Did Somthing Happen December 28th?

The main aim of the FUNcube project is provide educationalists access to information about a real spacecraft in Low Earth Orbit. Please use this forum to discuss classroom projects and similar matters. FUNcube support is provided elsewhere in the forum.

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Re: Did Somthing Happen December 28th?

Postby wa8sme » Sat Jun 28, 2014 2:42 pm

I continue my quest to study the rotation behavior of the FunCube, and frankly that study generates more questions and theories than answers; and that's a good thing. I have tried to generate a visual image that helps to explain the behavior that is illustrated in the graph of the data (note the rotation rate on the Y-axis is a log scale to help deal with the range of rotation rates to date).

Previous I had developed a turn-table thingy that can be used to demonstrate the range of rotation rates expected for the Fox constellation of satellites. The turn-table is basically a geared DC motor with a controller and GUI. The motor rotation rate is controlled with PWM and an H-bridge, it has a maximum RPM of 2, the minimum depends on the stall characteristics, but is slow enough for this application.

So what I did was divide the life span of the FunCube into 25 day sections and picked a representative rotation rate for each 25 day interval. For the video, I set 10 seconds to scale the 25 days, and programmed the turn-table to rotate at the representative rotation rate for that segment of the life span. In the video, you see a portion of the GUI with the day in orbit and the rotation rate in RPM during that 25 day segment, and the FunCube model on the turn-table. The video can be downloaded from here: https://www.dropbox.com/l/9Wo0by0lYW4knaxkSNrIqu?

Admittedly it is sort of like watching grass grow, but perhaps it might be useful for some students to visualize the orders of magnitude of the rotation rate, and just what is being attempted by monitoring that rotation rate. I think some "bird walk" questions for discussion might be: why rotate the satellite?, what rotation rate is too fast or too slow?, what happens if it rotates too fast, too slow, or not at all?, what are the forces involved with slowing it down and speeding it up?, are there any connections or interaction between these forces?, just to mention a few.

I still maintain that the FunCube is a resource that just keeps on giving. I know I have expended a bunch of the few remaining brain cells I have left contemplating the wonders of the FunCube and I am in the early stages of developing follow-on experiments for possible time on orbit, and certainly for on-the-bench work in the classroom. There are probably better ways to expend those brain cells, but then again, those ways are probably illegal someplace.

Mark, WA8SME, mspencer@arrl.org, [The Connecticut Yankee in the FunCube Court...sorry, gotta try and lighten this thing up a bit.]
Rotation Graphic day 225.png
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Re: Did Somthing Happen December 28th?

Postby wa8sme » Wed Jul 23, 2014 11:08 pm

Hope you all have a great symposium next week. This is my latest summary of the rotation rate to date, currently at 5 minutes per revolution and going down.

Please do me a couple of favors. If the topic of the rotation rate comes up, can you give me a short summary of the discussion?

Second, please take Steve Ford from the ARRL out for a plowman's pub lunch, with some Stilton Cheese and a pint of Green King Bitter. TNX

Mark, WA8SME (at one time G5EPV)
Rotation Rate Jul 23.jpg
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Re: Did Somthing Happen December 28th?

Postby wa8sme » Sat Aug 23, 2014 7:17 pm

Hi All,
Well the FC has been on orbit for over 9 months now and I still am monitoring the rotation rate via the MSE temperatures. Still have more questions than answers however. Currently it is slowing down, today at 15 minutes per revolution as near as I can tell. Soon it will be very difficult to infer the rotation rate from the temperatures and the data will be pure speculation until the bird starts to wrap up again.

I am almost to the point of inferring a period of these rotation rate oscillations, but not just yet. I am still haunted by two possibilities to explain the rotation behavior, coupled oscillators and the YORP Effect. One of these days I am going to have to clear the old noggin and take a fresh look at it just in case the old stale theories are clouding the judgment. If I or the bird lives long enough, there just might be enough data to speculate about chaos and strange attractors in relation to the rotational behavior.

Anyway, here are the latest graphics of the data. I close as I continue to maintain, the FC is one bird that just keeps on giving.

Mark, WA8SME
Data at 270 Days.jpg
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Re: Did Somthing Happen December 28th?

Postby wa8sme » Sat Jan 24, 2015 4:00 pm

This is one of those "for what it's worth" items. I finally captured enough data, and I had the time, to do a Fast Fourier Transform on the rotation behavior of the satellite. I have long speculated that the rotation behavior reminded me of a coupled oscillator, and I still feel that this may be a contributor. I have attached the current summary graphic of the rotation rate as a function of day on orbit. Note the Y-axis is logarithmic to try and capture the dynamic range of the satellite which runs from virtually stopped rotating to over one revolution per minute.

The next graphic is the plot of the manual FFT that I performed on the data. I am still trying to figure out what the FFT is telling me, if anything. I am not even confident that an FFT is of any value in trying to interpret the data due to the huge periods of the wave form that we are dealing with. That being said, and being so close to the problem, I am seeing hints of the coupled oscillator in the FFT plot. I am also seeing some hints of a beat note in the plot.

So it is what it is. As I have said before, the FC is one bird that keeps on giving, and there are so many lessons to be learned from scrutinizing what it is trying to tell us.

For those of you who are active transponder users, I have noted a correlation between the rotation rate of the bird, and the amount that I have to chase the frequency of the downlink (due to the heating issue). This is a case where the data supports what you have had first hand experience with during your operations.

Mark wa8sme@comcast.net
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Fun cube is no fun

Postby ve3akjeff » Fri Jun 12, 2015 2:41 am

Hi ... This is my first post and I have a FunCube Pro that can't hear anything.
Let me first say that I bought this device when they first came out... maybe three years ago.
I could hear a few aircraft calls using my 137 mHz quadrifier antenna in the attic. This antenna
always worked well with my NOAA's from Fla... to James Bay using a home-brew receiver.

I connected the FunCube... it could not hear the NOAA's even when overhead. A friend tested it
with a commercial piece of test equipment and it was replaced by the supplier in the UK. Got the second one
and same thing... This week I followed the instruction to make the upgrade exactly by the instructions. it checked ok
with version 18f. Plugged it in the usb using SDR Sharp (drivers loaded ok) and when a NOAA went over top... it
didn't hear it. I quickly inserted my NooElectric dongle and copied the satellite solid.

I would like to send the FC to someone in the US or Canada that has success with one to see if I have another deaf FC
Please let me know if you can help... I have burnt myself out trying to get this FC to work ... Jeff ve3ak / ve3coj
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