I'm not sure what the best approach is to measure the angle of floating platform. It is flat most of the time but it might see some wave action. The roll period of the platform is around 4-5 seconds. I will new trinity to measure only the inclination angle and filter the change due to the wave action.
What sensor I should use for that project? Is 6050 going to work?
If the platform was relatively stable, and is tilted lets say 15deg can the measurement be consistent over few hours?
Can there be such low,low,low pass filter to filter the 4-5 sec own roll period of the platform?
Thank you,
I'm not sure what the best approach is to measure the angle of floating platform. It is flat most of the time but it might see some wave action. The roll period of the platform is around 4-5 seconds. I will new trinity to measure only the inclination angle and filter the change due to the wave action.
Have no idea what your talking about. You need to provide a photo or drawing and explain why this thing is rolling.
This isn't anything we should be expected to be familiar with. Start at the beginning and explain what your talking about.
We're geeks, not salty dogs...
imagine boat with crane on it in calm water. the deck on the boat is parallel to the water. If the crane's arm is protruded out and weight is lifted the angle of the deck of the boat will change. then there could be a wave action that will roll the boat an the top of the list created by the lifted weight. I would like to measure and filter that with Arduino and sensor.
the running time of the device will be more then an hour and that's why i was concerned (or should I?) about drift.
the accuracy of 0.5 deg is plenty. sampling as often as needed, but the output 2 to 5Hz.
the sensor I was asking about was http://playground.arduino.cc/Main/MPU-6050
i hope that clarifies it a bit.
I think of the wave action as cyclic in the sense that it will cause the tip of the jib to swing up and down (or whatever).
But the nature of the effect of the waves on a heavy object with a varying centre of mass (as the load is lifted or slewed) seems like it would be very complex indeed.
Even in flat-calm water the act of lifting a load or slewing the jib will cause the deck to oscillate. I have no idea how you would distinguish crane-induced oscillations from wave induced oscillations.
Could you use a second sensor on a nearby small lightweight floating platform to detect the natural movements of the waves?
Presumably with that 6050 device you could record angles to your heart's content. But what then?
Perhaps if you explain why you want to do this your project would be easier to understand. I presume it has nothing to do with the crane falling over.
seamaster:
i was concerned (or should I?) about drift.
Do you mean the vessel drifting on its anchor, or drift of the readings from the '6050 sensor over time? If the latter, then drift is not a problem. The '6050 has an accelerometer, so it always knows exactly which way is down (in calm water, at least).
seamaster:
the accuracy of 0.5 deg is plenty. sampling as often as needed, but the output 2 to 5Hz.
Well, that's trickier. You seem to be asking for the swell-compensated tilt reading to be able to react very quickly, in a much shorter time than the wavelength of the swell, contradicting the subject you put. This will mean the Arduino must analyse the swell in 3 dimensions, determining wavelength and amplitude, so it can remove the effect of the swell from each reading at any instant in time. An interesting challenge to be sure! You'll need someone with a Maths degree to help you!
If the output could be slower, i.e. much slower than the wavelength of the swell, like your subject suggests then it would be a simple matter of averaging the readings, but that would have to be over a period of at least a minute I would have thought.
If the moving platform was only moving a little bit then you could just average the nett acceleration vector over a long enough time to average out the movements. The result would be the acceleration due to gravity, and from that you could work out the orientation of the platform.
PeterH:
If the moving platform was only moving a little bit then you could just average the nett acceleration vector over a long enough time to average out the movements. The result would be the acceleration due to gravity, and from that you could work out the orientation of the platform.
What is the formula to use for average the movements?
Would this work: Imagine you install the 6050 with z axis vertical, y axis across the beam and x axis fore/aft. You then take a straight average of the x, y & z values over the long period. Use pythagoras on the x & y averages to work out the magnitude of the vector in the horzontal plane. Then use trigonometry to calculate the angle to the vertical using the result and the z average.
seamaster:
What is the formula to use for average the movements?
For each axis, add up all the samples over a period and divide by the number of samples. This gives you an average for each axis. Then use simple trig to calculate the direction of the resulting vector - that's your vertical.
Hi all, there was a much simpler solution to my problem:
As the roll period of the platform is know, I needed to delay the alarm with 1/2 of the roll period of the platform . When the timer exceeds the 1/2 roll period, i compare the angle to the critical angle. if the critical angle is exceeded i trigger alarm otherwise the timer gets reset.
For example
so if the roll period is 5sec. and the critical angle is set to 10 degrees, the platform is listing 8 deg, then wave hits the platform and let's say it rolls it to 12deg, when the roll angle reaches 10 deg the timer starts. I delay the alarm for 1/2 roll period or in this case 2.5 sec., which means that the platform is back at 8 deg and not exceeding the critical angle after the 1/2 roll period has past.
thank everyone for the posts