Hall Effect Sensor.

[Sparks333]

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.

Sparks

[Rickertsen2]

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.

[Nixterrimus]

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?

[Adam Y.]

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.

[Caleb Fulton]

Here are a few tips on the Hall Effect sensors:

These guys simply output a digital signal corresponding to whether or not a gear tooth is in front of them or not, and the polarity of the signal depends on the direction of gear rotation wrt the sensor itself (see the data sheet for more details: http://www.allegromicro.com/datafile/0660.pdf). Think of this device as a one-bit wheel encoder when you program for it.

The air gap, according to the manufacturer, should be 0.5-2.5mm, though they assure us that their adaptive sensing technology can make it work for an even bigger gap, especially with larger gear teeth.

The device has an open-drain output stage, but the digital inputs on the RC have pull-up resistors built-in, so you can directly connect the signal to the RC's inputs. Try to avoid grounding the signal wire, though, as this would technically be a short-circuit. Don't worry if you do -- the manufacturer says it has short-circuit protection on the output stage.

[cdawzrd]

So... They are sprocket-tooth encoders. Check.

How do we wire them? They have 4 pins, I haven't checked but it seems like they might fit on a PWM cable, but that only has 3 pins, so is it possible to wire it with only 3 pins or do we need to make new cables?

--Jonathan

[scottm87]

Originally Posted by cdawzrd

So... They are sprocket-tooth encoders. Check.

How do we wire them? They have 4 pins, I haven't checked but it seems like they might fit on a PWM cable, but that only has 3 pins, so is it possible to wire it with only 3 pins or do we need to make new cables?

--Jonathan

To wire this sensor, I suggest you check out the spec sheet that is linked numerous times in this thread. A link to the sheet is on the FIRST site at:
http://www2.usfirst.org/2005comp/Specs/gths1.pdf

For a basic overview, looking from the top of the sensor, the pins from left to right are supply, output, int. connection, and ground. it can take 4.5 to 24 volts input voltage (you would probably use 12), and the output will provide a digital signal whenever a gear tooth passes by (whether or not the output is high or low when a tooth goes by depends on the direction of rotation).

CHECK the spec sheet before you try it. It is helpful to see the diagram and check for yourself.

Scott

[Derder1625]

[font=Comic Sans MS][font=Comic Sans MS]hm.. so afterall that has been said..
does anyone know where could we find the manual
for the hall effect sensor??~
thank yoU~~

[Derder1625]

=] May someone please tell me
where could we find the manual
of the hall effect sensor?? =] thank you

[Mike Betts]

Originally Posted by Derder1625

=] May someone please tell me
where could we find the manual
of the hall effect sensor?? =] thank you

Please read this thread. The data sheet link is given.

[seanwitte]

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.

[scottm87]

Originally Posted by seanwitte

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.

Oops! You are right... With all the accelerometer discussion, I got all mixed up. The ADXRS sensors are nice, but you need to deal with the packaging. I think (not sure) the price limitations have been loosened enough that you can get an evaluation version of the accelerometer with some support circuitry brought out header pins that can be plugged into a board. This is much easier than dealing with a surface mount part, if you do decide to use it. Since there are more suppliers, it may also be possible to pick up other sensors now (the Memsic ones are also nice... and if it is allowed, you can buy it from Parallax pretty cheap.) Heh, you may even be able to get the old FIRST accelerometers from some supplier.

[Joe Ross]

Nixterrimus, Is Ken Wittlief still on your team? He should be able to explain the sensors and demonstrate their usage.

[Tom Bottiglieri]

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]

[Nixterrimus]

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.