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Old 11-12-2017, 09:38   #1
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Satellite TV on a boat - anyone know a DIY stabilised platform?

Not sure if the topic is right for this but here we go......
I sail UK and France. I have used a campng satellite dish for TV in France where it is nice and calm in the marina but my home port is mooring on a pontoon which is tidal and susceptible to wind and passing boats.

I have built a gimballed holder for the dish as an expermiment and it works but the dish keeps swinging unless I have a really heavy weight and a long pole in it.

I am electronics engineer so I am quite happy to design a PIC processor circuit that works with 3 axis detectors and make a mororised system. Yes its great fun daydreaming the design but its faster to copy someone elses design a la "open source".

Does anyone know anyone who has successfully designed their own stabilised (UK spelling) platform etc without it costing £1000's?

I envisage a small box with three servos yaw, pitch, roll and when setup you push a button and it keeps the platform stable. I don't have any drawings in mind as its such an early stage.
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Old 11-12-2017, 11:01   #2
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Hi Fiona,

I don't know of an open source resource to point you to, but wanted to mention my boat had an 'economy' dish tracking device when I acquired it. It purportedly worked with any sat dish TV service.

It was branded Follow Me TV and appears to still be manufactured in case it is of interest.

I never used it and therefore cannot comment on its efficacy. [It is relegated to storage until such time that I need to make more room...]

Best wishes finding/creating what will best suit your needs.

Cheers! Bill
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Old 11-12-2017, 11:18   #3
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

The KVH systems like the one I have stabilize in both vertical and horizontal axis, the Follow Me TV only in horizontal.
A home type dish is much larger than a KVH and therefore has a much wider focus Beam, it tracks all sats without moving, the KVH has to move for each different sat, I bring this up because if you use a bigger home type dish, it’s likely your tracking doesn’t need to be as accurate as a KVH, just you have a big dish on board.
I don’t have an answer, I don’t think it’s simple as I think you need a system to track signal strength and move so that signal strength is strongest, the KVH does it exceedingly well, I have yet to get into weather that it wouldn’t track a satellite, heavy rain of course shuts it down, it can’t “see” through heavy rain.
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Old 11-12-2017, 11:35   #4
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Thanks Bill and A64pilot for the posts

The track-it looks like a simple motor on a stick driven by an electronic compass, the KVH system does what I'm thinking about but there are too many characters to the left of the decimal point in the price but thanks for the ideas, keep them coming.

What I'm thinking about is a LSM303 3 axis and magnetic detector driving a PIC or Arduino controller driving servo's. I have several ideas in my head of how to do this but rather than do it from scratch I would love to talk to someone who has already tried it and won and then share how to do it.

I can see see so many applications for this from an auto-helm to a searchlight It might even keep my tea from spilling without using sealed mugs!

Fiona
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Old 11-12-2017, 15:56   #5
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Sounds like off the shelf drone stuff. They use stabilized cameras all the time and all you would need is larger servos.......
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Old 11-12-2017, 16:49   #6
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

I think you need a six-axis sensor with a fairly quick response; and servos that can aim the dish against six directions of motion.

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.

Sway might seem unimportant initially, since I immediately assumed the boat will not move enough to misalign the antenna. But then, well, the wind does shift. And the boat swings around to follow, which is just sway about a fixed point. If you want to remain in alignment with a wind shift, this sensor is necessary.

The importance of surge, I think, will be directly related to the longitudinal position of the yacht relative to the satellite orbit. But it probably just won't be important. If the yacht at anchor is surging violently enough to cause the antenna alignment to go out of whack, you're problem also suffering from total rain fade and not really feeling like watching TV anyway.

Yaw, I think, is probably much like surge in the context of an anchored yacht. Outside of some unpleasant weather, there should be little of it, as the boat is held tight by a stretched rode against a nifty breeze.

And of course, roll and pitch must be accounted for.

You can buy an off-the-shelf six-axis sensor for a few hundred bucks. If you have an autopilot, your boat probably already has one. Then you'd need to build a gimballed antenna mount (a true gimbal, not like the smooth pin joint on your stove that everyone calls a gimbal) that is six-axis controlled by your servos. The servos might be pricey, they need to be pretty fast and smooth in their operation. Finally you need a control board that reads the sensor data (NMEA 2000) and coverts it to reciprocal motion instructions for the servos.

It sounds like a fair bit of fun to design and build, actually. But if I just wanted to watch TV, I might just buy one instead. Or go to the sports bar nearest the dinghy dock...
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Old 11-12-2017, 17:30   #7
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

https://www.basecamelectronics.com/pro/
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Old 12-12-2017, 09:17   #8
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Thanks Caribbeachbum and Blue Chicago for the advice. I started this as my multi channel terestial aeriel doesnt work that well all the time.

Since thinking about this overnight and reading all the comments its becoming more of a quest and possibly a project over Christmas. I saw this video and read the source code.

I am going to play with an Arduino, stepper motors/20Kg servos and a six axis accellerometer with a magnetometer and a Zehdnder Mutimo dish.

I reckon I can do this for an outlay less that £300. I only need to tune in to Astra and I can make the dome in fibre glass.

Anyone else interested in my progress or got any more advice please?
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Old 12-12-2017, 09:23   #9
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Quote:
Originally Posted by Caribbeachbum View Post
You can buy an off-the-shelf six-axis sensor for a few hundred bucks. If you have an autopilot, your boat probably already has one..
I have an autohelm 4000 with a wheel pilot which I am thinking of replacing, recently re-did all the electronics on the engine using PIC and repeaters in the cockpit, this does all the engine, bilge data with horn, GSM alerts and intruder alarm. AIS was next but this seems a bit more fun.
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Old 12-12-2017, 09:53   #10
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

I am a software engineer who used to work for KVH, on their first generation of actively stabilized antenna platforms. It is a very tough nut you're trying to crack, and you'll need a lot more power than a PIC processor has to offer. A Raspberry Pi 3 should have the horsepower, but then you have several issues you need to think about.
- You need stable and accurate pitch and roll, and yaw (compass heading).
- You need your current location (GPS position)
- You need to know what satellite to point at, and it's orbital parameters.
- From the attitude inputs, GPS position, and satellite info, you need to calculate where in the sky you need to point your antenna.
- Once you know where to point, you need the motor control (azimuth and elevation) to point it there.
- Now you need signal strength as an input to fine tune the whole solution.
- And finally repeat the entire process many times per second to keep the antenna pointed as your boat moves. Even in a calm anchorage.

Is it doable as a DIY project? Sure, if you have the time and resources to invest. Just know what you're getting into...

Regards,
David
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Old 12-12-2017, 10:23   #11
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

I have installed a lot of sat dishes for DTV and Dish TV.
The satellites are 22,000 miles from earth and just of the end of
south of Texas in a stationary orbit, If you move a dish just a 1/4 of an inch you will lose the satellite feed.

Something has to measure the signal strength from satellite and adjust
dish accordingly. Azimuth and Elevation.

So the trouble is when you lose signal it takes time for the system to acquire
the signal again, good systems will have a big buffer and store data in advance so
when you turn there is hopefully enough time for the dish to get its signal back.

Simple. or NOT

http://www.satsig.net/azelhelp.htm

-
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Old 12-12-2017, 13:30   #12
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Quote:
Originally Posted by FionaJC View Post
Thanks Caribbeachbum and Blue Chicago for the advice. I started this as my multi channel terestial aeriel doesnt work that well all the time.

Since thinking about this overnight and reading all the comments its becoming more of a quest and possibly a project over Christmas. I saw this video and read the source code.

I am going to play with an Arduino, stepper motors/20Kg servos and a six axis accellerometer with a magnetometer and a Zehdnder Mutimo dish.

I reckon I can do this for an outlay less that £300. I only need to tune in to Astra and I can make the dome in fibre glass.

Anyone else interested in my progress or got any more advice please?
Fiona,

The basecam comes in a 3 axis version that will cost you about $200 for the board and sensors. They leverage brushless motors - similar technology to what is used to spin drone propellers. These motors will be silent and smooth and fast, especially when compared to a hobby servo. This particular board comes with tuning software for optimizing the stabilization.

This is the technology that is frequently used to create highly stabilized video camera platforms. What I have seen is incredibly impressive (youTube has quite a few videos)

If you do embark on this project, I would suggest that you create a gimbal for your dish, such that it is perfectly balanced when no power is applied. By doing this, you will find that much less power is needed to keep your dish stabilized and pointed where you want it (I suspect that strong winds will be another challenge).

Also, whether the precision is there to keep your dish pointed precisely on a rocking boat, I can't say.

Finally, be aware that hollow shafts on your motors along with the use of slip rings may be desirable, depending on the amount of rotation you are looking for (especially at anchor).

Best of luck on your project

-BC
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Old 12-12-2017, 17:19   #13
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

Quote:
Originally Posted by Davidhoy View Post
... It is a very tough nut you're trying to crack, and you'll need a lot more power than a PIC processor has to offer.

...

Is it doable as a DIY project? Sure, if you have the time and resources to invest. Just know what you're getting into...
Some very good points there, David! I guess if it were something an engineer with your background can built in a few weeks you would've already done it?

When I thought about such a system a few years back I also envisioned using two (perpendicular) gyroscopes on the platform and spin them up once the dish is pointing roughly where it needs to. That could make the stabilisation easier and smoother. WDYT?
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Old 12-12-2017, 17:56   #14
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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Originally Posted by hzcruiser View Post
Some very good points there, David! I guess if it were something an engineer with your background can built in a few weeks you would've already done it?

When I thought about such a system a few years back I also envisioned using two (perpendicular) gyroscopes on the platform and spin them up once the dish is pointing roughly where it needs to. That could make the stabilisation easier and smoother. WDYT?


The problem with gyros is precession and drift. They are a great short term reference, not so good as a long term reference. Inclinometers and compasses, on the other hand, are great long term references (with an appropriate sliding window average), while being poor short term references. The key to accurate instantaneous pitch, roll and yaw is to combine the short term accuracy of a pair of rate gyros with an inclinometer and a fluxgate compass.

You need to keep the antenna pointed within a roughly 1 degree error cone, as your boat moves. As the boat moves it will induce precession in any gyros you are using, hence moving your antenna even further off target. I think you will find than regular gyros are not going to be of much help on a moving platform.

The rate gyros I mentioned earlier are different in that they measure rate of change rather than provide mechanical stabilization.

Regards,
David
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Old 12-12-2017, 18:00   #15
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Re: Satellite TV on a boat - anyone know a DIY stabilised platform?

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.
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