how can i usa a radio controll model gyro and servo to make a turntable point in the same direction?

i live on a sail boat and i can get wifi but each time the boat swings i lose the signal so want to mount the antena on a turntabe to keep it pointing in the same direction?

sort by: active | newest | oldest
spook7777 years ago
I live on a boat too and I have solved this problem simply.  A bowl of water, a big bar magnet, styrofoam, and a swivelling antenna connector. 
  Insert the magnet into a circle of foam to make a primitive compass.  Float it in the bowl.  Suspend your antenna (mine's a biquad) from the swivelling connector over the bowl.  When the station a acceptable, drop the antenna.  Let it float on the compass foam and rotate.
What's the antenna connected to ? A router ? or direct to your PC ? 
Do you only have a marginal signal ? 
How much "swing" can you experience ? 

Poppy_Ann (author)  steveastrouk7 years ago
hi antena is conected to desktop computer below decks so when the boat swings i only find out when i lose the signal.

i have not done that much with electronics but i can follow a circuit diagram and make it.
i will look into a directional + rotational (6 axis) accelerometer as stated by frollard and see how much that would work out to cost and how much work to build it.

i have never designed any circuits before i was thinking that if i just pluged in the gyro to the servo with some form of powering them then it would try to follow the direction i first conected power to it.

it looks like it will be a much larger project then i was thinking of but if i can get the items easy then i may still try and build it.
the antena is around 16" x 14" and 1 1/2" thick it is a high gain so works over good distance up to 2 Km but only 22 deg swing.

many thanks for everons help when i get more facts to work with i wil get back to everone
regards paul
Can I presume you have a decent GPS unit on board ? And can I also presume that produces heading information for you ? Then the signal you need is already on board, and available for further processing. You need to link the serial port from the GPS, and read the NMEA information it produces. Somewhere I expect there'll be a heading number. Line up the antenna with the source, press a button to record the current heading, and then a simple servo keeps that correct relative to the GPS reading.
I've spent a bit of time studying the NMEA codes. There are various things you can ask for  that the GPS can produce on demand, including various bearings, delivered to 0.1 degree of angle,  that could well be all you need. 

Exactly what antenna are you using Paul ? You might be better changing antenna design than messing around with tracking antennae. Something with a reasonably high gain in a narrow altitude, but 360 deg azimuth would be ideal

Poppy_Ann (author)  steveastrouk7 years ago
hi there no chance of using 360 deg antena as quite oftern i have to anchor quite a way from land / wifi server and no 360 antena will give me the range i have been able to pick up a good signal at over 1Km and when there is not to much wind it is ok but as soon as the wind picks up i lose the signal due to the boat swinging around.
Designs like the Slim Jim have a very narrow vertical angle radation pattern - that'll give you 6dB of gain for free- that might be enough, and will save you a lot of effort.
seandogue7 years ago
Presumably you're using the gyro to implement a digital compass of some sort?  If so, you need to implement a control loop to track the turntable position to a fixed compass value, using the difference between the gyro's set position and the realtime position as the drive for the servo.

That is, once you've achieved a good signal by manually adjusting the antenna, you press "lock" on the imagined "circuit"...any difference in output form the gyro is interpreted as error voltage which is fed to the servo drive.

Finding it difficult to explain, but it's pretty straightforward if you think about it.

Let's say you have a computer/microcontroller/datalogger/etc...

The gyro's compasses output is fed to the analog input (presuming a simple analog output compass for the sake of discussion) and read at a speficied sampling rate.

some user-control instigates capture the value when you say "go" (when the antenna is set for optimum signal strength) and triggers the control routine

the control routine then use that captured value as the setpoint for a first order tracking routine in which

 Error = setpoint - realtime_compass_signal

Error is then fed to the servo control thru signal conditioning (amplification and filtering) to drive it either +deg or -deg to regain lock with the desired compass heading
A cunning solution sir, I salute you.
but why not just mount the antenna on the mast ? 
why for the mast, I guess my short, quick, off the cuff anwer would be that it doens't spin in relation to the compass heading ... ;-)

(Here I suspect that the author is using a directional antenna to increase his/her effective range already, which is why he/she asks about aiming)

Pity the OP hasn't come back: its an interesting little project.

Poppy_Ann (author)  steveastrouk7 years ago
sorry i did not get back to you faster but being that i live on a sail boat and move around a lot i dont always have internet conection.
at moment i am in the british virgin isles untill new year then i will try to locate more of the parts i need to try to build a circuit.

i think the turntable should be easy to build its just the electronics.
also living on the boat is hard to obtain parts unlike when you are in a house and have a permanent address for reciving post
what's the OP project?
The Original Poster, and his tracking wi-fi
Doh!  sometimes I amaze m'self with my befuddledness
I would figure a directional + rotational (6 axis) accelerometer would be accurate enough to maintain a lock by itself - I find magnetic sensors are brutally inaccurate/slow updating...

An addendum to the circuit could include a signal strength monitor, and constant spiral scanning to keep a positive lock on the signal.  A small script could poll the wifi card's drivers for the strength and correlate that to the microcontroller circuit.
RE: accelerometers...Agreed...Although I believe many of the newer single chip electronic compasses are plenty quick enough for this application, and use of a compass rather than strictly referential measurements could bring some interesting development possibilities to the table...still, I can't argue with your logic... Can't say for a traditional gyro, but assuming chip scale I think it's doable. There's more than one way to skin a cat. (although I'm not sure why anyone would skin a cat)

(on the single chip electronic compasses, I looked into a bunch of them for an application I was considering ~ a year ago. I'm afraid I have no links available anymore, but you know how to find them as well as I do. They're not cheap, but they are nice...(the not cheap, coupled with over farming of "oooh! free" parts by non-engineering types from mfg samples pages over the last decade is why I'm not in possession of a few m' it)

wrt addendums...In fact, I originally read the query as being one of a moving target, rather than just a stationary receiver subject to "jostling" and had to re-write once I realized that the author is concerned with little more than yaw issues. Many fun things could be done...I just realized I could write a book if I started appending his original parameters. I like your ides though...good thinking.
lemonie7 years ago
That's a good question, but I'm thinking a motor-driven gyro' might be better?
(don't know otherwise)