Creating an Electronics Bay For the First Time, Need Your Two Cents

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thef-equals-ma-isstrong

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Designing an electronics bay for my college's rocket team. I'm actually going to school for mechanical engineering, but the masochistic part of me decided that I should step out of my lane and design a low-EE-skill-required electronics bay, so here I am.

I'm creating a high-powered rocket electronics bay for the first time, estimated apogee is 10,000 feet, would love people to tear apart my initial design so I can make the necessary adjustments before I find out the hard way.
-----

My plan is to use two StratologgerCfs for redundant flight data tracking. They'll both be powered by two 9-volt batteries. I'll be integrating two remove-before-flight switches as well for both of the stratologgers.

For telemetry we're planning to use an Altus metrum telemega (AMT), and looking into seeing if we can hook in our stratologgers for active telemetry reporting. I'm currently in the process of getting my ham radio license so we have all the legalities sorted out before using it.
-----

A couple questions I have:
1. Are their more inexpensive components that are just as reliable that don't take a whole lot of electrical-engineering know-how?

2. We're looking into redundant telemetry/rocket-locator components: As last year's rocket we ended up relying on one mediocre GPS module that ended up not working (read: We spent 12 hours in a New Mexico desert in the hottest week of the year looking for our rocket so we really don't want to make this mistake again). Seemed a bit overkill to get two AMT's, are there any suggestions about a backup system we could get that wouldn't be ask expensive?

3. Any other things I forgot/should be paying extra-special attention to when designing this electronics bay?

Thank you so much in advance for any advice you have to offer.
 
1. The Eggtimer (these have to be built from a kit) and Missile Works range of altimeters and GPS tracking hardware are cheaper alternatives to Altus Metrum devices. The AM EasyMega and TeleMega are very good, but would be a better choice for 2-stage rockets with their angular sensing capability for staging.

2. Any of the above would be good for backup. The StratologgerCFs are a good choice for an altimeter with telemetry output. The Missile Works RRC3 with the RTx GPS system offers combined telemetry. The MW T3 GPS system is a cost effective tracking system, too. The Eggtimer TRS system offers an altimeter with GPS telemetry.

3. You can obtain 3D-printed avbay sleds from various vendors, e.g., Missile Works.
 
What exactly are you wanting to come through the telemetry link? Just GPS location or do you want speed, altitude, distance from you, bearing to rocket, heading and all that stuff?

I am not familiar with the Telemega but I think a few guys at our launch uses them and they work pretty well. Not sure if the Stratologger has telemetry capabilities, but I have never flown one of those either.
Missileworks has a telemetry and tracking system with a smaller price tag than the AMT. Never used that particular setup but I have used the RRC2+ and RRC3 quite a bit.

If you are up for building some electronics or having one on your team do it, you can save some money by going with Eggtimer products. The Quark and Eggtimer have telemetry capabilities but you have to have a 3DR type radio and some sort of program to decode the data. I have the two Quarks, an Eggtimer and a radio but haven't made any progress toward the software side of things. The Eggfinder and Eggfinder mini are GPS locators, as well as the Eggtimer TRS which brings dual deploy and GPS all in one package.
 
I love the Altus Metrum TeleMega. Works well and the software is worth paying money for. Very professional. Unfortunately not entirely inexpensive.

The Egg products are quite good also, and very well priced. I have built a few but never quite got around to flying them yet.

Remember when building the avionics bay that everything needs to be able to withstand the maximum acceleration of the rocket with highest peak thrust motor you plan on putting in it. If you expect 25G acceleration then everything "weighs" 25 times more than it usually does. There are also impulse accelerations that are caused by things like ejection charges that need to be allowed for.

Lots of things to consider. I am sure others will chime in with many thoughts. Thanks for asking ;).

Here is an example of one of mine FYI. Many ways to skin a cat: https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019&start=60
 
A few questions.

What do you want to accomplish/track with the logging?

Are you set on your electronics?

What is your budget?

As others have mention the egg timer stuff is reasonable and should work fine for your application.

The Missileworks stuff is solid. An RRC3 with the RTx would set you back less that $400, and will give you a solid 3 event flight computer, gps, and data logging. An Rrc2+ cannot he beat as a backup altimeter in my estimation.
 
As far as assembly, the Stratologger CF is easy to use and easy to wire. I like the feature of having a set of terminals for the switch as opposed to having the switch inline with the battery. It's not really a big deal, but I find it easier. The Missileworks RRC3 looks pretty similar although I've only used (and been happy with) the RRC2. Whatever you do, make sure you ziptie or otherwise secure all wires to the sled at the altimeter, at the switches or terminal blocks they connect to, and along the way if they have long runs. You can't have too many zip ties.

Reading between the lines, it looks like you're planning for IREC. If so, you might not be able to use Eggtimer products if IREC's safety rules require professionally-soldered deployment altimeters. I'm not exactly sure what the rules are, so check them out. There is a possible loophole where there's a guy who will assemble the Egg products for you--you might check that out because that may still be less money than the other options.
 
I started a company called SMT Designs a while back. I just became a sponsor this morning because of your question. I have created a series of parts that can be used in the design of electronics bays. The parts are for both traditional bay designs, as well as my own "all-in-one" modular bay. You may find some ideas in the parts, documentation, photos of my past projects, etc. Naturally, it would be great if you decided some of SMT Designs parts are what you were looking for. If all you find are schematics and some photo that takes you in the direction you want to go in your project, frankly that is just as good.

best regards, Steve Thatcher
 
MikeyDSlagle said:
What exactly are you wanting to come through the telemetry link? Just GPS location or do you want speed, altitude, distance from you, bearing to rocket, heading and all that stuff?

I am not familiar with the Telemega but I think a few guys at our launch uses them and they work pretty well. Not sure if the Stratologger has telemetry capabilities, but I have never flown one of those either.
Missileworks has a telemetry and tracking system with a smaller price tag than the AMT. Never used that particular setup but I have used the RRC2+ and RRC3 quite a bit.

If you are up for building some electronics or having one on your team do it, you can save some money by going with Eggtimer products. The Quark and Eggtimer have telemetry capabilities but you have to have a 3DR type radio and some sort of program to decode the data. I have the two Quarks, an Eggtimer and a radio but haven't made any progress toward the software side of things. The Eggfinder and Eggfinder mini are GPS locators, as well as the Eggtimer TRS which brings dual deploy and GPS all in one package.
Click to expand...

GPS location at a minimum, the rest would be nice but would be contingent on setup/expense.
 
OverTheTop said:
I love the Altus Metrum TeleMega. Works well and the software is worth paying money for. Very professional. Unfortunately not entirely inexpensive.

The Egg products are quite good also, and very well priced. I have built a few but never quite got around to flying them yet.

Remember when building the avionics bay that everything needs to be able to withstand the maximum acceleration of the rocket with highest peak thrust motor you plan on putting in it. If you expect 25G acceleration then everything "weighs" 25 times more than it usually does. There are also impulse accelerations that are caused by things like ejection charges that need to be allowed for.

Lots of things to consider. I am sure others will chime in with many thoughts. Thanks for asking ;).

Here is an example of one of mine FYI. Many ways to skin a cat: https://forum.ausrocketry.com/viewtopic.php?f=6&t=5019&start=60
Click to expand...

Good to know. I'm planning to run random vibration simulations in Solidworks as I've done similar testing with another club I'm part of: So will definitely be sure to verify that the boards can survive 25g.

Also checked out your post: Beautiful altimeter bay. Also never would've thought to have used the fiberglass/lathe/manual mill combination as I would've probably just 3D-printed my whole avionics bay like a plebian. Will definitely be taking some pointers haha
 
markkoelsch said:
A few questions.

What do you want to accomplish/track with the logging?

Are you set on your electronics?

What is your budget?

As others have mention the egg timer stuff is reasonable and should work fine for your application.

The Missileworks stuff is solid. An RRC3 with the RTx would set you back less that $400, and will give you a solid 3 event flight computer, gps, and data logging. An Rrc2+ cannot he beat as a backup altimeter in my estimation.
Click to expand...
What do you want to accomplish/track with the logging?

GPS tracking at a very minimum. Altitude/bearing/heading would be nice as well but not necessary.

Budget:
For the avionics bay around $500-1k. Might be getting more depending on how fundraising goes (also a duty that's falling on my shoulders), but this is the rough range.

Not set on my electronics: Was mostly just positing the ones we used on our previous rocket and seeing what improvements people had.
 
boatgeek said:
As far as assembly, the Stratologger CF is easy to use and easy to wire. I like the feature of having a set of terminals for the switch as opposed to having the switch inline with the battery. It's not really a big deal, but I find it easier. The Missileworks RRC3 looks pretty similar although I've only used (and been happy with) the RRC2. Whatever you do, make sure you ziptie or otherwise secure all wires to the sled at the altimeter, at the switches or terminal blocks they connect to, and along the way if they have long runs. You can't have too many zip ties.

Reading between the lines, it looks like you're planning for IREC. If so, you might not be able to use Eggtimer products if IREC's safety rules require professionally-soldered deployment altimeters. I'm not exactly sure what the rules are, so check them out. There is a possible loophole where there's a guy who will assemble the Egg products for you--you might check that out because that may still be less money than the other options.
Click to expand...

Zipties were a club favorite for last competition's launch: Will be sure to repeat.

I mean, I can neither confirm or deny that IREC's the plan again, but the rule about professionally-soldered altimeters is something I didn't know about till now. Will be sure to keep that in mind when looking at components.
 
If professionally soldered components is a requirement, then Eggtimer would be out. Unless you can hire someone to do it for you professionally, as boatgeek mentioned. I guess it would depend on their definition of "professional". I am an Electronics Tech by title...but I don't solder as part of my job.

You could get the Missileworks T3 GPS tracker and an RRC2+ altimeter and come in under 200 bucks. The RRC3 is a bit more expensive but has lots more features: it has software so you can program via a computer, download flight data and so on. Run one as a primary and one as a backup, you will still come in under 300. Add some of the screw switches and sleds for the altimeters and T3 and your all set. All you have to do is hook up the wires. You can actually make a solder free sled if you wanted to.

Jim (Missileworks) has mentioned a telemetry package (real time altitude and velocity maybe) in the works that will hook right into the RRC3.
 
thef-equals-ma-isstrong said:
Good to know. I'm planning to run random vibration simulations in Solidworks as I've done similar testing with another club I'm part of: So will definitely be sure to verify that the boards can survive 25g.

Also checked out your post: Beautiful altimeter bay. Also never would've thought to have used the fiberglass/lathe/manual mill combination as I would've probably just 3D-printed my whole avionics bay like a plebian. Will definitely be taking some pointers haha
Click to expand...
Vibration sims are probably not entirely in line with what forces rocket components experience. They are generally quite one-sided and forceful in their environment, and I assume the simulations are swept-sine or random frequencies for finding resonances. You will learn something but it will probably require careful interpretation.

Thanks regarding the alt bay. 3D printing is great. Don't add more fiberglass just because that is what I have used. Materials, including 3D printed plastics, have strengths that are calculable and you can design with suitable parts with the different materials. Design and work with what you have available and within reasonable reach of your skillset and tools to improve chances of success. Don't be afraid to push the envelope if you are comfortable in extending that space :).

boatgeek said:
Whatever you do, make sure you ziptie or otherwise secure all wires to the sled at the altimeter, at the switches or terminal blocks they connect to, and along the way if they have long runs.
Click to expand...
I don't move my wiring around much so I generally fix the wires in place on the sled with small drops of CA adhesive (I use Loctite 401 tyipcally). Lots of options and methods.
 
Last edited:
What I've learned from watching college teams at my local club is this- make darn sure you can reach your avbay! A key switch does you no good if you can't turn it.
 
1. Since you will get a ham license, my comments will pertain to ham frequency units (although the egg finder units are also very good). You may want to consider a 440 MHz tracking transmitter as a back up to a GPS tracker. I highly recommend the BRB 440 MHz tracking transmitter (the 100 mw choice). If fully charged, it transmits for over 12 hours and with the right yagi and hand transceiver will work very well. I use it on all my flights.
2. In terms of telemetry, you'll have to check the coding and compatibility of the stratologger CF output with the transmitter you want to use, there is minimal info on that in the stratologger instructions. BTW the stratologger is a great choice for an altimeter. Also, as stated above, your GPS unit will report changes in altitude with the coordinate NMEA strains for many ham frequency based GPS units (e.g. BRB, Byonics MT-1000, etc). I highly recommend the Byonics MT-1000, it transmits NMEA, altitude, battery voltage, and temperature. If you receive the Byonics (or BRB) transmissions on a Kenwood 72A (or similar HT) then the altitude, and GPS coordinates are readily available. I believe the BRB records flight NMEA info for later downloading. I simply installed an OpenLogger on a Byonics MT-1000 and easily view flight info/trajectory profiles on Google earth. The BRB GPS unit transmits at 100 mw on the 70 cm band; whereas, the MT-1000 transmits 1 watt on the 2 meter band. Also, the BRB has a smaller foot print than the MT-1000.
3. As stated above, placement of your switches/AV-bay is important if you want to avoid the need for a ladder. There are several ways around that such as : use the eggfinder Wi-Fi switches or use a magnet on a long rod with the featherweight magnetic switches.
4. With regards to the micro snap switches, you may want to 3D print an enclosure that holds 2 switches adjacent so that only one pull-pin is needed to activate (sequentially) both switches (I posted my set up on this some time ago with pictures-if interested, you can do a TRF search or PM me).

Good Luck!
Fred, L2
member ICBM,
Camden, S.C.
KG4YGP
 
FMarvinS said:
3. As stated above, placement of your switches/AV-bay is important if you want to avoid the need for a ladder. There are several ways around that such as : use the eggfinder Wi-Fi switches or use a magnet on a long rod with the featherweight magnetic switches.
4. With regards to the micro snap switches, you may want to 3D print an enclosure that holds 2 switches adjacent so that only one pull-pin is needed to activate (sequentially) both switches (I posted my set up on this some time ago with pictures-if interested, you can do a TRF search or PM me).
Click to expand...

I use pullpins exclusively these days. So easy. I have used up to four switches on each pin.

As for pulling them out, just attach a long string to the pin and pull it out from ground level. No ladder needed ;).
 
OverTheTop said:
I use pullpins exclusively these days. So easy. I have used up to four switches on each pin.

As for pulling them out, just attach a long string to the pin and pull it out from ground level. No ladder needed ;).
Click to expand...

But what kind of switch? Please tell me you are not using phono jacks
 
NEVER use phono jacks. They rely on the side force generated by the tip connections to ensure the outer ring connection is happening (maybe). The switch contacts in them are rubbish too.

AltsCompleted.JPG SuperCap.JPG

Omron microminiatures. Don't forget to buy the ones with NORMALLY CLOSED contacts ;)
 
As a follow up to my earlier post- The attached picture portrays the 2-switch arrangement with the "pull-pin" removed. Of note the width is 2 and 1/8th inch, depth-3/8 of an inch, and the height is 1 and 1/8th inch. As is, the 2 and 1/8th inch width is equivalent to 53.975 mm. I currently use these in 2.6 inch diameter rockets and larger. The pull pin diameter is 3/32 inches; thus, it easily slides through a 1/8th inch vent hole. A smaller encasement could be 3D printed for 54 mm diameter rockets if desired. Like Over the Top, I've printed assemblies for 4 switches utilizing only one pull pin. However, the 4 switch assembly fits 3 inch diameter rockets and larger.
I purchase SS-5GL13 switches from Digi-Key (about $2 each) and slightly modify the "arm" to more readily fit the enclosures.

Fred, L2

upload_2018-7-18_22-20-11.png
 
OverTheTop said:
Vibration sims are probably not entirely in line with what forces rocket components experience. They are generally quite one-sided and forceful in their environment, and I assume the simulations are swept-sine or random frequencies for finding resonances. You will learn something but it will probably require careful interpretation.

Thanks regarding the alt bay. 3D printing is great. Don't add more fiberglass just because that is what I have used. Materials, including 3D printed plastics, have strengths that are calculable and you can design with suitable parts with the different materials. Design and work with what you have available and within reasonable reach of your skillset and tools to improve chances of success. Don't be afraid to push the envelope if you are comfortable in extending that space :).


I don't move my wiring around much so I generally fix the wires in place on the sled with small drops of CA adhesive (I use Loctite 401 tyipcally). Lots of options and methods.
Click to expand...

Are you sure the sine sweep and random vibration simulations aren't enough for the forces on our electronics? Could possible be leaving out shock testing. Part of a club that's doing testing for a satellite that's most likely going on an ISS-resupply launch in a year or two, and according to the P-Pod/GEVS standards the only testing we're required to do for our satellite are the three tests above.

And good to know about the 3D printed stuff. Still super impressed by the fiberglass assembly haha
 
FMarvinS said:
1. Since you will get a ham license, my comments will pertain to ham frequency units (although the egg finder units are also very good). You may want to consider a 440 MHz tracking transmitter as a back up to a GPS tracker. I highly recommend the BRB 440 MHz tracking transmitter (the 100 mw choice). If fully charged, it transmits for over 12 hours and with the right yagi and hand transceiver will work very well. I use it on all my flights.
2. In terms of telemetry, you'll have to check the coding and compatibility of the stratologger CF output with the transmitter you want to use, there is minimal info on that in the stratologger instructions. BTW the stratologger is a great choice for an altimeter. Also, as stated above, your GPS unit will report changes in altitude with the coordinate NMEA strains for many ham frequency based GPS units (e.g. BRB, Byonics MT-1000, etc). I highly recommend the Byonics MT-1000, it transmits NMEA, altitude, battery voltage, and temperature. If you receive the Byonics (or BRB) transmissions on a Kenwood 72A (or similar HT) then the altitude, and GPS coordinates are readily available. I believe the BRB records flight NMEA info for later downloading. I simply installed an OpenLogger on a Byonics MT-1000 and easily view flight info/trajectory profiles on Google earth. The BRB GPS unit transmits at 100 mw on the 70 cm band; whereas, the MT-1000 transmits 1 watt on the 2 meter band. Also, the BRB has a smaller foot print than the MT-1000.
3. As stated above, placement of your switches/AV-bay is important if you want to avoid the need for a ladder. There are several ways around that such as : use the eggfinder Wi-Fi switches or use a magnet on a long rod with the featherweight magnetic switches.
4. With regards to the micro snap switches, you may want to 3D print an enclosure that holds 2 switches adjacent so that only one pull-pin is needed to activate (sequentially) both switches (I posted my set up on this some time ago with pictures-if interested, you can do a TRF search or PM me).

Good Luck!
Fred, L2
member ICBM,
Camden, S.C.
KG4YGP
Click to expand...

Super, super helpful advice: Really appreciate you going into this level of detail. Will definitely be double checking the telemetry output of the StratologgerCF to make sure it'll interface with our transmitter. In regards to switches: We're planning to put two snap-acting switches with the lever's perpendicular to a tiny hole on the outside so we can just slide in a long RBF pin to activate/deactivate them. Worked for our last launch pretty well, depending on where the electronics bay ends up getting placed we'll probably be doing that again.
 
thef-equals-ma-isstrong said:
Are you sure the sine sweep and random vibration simulations aren't enough for the forces on our electronics? Could possible be leaving out shock testing. Part of a club that's doing testing for a satellite that's most likely going on an ISS-resupply launch in a year or two, and according to the P-Pod/GEVS standards the only testing we're required to do for our satellite are the three tests above.
Click to expand...
You are right regarding vibration testing. If you are building satellites then the more robust vibration tests are needed. The ride to orbit is greatly extended compared to our HPR stuff. Peak accel there is typically a lot less, the boost phase much longer and a much longer duration aeroaccoustic problem as she slides off the pad. Shock testing would would be a much better approximation to our launch forces.
 
Last edited:
thef-equals-ma-isstrong said:
Super, super helpful advice: Really appreciate you going into this level of detail. Will definitely be double checking the telemetry output of the StratologgerCF to make sure it'll interface with our transmitter. In regards to switches: We're planning to put two snap-acting switches with the lever's perpendicular to a tiny hole on the outside so we can just slide in a long RBF pin to activate/deactivate them. Worked for our last launch pretty well, depending on where the electronics bay ends up getting placed we'll probably be doing that again.
Click to expand...

The StratoLoggerCF outputs ASCII at 9600 baud 8 bits 1 stop no parity. Electronically it is a 3.3v logic level and it only outputs data on the Tx line. It is advertised as real time and the altimeter is sampling at 50ms intervals, so I would expect output strings for the current AGL every 50ms or 20 times a second. It should work by just a two wire connection to anything that can take a serial link as long as the attached device uses TTL levels and does not have any pullups to +5 or anything higher than 3.3v.
 

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