Soft mounting altimeters

Every altimeter installation I've seen mounts the altimeter rigidly to some part of the rocket--an AV bay sled, a nosecone, between fins behind a hatch, etc. For altimeters that rely on inertial measurements (accelerometers, "tiltometers," etc.) this is paramount. I wonder about non-rigid installation for purely barometric altimeters.

I'm imagining an AV bay that has screw-on caps on both ends and terminal blocks with requisite wiring. I connect the altimeter as necessary and then wrap it in an old t-shirt or a sock and stuff it into the AV bay. Then I screw the cap on, and I'm ready to go. The fabric holds my electronics securely, lets air pressure pass through and provides a measure of shock absorption in a hard landing.

As I've not seen anyone do this, I wonder if people have found out this idea is problematic somehow.

Ari.

When I screwed mine to the sled, I put rubber washers underneath to provide clearance. Also serves as shock-absorbers.

I'd imagine the shirt or sock would interfere with getting a good pressure reading. I also wouldn't want to risk the chance of a wire pulling free during the tumble from apogee to main.

One of our club members puts his tracking into pvc pipe with screw caps on the ends and stashes it somewhere - but I agree with DizWolf that it sounds risky for anything which has wires running from it to the rest of the rocket.

Pretty sure this is how it used to be done "back in the day." I'm no expert, but I don't see why it would not work with a baro-only altimeter.

I've also heard of people using velcro to attach an altimeter to a board. I think we can all agree that you shouldn't do that.

To clarify, my idea is about using fabric to fixate an altimeter inside an av bay, instead of using a sled. I don't want a bare altimeter flopping around inside a body tube or hanging off a shock cord after deployment.

Ari.

You could consider using Nylon stand-offs instead of steel. That would give you some shock absorption without any additional issues of blocking the pressure port. That said, I don't think the forces to which electronics are subjected during a normal flight will be a problem.

I think that he is looking for a way to use an altimeter with no sled at all.

My idea is to have simpler installation that allows me to transfer electronics from one rocket to another without designing new A/V bays and sleds for each one. This allows me to test many rocket designs without spending too much work on parts that aren't part of the experiment. Damping landing loads is a side benefit--though it become more important the more "experimental" rockets I fly :=)

Ari.

iter said:

My idea is to have simpler installation that allows me to transfer electronics from one rocket to another without designing new A/V bays and sleds for each one. This allows me to test many rocket designs without spending too much work on parts that aren't part of the experiment. Damping landing loads is a side benefit--though it become more important the more "experimental" rockets I fly :=)

Ari.

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I agree ..just having standoffs and nuts afixed to the sled make a huge difference in in field use and prep.

Am starting to standardize my wiring set up also and like bringing the wire to the altimeter 'missile works' style .. run the wires on underside of sled and 'one wire per hole' coming through for attachment. When I disconnect the wires from the altimeter they stay in the proper location for reattachment without having to trace them down.

Kenny

One thing that i am doing is starting to replace my sleds with Landru's 3d printed ones. My theory is that if I have a standard sled with an altimeter permanently mounted on it, all I have to do is swap the sled out between the different airframes. All you need to do then is standardize on the threaded rod placement for non-standard tube sizes.

Example: I have a Vindicator Jr and Warrior Jr both of which have different sleds today - while swapping out the altimeter isn't *that* much of a hassle, it certainly makes life easier for me to just drop in the new sled, wire up the charges and be on my way. Before standardizing, I would just plan on just using one rocket or the other when I went flying.

For altimeters with the battery on the board I have wrapped them in the thin foam used for window air conditioner filters. Slide into a 29mm or 38mm tube.
I use this technique even on big rockets where space is not a problem. I have made few "sleds" to hold altimeters.
Velcro also works. Get the adhesive backed kind, sometimes if the back of the alt is rough I use rubber cement to attach the Velcro.

M

iter said:

My idea is to have simpler installation that allows me to transfer electronics from one rocket to another without designing new A/V bays and sleds for each one.

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Why not simply design your sled around a 29 (or 38 - whatever best fits)mm _coupler_ tube of a length that makes sense. Then, simply mount that size body/motor tube in each rocket where you plan to use it. Configure a base/cover plate (that could have 'pass-thru' terminals) to close everything up (and this plate would only need to be one size larger than the sled tube - allowing re-use of this item as well). At that point, simply drop the base/cover plate, extract the altimeter and move it over to the other vehicle and close things back up.

Obviously, static vents, etc would need coordination so everything lines up (could install 'keys' in the mount tube to assure alignment).

As for shock absorbency, I've often thought of using some of that honeycomb cardboard (circa 3/4" thick) like is used for shipping protection of the doors of refrigerators/freezers etc (go check out your local appliance store or Sears) installed as a few layer(s ?) 'up front' (i.e. ahead of the AV bay) as a sacrificial element to take the brunt of a hard impact (or worse). (The military does this when they air deploy Humvees, etc - under the vehicle to take the force of landing. It's 'wasted' on landing, but in the rocketry sense, that hardly matters if it saves the altimeter). Could even place varying densities of foam (from the soft spongy kind to harder, polystyrene types) between the honeycomb and the electronics - to allow for a 'progressive' protection.

-- john.

jcato said:

Why not simply design your sled around a 29 (or 38 - whatever best fits)mm _coupler_ tube of a length that makes sense. Then, simply mount that size body/motor tube in each rocket where you plan to use it. Configure a base/cover plate (that could have 'pass-thru' terminals) to close everything up (and this plate would only need to be one size larger than the sled tube - allowing re-use of this item as well). At that point, simply drop the base/cover plate, extract the altimeter and move it over to the other vehicle and close things back up.

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That's what I was thinking, as well.

-Kevin

We may be trying to address different problems. The problem you want to solve is "I have <smallnum> altimeters and <bignum> rockets. I want to move similar altimeters from one rocket to another." My problem is "I am experimenting with different electronics in a couple of different rockets. One day I want GPS telemetry onboard, the next day I want baro telemetry as well, on the same battery as my deployment altimeter or maybe on separate ones. Some of my rockets are fat enough to accommodate all this, some are too skinny and some are too short."

Ari.

MClark said:

Velcro also works. Get the adhesive backed kind, sometimes if the back of the alt is rough I use rubber cement to attach the Velcro.

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I was under the impression that this is a bad idea, due to the fact that Velcro can give off static electricity "shocks" - which could be a very bad thing inside your AV bay during a flight (or worse, on the launch pad during setup).

s6

for NAR altimeter altitiude competitions we use soft or NO mounted Altimeters all the time. Just design the altimeter housing to slip fit the altimeter/power supply and add a cottom ball or two top and bottom this altimeter pod slips into the model body adding only minimal excess weight as I seem to see all the time with Sled electronics bay add-on. Perhaps with the HPR stuff this excess mass isn't that important with micro and low power models any mass that can be eliminated is a plus.

I've done it quite often with Stratologgers, Eggtimers and Pet2 timers, and almost regularly with my Beeline trackers. I use paper towels to wrap them. Usually a small piece of masking tape goes on the paper towel to make sure the altimeter doesn't slide out of the protection, and depending on the size of the altimeter bay, I'll either attach the battery to the out side of the paper towel bundle with tape and more paper towels or slide it in next to the altimeter. Not had a problem with this setup in 30+ flights, though none of those were over 10gs or so.

stealth6 said:

I was under the impression that this is a bad idea, due to the fact that Velcro can give off static electricity "shocks" - which could be a very bad thing inside your AV bay during a flight (or worse, on the launch pad during setup).

s6

Click to expand...

I had not heard that but have had no problems.
Maybe I have enough glue on it to insulate.

M