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Pitch & Roll sensor with USB output
Does anyone know of a pitch & roll sensor suitable for installation on a
vessel? I need to log pitch & roll on a boat & compare it with signal strength from a satellite receiver, so I need a sensor that will output as USB for me to connect to a notebook & log it, along with signal strength data from the satellite receiver. If necessary I could use an RS232 sensor. I'm hoping for something reasonably cheap. Definitely less than US$500. Dave |
Pitch & Roll sensor
On Thu, 18 Sep 2003 15:16:54 +0800, Dave Baker wrote:
Does anyone know of a pitch & roll sensor suitable for installation on a vessel? I need to log pitch & roll on a boat I'll have another go at this, seeing that I didn't get an answer a while back, and some units that I have found since have turned out to be unsuitable. Anyone know of any pitch/roll sensors that are designed specifically for measuring pitch & roll in vessels? The units that I have found apparently are more for static applications, and are affected by acceleration, so are not accurate in dynamic situations. I'd settle for any USB or serial output, and if absolutely necessary then I'd go for 4-20mA output & shove a converter on the end. Dave |
Pitch & Roll sensor
Dave,
I suspect that you are looking for a ready-made solution for measuring pitch/roll. Perhaps something exists out there but I suspect that the price would be high. If you are looking for something ready-to-go I can't help you. If you have some electronic skills and some programming skills you can build something that will work and most likely be way less costly than the ready-made solutions. There is a solid state sensor that is a two axis accelerometer made by Analog Devices. It is the ADXL202 chip and you can find numererous references to it with a google search on the part number. I have been experimenting, on and off, with the device and a microprocessor for several years and find it rather easy to interface and get working. I am in the process of selling my home and plan to live-aboard and I have sort of thought that a pitch/roll sensor would be a neat thing to do for a "boat project" and I will visit this when I get set up on a boat. I would consider a project of this type to be relatively simple to accomplish if one had some electronic skills. All it would take is a ADXL, a simple micro and a LCD display device and some programming to prototype a working instrument. HTH Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus | On Thu, 18 Sep 2003 15:16:54 +0800, Dave Baker wrote: | | Does anyone know of a pitch & roll sensor suitable for installation on a | vessel? I need to log pitch & roll on a boat | |
Pitch & Roll sensor
On Tue, 06 Jan 2004 10:34:51 GMT, "Vic Fraenckel"
wrote: I suspect that you are looking for a ready-made solution for measuring pitch/roll. Perhaps something exists out there but I suspect that the price would be high. Yeah, basically (unless really necessary), I'm looking for something ready-made. I need 2 units & they need to get installed on 2 ocean going ships for about 2 or 3 months for some testing of satellite transceiver performance vs sea state, so it's important that it works properly - I won't be able to go & make service calls! :-) It will need to be reliable as well as accurate to a degree or so over the expected pitch/roll range of the vessel. There is a solid state sensor that is a two axis accelerometer made by Analog Devices. It is the ADXL202 chip Coincidentally I have one sitting on my desk at the moment - one of those projects that got started but not finished. I was looking at using these accelerometers to strap to engine blocks on boats to determine whether the particular engine was running or not - we had a client that wanted monitoring of engine hours for 4 diesel propulsion engines & 2 diesel generators on a boat. I thought that I might be able to strap these units onto the engine blocks of each engine & get at least an on/off indication, and maybe as a bonus an RPM count. I hadn't considered using them as pitch/roll sensors before. Calibration would be the hard part. I've seen some good rate sensors at http://www.atasensors.com/Sensors2/index.htm and have toyed with somehow getting pitch & roll from these, but don't actually know how to do that yet - integration or something similar I guess? The sensors themselves have good characteristics - fast response, etc. It would definitely be nice to find something that provided pitch & roll in RS232 format without any work on my part. :-) Dave |
Pitch & Roll sensor
Yeah, basically (unless really necessary), I'm looking for something
ready-made. I need 2 units & they need to get installed on 2 ocean going ships for about 2 or 3 months for some testing of satellite transceiver performance vs sea state, so it's Here's a link that might be useful, I don't know what the prices are like. http://www.datawell.nl/products_motion_sensors.html Dennis |
Pitch & Roll sensor
Oddly enough, my goals are the same. I intend to retire this spring, and buy a boat for coastal
cruising. One project I have in mind is a "wave-meter", i.e., a device which will tell me how high the waves are....swells and wind chop. Roll and pitch should be do-able also. My approach is the same as below. But, as pointed out in another post, calibration is the problem. I'll follow this thread with a great deal of interest. Norm On Tue, 06 Jan 2004 10:34:51 GMT, "Vic Fraenckel" wrote: Dave, I suspect that you are looking for a ready-made solution for measuring pitch/roll. Perhaps something exists out there but I suspect that the price would be high. If you are looking for something ready-to-go I can't help you. If you have some electronic skills and some programming skills you can build something that will work and most likely be way less costly than the ready-made solutions. There is a solid state sensor that is a two axis accelerometer made by Analog Devices. It is the ADXL202 chip and you can find numererous references to it with a google search on the part number. I have been experimenting, on and off, with the device and a microprocessor for several years and find it rather easy to interface and get working. I am in the process of selling my home and plan to live-aboard and I have sort of thought that a pitch/roll sensor would be a neat thing to do for a "boat project" and I will visit this when I get set up on a boat. I would consider a project of this type to be relatively simple to accomplish if one had some electronic skills. All it would take is a ADXL, a simple micro and a LCD display device and some programming to prototype a working instrument. HTH Vic |
Pitch & Roll sensor
"Dave Baker" wrote in message ... On Thu, 18 Sep 2003 15:16:54 +0800, Dave Baker wrote: Does anyone know of a pitch & roll sensor suitable for installation on a vessel? I need to log pitch & roll on a boat I'll have another go at this, seeing that I didn't get an answer a while back, and some units that I have found since have turned out to be unsuitable. Anyone know of any pitch/roll sensors that are designed specifically for measuring pitch & roll in vessels? The units that I have found apparently are more for static applications, and are affected by acceleration, so are not accurate in dynamic situations. I'd settle for any USB or serial output, and if absolutely necessary then I'd go for 4-20mA output & shove a converter on the end. Dave I have sailed on Dynamic Positioned vessels that used Hippy pitch and roll sensors from Datawell, they are basically about the size of a dustbin, and have a pendulum supported inside some fluid, never had one open, but as far as I remember the output was 4-20mA current loop. The other type were made by Robertson or Kongsberg , (Now Simrad), they used the gyropscopic principal to measure pitch and roll, and I think they were probably adapted from aircraft use, because they used a strange AC power source 440Hz/48V. Both units were fairly expensive, contact either Datawell or Simrad for details garry crothers |
Pitch & Roll sensor
wrote in message
... | Oddly enough, my goals are the same. I intend to retire this spring, and buy a boat for coastal | cruising. One project I have in mind is a "wave-meter", i.e., a device which will tell me how high | the waves are....swells and wind chop. Roll and pitch should be do-able also. | | My approach is the same as below. But, as pointed out in another post, calibration is the problem. | Norm, There is no calibration problem with the ADXL202. What is a problem, at least with my application, is insuring that the accelerometer is mounted perpendicular to the roll and pitch axes. I am attempting to mount the ADXL on a telescope (not astronomical) to measure the inclination of the optical axis of the system. After trying to align the accelerometer mrchanically to the axes, I am now trying to write a routine to compute the off-axisness and use the results to compensate for the mis-alignment. To understand the ADXL go to the AMD site http://www.amd.com/us-en/ and download the ADXL202 data sheets. There are also some app notes that are interesting. You might also explore U.S. Digital http://www.usdigital.com/ as they have an inclinometer that might do the trick. Check out the T6 unit. I have used their shaft encoder products and am seriously considering the T6. HTH Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus |
Pitch & Roll sensor
To tell if an engine is running or not what about monitoring oil or
fuel pressure? For the pitch and roll, I don't think an accelerometer is not going to do it. It will give you rate of change. You could do some math and get degrees but it would not be accurate if the rate was different the next time you had a pitch or roll. A gyro would be best. The pendulums attached to a potentiometer will work. I saw one that a friend made from an old joystick for a computer. It has two pots in it. He removed the joystick and attached a weighted pendulum in its place. Putting that in a jug of light oil would make it more stable. Can hook directly to computer input. Regards Gary On Tue, 06 Jan 2004 19:52:27 +0800, Dave Baker wrote: On Tue, 06 Jan 2004 10:34:51 GMT, "Vic Fraenckel" wrote: I suspect that you are looking for a ready-made solution for measuring pitch/roll. Perhaps something exists out there but I suspect that the price would be high. Yeah, basically (unless really necessary), I'm looking for something ready-made. I need 2 units & they need to get installed on 2 ocean going ships for about 2 or 3 months for some testing of satellite transceiver performance vs sea state, so it's important that it works properly - I won't be able to go & make service calls! :-) It will need to be reliable as well as accurate to a degree or so over the expected pitch/roll range of the vessel. There is a solid state sensor that is a two axis accelerometer made by Analog Devices. It is the ADXL202 chip Coincidentally I have one sitting on my desk at the moment - one of those projects that got started but not finished. I was looking at using these accelerometers to strap to engine blocks on boats to determine whether the particular engine was running or not - we had a client that wanted monitoring of engine hours for 4 diesel propulsion engines & 2 diesel generators on a boat. I thought that I might be able to strap these units onto the engine blocks of each engine & get at least an on/off indication, and maybe as a bonus an RPM count. I hadn't considered using them as pitch/roll sensors before. Calibration would be the hard part. I've seen some good rate sensors at http://www.atasensors.com/Sensors2/index.htm and have toyed with somehow getting pitch & roll from these, but don't actually know how to do that yet - integration or something similar I guess? The sensors themselves have good characteristics - fast response, etc. It would definitely be nice to find something that provided pitch & roll in RS232 format without any work on my part. :-) Dave |
Pitch & Roll sensor
On Tue, 06 Jan 2004 20:27:08 GMT, "Vic Fraenckel" wrote:
wrote in message .. . | Oddly enough, my goals are the same. I intend to retire this spring, and buy a boat for coastal | cruising. One project I have in mind is a "wave-meter", i.e., a device which will tell me how high | the waves are....swells and wind chop. Roll and pitch should be do-able also. | | My approach is the same as below. But, as pointed out in another post, calibration is the problem. | Norm, There is no calibration problem with the ADXL202. What is a problem, at least with my application, is insuring that the accelerometer is mounted perpendicular to the roll and pitch axes. I am attempting to mount the ADXL on a telescope (not astronomical) to measure the inclination of the optical axis of the system. After trying to align the accelerometer mrchanically to the axes, I am now trying to write a routine to compute the off-axisness and use the results to compensate for the mis-alignment. Have you considered integrating the signal? I'd suspect that on average, "up" would be the 'average' of the roll and pitch over a period of time. Interesting engineering problem. I'll check out usdigital's web site...thanks. snip HTH Vic |
Pitch & Roll sensor
"Gary Schafer" wrote
|For the pitch and roll, I don't think an accelerometer is not going to | do it. It will give you rate of change. You could do some math and get | degrees but it would not be accurate if the rate was different the | next time you had a pitch or roll. | This is NOT correct. The ADXL is NOT measuring rate of change. It's output measures the gravitational acceleration directly. I suggest that you read AMD's data sheet on this product to understand how it works. I have used the ADXL to measure the inclination of a telescope tube with some success. Regards, Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) | |
Pitch & Roll sensor
| Have you considered integrating the signal? I'd suspect that on average, | "up" would be the 'average' of the roll and pitch over a period of time. | Interesting engineering problem. The ADXL202 is a two axis device. It measures the gravitional acceleration vector on mutually perpendicular axes defined by the top face of the IC. Check the data sheets at Advanced Micro Devices' web site to see how this works. I routinely integrate the measurements on both axes by making 10 readings on each. This does nothing to compensate for the skewing of the ADXL's axes relative to the axes of the device that it is mounted on. I believe this to be a geometry problem. HTH Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus | |
Pitch & Roll sensor
Well, it IS pretty close to correct. An accelerometer measures exactly what
its name implies - acceleration. And 99% of the time the name implies linear acceleration. So if you integrate that once, you have velocity. But nowhere in this process do you get pitch, roll, azimuth, or any other angular measurement. In order to get angular measurement, you need either a pendulum, or some sort of gyro-stabilized platform. In all cases with which I am familiar, the problem involves instruments which are fairly expensive. The least expensive would be the sort of instruments which are used to display attitude in aircraft. Start with the needle and ball and all the implementations of artificial horizons that have evolved over the years. The most accurate and stable over long term would be some sort of inertial navigator. There may be newer, solid state gyros which have evoved over the last few years, but I doubt that cost has decreased significantly. "Vic Fraenckel" wrote in message ... "Gary Schafer" wrote |For the pitch and roll, I don't think an accelerometer is not going to | do it. It will give you rate of change. You could do some math and get | degrees but it would not be accurate if the rate was different the | next time you had a pitch or roll. | This is NOT correct. The ADXL is NOT measuring rate of change. It's output measures the gravitational acceleration directly. I suggest that you read AMD's data sheet on this product to understand how it works. I have used the ADXL to measure the inclination of a telescope tube with some success. Regards, Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) | |
Pitch & Roll sensor
On Wed, 07 Jan 2004 02:34:27 GMT, "Vic Fraenckel" wrote:
| Have you considered integrating the signal? I'd suspect that on average, | "up" would be the 'average' of the roll and pitch over a period of time. | Interesting engineering problem. The ADXL202 is a two axis device. It measures the gravitional acceleration vector on mutually perpendicular axes defined by the top face of the IC. Check the data sheets at Advanced Micro Devices' web site to see how this works. I routinely integrate the measurements on both axes by making 10 readings on each. This does nothing to compensate for the skewing of the ADXL's axes relative to the axes of the device that it is mounted on. I believe this to be a geometry problem. HTH Vic I took a look at the usdigital web site, and their inclinometers seem to fit the bill. For two of each, ( $700), I wouldn't hesitate for a second if it were a customer job. If a 'home' project, your appraoch is probably the correct one. Either way, the problem of mounting the device(s) so that 'up' is really up is ongoing. Any ideas how to 'calibrate' up in the field....er, on the boat? Norm |
Pitch & Roll sensor
"maxlynn" wrote in message
news:VpLKb.102178$pY.42460@fed1read04... Well, it IS pretty close to correct. An accelerometer measures exactly what its name implies - acceleration. And 99% of the time the name implies linear acceleration. So if you integrate that once, you have velocity. But nowhere in this process do you get pitch, roll, azimuth, or any other angular measurement. ?????? If I mount an ADXL with one axis vertical and the other horzontal, I measure a constant gravitational acceleration on the vert. axis and 0 on the hor. axis. If I now rotate the sensor, I get a nice sine/cosine relation between the signals on both axes. So there's my angular measurement! Meindert |
Pitch & Roll sensor
On Tue, 06 Jan 2004 20:27:08 GMT, "Vic Fraenckel"
wrote: You might also explore U.S. Digital http://www.usdigital.com/ as they have an inclinometer that might do the trick. Check out the T6 unit. I have used their shaft encoder products and am seriously considering the T6. Hey, nice products. The A2T looks like it might fit the bill for me, and the serial interface they use means I can hook a few of them into the 1 serial port! Only question is the dynamic performance - 250mSec settling time is a bit slow. If we have 30° roll with a period of 10 seconds (pretty severe, but it might happen), then that is 3 degrees per second. I guess that's still better than 1 degree accuracy - just. At that price I might grab a couple of them & have a play regardless, while waiting for the Hippy price to come back to me! Thanks for all the help guys - I'll let you know how it works in the real world as we are doing these tests for a project with DNV, so the results should be public. Dave |
Pitch & Roll sensor
Norm,
| I took a look at the usdigital web site, and their inclinometers seem to fit the bill. For two of | each, ( $700), I wouldn't hesitate for a second if it were a customer job. If a 'home' project, I suggest that you check out the U.S. Digital T6 incremental inclinometer ($82). I believe it would do the job for you, especially since it has an indexing feature. The absolute models is way to expensive. Also check out their ICs for interfacing the encoder to a micro - perhaps the 7166. This is the way I will probably go if and when! Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus |
Pitch & Roll sensor
maxlynn wrote:
| Well, it IS pretty close to correct. An accelerometer measures exactly what | its name implies - acceleration. And 99% of the time the name implies | linear acceleration. So if you integrate that once, you have velocity. But | nowhere in this process do you get pitch, roll, azimuth, or any other | angular measurement. In order to get angular measurement, you need either a | pendulum, or some sort of gyro-stabilized platform. | All I can suggest is to go to the AMD web site and get the data sheets and app notes and find out how the ADXL line of accelerometers work! HTH Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus |
Pitch & Roll sensor
What you say is true in a fixed one-g environment. You can derive a crude
measurement of angular rotation in any fixed, uni-directional acceleration environment in the manner that you suggest. But as I understand the proposed application, the accelerometer(s)/instruments are to be mounted in a dynamic environment. The accelerometers mentioned are designed to measure linear acceleration. That is what the manufacturer designed them to do. They are NOT designed to measure rotation or rotational rates. That is generally a domain reserved for gyroscopes and related insruments or systems. As an exercise, consider how you would perform your suggested computation in an orbiting spacecraft(i.e., zero g). Max Lynn "Meindert Sprang" wrote in message ... "maxlynn" wrote in message news:VpLKb.102178$pY.42460@fed1read04... Well, it IS pretty close to correct. An accelerometer measures exactly what its name implies - acceleration. And 99% of the time the name implies linear acceleration. So if you integrate that once, you have velocity. But nowhere in this process do you get pitch, roll, azimuth, or any other angular measurement. ?????? If I mount an ADXL with one axis vertical and the other horzontal, I measure a constant gravitational acceleration on the vert. axis and 0 on the hor. axis. If I now rotate the sensor, I get a nice sine/cosine relation between the signals on both axes. So there's my angular measurement! Meindert |
Pitch & Roll sensor
Dave Baker wrote:
Anyone know of any pitch/roll sensors that are designed specifically for measuring pitch & roll in vessels? The units that I have found apparently are more for static applications, and are affected by acceleration, so are not accurate in dynamic situations. Try this for a start. There are several manufacturers of electrolytic sensors and I am sure you can get what you need in just about any output configuration. http://www.microstrain.com/FAS-E.htm You might also try and contact BP Oil Shipping, they installed strain monitoring on their Alaska tankers a few years ago. Rick |
Pitch & Roll sensor
Max Lynn wrote:
| As an exercise, consider how you would perform your suggested computation in | an orbiting spacecraft(i.e., zero g). Do you understand the concept of how the ADXL202 works? They are designed to work in a one g environment. The gravitational force is exerted on a solid state (silicon) beam and the beam deflection produces the output which is a function of the sensed gravitational field which is essentially 1g when the beam is perpindicular to the gravity field and 0g when the beam is parallel to the field. Read the data sheets and the application notes that you can easily find at the AMD site ( http://www.amd.com/us-en/ ). I urge you to do so. Very few boats will ever find temselves in a zero g environment. My comments are directed to a query about a pitch/roll sensor for a sailboat. Just trying to stay on topic. HTH Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus |
Pitch & Roll sensor
Vic:
I was also trying to stay on topic. And I completely understand the function of the accelerometer which you reference, as well as a number of other similar instruments. I would similarly invite you to reconsider my question regarding a zero-g environment for such an instrument. You state that the accelerometer is built to function in a one-g environment. I submit to you that the instrument is built to function in a +/- 2 g environment. If you place this instrument's two sensitive axes in a local horizzontal plane in your laboratory, neither axis will see a gravitational input, and therefore will provide no output. Now, rotate the instriment about one axis. The opposite axis will begin to sense a component of gravity as a function of the angle which you have rotated about the other axis. Vic will say AHA, I have sensed a rotation. But now, let me simply slide the accelerometer across the table, moving along that same axis which just provided the output previously, but not rotating the instrument about either axis. As you can see, the indication from the instrument is the same in either case. In both cases, all you have "sensed" is linear acceleration, in one case, the amount proportional to the component of gravity, and in the other case, the amount proportional to the force exerted on the case to provide the linear motion. Picture the accelerometer on a boat in turbulent conditions with the input axes similarly aligned(both horizontal), and consider how you would remove the component of acceleration due to a wave passing under a boat and lifting the boat several feet and then allowing it to sink several feet, simultaneously causing both roll and pitch motion. Consider, please, that the wave may cause vertical and horizontal displacement of the boat, as well as rotational motion about the pitch and roll axes. Then please explain to me how you plan to discriminate on an instantaneous basis between the two totally independent types of motion using only the two outputs from your accelerometer. I really wish you would stop and consider my original post where I pointed out that an accelerometer, and particularly the Analog Devices ADXL 202(not made by AMD as your URL directed us) is an instrument built to sense LINEAR acceleration along an axis, NOT ROTATION about an axis. Gyros are used to sense rotational motion, not accelerometers. Pendulums(sometimes also called inclinometers) are also used for limited rotational sensors, provided the motion is not too large and/or the frequency of the rotational motion is not too high. I did not mean to get so wrapped up, so please excuse my fervor.(rant??) "Vic Fraenckel" wrote in message ... Max Lynn wrote: | As an exercise, consider how you would perform your suggested computation in | an orbiting spacecraft(i.e., zero g). Do you understand the concept of how the ADXL202 works? They are designed to work in a one g environment. The gravitational force is exerted on a solid state (silicon) beam and the beam deflection produces the output which is a function of the sensed gravitational field which is essentially 1g when the beam is perpindicular to the gravity field and 0g when the beam is parallel to the field. Read the data sheets and the application notes that you can easily find at the AMD site ( http://www.amd.com/us-en/ ). I urge you to do so. Very few boats will ever find temselves in a zero g environment. My comments are directed to a query about a pitch/roll sensor for a sailboat. Just trying to stay on topic. HTH Vic -- __________________________________________________ ______ Victor Fraenckel - The Windman vfraenc1 ATSIGN nycap DOT rr DOTcom KC2GUI Home of the WindReader Electronic Theodolite Read the WIND "Victory at all costs, victory in spite of all terror, victory however long and hard the road may be; for without victory there is no survival." - Winston [Leonard Spencer] Churchill (1874 - 1965) Dost thou not know, my son, with how little wisdom the world is governed? -Count Oxenstierna (ca 1620) to the young King Gustavus Adolphus |
Pitch & Roll sensor
"maxlynn" wrote in message
news:9tXKb.103004$pY.50340@fed1read04... What you say is true in a fixed one-g environment. You can derive a crude measurement of angular rotation in any fixed, uni-directional acceleration environment in the manner that you suggest. But as I understand the proposed application, the accelerometer(s)/instruments are to be mounted in a dynamic environment. The accelerometers mentioned are designed to measure linear acceleration. That is what the manufacturer designed them to do. They are NOT designed to measure rotation or rotational rates. That is generally a domain reserved for gyroscopes and related insruments or systems. Well, read the datasheets. AD says specifically in their datasheets that the ADXL's can be used as an inclinometer. Apart from that, a boat seems an 'almost fixed' one-g environmet to me. Meindert |
Pitch & Roll sensor
"maxlynn" wrote in message news:j90Lb.103199$pY.54961@fed1read04... Vic: I was also trying to stay on topic. And I completely understand the function of the accelerometer which you reference, as well as a number of other similar instruments. I would similarly invite you to reconsider my question regarding a zero-g environment for such an instrument. You state that the accelerometer is built to function in a one-g environment. I submit to you that the instrument is built to function in a +/- 2 g environment. If you place this instrument's two sensitive axes in a local horizzontal plane in your laboratory, neither axis will see a gravitational input, and therefore will provide no output. Now, rotate the instriment about one axis. The opposite axis will begin to sense a component of gravity as a function of the angle which you have rotated about the other axis. Vic will say AHA, I have sensed a rotation. But now, let me simply slide the accelerometer across the table, moving along that same axis which just provided the output previously, but not rotating the instrument about either axis. As you can see, the indication from the instrument is the same in either case. In both cases, all you have "sensed" is linear acceleration, in one case, the amount proportional to the component of gravity, and in the other case, the amount proportional to the force exerted on the case to provide the linear motion. Picture the accelerometer on a boat in turbulent conditions with the input axes similarly aligned(both horizontal), and consider how you would remove the component of acceleration due to a wave passing under a boat and lifting the boat several feet and then allowing it to sink several feet, simultaneously causing both roll and pitch motion. Consider, please, that the wave may cause vertical and horizontal displacement of the boat, as well as rotational motion about the pitch and roll axes. Then please explain to me how you plan to discriminate on an instantaneous basis between the two totally independent types of motion using only the two outputs from your accelerometer. I really wish you would stop and consider my original post where I pointed out that an accelerometer, and particularly the Analog Devices ADXL 202(not made by AMD as your URL directed us) is an instrument built to sense LINEAR acceleration along an axis, NOT ROTATION about an axis. Gyros are used to sense rotational motion, not accelerometers. Pendulums(sometimes also called inclinometers) are also used for limited rotational sensors, provided the motion is not too large and/or the frequency of the rotational motion is not too high. I did not mean to get so wrapped up, so please excuse my fervor.(rant??) "Vic Fraenckel" wrote in message ... Max Lynn wrote: | As an exercise, consider how you would perform your suggested computation in | an orbiting spacecraft(i.e., zero g). Do you understand the concept of how the ADXL202 works? They are designed to work in a one g environment. The gravitational force is exerted on a solid state (silicon) beam and the beam deflection produces the output which is a function of the sensed gravitational field which is essentially 1g when the beam is perpindicular to the gravity field and 0g when the beam is parallel to the field. Read the data sheets and the application notes that you can easily find at the AMD site ( http://www.amd.com/us-en/ ). I urge you to do so. Very few boats will ever find temselves in a zero g environment. My comments are directed to a query about a pitch/roll sensor for a sailboat. Just trying to stay on topic. HTH Vic Excellent explanation of the problem, and thats why we used two dirty great big Datawell Hippi's filled with glycerin or some such thick fluid. garry |
Pitch & Roll sensor
I've read a lot of data sheets, Meindert, and so have you, I'm sure. Under
the right conditions, and applying a lot of knowledge of its limitations, the device could be used as an inclinometer. But that's another topic. If you constrain the boat to always be anchored, we get closer to an application in which it could be used as an inclinometer, but again, that seems to me to be another topic. I have, in fact, used similar(single axis) accelerometers, but usually as vibration pickups. That particular instrument is not a high-grade device, in spite of what you think you might read from the data sheet. This class of device typically has a bias output which, while capable of being calibrated, is often unstable and/or temperature dependent, and/or g-sensitive. So when you say it is usable in an application, you always must specify to what level of accuracy, etc. And to use it as a generalized rotational sensor is a total misapplication. And we weren't discussing horeshoes, so I do not consider "almost 1 g" to be close enough. Max Lynn "Meindert Sprang" wrote in message ... "maxlynn" wrote in message news:9tXKb.103004$pY.50340@fed1read04... What you say is true in a fixed one-g environment. You can derive a crude measurement of angular rotation in any fixed, uni-directional acceleration environment in the manner that you suggest. But as I understand the proposed application, the accelerometer(s)/instruments are to be mounted in a dynamic environment. The accelerometers mentioned are designed to measure linear acceleration. That is what the manufacturer designed them to do. They are NOT designed to measure rotation or rotational rates. That is generally a domain reserved for gyroscopes and related insruments or systems. Well, read the datasheets. AD says specifically in their datasheets that the ADXL's can be used as an inclinometer. Apart from that, a boat seems an 'almost fixed' one-g environmet to me. Meindert |
Pitch & Roll sensor
On Wed, 07 Jan 2004 18:32:24 GMT, Rick wrote:
Try this for a start. There are several manufacturers of electrolytic sensors and I am sure you can get what you need in just about any output configuration. http://www.microstrain.com/FAS-E.htm The FAS-E looks slightly interesting, though they have a FAS-G which looks a lot better. In fact the PDF manual for the FAS-G has some useful information which might help in the lively debate going on regarding suitability of accelerometers for this task! :-) "What makes FAS-G unique is not only its ability to measure static angles, but also dynamic, fast angular movements. Through the use of the two accelerometers and one piezo-ceramic gyro coupled with the requisite digital filtering and embedded software tracking algorithms, FAS-G provides dynamic response while maintaining the DC (static) measurement accuracy. As a result, during rapid angular movements, both static and the dynamic components of movement can be measured. This is not possible with conventional inclinometers based on fluidic electrolytes or DC response accelerometers." Ooh - just spotted the 3DM-G on the same site - seems to be exactly what I need, for about US$1500. This looks good. 3 weeks lead time is about the only worry. Thanks, Dave |
Pitch & Roll sensor
You are on to a possibility. You should know that there is a lot more than
meets the eye in what you are buying. These devices require high computational capabilities. Hopefully there are canned algorithms available to provide the outputs that you require. But they have the potential to provide proper pitch and roll outputs AND simultaneous acceleration outputs Max Lynn "Dave Baker" wrote in message ... On Wed, 07 Jan 2004 18:32:24 GMT, Rick wrote: Try this for a start. There are several manufacturers of electrolytic sensors and I am sure you can get what you need in just about any output configuration. http://www.microstrain.com/FAS-E.htm The FAS-E looks slightly interesting, though they have a FAS-G which looks a lot better. In fact the PDF manual for the FAS-G has some useful information which might help in the lively debate going on regarding suitability of accelerometers for this task! :-) "What makes FAS-G unique is not only its ability to measure static angles, but also dynamic, fast angular movements. Through the use of the two accelerometers and one piezo-ceramic gyro coupled with the requisite digital filtering and embedded software tracking algorithms, FAS-G provides dynamic response while maintaining the DC (static) measurement accuracy. As a result, during rapid angular movements, both static and the dynamic components of movement can be measured. This is not possible with conventional inclinometers based on fluidic electrolytes or DC response accelerometers." Ooh - just spotted the 3DM-G on the same site - seems to be exactly what I need, for about US$1500. This looks good. 3 weeks lead time is about the only worry. Thanks, Dave |
Pitch & Roll sensor
On Wed, 7 Jan 2004 21:02:09 -0800, "maxlynn" wrote:
You are on to a possibility. You should know that there is a lot more than meets the eye in what you are buying. These devices require high computational capabilities. Hopefully there are canned algorithms available to provide the outputs that you require. But they have the potential to provide proper pitch and roll outputs AND simultaneous acceleration outputs I'll just log all the data - my boss has the degrees in Maths & Surveying, so he can be the one that has to make sense of it all! :-) Dave |
Pitch & Roll sensor
Hello Dave,
My company has been marketing a system for ship-motions measurement for some time. It is called ship-motion-controller (SMC) and consists of an electrolytic sensor and accompanying sotware for logging and analysis. The sensor measures accelerations and angles on all three axis and is connected to a PC via USB. The angular accuracy is better than 0.01 degree. The system has been extensively tested, and can easily log three months of data. It is a commercial-of-the-shelf-system and we have a system available for rent if required. Maybe this could be helpfull to your project. Willem Amels Dave Baker wrote in : On Wed, 7 Jan 2004 21:02:09 -0800, "maxlynn" wrote: You are on to a possibility. You should know that there is a lot more than meets the eye in what you are buying. These devices require high computational capabilities. Hopefully there are canned algorithms available to provide the outputs that you require. But they have the potential to provide proper pitch and roll outputs AND simultaneous acceleration outputs I'll just log all the data - my boss has the degrees in Maths & Surveying, so he can be the one that has to make sense of it all! :-) Dave |
Pitch & Roll sensor
On 08 Jan 2004 18:51:11 GMT, Willem Amels wrote:
The sensor measures accelerations and angles on all three axis and is connected to a PC via USB. The angular accuracy is better than 0.01 degree. The system has been extensively tested, and can easily log three months of data. If it can output in real time (so I can correlate it with Inmarsat transceiver signal strength) then it sounds interesting. I'll email you to get more info (if I can guess your real email address correctly) Dave |
Pitch & Roll sensor
On Mon, 12 Jan 2004 17:52:40 GMT, Terry Spragg
wrote: How much accuracy do you need? To resolve satellite pointing issues, a fixed 3 axis setup (six sensors) will be required, with integration of the outputs to derive azimuth and elevation, unless you servo the yaw efficiently and then sense the elevation, then you only need juggle two indications. You might use an electronic compass to control the yaw of the antenna platform. Daily adjustments of magnetic variation might be needed in passage, and as well, you would need to integrate compass variations due to local ferrous masses at various headings. Perhaps a gyrocompass? The (Inmarsat D+) satellite transceiver uses an omnidirectional antenna, so no moving parts. According to the specs it has an elevation mask angle of 5° so one can theoretically work out where in the world it will have coverage of the Inmarsat satellites. However, the certifying body wants practical tests done in real-life conditions before certifying it for marine use. We aren't the manufacturer, only end-users, but need certification for our work. The units may work up to the theoretical limits in perfect weather, but the aim is to see how much degradation of performance there is in bad weather - when the units would be more likely used. Dave |
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