DESCRIPTION:
The Memsic 2125 is a low cost, dual-axis thermal accelerometer capable of measuring dynamic acceleration (vibration) and static acceleration (gravity) with a range of ±2 g. For integration into existing applications, the Memsic 2125 is electrically compatible with other popular accelerometers.
Key Features of the Memsic 2125:
* Measure 0 to ±2 g on either axis; less than 1 mg resolution
* Fully temperature compensated over 0° to 70° C range
* Simple, pulse output of g-force for X and Y axis
* Analog output of temperature (TOut pin)
* Low current operation: less than 4 mA at 5 vdc
A sampling of possible BASIC Stamp module applications with the Memsic 2125 include:
* Dual-axis tilt sensing for autonomous robotics applications
* Single-axis rotational position sensing
* Movement/Lack-of-movement sensing for alarm systems
* R/C hobby projects such as autopilots
If you use this part, you can get support and coding examples directly from parallax. and it's cheaper too!
Isnt there a difference between a gyroscope and an accelerometer tho?
The accelerometer specs say "* Dual-axis tilt sensing for autonomous robotics applications"
but is that the same as a gyro?
Maybe the gyro has more than just tilt sensing and gives a tilt value?
I am just guessing here..
and I allready have the memsic 2125, just havnt had a chance to put it on my project yet
The traditional gyro used a spinning mass in the center and the motors were both large and often prone to failure.
The new gyros are quite small and in some way I begin to think they are just the same as an accelerometer. Both are operating on 'one plane' which is 'dual axis'
The Memsics do not have a complete 360 degree range, but three together will give comprehensive coverage in any direction. It seems that three gyros are required to do the same task.
The Memsics come in 2g force and 10g force, maybe more options.
So again, I have a bit of trouble sorting out the differences. Is the Memsic the OEM product that is calibrated and repackaged as a gyro?
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Well to be precise the MEMSIC is not a gyroscope.
It doesnt use the spinning mass technology but a weaton bridge of thermistances around a packaged box in which a gaz bubble is heated. It is the inertia of the buble gaz that is used to detect accelerations through temperature rising of some of thermistances when the bubble has moved. Im a clear [noparse]:)[/noparse]) ??
Perhaps the memsic accelerometer is constructed differently, but when I took a course on MEMS (technology used to produce both modern day accelerometers and gyroscopes), We were taught there·are two types of accelerometers, the first uses a doped·silicon spring whose shifted mass produces a change in resistance through the spring (this is the type employed for air bag deployment).·The second type of accelerometer was described as a ring of thermoresistors around the perifry of a heater core. The bubble of heated air is shifted via acceleration (accelerometer function) or gas expansion (tilt function). An accelerometer experiencing a pure angular velocity seems like the bubble would stay in the center because the gas would experience a centifugal effect, since the colder gas is more dense it would spin out to the perifry where the theroresistors are and the heated bubble would stay in the center. A change in the angular acceleration woud produce no measurable effect as a gyroscope would. A lateral acceleration would be detectable (like the gyroscope would) but again this falls into the accelerometer's designed function. I think accelerometers are sometimes referenced as gryroscopes because they do measure some of the traditional forces a gyroscope has been used to measure, but it cannot measure all forces a gyrocope can (changes in angular acceleration). If someone with a background in physics can refute this argument, I would be interested in hearing why my conclusion is incorrect.
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Post Edited (Paul Baker) : 2/11/2006 7:03:17 PM GMT
What's the argument? If anyone has looked at a six DOF sensor, 3 of them are ' gyros' and three are accelerometers. Why? because one is for angular rotation, the other for tilt / accel. Give an accelerometer a spin, what does it do? Nothing. Put an accelerometer parallel to the z plane, it still only gives tilt. Now, what is the difference between a gyro and a compass?
I suppose that GPS is really an extended·analogue for a compass => both provide an external reference with certain limitations.·The GPS triangulates [noparse][[/noparse]which is better], while the compass merely indicates a somewhat stationary locaton [noparse][[/noparse]or direction].
Parallax is now selling a 3-axis Hitachi unit [noparse][[/noparse]accelerometer].· Rated at 3 Gs. How does that fit into the comparison?· I guess it is still just accelerometers in a better package.
From what I thought, the traditional gyros·were considered genrally obsolete.· Technically interesting, but no longer in use.· [noparse][[/noparse]Apparently GPS has taken over much of their navigational role].
On the other hand, you refer to a DOF [noparse]/noparse]Department of Defence?[noparse][[/noparse]OH! you mean Six Degrees of Freedom unit that has 3 of each.· Apparently for some things [noparse][[/noparse]like cruise missles] they still require the inertial guidance because they need to be fully autonomous and highly responsive to whatever motion they produce [noparse][[/noparse]including spin about themselves].
I begin to see that the spinning really separates the utility of the accelerometer from the gyro.
I went to the site refered and see a 'breakout board' for a small gyro, but does the price include the gyro? And do you need 3 of these gyros for X, Y, and Z?
Still, gyros require a period of time to get up to speed and to be set to a reference before they are functional. Right?
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Tibot said...
did you look at the doc provided with the link above ?
Which doc are you refering to? Vern's link to Parallax's product and accompanying docs? I see the example in the second document of turning it on it's side. But this configuration isn't for angular velocity or a measurement of angular force, it is only a measure of angular position, which in theory the dervivative with respect·to time could be taken to get the higher orders. But there is a serious problem with this approach, and that is the viscosity of the gas makes it so you can only measure a rotation of a fairly small rotational speed. You may be able to measure the angular velocity of a record player, but not a top. Also from what I can tell this setup would only work for an object whose axis of rotation is perpendicular to gravity (a spinning Boe-Bot wheel), but is ineffective for measuring an axis of rotation parallel to gravity (a record player or top, which is the original configuration I was speaking of in the previous post).
The system used by the AS5020-E refered to in the N&V#92 is much more capable of measuring angular velocities, but this isn't the memsic.
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Post Edited (Paul Baker) : 2/13/2006 7:41:40 PM GMT
I went to the site refered and see a 'breakout board' for a small gyro, but does the price include the gyro? And do you need 3 of these gyros for X, Y, and Z?
Still, gyros require a period of time to get up to speed and to be set to a reference before they are functional. Right?
1. Yes the price includes the gyro, this is evident because they have a drop down menu of 3 gyros to choose from (they all have the same packaging), also thier statements of how difficult it is for a hobbyist to deal with BGA themselves indicate its already mounted. Yes, you would need 3 gyros to measure roll pitch and yaw. Thier 6-DOF board (http://www.sparkfun.com/commerce/product_info.php?products_id=411) has 3 to measure each.
2.Yes all gyros should be at thier operating speed to get reliable readings, the benifit of MEMs gyros is the reduced mass undergoing rotation typically means the start up time is less than traditional gyros. Id check out the docs from Analog Devices to see what the start up time is.
This is useful information. Seattle Robotics' Encoder had an article that said gyros were essentially obsolete, but obviously the author had some misinformation. The article does constructively discuss problems of noise in relationship to getting good data though.
Sadly, the Encoder hasn't put out anything since Winter of 2004.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
The Analog devices ADXRS series gyros come up to speed in a couple of seconds. They are based upon a vibrating mass and output rate of change in angular velocity. They are very small (about the size of a PIC) and are relatively cheap. You should check them out.
I have a need in determining the difference between acceleration due to a change in lateral motion and that which is due to the force of gravity. I needed something with a completely different reference then that of the accelerometer alone in order to achieve this.
I have been searching however for some BASIC code help with integrating the data so that I end up with degrees or position. I hope thay you or someone out there can help me.
TG
Posts: 36
Comments
read through the documentation (@ Analog Devices) to make sure it can be interfaced with a stamp.
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Many people use the Memsic 2125 available directly from parallax to measure angular acceleration:
http://www.parallax.com/detail.asp?product_id=28017
Description from the page:
If you use this part, you can get support and coding examples directly from parallax. and it's cheaper too!
Vern
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The accelerometer specs say "* Dual-axis tilt sensing for autonomous robotics applications"
but is that the same as a gyro?
Maybe the gyro has more than just tilt sensing and gives a tilt value?
I am just guessing here..
and I allready have the memsic 2125, just havnt had a chance to put it on my project yet
++
The traditional gyro used a spinning mass in the center and the motors were both large and often prone to failure.
The new gyros are quite small and in some way I begin to think they are just the same as an accelerometer. Both are operating on 'one plane' which is 'dual axis'
The Memsics do not have a complete 360 degree range, but three together will give comprehensive coverage in any direction. It seems that three gyros are required to do the same task.
The Memsics come in 2g force and 10g force, maybe more options.
So again, I have a bit of trouble sorting out the differences. Is the Memsic the OEM product that is calibrated and repackaged as a gyro?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 2/12/2006 3:20:05 PM GMT
It doesnt use the spinning mass technology but a weaton bridge of thermistances around a packaged box in which a gaz bubble is heated. It is the inertia of the buble gaz that is used to detect accelerations through temperature rising of some of thermistances when the bubble has moved. Im a clear [noparse]:)[/noparse]) ??
Can you tell us more about the project ?
++
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·1+1=10
Post Edited (Paul Baker) : 2/11/2006 7:03:17 PM GMT
kelvin
Parallax is now selling a 3-axis Hitachi unit [noparse][[/noparse]accelerometer].· Rated at 3 Gs. How does that fit into the comparison?· I guess it is still just accelerometers in a better package.
From what I thought, the traditional gyros·were considered genrally obsolete.· Technically interesting, but no longer in use.· [noparse][[/noparse]Apparently GPS has taken over much of their navigational role].
On the other hand, you refer to a DOF [noparse]/noparse]Department of Defence?[noparse][[/noparse]OH! you mean Six Degrees of Freedom unit that has 3 of each.· Apparently for some things [noparse][[/noparse]like cruise missles] they still require the inertial guidance because they need to be fully autonomous and highly responsive to whatever motion they produce [noparse][[/noparse]including spin about themselves].
I begin to see that the spinning really separates the utility of the accelerometer from the gyro.
I went to the site refered and see a 'breakout board' for a small gyro, but does the price include the gyro? And do you need 3 of these gyros for X, Y, and Z?
Still, gyros require a period of time to get up to speed and to be set to a reference before they are functional. Right?
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
Post Edited (Kramer) : 2/15/2006 3:10:52 PM GMT
The system used by the AS5020-E refered to in the N&V#92 is much more capable of measuring angular velocities, but this isn't the memsic.
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·1+1=10
Post Edited (Paul Baker) : 2/13/2006 7:41:40 PM GMT
2.Yes all gyros should be at thier operating speed to get reliable readings, the benifit of MEMs gyros is the reduced mass undergoing rotation typically means the start up time is less than traditional gyros. Id check out the docs from Analog Devices to see what the start up time is.
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Sadly, the Encoder hasn't put out anything since Winter of 2004.
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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)
······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
I have a suggestion.· "Muffin fans" make effective gyroscopes, 6V or 12V fans should do nicely (??).
I have a need in determining the difference between acceleration due to a change in lateral motion and that which is due to the force of gravity. I needed something with a completely different reference then that of the accelerometer alone in order to achieve this.
I have been searching however for some BASIC code help with integrating the data so that I end up with degrees or position. I hope thay you or someone out there can help me.