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Old 12-12-2017, 18:04   #16
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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There are I believe quite a few outdated KVH antennas out there that no longer work, might could get one cheap and harvest it’s electronics?
There was some sort of change to the Satellites I think that made some series of self pointing dishes obsolete, I think.


The original antennas were circularly polarized, and were later superseded by linearly polarized ones.
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Old 12-12-2017, 18:35   #17
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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The problem with gyros is precession and drift.

...

The rate gyros I mentioned earlier are different in that they measure rate of change rather than provide mechanical stabilization.
Understood. And yes, I was thinking a combination of gyroscopes and gyro sensors to feed a microcontroller which controls the stepper motors via H-bridge drivers.

Fiona, I take it you've already looked into patch antennas as a possibly easier to adjust solution with less windage?
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Old 12-12-2017, 19:00   #18
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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The original antennas were circularly polarized, and were later superseded by linearly polarized ones.


Assumption being they will still track a Satellite, and if coupled to a correct antenna, you have a working system?
Tracking a satellite is I believe the tough nut to crack here? Possibly if nothing else cannabalize the electronics to drive servos of your own?
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Old 12-12-2017, 19:31   #19
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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Assumption being they will still track a Satellite, and if coupled to a correct antenna, you have a working system?
Tracking a satellite is I believe the tough nut to crack here? Possibly if nothing else cannabalize the electronics to drive servos of your own?


An aiming mechanism for a circularly polarized antenna can rotate the antenna about its central axis, and still work correctly. If you put a linearly polarized antenna on the same mechanism, you’d rotate the antenna off its polarization axis, and it would no longer receive the signal correctly.
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Old 12-12-2017, 19:48   #20
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

There is obviously more to this than I know about
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Old 12-12-2017, 19:53   #21
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

is your plan to aim it manually. then hit a button to try and stabilize it, holding it in the same direction? I can't see that happening very well. maybe for a short while. but you'd be constally trying to manually recenter it as it slowly drifts off.

the commercial ones aim it by reading signal strength coming in. and move bassed on signal, not trying to hold a pre set location. and also can tell which sat they are locked on.
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Old 12-12-2017, 19:54   #22
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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There is obviously more to this than I know about


LOL! Believe me, I don’t know that much either. Enough to be dangerous, as the saying goes. I worked at KVH years ago and things may have changed substantially since then. Some principles remain, though, and hopefully I have not confused them too much.
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Old 12-12-2017, 23:13   #23
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Hi

Photographers have been known to use a few old 5.25" hard drives as cheap gyros when making a steadycam. They also add weight where it is needed. You will probably need the active system you initially contemplated, but adding the gyros should help with stabilisation.

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Old 13-12-2017, 00:18   #24
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

I suspect the US Navy has this figured out.
You could probably get the parts cheap off of a used nuclear submarine that is being scraped out. Maybe even a destroyer.
Just showing I know less than a64pilot.
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Old 13-12-2017, 01:41   #25
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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Sure, heave introduces little or no error at the equator, but at the latitude of the UK or France, a regular three-foot swell might easily keep the antenna misaligned by several degrees some 66 percent of the time, and that's without even accounting for roll.
I think we can ignore heave. Even at the pole, a 3 ft change in elevation results in less than a 0.4 nanodegree change in angle towards a target in equatorial orbit (22,000 miles up). The other axes are a problem, though.
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Old 13-12-2017, 05:30   #26
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Wow did I ever start a thread!

Thank you all ever so much for all your ideas, and keep them coming please, its great.

I built a mechanical gimbal to see what it could do. Let me just say it was interesting. I thought about motor driven gyro's but the power consumption, and as said earlier, the drift made me reject this.

My decision thus far;
I have decided the end result will be encased in a dome to avoid windage.
I want to point it at ASTRA only (initially) so it points in the right direction, I manually check the signal and then lock it. I'm only going to use this on the pontoon, marina or possibly at anchor.

It will be based on a fluxgate for direction and then use a six axis 6050 driving initially an arduino (I think the Pi will be too slow)and probably stepper motors using proportional–integral–derivative drivers.

Ill try and get the dish balanced in a mechanical gimbal and I'm looking at possibly a Gregorian flat dish.

Knowing that there can be movement in all the axis at once will make it interesting. I intend to perfect the code for a single axis and then add to it. Most of the gyro copters Ive seen have too much hysterisis, I think I will have to have some predictability about it (with the sea!) but at this stage I dont know how much if any.

At this stage all the advice is excellent and food for further thought. I now work in IT so I dont do as much electronics as I used to so this is something to really get my teeth into.
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Old 13-12-2017, 07:31   #27
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Hi Fiona,

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Originally Posted by FionaJC View Post
I built a mechanical gimbal to see what it could do. Let me just say it was interesting. I thought about motor driven gyro's but the power consumption, and as said earlier, the drift made me reject this.
Yes, drift and precession, and power consumption, all but eliminate a purely gyro driven stabilization system.

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It will be based on a fluxgate for direction and then use a six axis 6050 driving initially an arduino (I think the Pi will be too slow)and probably stepper motors using proportional–integral–derivative drivers.
That six-axis 6050 is a pretty cool device. We did not have those back in the day, they might have made the job a bit easier. We essentially had to create the mechanical equivalent using two spinning rate gyros, an inclinometer (accelerometer) and a fluxgate compass.

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Knowing that there can be movement in all the axis at once will make it interesting. I intend to perfect the code for a single axis and then add to it. Most of the gyro copters I've seen have too much hysteresis, I think I will have to have some predictability about it (with the sea!) but at this stage I don't know how much if any.
Yes, that is where the fun starts! Except I'm not sure doing one axis at a time will help much, you pretty much need all three axes working together to keep the antenna pointed at the satellite. I guess you could do one at a time by eliminating the other variables, mount your device on a swinging platform that restricts motion to a single axis, say your pitch axis. Attach a laser pointer to the antenna and aim at a paper target some distance away and see how close you can stay to the "bullseye" as your "boat" pitches fore and aft. When you add the second axis you could rotate the device on the swing table by 45 degrees, mimicking motion in pitch and roll.

Interesting project :-)

-David
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Old 13-12-2017, 07:45   #28
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

I got into sailing to get away from TV!
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Old 13-12-2017, 08:03   #29
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

David,

I appreciate your comments and that's the line I am thinking, perfect one axis and add another using the same method, then tweak it, then add the third and so on gradually building up. I was thinking how I could add two 6050 and why, its just they are so cheap and I could add one to the boat for comparatives.

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I have projects like this at home to avoid TV, I continue them on board. I only watch TV when I have nothing else to do and Ive settled down with a glass of wine in the evening with HWMBO.
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Old 13-12-2017, 08:13   #30
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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David,

I appreciate your comments and that's the line I am thinking, perfect one axis and add another using the same method, then tweak it, then add the third and so on gradually building up. I was thinking how I could add two 6050 and why, its just they are so cheap and I could add one to the boat for comparatives.

Geoleo
I have projects like this at home to avoid TV, I continue them on board. I only watch TV when I have nothing else to do and Ive settled down with a glass of wine in the evening with HWMBO.
Wine! Now you're talking my language ;-)
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