Getting rid of all-thread

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BDB

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I've been kicking around some ideas for building an avionics bay without all-thread. That way I can simply mount my GPS to the sled without worrying about interference, and I wouldn't have to worry about a bulkhead-mounted antenna getting damaged during recovery. (That's happened to me twice so far.)

I'm thinking of attaching the sled to the bulkheads and running a length of kevlar through the bay with loops on each end to serve as attachment points for the recovery harnesses. The kevlar would be simply tied to the center of the bay. I'll try to draw something up when I get home in a few hours to better show my idea.

Has anyone ever done something like this before? Or are their other alternatives?
 

mpitfield

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Landru had a 3D printed sled similar to what you are describing. I have a 29mm one, not used, and it has a channel that goes down the center for the recovery harness. I don't see it on his site anymore but I can try to dig it up and send pics for inspiration?
 

Steve Shannon

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I've been kicking around some ideas for building an avionics bay without all-thread. That way I can simply mount my GPS to the sled without worrying about interference, and I wouldn't have to worry about a bulkhead-mounted antenna getting damaged during recovery. (That's happened to me twice so far.)

I'm thinking of attaching the sled to the bulkheads and running a length of kevlar through the bay with loops on each end to serve as attachment points for the recovery harnesses. The kevlar would be simply tied to the center of the bay. I'll try to draw something up when I get home in a few hours to better show my idea.

Has anyone ever done something like this before? Or are their other alternatives?
I've thought a lot about using one or two pieces of g12 body tube to connect the two bulkheads together and then slide a coupler holding the electronics into each tube. That would be similar to the old Smokin Rockets design. I would use a motor retainer to secure it in place.

Here's a picture from PML of something similar:




Steve Shannon
 

rharshberger

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Is aluminum rod any better than steel for RF purposes? I have several smaller rockets ( less than 10lbs) in which I thread the ends of 1/4" aluminum rod and use that to mount the sled and bulkheads.
 

new2hpr

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Adrian did the kevlar through the AV-bay method quite a while back with his altitude record rockets. So yes, it's been done, and successfully. I believe there's a build thread, or at least photos of the method on here somewhere.
-Ken
 

Lowpuller

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I've been considering an open AV Bay. Use standard bulkheads but two short sections of coupler tubing with plywood spanning between them. Thus eliminates the need for all thread and you can easily see the entire AV Bay.

I would design it to remain in the payload section.

It might require the sled to have a couple of stiffness on the bottom.
 

BDB

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I've been considering an open AV Bay. Use standard bulkheads but two short sections of coupler tubing with plywood spanning between them. Thus eliminates the need for all thread and you can easily see the entire AV Bay.

I would design it to remain in the payload section.

It might require the sled to have a couple of stiffness on the bottom.
I've thought about something like this too. I think a better alternative could be to use a hatch-accessible bay, something like what John Coker did in his Minnie Magg.
 

Igotnothing

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The specs on nylon all-thread:
"Not rated for tensile strength or hardness. "
On the other hand, I did bolt a wing onto an RC plane with 4 nylon 1/4-20 bolts and they were fine in tension and shear. That plane had a 48cc chainsaw motor. Always expected it to separate in high-g maneuvers, but it never did.
 

Bat-mite

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The specs on nylon all-thread:
"Not rated for tensile strength or hardness. "
On the other hand, I did bolt a wing onto an RC plane with 4 nylon 1/4-20 bolts and they were fine in tension and shear. That plane had a 48cc chainsaw motor. Always expected it to separate in high-g maneuvers, but it never did.
Shouldn't be any shearing force on AV bay rods. To avoid metal completely, you'd still have to have Kevlar straps at each end.
 

Igotnothing

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I have done this, but have not tested it. I opened an eye bolt, slipped it through a hole-and-slot in the sled, welded the bolt back shut, and bonded G10 reinforcement around the bridge of G10 through the eye bolt. The reinforcements kind of lock the bolt in place sticking out to the left in the photo. Tape and screwdriver are to protect the G10 from the weld heat.
Repeat at other end. Now the G10 sled is in tension.
Test to come this summer in a 38mm MD design.
no threaded rod av bay.JPG
 

cerving

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I've thought about something like this too. I think a better alternative could be to use a hatch-accessible bay, something like what John Coker did in his Minnie Magg.
I've done a few Kevlar-through-the-coupler AV bays, in some builds (especially skinny rockets like a Mongoose 29) it makes sense because you don't have room for or don't want allthreads. It doesn't put any load on the AV bay or the bulkplates, either. If you do have a lot of room but you just don't want metal allthreads, you can use it too, with a nylon allthread to hold the bulkplates in place.
 

BDB

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Just stumbled across this thread. Post #16 is an incredibly simple solution.
 

watermelonman

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Many of my avbays have a single all thread rod down the middle. I have not had notable radio problems even when run alongside the all through, but I am sure that the exact configuration is important.

I definitely would like to try an avbay with no rod at all at some point. I would probably only try it with fiberglass components, and some creative means of affixing the lids.
 

jderimig

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Is aluminum rod any better than steel for RF purposes? I have several smaller rockets ( less than 10lbs) in which I thread the ends of 1/4" aluminum rod and use that to mount the sled and bulkheads.
No.
 

ksaves2

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An alternative would be to run a cable from your ebay mounted tracker to the aft bulkhead and have an aft pointing antenna that's ejected into the open when the apogee charge blows. That assumes your tracking device has an SMA or RP-SMA socket on the board. Ebay has a variety of cable interconnect/bulkhead sockets available. Just screw on a "floppy" antenna and fly.

Since it faces aft, one avoids the paralleling of the all-thread and the antenna is out in "free space" without encumbrances to the Rf on the all important descent from apogee. Kurt
 

BDB

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An alternative would be to run a cable from your ebay mounted tracker to the aft bulkhead and have an aft pointing antenna that's ejected into the open when the apogee charge blows. That assumes your tracking device has an SMA or RP-SMA socket on the board. Ebay has a variety of cable interconnect/bulkhead sockets available. Just screw on a "floppy" antenna and fly.

Since it faces aft, one avoids the paralleling of the all-thread and the antenna is out in "free space" without encumbrances to the Rf on the all important descent from apogee. Kurt
That's what I've been doing. The harness has gotten tangled up with the antenna twice, so I replaced my rubber duck antenna two times last year. I know people have had success with this method--I'm probably just unlucky.
 

ksaves2

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That's what I've been doing. The harness has gotten tangled up with the antenna twice, so I replaced my rubber duck antenna two times last year. I know people have had success with this method--I'm probably just unlucky.
The other thing I've read in that regard is to screw a short lead cable into the aft bulkhead mount, screw on your antenna and ziptie the assembly to the harness in several places. I believe I read that in some of Cris Cervings guides. Haven't tried it myself though. Kurt
 

MikeyDSlagle

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I've been kicking around some ideas for building an avionics bay without all-thread. That way I can simply mount my GPS to the sled without worrying about interference, and I wouldn't have to worry about a bulkhead-mounted antenna getting damaged during recovery. (That's happened to me twice so far.)

I'm thinking of attaching the sled to the bulkheads and running a length of kevlar through the bay with loops on each end to serve as attachment points for the recovery harnesses. The kevlar would be simply tied to the center of the bay. I'll try to draw something up when I get home in a few hours to better show my idea.

Has anyone ever done something like this before? Or are their other alternatives?
I've brainstormed a bit about this idea a few times too. Always like to try new things. I haven't got into tracking yet but will eventually. You say the kevlar will be simply tied to the center of the bay. What will it tie to exactly? This point will take all the shock from the recovery correct? I'm really curious to see how you intend to do it so I may can copy it.

Also looking at ideas for side/hatch access bays as well. Though no for the same reasons mentioned in this thread. Got one idea to do a side deployed drogue...just to see how that will work.

McMaster also has fiberglass threaded rod, but its pretty pricey.

Mikey D
 

ksaves2

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https://www.amazon.com/gp/product/B010V7D8KK/?tag=skimlinks_replacement-20

Found these to use with my Big Red Bee gps. Used this on a flight at Balls that went over 44,000'. Landed 6+ miles away and had signal the whole time until touch down.

Dennis
The "stubbies" are less efficient but 6 miles is pretty good range. Was that with the low powered BLGPS or the high powered one on 70cm? More power can make up for less antenna efficiency of course. I picked up a few coil spring antennas on Ebay some time ago but haven't done a range test or flown them yet. I've looked for them again but no longer offered I think. Kurt
 
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bill2654

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That's what I've been doing. The harness has gotten tangled up with the antenna twice, so I replaced my rubber duck antenna two times last year. I know people have had success with this method--I'm probably just unlucky.
I'm doing a setup like Kurt describes but I'm installing my antenna on the main bulkhead. My theory is it stays inside and safe till 500' or so. And if it does get snapped off at least I should still be able to get close. I'm putting one of the little "screamer" alarms on the shock cord so at least I'll hear it.
 

sl98

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I've done a few Kevlar-through-the-coupler AV bays, in some builds (especially skinny rockets like a Mongoose 29) it makes sense because you don't have room for or don't want allthreads. It doesn't put any load on the AV bay or the bulkplates, either. If you do have a lot of room but you just don't want metal allthreads, you can use it too, with a nylon allthread to hold the bulkplates in place.
How do you secure the bulkheads in place with the Kevlar? A couple of overhand knots?
 

FredA

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Seems like a solution looking for a problem.....nothing wrong with all-thread....serves the purpose well and I've not seen any evidence it perturbs tracking radios.

Without decent compression I'm not sure how you are going to make the bulkheads airtight so the charges don't effect the barometric sensor.
 

dhbarr

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Seems like a solution looking for a problem.....nothing wrong with all-thread....serves the purpose well and I've not seen any evidence it perturbs tracking radios.
I mean, if one doesn't believe ferrous metals adjacent to transmitters have real measurable effects, I don't know what to say.

If instead one is saying that, given the fields one visits, one hasn't seen proof of interference: that's a story I can see myself hearing.
 

jderimig

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I mean, if one doesn't believe ferrous metals adjacent to transmitters have real measurable effects, I don't know what to say.
It may distort the "pattern" somewhat (but that isn't probably not measureable with ordinary receivers), but all the RF energy gets out. Take a look at commercial antenna installations and antenna farms when you are out and about. They are generally surrounded by metal, towers, guy wires etc. Not an issue.
 
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dhbarr

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It may distort the "pattern" somewhat, but all the RF energy gets out. Take a look at commercial antenna installations and antenna farms when you are out and about. They are generally surrounded by metal, towers, guy wires etc. Not an issue.
Give me a medium voltage line, and it won't be an issue provided I'm broadcasting 360 to hit verticals in the same plane.

Tiny antennas and batteries are just that; and the level of interference + the distance b/w TX/RX makes ( or breaks ) the linkage ( over rocket flight scales ).
 

jderimig

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Give me a medium voltage line, and it won't be an issue provided I'm broadcasting 360 to hit verticals in the same plane.

Tiny antennas and batteries are just that; and the level of interference + the distance b/w TX/RX makes ( or breaks ) the linkage ( over rocket flight scales ).
Nope. 2 all-threads won't do anything measureable. This is not the first thread on this, experiments were done, no one could detect any signal strength effects in their backyard tests. Unless you have data that shows otherwise please share.

You haven't seen any cell phone towers where the antennas are mounted 1/2 to 3/4 up the tower?
 
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