A Better Gear Tooth sensor

[Alan Anderson]

Originally Posted by Tim Skloss

Get a couple of Honeywell 1GT101DC sensors from DigiKey ($25 each). These give you a pulse every time a tooth comes by the tip of the sensor. Sprocket teeth work well too.

The sensors in the KOP only give you rate information and therefore make distance measuring nearly impossible. Besides, they are hard to use.

According to the 2008 Sensor Manual, the KOP gear tooth sensors give a pulse every time a tooth comes by. Where are you finding information saying they only give rate information? And what do you mean by "hard to use"? We used the ones in the 2006 kit with substantially the same software you suggest for the Honeywell parts.

[Tim Skloss]

Originally Posted by Alan Anderson

According to the 2008 Sensor Manual, the KOP gear tooth sensors give a pulse every time a tooth comes by. Where are you finding information saying they only give rate information? And what do you mean by "hard to use"? We used the ones in the 2006 kit with substantially the same software you suggest for the Honeywell parts.

Well, it says the output is a "PWM" signal with a period of 45 us. When I read that I imagine a train of pulses that flows regardless of gear motion. Add to that description the statement of "duty cycle varies from 41-61 percent" and you have a good description of a classic PWM rate-type signal.

Now that I have read the Allegro data sheet I find that you are correct and the sensor manual to be misleading. The sensor manual should say: "Each time a gear tooth passes the sensor a 45 (nominal) microsecond pulse will be transmitted on the S output with no indication of the direction of rotation." Saying it is a PWM signal, when it isn't (no width modulation) only leads to confusion. The variation in pulse width comes from the distance between the sensor and the gear, according to the data sheet.

Thanks for pointing that out. We will try them this year on the gearboxes and save the Honeywell sensors for other sensing jobs. The Honeywell sensors are easier to mount and extremely durable, that much is for sure. Plus you only need 3 wires.

[Alan Anderson]

Originally Posted by Tim Skloss

The Honeywell sensors are easier to mount...

Easier to mount than what? The KOP gearbox has a perfect spot for placing the KOP gear tooth sensor, complete with mounting holes.

[Tim Skloss]

Originally Posted by Alan Anderson

Easier to mount than what? The KOP gearbox has a perfect spot for placing the KOP gear tooth sensor, complete with mounting holes.

The FIRST GTS boards are designed to mount in the gearboxes. The features are provided (although the fasteners are not!). That is where we will use them.

But what about everywhere else on the robot? Placing the fragile board anywhere on the robot other than the inside the protective confines of the gearbox would be inviting disaster. Building protection would be required, but we only have so much time and resources.

The Honeywell sensors are cheap, very reliable, have a very clean signal, easy to use and are nearly bullet-proof.

[Tim Skloss]

We installed the sensors in the Andy Mark gearboxes today.

You can read about it here.