Looking for volunteers to test a new altimeter

gtg738w

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Hello all - as the title says, I’m looking for some help to test a new altimeter. It is a small, recording altimeter - just data logging, no events. The device connects wirelessly to an iOS app to download flight data from the unit (altitude & vertical velocity) and then upload it to a web service. The web site will then log all of your flights and create zoomable/scrollable plots of the data. You can see an example here: https://flightsketch.com/flights/22/

I’m looking for a variety of test platforms, about 5 people. This is primarily geared towards low power models but I would like to see how it performs under more extreme flight profiles as well. This sensor/code will be the base (hopefully) for future, more capable versions. We have tested so far in normal av-bay layouts as well as just being tethered to the shock cord in a simple model with a couple of static ports drilled. You should be able to drop it in almost anything (18mm tube+) if you’re willing to poke a couple of holes. Same with users, we’re looking for feedback from experienced modelers that can fly it next to proven computers to compare data as well as people who have never flown electronics before.

Basic specs/requirements are:
  • 4.2g with battery installed
  • 0.65” wide x 1.2” long, Fits in 18mm body tubes
  • Requires iPhone 6 or newer (or a recent iPad) with iOS 11+
  • Can be mounted with double sided tape in av-bay or tethered to shock cord in a vented body tube
If you would like to help, please let me know and I will send you a sample for (almost) free. It will be $0.01 so we can test the store and shipping system as well.

This project is also open source - I’ll answer any questions you have but I would like to keep this thread technical so it will hopefully stay here. I will post product/store info in the vendor area when it is appropriate to do so.

Thanks for the help - this forum has been incredibly useful. The community as a whole has been inspiring, hopefully we can give a little back.

Thanks,
Russ
 

gtg738w

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That was quick! The units I have are spoken for. Thanks for the support, I’ll keep this updated with news.

Russ
 

BEC

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Drat - missed it! Would have been happy to try it standalone or alongside one or more of AltimeterThree, FireFly, MicroPeak, Adrel ALT-BMP.....

I like the small mass in particular. More than an Adrel or a MicroPeak but far less than AltimeterOne/Two/Three or Pnut.
 
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gtg738w

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Thanks for all of the comments. I wanted this to be small enough be fit in almost every rocket but still have wireless communication for data access. I think this is the sweet spot for that trade. I'll let you guys be the judge of that though.

For Android, I have no experience there yet. I do know a fair bit of Java and recently bought a Samsung tablet to play with, so it is in the plan eventually. My priority will be on the dual deploy version and one other project I'm considering first though. If there is significant interest, I could be convinced otherwise.

The orders that are in so far will ship in the morning.

Russ
 

SpaceManMat

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That’s a seriously nice product for LPR at a great price. Will be watching to see how they do.
 

SpaceManMat

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Having watched the videos, a few thoughts come to mind...
1. As the flight is stored in volatile memory, I think as soon as the phone reconnects it should automatically download a copy for safe keeping.
2. There should be a way to name your altimiter so you don’t accidentally use someone else’s. Your phone would simply associate a serial number with a name and display the name instead.
3. From the video it does not appear to be any way to display the results except uploading it. Since you may not have an internet connection at the launch site, I think you should add this as a feature.
4. Along with the above there should perhaps be a flight summary, probably want to obtain the summary data after it is downloaded to the phone rather than having the altimiter process it. Also, the summary should be online too.
5. Not sure about how possible it is, but some sort of tracking notification option to help you locate your rocket would be nice. IE beep when you get a connection and show you signal strength to help you narrow down its location.

Anyway, looks like a great product.
 

gtg738w

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  1. I like that, had not thought of an auto download before. Would work well with #3
  2. Agreed, we need to reserve a section of flash for storage of things like deployment settings and I would like to have a user defined name as well. I would prefer it to be on the device so is shows the same name across different phones or iPad.
  3. I want to add a flight queue so you can cache data and upload at some other time. For plotting on the phone, this has been low priority since it is available online. I’d like to wait for the Android app to see if something will work and look the same across all platforms.
  4. Not sure what you mean by flight profile. Is this the overview chart?
  5. It does show RSSI updates in real time and I have found a rocket in tall grass with it. It is really short range in the clutter, maybe 50ft. Also non directional but it will show if you walked past it. Bluetooth just announced updates to their location work. Still has the same range limitations but I’m keeping an eye on it. I think someone should just work on a low cost tracker for lpr...:)
 

sl98

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Received today. App is installed and video's reviewed. Looking forward to using it tomorrow and uploading some flight data.


IMG_5925.jpg IMG_5926.jpg IMG_5927.jpg
 

SpaceManMat

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  1. I like that, had not thought of an auto download before. Would work well with #3
  2. Agreed, we need to reserve a section of flash for storage of things like deployment settings and I would like to have a user defined name as well. I would prefer it to be on the device so is shows the same name across different phones or iPad.
  3. I want to add a flight queue so you can cache data and upload at some other time. For plotting on the phone, this has been low priority since it is available online. I’d like to wait for the Android app to see if something will work and look the same across all platforms.
  4. Not sure what you mean by flight profile. Is this the overview chart?
  5. It does show RSSI updates in real time and I have found a rocket in tall grass with it. It is really short range in the clutter, maybe 50ft. Also non directional but it will show if you walked past it. Bluetooth just announced updates to their location work. Still has the same range limitations but I’m keeping an eye on it. I think someone should just work on a low cost tracker for lpr...:)

Sounds good.

For a summary I was just thinking of basic stats not a graph. Ie Max altitude, max velocity, time to apogee, burn time, flight time, decent rate etc. Thinking back to your aim of the project, to make details of the flight easily available, then particularly the “how high did we fly” question is not easily answered when you have no internet connection. A quick run through the data after upload should be able to determine these values and you don’t need any graphics processing for this.
 

gtg738w

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Received today.

Glad to hear, looks like it survived the trip ok.

For a summary I was just thinking of basic stats not a graph. Ie Max altitude, max velocity, time to apogee, burn time, flight time, decent rate etc.

Ah, makes sense. It does show max alt now but most of the other values are already tracked in real time. Would be easy to display. I'll add it to the list. - Thanks
 

BEC

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I don’t have one of these (yet) but I did see one today (and flew it once, alongside an AlitmeterThree in the same model).

I was surprised at its size, in spite of the info on the FlightSketch web page. It’s actually just barely bigger than a PerfectFlite FireFly.

First image is the FlightSketch Mini with a FireFly and an Altus Metrum MicroPeak (top to bottom). The second is the FlightSketch Mini (in its little orange ripstop bag) on top of the AltimeterThree in the payload section of my currently active Nova Payloader (this was prior to its 52nd flight, this one on a Q-Jet C12-6). The reported altitudes were within two feet of one another.

[For those of you not familiar with the Nova Payloader, it’s a BT-50-based payload design which first appeared in 1986. So you’re looking at the top half - about two inches - of the payload section plus part of the nose cone in that picture.]
 

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BEC

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Got one today. Quick test using the little vacuum bottle that Adept used to sell with an AltimeterThree also in the bottle. See pictures....

One note: seeing differences like this using this bottle is not unusual for me.

added: I should explain that first picture. It's the data, on the FlightSketch web site, for the test on the left side, and the app that controls the device open on the right side....this is the split screen mode on an iPad. Second picture is a screen cap of the AltimeterThree graph for the same test.
 

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gtg738w

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Thanks to everyone who has started sending data so far!

A note about the vacuum chamber tests. The Mini does not have an accelerometer, it is barometric only. Because of this, the code uses a Kalman filter based on a kinematic model of the system to estimate the velocity profile. Rapid changes in pressure that don't match the expected model behavior will give you some "coast" and overshoot as the filter turns the velocity around. On a real flight, the system works pretty well.

Bernard was kind enough to send accelerometer data from the flight he posted. I've been looking at this today. The apogee estimates were within ~0.2%. That's the easy part... the velocity profile has been much harder to get right with the baro only setup. My test flights over predicted the max velocity with short burn, high G motors. This flight showed the same behavior. The attachments show the various velocity data.

Red = sim data, Openrocket
Green = raw velocity from the barometer (delta Alt/dt for each point)
Magenta = Velocity profile from integrated accelerometer data
Blue = Velocity recorded by FlightSketch Mini onboard the flight
Black = Current filter in next firmware simulated with recorded pressure from flight

The sim gave an alt of 714ft vs 705ft recorded. Sim velocity was 308ft/s vs 304ft/s from the accelerometer data. Looks like the sim is doing quite well.

The original FlightSketch filter over predicts the velocity by ~20%. I'm still working on the next firmware that has a few updates. The improved model still overshoots but is within 7% of the accelerometer derived max. The oscillations during recovery are also reduced as well.

I'm interested to see if this holds up for more flights. If anyone can send sim or accel data with a flight, that would be wonderful.

Overview:
overview.png

Boost:
boost.png

Recovery:
recovery.png
 

BEC

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The data Russ is referring to is the AltimeterThree data for the Nova Payloader flight I flew yesterday using Larry Kennedy’s FlightSketch Mini (post 20 above). For a model of that size, it is a relatively “high acceleration” flight since the Q-Jet C12 has a pretty good kick off the pad and the thrust goes UP as the burn progresses. A3 reported a peak of 15.45Gs on that flight. I need to take the same model out and fly it with the same setup but use a D16 (!).

I’m not sure I’d worry too much about getting good velocities from baro-only data....but this suggests that I need to fly the FlightSketch Mini with other recording pressure-only devices (Pnut and MicroPeak) and share that data out for comparison. One of the real challenges for any barometric altimeter is getting the “real” apogee when things are bumped around by an ejection charge, which can cause spikes both up and down from either pressure changes or acceleration loads on the sensor or both. Research to be conducted in the next few weeks.....

As I recall Larry flew his FlightSketch Mini alongside at least one other altimeter (he will have to step in and say which one) and got good apogee agreement there as well, though the spread was a little wider than the <2 feet on my particular flight. Having flown a BUNCH of multiple-altimeter flights with many different kinds of devices, these preliminary results look pretty darn good.
 

gtg738w

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There should be an app update (0.2.1) available for download that addresses some of the early comments:

  • Fixed crash if commands sent without device connected
  • Removed “Start Recording” button
  • Added “Connections” button to home screen
  • Phone will remember last device connected and will attempt to auto re-connect after landing
  • Updated field order and labels on download page
Still working the firmware update, hopefully next week.

Thanks for the feedback-
 

BEC

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Just got the app update. Thanks.

I may get a chance to fly it a little today (though right now it looks like it will be too windy) with another chance Sunday.
 
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gtg738w

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I just posted a firmware update (Firmware 16) to the beta instructions page https://flightsketch.com/demo/. There is also a new video showing how to use the Nordic nRF Toolbox app to update the altimeter. This function will be built in with the FlightSketch app eventually but I wanted to get this out to those that have a chance to fly today.

I just flew the new firmware and I think it addresses a few more of the comments so far. Flight with the new firmware is https://flightsketch.com/flights/113/. The highlights are below:

  • Updated filters. This should give a better a velocity profile and smoother data during recovery. This is still being worked for future updates.
  • Recordings now start ~1 second before launch is detected
  • Changed data storage map to allow persistent storage. Data from last flight can be downloaded after altimeter is powered off.
  • Memory scan on power up. Partial data files will be recovered and availible for download if power was lost mid flight.
  • Previous firmware was limited to 2 minutes recording time. This has been extended to the full memory space available ~9 minutes.
  • Improved power use. Significant power reduction in advertising and connected states
  • Idle state turns off barometer when not armed for launch or in flight (further power reduction)


The basic steps to upgrade (shown in video):

  • On your iPhone or iPad, download Firmware 16 from https://flightsketch.com/demo/
  • Send the downloaded zip package to the nRF Toolbox app
  • Put the altimeter into DFU mode by holding down the pushbutton while powering on
  • Select “DfuTarg” in the Toolbox app as device to upgrade
  • Select “Upload” to start the transfer
  • After the transfer you may need to turn off Bluetooth on your phone and re-enable for the new firmware to be recognized.

Note - with the new firmware you will not see the altitude readings update until it is armed for launch.

Thanks, good luck flying!

Russ
 

roytyson

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FIrmware update went flawlessly. I do like the fact you did away with the Start Recording button. This was a little confusing once I got to the field as to which button I was supposed to use.
 
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