Smallest Accel (baro not necessary) only Alt

I already am set on my 3X upscale interceptor project (yep its been delayed almost a year now but this winter its getting done!) but I like fast rockets, and I also need/wanted something that can fly on cheaper motors... So my thought is to also make an all carbon fiber and glass 38mm rocket for the H999 or I1129 warp 9 loads...

Top section will have my GPS tracker as well as an alt...

Altitude is cool but obviously this thing will be built for performance, most likely under the optimal altitude mass.... So Baro would be nice but its not necessary.

I am just looking for something that is light weight, uses a small battery (would be awesome if it was board mounted), and stores acceleromic data and can detect apogee and fire an ejection charge...

Now that I think about it, not having apogee would make things easier... I could simply tightly wrap it in foam and place it in the bay (38mm coupler, tube, vertical motion would be none/minimal to keep the accel data accurate in the foam).

So what do you guys think?

Doesn't the Parrot do just what you're asking for (but no deployment...thats in the next version) Very small, lightweight, onboard battery, baro(maybe accel, can't remember) and fairly cheap (think they were like $100) I think a pico might be smaller but the parrot has more features.

-Aaron

Ill have to look into pico...

Hmmm perhaps I can test the new Parrot with deployment...

Ya baro is nice but what I really want is accel data..

Sounds like what I need!

And something that can take a decent load of G force..

I already have an MC2 (does what I need but is much to large), a timer and two MAWD's... The MAWD's would work but baro only, and no onboard battery.

I recall adept having something like this at one point but now all I see are baro based alts.

edit: you beat me to it, but yes: featherweightaltimeters.com
I think with slight mods it can deploy

I look into that...

Pico has an accel only, one event (apogee) alt, recording...

Could be the perfect one...

Are they reliable?

Could I get away with a smaller battery then a 9v (lighter as well)?

Stock 50 G max, but they say you can get a 120 G which I may need for the warp 9 loads...

The Parrot peaks out at 70G though. Adrian might be able to add on a higher G accel on request - that could be something to look into.

Also note that the Parrot has an onboard battery, so no need for anything like a 9v.

Ill have to talk to him about that... have not done enough sims yet to see if I would need more then 70 but I would assume with a warp 9 and a CF bird I definetly would...

His unit does look awesome! And I see something on his site about apogee deployment...

Might be nice to get extra data (barometric)...

Well, I was right around 60 with a Cirrus and an I600, so with any decently light 38mm rocket an an I1299, you would probably exceed 70.

Yeah...

I am thinking 2 wraps 5.7oz CF for the lower airframe with 1/32" G10 fins and some CF tip-tip.... That will be nearly weightless... Then upper airframe will be two wraps of glass (RF transparent) with an internal PML coupler tube to hold the alt and GPS...

And I hope to be extra simplistic on the alt bay, on my 54mm carbon bird the alt bay was literally over 90 percent of the rockets weight.

I was thinking everything will be "friction fit" (all the electronics) and rivets will hold the couplers into the glass tubing to keep it all together... Recovery system will just be a small chute and my favorite 1/8" kevlar harness... Should be real light weight.

The Parrot was designed for just the sort of application you have in mind. It has the lightest as-flown mass of any altimeter on the market, about half that of the Pico-AA1 when you consider the battery mass.

It does do apogee deployment, if you use a separate battery for the charge, and an arm switch. I also have some ~1g arm switches, and I'll be happy to throw one in if you want. I have used it successfully for apogee deployment using a 1.5 gram battery to power both a BeeLine transmitter and the deployment charge. Tomorrow I'm planning to fly a setup that has the Parrot doing apogee deployment and a BeeLine for under 20 grams.

The accelerometer is within its spec range at 70 Gs. I don't know how accurate the readings would be above that, but the interface to the microcontroller would be fine with accel outputs over 90 Gs. I regularly subject the Parrots to G levels from impacts and deployments that are too high for it to measure, with no apparent damage.

I've got to go now but later I'll post more on the comparison between the two alts.

Adrian

IMO it's a bad practice to use a ~1 G arming switch. That's way too sensitive.

I wouldn't use anything less than 2.2 G. That way if you flip the rocket over, it doesn't arm. (Flippping a rocket over gives a 2G difference.)

Robert DeHate's Picoalt accelerometer, unlike his altimeters, was never designed to be a super lightweight unit. I believe it was basically designed for his L3 Black Rock Mach 3 flights. The basic accelerometer weights 8 grams and the screw connectors probably account for at least a couple of grams. If you remove the connectors and use two 30 maH LiPo batteries, you could get the package weight down to ~8-9 grams. You can get +/- 120 G and +/- 240 G accelerometer options for it. I don't think anyone has pegged his 240 G unit.

Most 2xxx, 4xxx, 5xxx and 6xxx accelerometer chips will typically withstand far in excess of the datasheet G shock limits. They have worked for me after 4 KG ground impact (intentional) power shovel recoveries.

Bob

Bob, sorry for the misunderstanding. By ~1g I meant 1 gram for the arming switch, not 1 gravity. The arming switch I'm referring to is this simple screw switch. The Parrot's liftoff detection algorithm looks for a delta-V of about 6 mph, which equates to a pretty good intentional shake. Tilting it up or down or even dropping it a few inches on the launch rail won't cause a false trigger.

I agree that someone could make their own 2-cell, Li-Po battery to use with the AA-1 to make the masses comparable. The user would also have to either get a single-cell Li-po charger and charge the cells individually, or a 2-cell charger and manage the cell balancing. For the Parrot, the USB connection does the charging, and includes limits on charging current and voltage, in addition to the cell's own independent cell protection circuitry that covers overcharge, overdischarge, and over-current faults.

Here is some more comparison information:
Advantages for the AA-1:
-1000 Hz accel sampling, vs. the Parrot's 200 Hz. From the data I've seen, this isn't very important for integrating the velocity, but it would provide significantly better data for looking at the details of the deployment dynamics.

-Custom interface software. Probably easier to use than the Parrot's method of capturing the data using Hyperterminal and then pasting into an Excel template.

-Blinks out the estimated altitude. With the Parrot, you have to use the Excel template before you know how high it went.

-Options for higher-range accelerometers. I think the Parrot uses the same accelerometer parts, but I didn't think to include some +/- 120 or +/- 250 G versions in the initial production run.

-More options for the deployment trigger. Can do it a configurable time after launch, burnout, or apogee.

-Audible continuity indication

Advantages for the Parrot:
-Barometric altimeter. Enables descent rate measurement and is used together with the accel for the best estimate of Cd. (explanation of why the baro would be useful for Cd calculation available on request)

-Lateral acceleration. Can be useful for estimating the rocket spin rate, getting visibility into deployment/landing dynamics, launch guide issues, or other times something goes wrong. I used data from it to determine that an unstable flight in one of my rockets was due primarily to CG/thrust misalignment rather than pure aerodynamic instability.

-Lighter, when using the manufacturer-recommended battery (9V).

-Measures and records temperature, battery voltage, and sensor reference voltage. These are mostly just for curiosity, except:

-All measurements have built-in temperature compensation, based on end-to-end calibrations at two different temperatures, and the in-flight temperature measurements. Without it, a 40 degree F temperature difference would cause about 1.5% (accel) to 3% (baro) errors in the sensor scale factors for the Parrot. I don't know how senstive the end-to-end system of the AA-1 is to temperaure, though I think it uses the same accelerometer.

-Records 5 flights, rather than 1. Useful if you don't want to bring a laptop out to the range.

-Records 5:08 of high-rate data, plus 25 minutes of low-rate data, compared to 33 seconds for the AA-1 (at its highest data rate). This isn't a key discriminator, except that it points out that without barometric data, there isn't really much to record after a few seconds after burnout.

-USB connection to the PC, rather than RS-232.

Everyone, feel free to let me know if I have any errors in the above.

Reading over this thread, I would be surprised if you didn't need more than 70 Gs for the accel range. I may be able to swap out the 70g accel on an already-built board to take advantage of all the other machine-placed parts. The accels in the higher ranges are only single-axis, but they have the same footprint as the 70/35 2-axis one I use, and they just don't use the extra pad. The rework would be tricky, but I'll take a closer look to see if I think I could do it.

If you could make a unit with some higher G ratings I would love to use it...

So does the extra battery for apogee deploy mount on the parrot? Would I be able to get the apogee deploy version to fit in a 38mm nose cone?

What I would like to do is get it to fit in a 38mm nose cone "bay", vent it threw the airframe and the nose cone shoulder and then the GPS beeline will go just below it, with the antenna going up into the nose cone...

The beeline is about 2 oucnes I think so weight is not SUPER critical with the parrot, I just dont want another 8 ounce alt bay (my 54mm rocket had a very heavy bay).

And how would you recommend I arm it while its on the pad? I could use your switch (or some others I have used in the past) and do it via a hole, although that does add some slight complexity...

This is going to be one fun project

So what do you guys say a modified parrot (can you do the higher G's?) or the pico?

Hmmm...

IIRC carbon fiber blocks signal, so for GPS
tracker you might need an external antenna or
fiberglassed payload bay...

...just a nagging feeling at the back of
my numb skull - I might be mistaken as well....

Edit: Duhh... 'antenna goes into nose cone...'
obviously didn't sink in at the first read... Sorry,
its been a loooong week...

So does the extra battery for apogee deploy mount on the parrot? Would I be able to get the apogee deploy version to fit in a 38mm nose cone?

Click to expand...

It will definitely fit inside a 38 mm nose cone. It fits inside a 24 mm nosecone, side by side with a Beeline tracker.

Since you're flying a GPS beeline also, you may be able to use the beeline's battery for the deployment charge. That's what I'm doing with my 29mm nosecone av bay, though with a beeline tracker. I'm using a Lipo cell I bought myself that doesn't have any cell protection circuitry that could limit the deployment current. The BeeLine tracker wouldn't mind a power interruption, though I don't know if that would be true for the BeeLine GPS.

In the past I've sketched out a 38 mm nosecone design that seals the electronics from the deployment charge and the rest of the airframe, and armed and vented through a hole in the shoulder. For my 29mm F record attempt rocket, I went a bit simpler and just had a non-sealed bulkhead between the electronics and a 13mm deployment piston. I will arm it at the pad in a partially-disassembled state.

Go with the PICO. They have an accelerometer that does pretty much anything you want it to. You can program it for airstart, staging, apogee, and timed delay. I am not sure if it is on their site, but if you contact Robert DeHate, I am sure he'll fill you in on the details.

Oh, I love his AA2 altimeter. Great board, its like the above mentioned pico but also has a barometer.

There is an accel only unit and I can get it with 120G's...

But the parrot is much smaller and has a built in battery...

The pico is 1" by 2"s I believe but thats without the battery...

Hmm I could ask Greg but the gps could lose lock if it had a power blip...

The lower tube (most of the rocket) and parachute bay will be 2 wraps of CF... Then there will be a small 2 wrap fiberglass sleeve over the alt bay coupler bay... So the GPS reciever is in the glass section and the transmitter antenna is in the FG or plastic nose cone...

WOW!

Check out this file...

Over 200G's with the H999... Dont even want to know what the I1229 is! Still only 1.5 mach...

Pretty cool...

I might just go with the H999 version considering it still gets well over a mile, supersonic and a ton of G's...

Also looks like Ill be going with the pico, the 240 G version!

I am going to do some sims with the I1229 as well as the slower burning loads for the same casings (not always going to want it to be quit this quick...)... Before I decide...

Any thoughts on pico mounting (will it still fit in the cone well?) and also, good small batteries (single use or rechargable) for it...

In the file you can see I have the alt in the nose cone, the GPS is the 3" by 1" inner tube just below the shoulder and is inside the coupler. The alt bay bulkplate is held inbetween the alt bay coupler and a small 1/4" coupler that will be glued in to the carbon tube...

So the coupler containing the GPS, and with wiring down to the ejection bulkplate will be placed in until it hits the .25" coupler, then the nose will be slid in (and will fit perfectly against the GPS/alt bay coupler) and riveted in place... Locking the GPS and bulkplate in place.

Seperation point will be at the bottom, motor casing acting as the coupler...

I am looking into plugged tapped closures (are their 38mm ones?) but I may do something as simple as tieing the harness (thin kevlar) around the forward closure, under the knurled section, and then maybe putting a tie wrap or something over it....

I did something similar as a backup but it never had any ejection force on it, seemed pretty solid though....

Any thoughts?

I would guess if the knot is tight enough, alone it would not be able to slip over the larger knurled section... and with say a small pipe clamp or tie wrap it should be on their pretty solid (again, will ground test).

View attachment Warp Nine.rkt

i've undertaken a similar project as yours, however, im going with a kit, to build upon...its a standard LOC aura, with the MMT left out...CF body tube, fiberglassed fins, and T2T CF over that...i was planning on using a PICO 240g unit (As advertised on their site) for apogee deployment, with everything mounted in the NC...recovery will be on as large a streamer as i can fit (so long as it's a safe descent rate...). since i dont have rocsim, i had CJL sim it out for me on an H999 and it simmed to 180g's and 1100+ mph. it should be a good time. i plan on painting it in super reflective chrome paint (the good stuff). anyway, i'd love to hear more about your project...all i really need for the rocket is the electronics, and some reliable way to mount the BP in the ejection well upside down (on the bottom of the nose cone) without it falling out (something tells me 180g's is a bit too much for masking tape to hold a gram of BP up)...anyway, i look forward to seeing more about your project...

That sounds awesome!

Ya it should be fun...

Let me know how the pico works out!

I will also most likely go with a streamer and a nice bright paint job...

Flights at my home field (farm land) will still require searching for it, but with GPS atleast I am only looking at a 16' diameter circle instead of miles of fields

I love working with composites so this is my kind of build...

I dont plan on having a BP container, just a charge... Most likely will be simple latex glove finger, the usual... I dont think G-force will cause to many problems with it as the recovery system will be under it to keep it from falling, and Ill give the wire a bit of slack just to be safe.

The I1229 would be fun but arent they making a mojave green for the 38/360? Ill probably stick with the H999 then...

Anybody done this or know if its possible? Can you mount an eyebolt on a 38mm plugged closure? Tom Rouse is a local so I could probalby purchase one from him, but Ill most likely get the motor hardware complete from someone else (I have a credit with them and plan to use it for this project)... So can the plugged closure be tapped?

well, i wont be able to fly mine until nerrf...thats the biggest field with the highest waiver around...it'll be built though, so i'll probably send it up on some F flights at CMASS to test everything...

as for an eyebolt in a 38mm forward closure...it CAN be done physically, but i dont think any manufacturers offer it currently...

Okay so if I get a plugged closure what would be the best way to go about doing it?

Also, I have been talking with Robert at Pico and he can do the 240G chip, no charge...

He also recommended a 100a LiPo battery, probably the same thing the parrot has...?

He said he has tested it and it fires a daveyfire with his unit. Ill probably test it with two e-matches for test purposes but fly with one.

Lastly, I believe the pico unit is 2" by 1"... That should fit well in a 38mm cone, correct? Worst case... it sticks out the bottom a little and adds an inch or two.

I was hoping this thing would get higher speeds (sims around mach 1.5) but the acceleration is what counts...

I may do the I1229 after all (instead of the H999) just to fully utilize the 240G capablilities

Lastly I will need to learn how to use a regular RDF tracker vs. the GPS.... If I loose GPS lock for any reason (probably due to acceleration) then I can still recieve jumbled "packets" and track them like a regular tracker... Ill probably have my GPS picpac reciever setup and have a buddy with a yagi tracking it the old fashion way, just in case it looses lock....

I have flown it successfuly however in a 54mm bird with a K1100, which is a decent kick.

for my rocket, i was going to sandwich a piece of aircraft plywood with a couple layers of CF, and then drill and tap it with an eyebolt and anchor it in place directly above the forward closure of a 38/360 (the H999 case)...that way it's a super secure attachment point, and it keeps the recovery bay all neat and tidy. heh. for the NC i plan on doing the same, a CF bulkhead with a thin piece of allthread (for the accellerometer sled), with an eyebolt or a U-bolt on the bottom for a recovery harness, as well as an ejection well.

the only problem with that setup is that i'll have to rely on electronic ejection 100% of the time, as the motor section and the recovery section will effectively be seperate airtight units.