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Unread 09-01-2005, 11:39
Nixterrimus Nixterrimus is offline
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Hall Effect Sensor.

The 2005 kit came with something a Hall Effect Sensor, after a bit of looking I found the manual for it, it's actually a ATS665LSG made by Allegro Microsystems. Allegro desribes it as a True Zero Speed, High Accuracy, Gear Tooth Sensor. What does that mean? Is this the "gyro" for this year? And does this work in congunction with the accelerometer. There are two of Hall Effect sensors so it seems we need to use them in twos. Also the Allegro manual mentions gears and gear tooth length. So I'm a bit confused and a bit curious and maybe even a bit excited. Anybody know anything about the Hall effect?
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Unread 09-01-2005, 11:48
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Re: Hall Effect Sensor.

My GUESS is that you would use these to count gear teeth - used for feedback to determine how fast/far your robot moves, or for sensing the motion of anything else using chain/sprocket. However ours were missing when we did our kit inventory ...
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Unread 09-01-2005, 11:50
scottm87 scottm87 is offline
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Nixterrimus
The 2005 kit came with something a Hall Effect Sensor, after a bit of looking I found the manual for it, it's actually a ATS665LSG made by Allegro Microsystems. Allegro desribes it as a True Zero Speed, High Accuracy, Gear Tooth Sensor. What does that mean? Is this the "gyro" for this year? And does this work in congunction with the accelerometer. There are two of Hall Effect sensors so it seems we need to use them in twos. Also the Allegro manual mentions gears and gear tooth length. So I'm a bit confused and a bit curious and maybe even a bit excited. Anybody know anything about the Hall effect?
Okay. A gear-tooth sensor sits in your gearbox and uses a magnetic field in order to sense each specific tooth go by. The Hall Effect is the concept that allows the integrated circuit to take a measurement of the magnetic field surrounding it. (Hall effect compasses are also popular) The amount of time that elapses between the each tooth gives the speed of the rotating gear, which can then be scaled to the speed of the wheel, etc.

This is not a gyro. A gyro returns your angular acceleration (NOT your angular heading... you would need to integrate the acceleration to get that)
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Unread 09-01-2005, 12:29
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Stu Bloom
However ours were missing when we did our kit inventory ...
Check the Accelerometer bag. They are very tiny things and many teams have found them stuck to the accelerometer so they look like part of it.
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Unread 09-01-2005, 12:34
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Re: Hall Effect Sensor.

Nixterrimus, Is Ken Wittlief still on your team? He should be able to explain the sensors and demonstrate their usage.
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Unread 09-01-2005, 12:40
Tom Bottiglieri Tom Bottiglieri is offline
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Re: Hall Effect Sensor.

This is a neat article I found on calculating heading with a rate gyro.

http://www.seattlerobotics.org/encod...onal_gyro.html

Not sure if FIRST provides us with this code though, I'll have to dig deeper into the documentation and report back.

[EDIT] I found this article from a Hall Effect sensor manufacturer about how they work. http://www.micronas.com/products/ove...sors/index.php [/DIT]
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Unread 09-01-2005, 12:41
Nixterrimus Nixterrimus is offline
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Joe Ross
Nixterrimus, Is Ken Wittlief still on your team? He should be able to explain the sensors and demonstrate their usage.
No, sadly Mr. Wittlief's son graduated and he isn't a part of the team this year.
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Unread 09-01-2005, 12:43
Nixterrimus Nixterrimus is offline
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Re: Hall Effect Sensor.

Quote:
Originally Posted by scottm87
This is not a gyro. A gyro returns your angular acceleration (NOT your angular heading... you would need to integrate the acceleration to get that)
Alright so this isn't a gyro, I'm good with that, but is this what was Demoed at the kickoff where the robot was able to correct its position? Does the hall effect sensor return your angular heading?
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Unread 09-01-2005, 12:45
Nixterrimus Nixterrimus is offline
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Tom Bottiglieri
[EDIT] I found this article from a Hall Effect sensor manufacturer about how they work. http://www.micronas.com/products/ove...sors/index.php [/DIT]
I looked at that too. Did you think that it was in English?
I thought that a lot of it was out there, I suppose I'm looking for just an intro to the hall effect.
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Unread 09-01-2005, 12:48
Tom Bottiglieri Tom Bottiglieri is offline
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Nixterrimus
I looked at that too. Did you think that it was in English?
I thought that a lot of it was out there, I suppose I'm looking for just an intro to the hall effect.
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Unread 09-01-2005, 12:57
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Re: Hall Effect Sensor.

Quote:
Originally Posted by scottm87
This is not a gyro. A gyro returns your angular acceleration (NOT your angular heading... you would need to integrate the acceleration to get that)
Gyros measure angular velocity, not acceleration. The first integral of the velocity it the distance, so integrating a gyro provides angular distance, or relative heading.

Using a gyro to measure the robot's heading is pretty common with FIRST robots. The parts teams used last year are the Analog Devices ADXRS150EB and ADXRS300EB. The only difference is that the 150 can measure +- 150 degrees per second and the 300 measures up to 300 degrees per second.

Lots of posts describing how to do it.
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Unread 09-01-2005, 15:43
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Nixterrimus
Alright so this isn't a gyro, I'm good with that, but is this what was Demoed at the kickoff where the robot was able to correct its position? Does the hall effect sensor return your angular heading?
I BELIEVE what was demoed at the kickoff (not 110% sure) was the accelerometer. An accelerometer gives back a reading that tells how fast you are accelerating, i.e. changing speed, in a given direction. Using some programming, you can sense when you are moving and take steps to remedy it. A hall-effect sensor uses a magnetic field to detect a metallic presence, and therefore does not return angular headings. I am pretty sure they put out pulses when a metallic presence is detected. It's just an FET, in other words.

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Unread 09-01-2005, 16:02
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Re: Hall Effect Sensor.

To clear things up, the HAL effect sensors have NOTHING TO DO WITH ACCELERATION, OR HEADING. They are a type of sensor that detects the presence of ferrous materias. They are designed to be mounted up against(but not touching) the teeth of a gear in a gearbox or other assembly. They will output 1 pulse for each gear tooth that goes by them. If for example you were to connect them to your drivetrain, you could count the number of pulses they output to figure out how far your robot had traveled. It is also possible to use them to determine the speed at which your robot (or some subassembly) is moving.
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Unread 09-01-2005, 17:42
Nixterrimus Nixterrimus is offline
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Re: Hall Effect Sensor.

Quote:
Originally Posted by Rickertsen2
If for example you were to connect them to your drivetrain, you could count the number of pulses they output to figure out how far your robot had traveled. It is also possible to use them to determine the speed at which your robot (or some subassembly) is moving.
So this is how FIRST is killing dead reckoning? Hooking these up next to gears tell you how far you've gone, the accelerometer could tell you if you were straight and now we can drive the robot any direction and know exactly how far. Right?
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Unread 09-01-2005, 18:01
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Re: Hall Effect Sensor.

Quote:
So this is how FIRST is killing dead reckoning? Hooking these up next to gears tell you how far you've gone, the accelerometer could tell you if you were straight and now we can drive the robot any direction and know exactly how far. Right?
No. To be honest it's still dead reackoning and you still do not percisely know where the robot is with 100% certainty.
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