Ralph's Digipod

LGoodhind

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Calibrating a fuel sender could be done by starting with an empty tank and then adding known units of fuel and recording the sender after each increment into an NVRAM lookup array. DavidH has a fuel flow computer that does all kinds of stuff with GPS integration- it knows where you're going, how fast you're burning fuel, where you are right now .. many calculated values can be derived from that. These sorts of devices use something in the fuel line the measures flow (more accurate) as opposed to remaining volume. The sender for one of these things is pricy.

Data recorder- another option to an onboard datalogger would be to spew the raw data and calculated fun stuff out the serial port in CSV format with a timebase. That could be fed into a PDA with a compact flash card or something similar.

Vibration- Integrating output from an accelerometer with rotor/prop position info from another sender (I/R reflected pulse?) could also be used to generate a polar plot for eliminating vibration.

G-meter- Rough figures can also be infered from the RRPM.

The only sane reason to do a homebrew project like this when somebody is already selling a similar solution for a couple hundred over the parts cost is "just because."

Even after defining and building a reference hardware platform the big job in terms of time would be coding and debugging the software- lots of frustration potential. Each feature would require a coding effort and some of them (things like doing anything meaningful with GPS data, trying to automate the process of tuning out a vibration in the prop or rotor, etc) could keep you busy for much much more time than it takes to describe what you want to do. It's all about what you want to do with your free time.
 

Dean_Dolph

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LGoodhind said:
.....The only sane reason to do a homebrew project like this when somebody is already selling a similar solution for a couple hundred over the parts cost is "just because."......
Well no one has ever accused this group of being sane!

I haven't had reason (yet!) to investigate the capabilitites and features of instruments similar to the Digipod so I don't know how it compares. I do know that there is an opportunity here to create something unique for gyros in particular and light aircraft in general. For that reason I would think this project would be worth while. It would be icing on the cake if the demand turned out to be larger than what can be supplied. What exactly are the capabilities and features of the EIS from Grand Rapids?

But I can't help but feel that those people that have an immediate need should be accomodated by building the 'as is' Digipod for them. Those who can wait would get the upgrade.
 

Red Sky

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Dean_Dolph said:
...But I can't help but feel that those people that have an immediate need should be accomodated by building the 'as is' Digipod for them. Those who can wait would get the upgrade.
Maybe I'm missing something, but I didn't think the Digipod was available. :( Even if Ralph okays the developement and offers up the plans, someone will have to make them. I wouldn't mind, doing for myself. I think many here will want a turnkey solution.
 

gyroblackwell

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turnkey AND Heathkit options

turnkey AND Heathkit options

O.K. .... I see this breaking into to groups ..... those that just want what the digipod does (but with some minor improvements) and those that are thinking BIG ... and want to include all sorts of stuff for analysis, and fly-by-wire, and etc.....

I will be going the route of the Improved Digipod .... And I will work on creating two groups in this area ..... those that want a turnkey setup, and those that want to build it themselves, and thereby hopefully get what they want for the cheapest price possible !!

IF a simple schematic can be created that shows the digipod assembled using a breadboard, then the average guy can follow this guide, put together the temp curcuit board, and then all he needs is the software to load into the eeprom, and then try it out on the engine, and in the air. Transfer his breadboard to a permanent curcuit board (that he/she will need to get made .... ) and viola ..... you got yourself a digipod II (minus the enclosure ... which will be different for each person...)
 

LGoodhind

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Here are some pictures of some prototypes that I've put together on the Heathkit approach.

Several years back, during the height of the "don't clowd the issue with factz about this 'things tend to rotate around their middle' thing- you school boiz don't no nuthin and nobody can prove nutin to me without a wind tunnel" debate, several of the participants on the old rotorcraft conference (all text, all the time) worked on doing a homemade flight recorder.

I put together a NASA SBIR grant request on an inference logic package for the alarm system- twice- which was rejected- twice. In retrospect getting government $'s seems to be a great way to paint a red circle on your chest ("bummer of a birthmark Hal") so that's okay. The second time we made it to finals before the same guy who shot it down the first time shot it down again and put a "please stop" comment in the rejection. We continued to march without the distraction of begging for money.

Picture 1 was my first wirewrap prototype on the BX-24 development board- I scavenged parts for the V2 so it's good for giggles but not much more. Underneath you can see a piezo buzzer (loud 'n low energy alert) and two pressure transducers- one differential for airspeed and another absolute for altitude.

Picture 2 was the second prototype. It includes a video character generator (BOB-II) that lets the device overlay simple text on an NTSC video channel. This was done so that a video camera could be used to track attitude of the aircraft with time, engine, and airspeed info- a bow to the "youse paper a$$holes don't no nuthin. If it ain't on a TV set it ain't real" Victims of Tesla gang. The LCD display is a crystalfontz (I've done a "Hello World" on it and not much more) .. the back side of the board shows people who know how to layout a board how little I know- no ground plane.

Picture 3 is the third generation- better selection of connectors and parts placement. The box with knobs simulates several senders and binary inputs (read: buttons) for testing the UI and alert inference system. The little black square with the blue thing sitting next to it is an XY accelerometer- never used. Ground plane improved under the ADC and power regulator. Never got as far as scaling and protection.

Features: 8 channels of 10bit ADC, 8 channels of 12bit ADC, 8 channels of tachometer input, video overlay, SPI bus and (I think) six data lines unspoken for.

Needless to say I am not a hardware geek. In software terms we call this sort of iterative process a drunkards walk. =) Trying to cookbook something like this without a recipe to follow is not my forte and hardware, unlike software, costs more than time. I'm past about $800+ in parts at this point. Ouch. By this time people were crossing the river on the CG/CLT thing without a video data recorder and so everything went into a plastic box and I went back to working on developing my metal working skills.

The software side fuzzy logic system (go ahead, snicker) is pretty solid. This is a technique that allows you to take the reading of a particular sensor and define a curve that represents the degree of truth for a particular fact. For example you might decide that an ERPM of 3000=low, 4000=medium, 5000=high, and 6000=insane. At 3000 you might decide that the degree of truth for "erpm is low" would be 1.0, "erpm is medium" would be 0.85, "erpm is high" is 0.15, and "erpm is insane" is 0.0 .. these curves can be joined using fuzzy logic set operations that are analogous to the boolean IF/THEN logic that programmers are familiar with. This lets you create a series of alarms that look like this:

"if ERPM is high and ASPEED is low then Alert(BehindPowerCurve)"
"if ERPM is insane then Alert(DangerWilRobinsonInsaneERPM)"

If you tried to get out of the BehindThePowerCurve problem by opening the throttle the second klaxon would fire. Of course making alarms that go off all the time is a great way to get people to turn off alarm systems .. it's a Skinner box thing.

If Al or some other competent solder geek wants to rework the hardware I'd be happy to help with cranking out open source software but am really apprehensive about having a bunch of customers wanting a product ... customers/users are almost always the bane of enjoying your free time on your own schedule.
 

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Al_Hammer

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That's great, Larry. Nice photos of your work, and nice write-up.
We're all doing the drunkard's walk around here.
 

Red Sky

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Just an Idea

Just an Idea

Now, I'm no hardware guy either, but here's an idea. What about trying to interface with a PDA? Wouldn't that have the processing power and storage you'd need? Take a look at this:

http://www.bb-elec.com/product_family.asp?FamilyId=21

"Turn your PDA into a measurement and control instrument with graphical capabilities. Show up to eleven analog and three digital inputs. Control three digital outputs. Use the popular B&B Model 232SDA12 I/O module (see page 50) and a special serial cable (page 58) to have a complete measurement solution for under $100. Compatible with all Palm PDAs running OS 3.5 or newer, SYPHON you to configure the name, scaling, units and resolution of each of the eleven 12-bit analog ports" :cool:
 
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LGoodhind

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That's a fun widget. The same company that makes the Domino embedded core that Ralph used makes a similar device (http://www.micromint.com/products/answerman.htm) called an AnswerMAN. Since it's RS232 you could also hook it to a WinCE or Linux PDA if you wanted to write a host program.

To use an AD for a tachometer input you would need some sort of circuit that converted pulses/second into a scaled voltage output.

Later...

Another posibility that might have advantages over a PalmOS, Linux, or Wince PDA would be to use a series-60 platform cellular phone (example: http://www.nokiausa.com/phones/6620) as the host .. multiple vendor consumer grade hardware with reasonable good LCD screens and keypads. From a programming standpoint there are APIs for controlling/reading the phone hardware. Depending on the phone that could include packet network support, a camera, voice recognition, bluetooth networking, and a serial/power connection- which could hook into to a fairly dumb A/D umbilical.

The data umbilical would provide conditioned (and monitored/reportable) power to the phone which would be running with the backlight on all the time. The host phone program could lock out multitasking (don't want to get bothered by pesky incoming calls or accidently bring up the address book) and then poll the umbilical, run any format/alerting routines, and display the readings on the phone. Repeat until exit. Symbian OS and C/C++, Java, or Python code.

Cellular coverage from the air should be excellent and you can play Space Invaders when you aren't monitoring your EGT/CHT and providing bluetooth GPS whereabouts info and BirdsI(tm) iPhoto(tm) updates to your website.
 
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Red Sky

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LGoodhind said:
Another posibility that might have advantages over a PalmOS, Linux, or Wince PDA would be to use a series-60 platform cellular phone (example: http://www.nokiausa.com/phones/6620) as the host .. multiple vendor consumer grade hardware with reasonable good LCD screens and keypads. From a programming standpoint there are APIs for controlling/reading the phone hardware. Depending on the phone that could include packet network support, a camera, voice recognition, bluetooth networking, and a serial/power connection- which could hook into to a fairly dumb A/D umbilical...
I like! Lots of flexibility in that phone. Might be a bit more pricy than a older Palm. You can get these for $100 easily. Athought one of the newest Palms run $700. :eek:
 
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LGoodhind

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The sender interface would need pretty much what Al summarized earlier- lots of AD channels, some lesser number of edge counters, and binary IO for grip switches. Something off the shelf or custom built would work. If the second it wouldn't need too much programming because it would only need to generate raw data and any self-tests or watchdogs.

You can use AD for all of these if you are willing to sacrifice precision on the tachometer inputs but I think you would need to worry about drift unless there was a way to calibrate the counter. For binary into an A/D you can connect a switch from a reference voltage.

The same type of channel can be used with a resistor network to detect the position of a rotary switch with n positions or let you read a hat style switch- 4/8 positions but only one active at a time.

Above the A/D you would want a user configurable scaling section that supports standard sender levels and types- voltage, resistance, current. Haven't read about transorbs ... sounds like a contraction of transient abosorber. Add any power conditioning (and maybe a NiMH backup battery?)
 
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