Laptop interface to TackTick NMEA

Discussion in 'OnBoard Electronics & Controls' started by tspeer, Mar 4, 2008.

  1. tspeer
    Joined: Feb 2002
    Posts: 2,319
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Success! I relocated the NMEA interface and Miniplex41BT to the aft cabin, and I'm recording consistent wind data, now. I finally have the entire architecture (minus autopilot) up and running. The old location was under a stainless sink, and the Dual Digital Display registered 0 signal from the masthead unit at that location. I tried several locations, including under the cabin sole where the hull transmitter is, but the best signal was on the backside of the bulkhead between the aft cabin and cockpit, as far outboard as possible. So that's where I mounted the two boxes. With regard to wiring, it only required running a power cable through the engine compartment and removing the GPS cable from that area.

    The moral of the story is, each Tacktick unit needs to have a good signal from all the other sensor units. The NMEA interface is not just a repeater, but independently does its own calculations of true wind, etc. The Dual Digital Display can be used as signal strength meter to survey best locations for installing the NMEA interface. I'm really glad I got the Bluetooth multiplexer, because it simplified siting the NMEA interface. (It would be really cool if Tacktick added a Bluetooth capability to the NMEA interface itself.)
     
  2. RHough
    Joined: Nov 2005
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    Location: BC Summers / Nayarit Winters

    RHough Retro Dude

    Good stuff Tom. Nice bit of trouble shooting there. Could you post another data stream? I'd like to have a good one to add to my files as reference.
     
  3. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Sure. This one was taken while sitting at the dock. I've not been out sailing since I moved the boxes.

    The dropouts in heading are troubling - I didn't check the signal strength for the hull transmitter in the aft cabin, and perhaps I should have. I may need to shift the NMEA interface again. If I do, this time I'll check all the signal strengths!

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  4. Jack Daniels Eq
    Joined: Aug 2008
    Posts: 50
    Likes: 1, Points: 0, Legacy Rep: 11
    Location: Phuket

    Jack Daniels Eq Shockwave

    I notice this thread is getting up there - any new feedback - have similar project
    BR>Jack
     
  5. tspeer
    Joined: Feb 2002
    Posts: 2,319
    Likes: 293, Points: 83, Legacy Rep: 1673
    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Nothing new, yet. Blue Skyz has been hauled out since mid January, and I don't expect to be sailing again until the end of March.

    However, I've been working on some new, low cost instrumentation. One of the reasons for scatter in the data is the motion of the boat. For example, if the wind instruments are 50 ft off the water and the apparent wind is 12 kt, it only takes an angular rate of 4 deg/sec to make a 10 deg change in the apparent wind angle. So being able to account for the motion of the boat is important to accurately determining the steady-state apparent wind and true wind.

    It turns out one can buy a unit for $40 that has a three-axis accelerometer sampled at rates up 80 hz, plus an infrared camera with a resolution of 1024x768 with hardware blob-tracking that can give the 2D position of 1 - 4 infrared LEDs in the 25 deg field of view, and communicates wirelessly via Bluetooth to a computer. Up to 4 of these units can be used simultaneously. They're called Wii remotes. Many people also buy video games to go with them.
    [​IMG] The latest in boat instrumentation

    Attached is a sample data log from a Wiimote. The first column is elapsed time, in seconds. The third, fourth, and fifth columns are acceleration. The Wiimote is first laid on each side and the ends to use gravity to find out the axes directions and signs. Then I manually did a frequency sweep in each direction to see the response of the accelerometers. The biggest problem that I see is the sample rate is not constant, but may depend on the amount of motion. I'm hoping normal boat motion will be enough to keep the Wiimote stimulated and transmitting continously.

    I plan to mount one Wiimote under the main cabin sole, next to where the compass transducer and TackTick hull transmitter are. I may put another Wiimote under the aft cabin with a light bar attached to a steering cable to both measure the acceleration at that location and the rudder position. Another Wiimote may go at the base of the mast, approximately 6' above the first Wiimote, to measure acceleration and boom position via a light bar on the boom. The difference between the mast and main cabin accelerations will provide pitch and roll angular acceleration. The difference between the aft cabin and forward accelerations will provide pitch and yaw angular acceleration.

    I plan to combine the high-rate data from the Wiimotes and the low-rate (1 hz) data from the TackTick instruments in a Kalman filter algorithm. The filter will estimate the angular rates and angular orientation (yaw, pitch, roll). It will also correct the wind data for the motion of the boat, providing a more stable estimate of the apparent wind and true wind. Similarly, the influence of wave motion can be estimated and removed from the data. I hope to be able to estimate the leeway angle, too, although that may require either some sort of hydrodynamic model of the lateral forces or input of currents. If I can get reliable data from the Wiimotes, this should drastically reduce the scatter in the performance estimates.

    Obviously, this is the start of a long-term experiment!
     
  6. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    Oops. The data didn't upload. Here it is.
     

    Attached Files:

  7. gradymorgan
    Joined: Dec 2009
    Posts: 1
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    Location: Seattle

    gradymorgan New Member

    How's it going?

    I know that my Raymarine ST60 wind meter does some sort of smoothing of wind data, so I don't see wind changing as the boat goes over waves and what not. It seems like a shame that the tacktick system doesn't spread that smoothing (and the true wind speed/dir) over the network, but I'd bet you can find a simpler algorithm for de-noising your wind data.

    Did you ever get anything going with the wiimote?

    I'm about to get a Tacktick compass, and try and wire that into a laptop with my raymarine wind and speed instruments. You're post has been enlightening.
     

  8. yipster
    Joined: Oct 2002
    Posts: 3,486
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    Location: netherlands

    yipster designer

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