LV3 Umbilical Ring

[Joedang]

So, we're definitely going to need a quick disconnect for LV3. (E: not for L-13 E: definitely for L-13) As far as I know, no one is working on that right now.

The vague consensus from the discussions I've been a part of is that we want a small aluminum ring with the male/female couplings on each end, much like the eNSR. IMO, the necessary boards and wiring should be self-contained, so we can put it on either end of the avionics module, and have the connectors reach 1" out of the top or bottom of the ring. Whoever handles the wiring for that will also have a "black box" requirement that their connectors reach 1" out of the top or bottom of the module (or something like that).

We're going to need at least one MME type to do the CAD and MFG for the ring and probably one ECE type to handle the wiring/boards. @natronics, @dsigma, and @DylanStephens, do you have any thoughts about this?

[Joedang]

Talking with @andrewgreenberg, it sounds like we should move away from a mechanically attached umbilical, in favor of something that has no chance of ever binding up.

I had some thoughts about how we might be able to do it magnetically (drawing below). The basic idea is that the connector on the rocket would be some large copper wires cast into a piece of epoxy. We'd have to mill or 3D print a mold for the casting and a jig for the wire bending. Once cast, the wire+epoxy block gets sanded and polished to expose the wires. The mating connector is just a PCB with some spring-loaded pins (COTS) and a PTFE faceplate.

The two are held together with magnets. The poles of the magnets are arranged so that as the rocket launches, the bottom magnets on the rocket align with the top magnets on the umbilical, pushing the umbilical away (see diagram).

The nice things about this design are that it would be completely flush with the surface of the airframe and have no risk of jamming.

The main issues I see with this design are that the wire bending and epoxy casting might be obnoxious and that the umbilical might hit the fins. Maybe we could play with the strength of the magnets to get it to push off harder or have some elastic line on the launch tower to pull it in a particular direction.

I'm sure ECE types will have opinions about this. Maybe there's some non-oxidizing metal or surface treatment that would be preferred over copper. Maybe charging batteries through spring-loaded pins is unreasonable. The curve of the airframe would limit how many pins we could have.

[JSRoland]

I have one question Joe, why are the arrows on that diagram not labelled as "space" and "not space"??

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On Mon, Apr 17, 2017 at 9:39 PM, Joe Shields ***@***.***> wrote: Talking with @andrewgreenberg <https://github.com/andrewgreenberg>, it sounds like we should move away from a mechanically attached umbilical, in favor of something that has no chance of ever binding up. I had some thoughts about how we might be able to do it magnetically (drawing below). The basic idea is that the connector on the rocket would be some large copper wires cast into a piece of epoxy. We'd have to mill or 3D print a mold for the casting and a jig for the wire bending. Once cast, the wire+epoxy block gets sanded and polished to expose the wires. The mating connector is just a PCB with some spring-loaded pins (COTS) <https://www.digikey.com/short/3w0mjc> and a PTFE faceplate. The two are held together with magnets. The poles of the magnets are arranged so that as the rocket launches, the bottom magnets on the rocket align with the top magnets on the umbilical, pushing the umbilical away (see diagram). The nice things about this design are that it would be completely flush with the surface of the airframe and have no risk of jamming. The main issues I see with this design are that the wire bending and epoxy casting might be obnoxious and that the umbilical might hit the fins. Maybe we could play with the strength of the magnets to get it to push off harder or have some elastic line on the launch tower to pull it in a particular direction. I'm sure ECE types will have opinions about this. Maybe there's some non-oxidizing metal or surface treatment that would be preferred over copper. Maybe charging batteries through spring-loaded pins is unreasonable. The curve of the airframe would limit how many pins we could have. [image: magneticdisconnectconcept] <https://cloud.githubusercontent.com/assets/16861664/25114383/38a3b234-23b3-11e7-88c2-74395dfa19d2.png> — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#1 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AH_dKe3e14ct_AzWxcaeTNZ2KS4LMOazks5rxD5kgaJpZM4KgoOX> .

[Joedang]

Hmmm, I may need to reinstall Inkscape. That's a pretty serious graphical error. Fixed.

[jalouke]

just curious, but why not just use a COTS connector? I was able to find some with up to 12 pins for data, as well as ones that have data and power combined on the same plug.

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On Mon, Apr 17, 2017 at 9:50 PM, Joe Shields ***@***.***> wrote: Hmmm, I may need to reinstall Inkscape. That's a pretty serious graphical error. Fixed. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#1 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AGxHjWQ74_3JdhPzU_77ZihsK8-vCSxHks5rxEEKgaJpZM4KgoOX> .

[Joedang]

why not just use a COTS connector?

... No, that would make wayyyy too much sense.

[Joedang]

Update: Crit. Path for L-13

We're actually required to have such a ring. So, this is actually critical path for L-13 now. Specifically, we need to be able to disarm and arm the igniter/telemetrum.

I'm not sure if we need physical switches, or if we can get away with putting a jumper on two of the leads coming from the umbilical to serve as a switch. I'll poke around the Tripoli site for any relevant reference material. Maybe @andrewgreenberg or @natronics know this off the top of their heads. (I like the screw switches that LV2.3 used, but mo' radial features mo' problems.)

E: This document specifies multiple times that we must be able to disarm the pyrotechnics, but doesn't specify how we disarm them.

[natronics]

There are commercial FCs that use magnetic (hall effect) arming switches[1]. So I doubt there is a requirement for an physical (mechanical) switch on the rocket.

1. https://www.featherweightaltimeters.com/store/p4/Magnetic_Switch.html

[Joedang]

Update:
We used the same umbilical disconnect as LV2.3 for L-13. It sat in a 3D printed nylon mounting that used the same generic windows as the cameras and switches. (see... https://github.com/psas/lv3.0-camera-ring/blob/master/mechanical/conjoined.SLDASM)

I'm going to keep this issue open, since it would still be nice if someone made a magnetic umbilical.