you kindly offer more info Also, a completely wired sled in a photo would also be informative.

Fred, L2
ICBM, Camden, S.C.
KG4YGP
 

g.pitts

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Nice work! You are more festidious than me. The detail work is excellent. I like the use of your lipo lead channels to confine the "clutter." I think I'll incorporate that concept into my future prints. I'm not familiar with all the ports on the surface pcb. Would you kindly offer more info Also, a completely wired sled in a photo would also be informative.

Fred, L2
ICBM, Camden, S.C.
KG4YGP
Good morning Fred! Thank you for the kind words, much appreciated. The two wire connectors (J3, J4, and J8) on the PCB route power to the two altimeters and tracker - one connector for each device. And the two four wire connectors (J5 and J9) are for the altimeter charge outputs. I have the tracker and receiver built and tested, will post a photo of that setup soon. I have not yet built the two Eggtimer Quantum altimeters. If I can get a quiet night or two this week, I'll build and test those. Hoping to have a photo of the completed work in a week or two. Never enough time! :(
 

MikeyDSlagle

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Nice work!
Who printed the PCB? I have wanted to do something similar for a while but don't know where to get them made. I'll start and get sidetracked, a cheap reliable source would help tremendously.
 

g.pitts

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Nice work!
Who printed the PCB? I have wanted to do something similar for a while but don't know where to get them made. I'll start and get sidetracked, a cheap reliable source would help tremendously.
Thank you! I used OSH Park (oshpark.com). If you use KiCAD or EagleCAD, you can directly upload the board file for fabrication. They have a minimum of three boards per proto order. It's about as inexpensive as you can get for PCB fabrication since their business model is to buy a panel and put multiple customer designs onto that panel.
 

g.pitts

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Slow progress - tweaked the e-bay design a bit to remove some weight. In the meantime, here's what the bulkheads are shaping up to look like:

IMG_3683.jpg


Fastener lengths are WIP. These are too short, but they're what I had in-hand to test fit things. Red wiring = primary charge, Black wiring = redundant charge.

IMG_3684.jpg


I plan to flood the wire egress point with epoxy to seal out any gasses. The hardware used in the charge cannisters is a sealing flat-head fastener to help keep gasses from the canisters from entering the electronics bay. I also plan to put some epoxy into the holes to further seal things up.
 

FMarvinS

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Looks good! some suggestions & questions PM'ed
 

FMarvinS

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Slow progress - tweaked the e-bay design a bit to remove some weight. In the meantime, here's what the bulkheads are shaping up to look like:

View attachment 403911

Fastener lengths are WIP. These are too short, but they're what I had in-hand to test fit things. Red wiring = primary charge, Black wiring = redundant charge.

View attachment 403912

I plan to flood the wire egress point with epoxy to seal out any gasses. The hardware used in the charge cannisters is a sealing flat-head fastener to help keep gasses from the canisters from entering the electronics bay. I also plan to put some epoxy into the holes to further seal things up.
Looks good!! PM sent
 

MikeyDSlagle

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Thank you! I used OSH Park (oshpark.com). If you use KiCAD or EagleCAD, you can directly upload the board file for fabrication. They have a minimum of three boards per proto order. It's about as inexpensive as you can get for PCB fabrication since their business model is to buy a panel and put multiple customer designs onto that panel.
Cool. Thanks. I'll give em a look.
 

cerving

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Wow, beautiful work! I would suggest that you cover those exposed solder joints on the bulkplate PCB with some silicone sealant or some other removable insulator (you may want to replace the wires later for some reason), to keep the BP residue from shorting them out.
 

Buckeye

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This is really nice! Puts my crudely-soldered, plywood, altimeter sleds to shame :(
 

g.pitts

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Wow, beautiful work! I would suggest that you cover those exposed solder joints on the bulkplate PCB with some silicone sealant or some other removable insulator (you may want to replace the wires later for some reason), to keep the BP residue from shorting them out.
Thank you, Cris! I am planning to coat it with RocketPoxy top-side and also on the backside clearance hole. But perhaps I should use silicone instead - it does allow for rework whereas RocketPoxy is kinda permanent! ;)
 

g.pitts

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More progress, albeit slower than I'd like. I need to place yet another McMaster-Carr order, this time for nylon #4-40 screws for the altimeters.The Eggfinder antenna support ended up in the right spot, which is a miracle in itself. I have 1/32" adhesive-backed foam that I plan to put under the antenna, and then secure it lightly with a couple of zip ties.

IMG_3687.jpg


A better look at the wiring from the altimeters.

Who recognizes the font used on the Eggtimer Quantum altimeter stickers? :D

IMG_3688.jpg


IMG_3689.jpg
 

spigalau

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I love your OCD Mr Pitts... that's looking real good.

Have you checked height of the primary & secondary loops vs a 4" tube, you might be getting very close.
 

g.pitts

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I love your OCD Mr Pitts... that's looking real good.

Have you checked height of the primary & secondary loops vs a 4" tube, you might be getting very close.
OCD? Me? You must be mistaking me for someone else. ;)

The wire lengths are a bit of a quandary. They are currently larger than the vertical clearance allows, but then they conform to the available height when the assembly is slid inside the tube. I'm concerned that if I significantly shorten them, I may introduce a persistent stress in the wire and (more importantly) in the solder joints. I have a couple of ideas on how I might be able to tidy things up just a bit. :D
 

Voyager1

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This is very nice work. However, I do agree with Steve. Common mode rejection is the goal here. Also, if there is sufficient flexibility in the wiring it might be a good idea to cable tie it down.

I’m also thinking that with the proximity of the wiring (particularly the power) to the tracker antenna, it might be prudent to install ferrite sleeves at the ends entering the altimeters. I don’t know how tolerant the altimeters are to radiated and conducted RF interference from the tracker, but ferrite sleeves will help attenuate any conducted interference coupled into the power wiring from the antenna, along with the twisted cables. I’d probably include the deployment wiring too, in this case.

Personally, I prefer to install trackers, particularly their antennas, away from altimeters. Maybe you can use a short SMA-SMA patch cable and install the antenna on the outside of the bulkhead. In any case, bench testing might be a good idea prior to flight to see if there are any issues with interference on the altimeters’ deployment functionality.

You might not have any issues at all, but one thing you can be certain of is that the tracker RF will couple into the adjacent wiring.
 

g.pitts

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I recommend twisting pairs of wires to help reject noise.
This is very nice work. However, I do agree with Steve. Common mode rejection is the goal here. Also, if there is sufficient flexibility in the wiring it might be a good idea to cable tie it down.

I’m also thinking that with the proximity of the wiring (particularly the power) to the tracker antenna, it might be prudent to install ferrite sleeves at the ends entering the altimeters. I don’t know how tolerant the altimeters are to radiated and conducted RF interference from the tracker, but ferrite sleeves will help attenuate any conducted interference coupled into the power wiring from the antenna, along with the twisted cables. I’d probably include the deployment wiring too, in this case.

Personally, I prefer to install trackers, particularly their antennas, away from altimeters. Maybe you can use a short SMA-SMA patch cable and install the antenna on the outside of the bulkhead. In any case, bench testing might be a good idea prior to flight to see if there are any issues with interference on the altimeters’ deployment functionality.

You might not have any issues at all, but one thing you can be certain of is that the tracker RF will couple into the adjacent wiring.
Thank you both - you've given me food for thought, but bear with me - I'm a digital guy and not so much an RF guy. The power and charge leads from the altimeter to the PCB are close to perpendicular to the tracker antenna, so I'm not sure twisting those will buy me much. The traces on the PCB run parallel to the antenna and I'd expect them to be more of a factor in coupling with the antenna energy. There isn't a great deal I can do on the PCB short of the ferrite idea. To that end, @Voyager1, is there a particular one you would recommend and I'll check it out.

Perhaps @cerving will chime in around any sensitivities of the Eggtimer Quantum altimeter design when in proximity to the Eggfinder TX.
 
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spigalau

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OCD? Me? You must be mistaking me for someone else. ;)

The wire lengths are a bit of a quandary. They are currently larger than the vertical clearance allows, but then they conform to the available height when the assembly is slid inside the tube. I'm concerned that if I significantly shorten them, I may introduce a persistent stress in the wire and (more importantly) in the solder joints. I have a couple of ideas on how I might be able to tidy things up just a bit. :D
Thinking old school - is there a ribbon cable that would work with that plug system ?
 

g.pitts

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Thinking old school - is there a ribbon cable that would work with that plug system ?
Ah, there's a flashback! :cool:

I am using JST's JWPF series connectors for the 2-pin (power and ground) and the 4-pin (main and drogue charge outputs) connectors. I'm actually not too worried about shortening the 22 gauge wires - I have a plan for that. The unknown at this time is around the RF coupling from the Eggfinder TX and the supporting wiring and altimeters. It may be that I just need to ground test the heck out of this configuration to gain the confidence I need prior to an April launch. Or some combination of adding a suitable (3-4 Amps in the case of the charge lines) ferrite onto the PCB for each wire coming into or going out of the PCB.
 

g.pitts

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OK, a reset after some very solid constructive feedback was provided (thanks!). Here's what we're gonna launch with in April.

Top-side view of the sled with PCB and Altimeters mounted. I decided to go with switches on this design variant, and have strapping options (not installed yet) to either be "always on" or to provide switched power to the altimeters. A 3D printed cover (that is not yet designed) will mount using the center four fasteners, which will serve to guide a pin the can be used to "safe" the rocket. With TRA's recent pronouncement that all rockets must be unpowered until they are past the RSO table and (I believe) out on or around the pads, I'm glad I put this feature in the design. Wires could be cleaner from the PCB to altimeters - improvement opportunity. Maybe a fixture for soldering the wires would yield a better outcome.

IMG_3703.jpg


BTW, no one has attempted to guess where the font on the altimeter labels originated. The zero should give it away. :)

Back side view of the battery compartment. I went with a self-locating cover and two screws which I believe is a better design.

IMG_3704.jpg


The Eggfinder TX is going to ride in the nosecone. I'm going to put a quarter-wave antenna on this tracker, and I made a 3D model of the antenna and located it where it should go IF the SMA PCB edge connector is soldered straight. That's a TBD at this point. The SMA connector doesn't allow for a 3D printed standoff the way I prefer them to be done since it is too close to the mounting hole, so I'll have two (I hope) nylon standoffs securing the Eggfinder TX and the antenna will be secured by two zip ties.

IMG_3706.jpg


And the backside showing the battery compartment.

IMG_3707.jpg


And with the lid.

IMG_3708.jpg
 
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