Sensors!

[JewishDan18]

Hey all, I need to make a list of all the sensors that can be hooked up to the crio. Any sensor you've seen hooked up, please post it!

My list so far:
gyroscope
accelerometer
touch
potentiometer
encoder
camera
ultrasonic
(i feel like I'm missing something obvious...)

any more will be appreciated greatly. Thanks in advance!

[Eugene Fang]

Originally Posted by JewishDan18

Hey all, I need to make a list of all the sensors that can be hooked up to the crio. Any sensor you've seen hooked up, please post it!

My list so far:
gyroscope
accelerometer
touch
potentiometer
encoder
camera
ultrasonic
(i feel like I'm missing something obvious...)

any more will be appreciated greatly. Thanks in advance!

Our team hooked up a photogate (I think that's what you call it) in 2006. Basically it was an IR light and a sensor, so when the line of sight was broken, it would send a signal. I know cRIOs weren't around back then, but it just used a digital input, same as on the cRIOs.

[EricVanWyk]

You forgot about the wonders of the hall effect!

Current Sensors (Hall Effect)
Gear Tooth Sensor (Hall Effect)
Magnetic Rotary Encoders
Magnetic Linear Encoders

[Stephen of REX]

Originally Posted by Pikat

Our team hooked up a photogate (I think that's what you call it) in 2006. Basically it was an IR light and a sensor, so when the line of sight was broken, it would send a signal. I know cRIOs weren't around back then, but it just used a digital input, same as on the cRIOs.

My team used that kind of photogate on the cRIO this year, I can ask the guy who worked on it for specifics if you like.

[Doug G]

Don't forget about:

Temperature sensor (thermocouple), I bet there's a team out there at some point who put this on a robot.

Light Sensor.. True a camera could do this as well, but a simple light sensor can be straightforward to program as long as you calibrate at the competition venue.

And then there was the IR beacon in 2004 (basically a light sensor).

[Eugene Fang]

Oh and I think I heard about some teams using current sensors this year for their traction control?

Not sure though.

[Gdeaver]

Don't forget the Panasonic IR distance sensors. Come in many different ranges in both digital and analog.

[AustinSchuh]

Originally Posted by Doug G

Temperature sensor (thermocouple), I bet there's a team out there at some point who put this on a robot.

We slapped a set of those on our practice robot, and used them to tell us when to give the robot a break to prevent overheating. Really useful, and I think all our future robots are going to be sporting one per motor.

[DonRotolo]

In fact, ANY sensor can be connected to the cRio; this then becomes a listing of 'all the different sensors that exist'.

This has some good info

[JewishDan18]

Thanks a ton; I knew CD would have a lot of knowledge on this.

Originally Posted by AustinSchuh

We slapped a set of those on our practice robot, and used them to tell us when to give the robot a break to prevent overheating. Really useful, and I think all our future robots are going to be sporting one per motor.

For lack of better words, that's awesome.

Originally Posted by Don Rotolo

In fact, ANY sensor can be connected to the cRio; this then becomes a listing of 'all the different sensors that exist'.

That's kinda what I wanted it to be, but mostly ones relevant to robots. Good link.

[Eugene Fang]

Originally Posted by JewishDan18

That's kinda what I wanted it to be, but mostly ones relevant to robots. Good link.

Looking at that link, I thought of one more that can be relevant to robots - a compass.

Pros: does not drift like a gyro does
Cons: can be affected by motors/metal/etc.

[JewishDan18]

Originally Posted by Pikat

Looking at that link, I thought of one more that can be relevant to robots - a compass.

Pros: does not drift like a gyro does
Cons: can be affected by motors/metal/etc.

That's an interesting idea. This is off topic, but how much drift would the gyro accumulate over the 2 minutes? I assume it will be greater the more time you hit another robot/wall. What were other teams experiencing?

[Eugene Fang]

Originally Posted by JewishDan18

That's an interesting idea. This is off topic, but how much drift would the gyro accumulate over the 2 minutes? I assume it will be greater the more time you hit another robot/wall. What were other teams experiencing?

I'm not sure, since our team has never actually used gyros. I've just heard of other teams using them. However, I seem to recall teams using accelerometers to counteract for drift (I don't know how). A crude way to fix drift is to have a trimming potentiometer on your DriverStation i guess.

Sorry I don't have any hard facts. Maybe someone else has had some experience with gyros personally?

[daltore]

The short answer is there's no way to say for sure.

The long answer is there's a way, but it's really complicated. Basically, the amount of drift accumulated is very dependent on the code running the gyro. Gyros have different responses based on temperature, so some gyros contain internal thermometers that are also output to the microcontroller. Another factor is noise. If you have a gyro that communicates by serial (good luck finding one, I haven't seen any), it'll be more accurate than if you have a wire running around carrying an analog voltage that's varying. With the analog signal, you have to do averaging to get any kind of usable data, and when you average, you lose resolution. Since the cRIO has such a high data rate, you could probably get away with it a little more easily. Also, MEMS devices in general work by using capacitance between a central mass and an outer edge. If you have any static charge on your robot, it may or may not affect the gyro. Also, calibration of a gyro will not necessarily work if you move it to a different location on the robot, because overall capacitance will change, and may or may not affect the capacitive difference.

[Jared Russell]

I have done quite a bit of work with gyros and drift is one of the more difficult things to characterize. What we call "drift" is the effect of integrating the output of a noisy signal. In the case of a MEMS gyroscope, this noise is caused by small thermal variations and vibrations that are impossible to completely correct for. Imagine a variable with noise of +/- 1 unit at any given time. What happens if you integrate this variable? You get what is called a "random walk", or drift.

Because electromechanical noise is usually modeled as a random variable (frequently as white noise with a mean and a variance, but no single exact value), you can never say for certain what your worst case drift will be. But, you can calculate things like your "average" drift rate over time, or your drift over various confidence intervals.

Drift rate is affected by several factors, including:
* The gyroscope's noise properties
* Sampling rate
* Temperature
* Filtering