Hall Effect Sensor.

[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?

[Stu Bloom]

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 ...

[sanddrag]

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.

[Stu Bloom]

Originally Posted by sanddrag

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.

Thanks, I haven't had a chance to re-check our kit yet, but I see that this is documented in the "Guidelines, Tips and Good Practices" document (page 26 - see attachment). IMO this should have been documented on the kit checklist (to look on the accelerometer). Seems these could be easily missed, even for those who know what they are looking for

[dez250]

http://www.allegromicro.com/datafile/0660.pdf

I can confirm that is the proper spec sheet for the hall effect gear tooth sensor that is included in the 2005 FRC KOP. It is labled Data sheet 27627.107

[Nucks]

Originally Posted by sanddrag

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.

We thought we didn't have it either, but after reading that, we checked and found it, thanks

[xxmaddjxx]

Arghhh! I don't understand lol.

Ok the Hall Effect sensor counts teeth and has to be mounted very close to the gear.

The accelerometer measures acceleration. How is that done and where does it have to be mounted.

How do all these values come together in the RC and help me?

What does the code that we get for both these sensors do?

[Al Skierkiewicz]

Originally Posted by xxmaddjxx

Arghhh! I don't understand lol.

Ok the Hall Effect sensor counts teeth and has to be mounted very close to the gear.

The accelerometer measures acceleration. How is that done and where does it have to be mounted.

How do all these values come together in the RC and help me?

What does the code that we get for both these sensors do?

If you know what your final gear ratio is (or you test to find out the correlation between counts and inches moved on the floor) you can determine how far the robot has moved. If it runs straight, you can tell where it is at any moment by keeping track of the counts. If you use the accelerometer, you can tell how much the robot has turned (or if it has turned the amount you want it to) so you now have direction and distance. Combine the two and get a rough idea where you are on the field. Be careful, the accelerometer output is proportional to the acceleration in one direction or the opposite direction. If it is mounted parallel to your direction of travel, it has no output. Read the spec sheet carefully to learn all of the nuances of the device and how to best filter out the info you need.

[xxmaddjxx]

Originally Posted by Al Skierkiewicz

If you use the accelerometer, you can tell how much the robot has turned (or if it has turned the amount you want it to) so you now have direction and distance.

How do you use the accelerometer to know how much you turned and in what direction?

What kind of value does it give out?

[Leav]

Has anyone had any luck with mounting the hall effect sensors?

i haven't found anything that fits them.......

also, if you haven't read the manual it states that you must connect pin 4 to pin 3 externally.

-Leav

[jimsmith2354]

Originally Posted by Leav

Has anyone had any luck with mounting the hall effect sensors?

i haven't found anything that fits them.......

also, if you haven't read the manual it states that you must connect pin 4 to pin 3 externally.

-Leav

Mounting of the Hall Effect sensors - We have drilled out the inside of two small connector housings, sanded off the middle ring on the outside, and will use jam nuts to hold them onto brackets placed near either the output gear or a tone wheel.

From another post, connect to controller using a PWM cable - RED to Pin1 - WHT to Pin2 - BLK to Pins 3 & 4

We will wire, test, then epoxy them into these homemade housings.

Mouser PNs 571-14454211 (x2) and 571-16041961 (x4)

Good Luck,
Jim

[MyFeetHurt]

Hey, Stu, it's Christine. I did some calculations.

Wheel radius = 4", Robot speed = 10 ft/sec, gear by sensor has 45 teeth

2 * pi * 4" / revolution

* 1 revolution / 45 teeth

* 1 sec / 120 "

* 1000 mSec / sec

= 4.65 mSec / tooth

In other words, you can't do this by polling the sensors in a 26 mSec cycle, and you probably can't do it in the fast cycle either.

I think the right way to do this is to hook the sensors to a digital counter and poll the counter. I could be wrong. I don't know squat about counters, it's after midnight, and I can't remember how quickly the fast code cycles.

I won't be there this weekend. See you all Monday.

[Joe Ross]

You can get very similar Hall effect sensors from Newark (they are actually just the next version newer, ATS665LSGTN) for $5. So, teams shouldn't limit themselves to just the two in the kit if they want more. There were 762 in stock when I posted this.

[scottm87]

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)

[Nixterrimus]

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?