Blue Raven in 29mm bulkhead form factor

[Adrian A]

This is probably premature, but I want to get this out there to gauge interest and to think through some last design decisions.

Background: I'm working on a 54mm-38mm 2 stage design for Balls this year that will be considered a Class 3 flight. Besides a bunch of documentation, one technical requirement that comes with a class-3 flight is redundant electronics. I already have a pretty tight 38mm av-bay for my sustainer with a Blue Raven and a tracker. How am I going to squeeze a redundant set of deployment electronics in there?



To make a long story short, after considering a bunch of options, I decided to try squeezing a Blue Raven into a circle that will fit into a 29mm coupler, with the same threaded rod concept as the Featherweight 29mm av-bay bulkhead. It was a very tight fit, but it looks like it can work:




This is a full-featured Blue Raven, with the same Bluetooth interface, measurement, storage, beeper, USB interface etc. as the original, which means that it will be 100% code-compatible with the Blue Raven. This is important, because while the hardware takes a month or two to design and get production boards done, the software for the Blue Raven has been a year and counting. This design also includes a battery connector and a magnetic switch built-in. Unlike the more flexible power options of the Blue Raven, it's only compatible with a 1s lipo. But the battery will be included. Ooh, I wonder if I could squeeze in a battery charger (doubtful)

I'm designing this so that you can put two of them on the same threaded rods for redundant deployment, and the space in between can be filled with two batteries and a Featherweight Tracker. The tracker will need to share power with one of the Blue Ravens. (that reminds me I need to squeeze in tracker power pads and a hole for the antenna.) The third and 4th channels that can be used for an airstart are accessible with plated through hole for soldering wires.

The idea is to go from this (my 29mm redundant Blue Raven av-bay, plus tracker):


to this (redundant Blue Ravens, 2 batteries and a tracker in one 2" long av-bay, where the Blue Ravens are simulated with 29mm passive bulkheads:


The spacing between one set of threaded rods is designed so that the tracker and the Blue Raven battery fit next to each other. For the other Blue Raven's battery, it will need to have a wired connection.

One question I have now is about the outer area of the board. Currently the outer boundary fits into a 29mm airframe, while the white circle shows the overlap area with the end of a coupler, which can be sanded off. I'm wondering if I should just leave off the outer overlap area. Since there are electrical components on both sides of the board, it can't be used to seal the end of a bay like the 29mm av-bay bulkhead can. Separate passive bulkheads will be needed to seal off the bay, so I think most installations would want to have the outer area sanded off anyway. Hmm.

 

[watheyak]

For the purposes of gauging interest, I would buy a few of these!

Cool idea for sure. I like short rockets.

 

[bad_idea]

1. This is amazing.
2. I would say leave off the outer ring.
3. Take my money! I'd be in for a few, and I've not even started designing avbays for my existing Blue Ravens yet.

 

[kjhambrick]

I love it Adrian.

.I vote: No outer ring.

I have been thinking about how to set up a 29mm AV-Bay and keep ejection gas away from the active end.

This would do it.

One Q ,,, can you provide 5 -or- 6 inch aluminum threaded rods too ?

-- kjh

p.s. Another learning experience from Saturday's launch: Mag Switches don't like to be near steel threaded rods

 

[Adrian A]

One Q ,,, can you provide 5 -or- 6 inch aluminum threaded rods too ?

-- kjh

p.s. Another learning experience from Saturday's launch: Mag Switches don't like to be near steel threaded rods

Only if I cut them myself, which I'm preparing to do. McMaster sells cut ones up to 2.5", but then the next size is 12" 24" or 36".

 

[kjhambrick]

Hmmm ...

Unless you want to cut the longer rods down for sale, it would seem that McMaster-Carr is the way to go.

And I would rather have you working on the 'good stuff' than something I can do myself

Thanks Adrian.

-- kjh

 

[manixFan]

I’ve been designing rockets using your 29 and 38mm AV bays and ended up buying several long threaded rods and a bunch of nuts and washers, and just cutting the rods myself. I think most folks who buy something like this would be willing to do the same, or you could include a 12” rod with the package to simplify it for both you and the user. I have found for my purposes I need a longer rod than your standard length.

I also now add magnetic switches to all my electronics, including trackers. Having a magnetic switch built into the altimeter would be a huge plus. I’d definitely be on board for a couple.


Tony.

 

[SolarYellow]

I like it fitting in the coupler. I'd probably look at fitting it in a nose cone shoulder with an Eggfinder Mini above it.

 

[kjhambrick]

One more Q.

Will the new AV-Bays come with the new Mag Switch and circuitry ?

Thanks

-- kjh

 

[Neutronium95]

Removing the outer ring would also work better for my use case as well.

I had thought thatthe avbay on my H13 rocket was as small as possible, and I'd love to shrink it further for the H14.

 

[OverTheTop]

One question I have now is about the outer area of the board. Currently the outer boundary fits into a 29mm airframe, while the white circle shows the overlap area with the end of a coupler, which can be sanded off. I'm wondering if I should just leave off the outer overlap area. Since there are electrical components on both sides of the board, it can't be used to seal the end of a bay like the 29mm av-bay bulkhead can. Separate passive bulkheads will be needed to seal off the bay, so I think most installations would want to have the outer area sanded off anyway. Hmm.

I would leave the outer annulus of PCB on. The outer ring of PCB provides support to reduce the board flexing. There are ceramic capacitors very close to the edge of the board that are prone to breaking and failing if too close to the edge. They are normally not placed within 3mm of the edge as a rule-of-thumb.

If people wanted to they could remove the outer sections as needed.

An alternative would be to remove the annulus and make the board thicker. A 2.4mm PCB is about 3.4 times stiffer.

 

[SolarYellow]

An alternative would be to remove the annulus and make the board thicker. A 2.4mm PCB is about 3.4 times stiffer.

I would happily absorb that weight where I'd use this. Actually looking for ways to hang more mass on the thing.

 

[bad_idea]

I would leave the outer annulus of PCB on. The outer ring of PCB provides support to reduce the board flexing. There are ceramic capacitors very close to the edge of the board that are prone to breaking and failing if too close to the edge. They are normally not placed within 3mm of the edge as a rule-of-thumb.

If people wanted to they could remove the outer sections as needed.

An alternative would be to remove the annulus and make the board thicker. A 2.4mm PCB is about 3.4 times stiffer.

Good points.

 

[Adrian A]

One more Q.

Will the new AV-Bays come with the new Mag Switch and circuitry ?

Thanks

-- kjh

Yes. Since it won't have to deal with higher-voltage batteries like the stand-alone mag switch is designed to do, the parts count is lower. The standby current should be even lower than the handful of micro-amps that the latest magnetic switch consumes (weeks to months of standby capability). And the range will still be 1.75".

I would leave the outer annulus of PCB on. The outer ring of PCB provides support to reduce the board flexing. There are ceramic capacitors very close to the edge of the board that are prone to breaking and failing if too close to the edge. They are normally not placed within 3mm of the edge as a rule-of-thumb.

If people wanted to they could remove the outer sections as needed.

An alternative would be to remove the annulus and make the board thicker. A 2.4mm PCB is about 3.4 times stiffer.

The board is only 1.0" diameter, so standard 62 mil thickness is already overkill. I might be tempted to go down to 31 mil, but it would only save a gram.

I couldn't come up with a good use case for keeping the overlap flange, so I put the board boundary at 1.0" diameter and squeezed the components in again to meet minimum clearance requirements from the edge. This is a very squeezed board. The main thing I lose with the overlap area is a place to label the connections. I'll see what I can do about that.

I would happily absorb that weight where I'd use this. Actually looking for ways to hang more mass on the thing.

You'll have room to hang what you want (as long as it's nonconductive) on the threaded rods. But my favorite way to add ballast is to mix up some powdered tungsten (available from a golf store) into epoxy and pour it into the nose.

 

[Adrian A]

Earlier this year a professional client tested a board of mine for an application that had 20,000 Gs. It did fine. It was a 1.5" diameter circular circuit board in 93 mil thickness, and honestly that extra thickness was probably overkill also, but that G level was a little out of my experience range so we went for some extra factor of safety. I've been producing 29mm and 38mm diameter rocketry circuit boards in standard thickness since 2010, and the weakest link on those products is the surface-mounted header connector for the Raven, if you put too much bending on the Raven while it's clamped onto the pins. No broken caps.

 

[SolarYellow]

You'll have room to hang what you want (as long as it's nonconductive) on the threaded rods. But my favorite way to add ballast is to mix up some powdered tungsten (available from a golf store) into epoxy and pour it into the nose.

Funny, there's powdered tungsten in my Amazon "saved for later" already.

 

[Adrian A]

I think the board is ready for the prototype. I moved the large aerogel capacitor to the same side as the USB connector, battery and buzzer so its leads wouldn't get in the way of the threaded rod nuts. It lays on top of the buzzer. I added wire pads to share switched power for the tracker or another item. Then spent a bunch of time messing with the silkscreen to make it not-quite-so-bad. This is a dense board. There are dozens if not hundreds of places where the copper features are pushed against each other with less than 0.001" of margin against the minimum 0.005 trace/space clearance. The board is 1.000" diameter, preserves all the features of the Blue Raven except wide input voltage range, and adds a battery connector and a magnetic switch with aux power outputs for a tracker.



I think it will also be a nice and easy way for someone to add a redundant altimeter to an existing larger project, with lots of data collection as a bonus. Let's say you have a 4" av-bay with bulkheads on either side. Just drill 3 holes in the bulkhead and attach this Blue Raven to the bulkhead with screws or short threaded rods that also make ematch wire terminals for two outputs on the outside of the bulkhead.

 

[cerving]

What a beast! How many layers is that board?

 

[Adrian A]

What a beast! How many layers is that board?

Four layers. 5 mil trace/space and 8 mil vias. Usually I use 6 mil and 10 mil to keep my board fab options open but it wouldn't fit that way.

 

[Conway Stevens]

I would be down for a couple.

 

[Neutronium95]

I think it will also be a nice and easy way for someone to add a redundant altimeter to an existing larger project, with lots of data collection as a bonus. Let's say you have a 4" av-bay with bulkheads on either side. Just drill 3 holes in the bulkhead and attach this Blue Raven to the bulkhead with screws or short threaded rods that also make ematch wire terminals for two outputs on the outside of the bulkhead.

I'm mostly interested in it from the perspective of wanting the smallest possible avbay for 29mm rockets. I don't know how feasible it would be, but if there was a battery that could lie flat on the board, you could get the length down to maybe 10mm or less, which would be amazing.

 

[kjhambrick]

I'm mostly interested in it from the perspective of wanting the smallest possible avbay for 29mm rockets. I don't know how feasible it would be, but if there was a battery that could lie flat on the board, you could get the length down to maybe 10mm or less, which would be amazing.

Yes ! ( to batteries that lie flat on the board )

I've been casually looking for squat cylindrical LiPo Batteries and there are a few of them out there ( squat, rather than slim form factors ).

I've not looked too hard yet because I will want a battery without circuit protection and something that fits within the radius of the threaded rods but it seems that such batteries may exist:

google: cylindrical lipo battery

I have been imagining a little AV-Bay packed into a cylindrical form factor that would slide as a unit into a sealable 29mm coupler tube with fool-proof squib connections -- an Avionics Appliance for small Rockets.

Fun stuff !

-- kjh

 

[Adrian A]

I'm mostly interested in it from the perspective of wanting the smallest possible avbay for 29mm rockets. I don't know how feasible it would be, but if there was a battery that could lie flat on the board, you could get the length down to maybe 10mm or less, which would be amazing.

A wired battery connector compatible with the connector on this board is available, and then you can use whatever battery you want. There is probably one that could work that could lay flat between the threaded rods.

But, if you're going for performance in 29mm, you'll need a tracker! This 29mm Blue Raven's battery is located so that when the battery is plugged in, a Featherweight tracker will also fit between the rails. That will make about 1.7" long 29mm av-bay with a tracker and Blue Raven, each with its own battery.

 

[kjhambrick]

A wired battery connector compatible with the connector on this board is available, and then you can use whatever battery you want. There is probably one that could work that could lay flat between the threaded rods.

But, if you're going for performance in 29mm, you'll need a tracker! This 29mm Blue Raven's battery is located so that when the battery is plugged in, a Featherweight tracker will also fit between the rails. That will make about 1.7" long 29mm av-bay with a tracker and Blue Raven, each with its own battery.

Adrian --

Have you thought about selling the new Blue Raven + Tracker + Hardware Accessories as a Kit ?

Probably so

-- kjh

 

[Adrian A]

Adrian --

Have you thought about selling the new Blue Raven + Tracker + Hardware Accessories as a Kit ?

Probably so

-- kjh

Actually, I hadn't, but that's a good idea!

 

[kjhambrick]

Just curious then ...

Does the circular Blue Raven form factor include an onboard JST 1.25mm Female Connector for the 40mm 150 mAh Batteries we now use ?

-- kjh

 

[dhbarr]

Who's going to be the first one to print up plastic for jamming Flat Raven + Tracker into the four off-the-shelf 29mm nosecones ?

• Madcow GoDevil 29
• Estes So Long
• Wildman BlackHawk29
• Apogee Aspire

( I didn't list the LOC/PML as it's solid urethane )

 

[Adrian A]

Just curious then ...

Does the circular Blue Raven form factor include an onboard JST 1.25mm Female Connector for the 40mm 150 mAh Batteries we now use ?

-- kjh

Yes.

 

[StreuB1]

You don't stop man. Its awesome.

You, Cris, and Vern, are doing amazing things for our little hobby. And I love it that you guys seem to feed of each others innovation and not be concerned with bleed or overlap.

Keep it up, honestly.

 

[charrington]

Yeeeeppppp, there goes my savings... Bring it on Adrian!