Optical sensors getting tricked

[Daryl Vogel]

In the last competition we had a number of IR and other optical sensors on our robot. Due to the halogen lights however, we kept getting a true when it shouldn't have detected anything. Are there any sensors that you guys use that aren't affected by them or how do you get around that.

[Mark McLeod]

We usually use shading cones or recess the receiving sensor deeper into an enclosing project box to limit the amount of ambient light striking it.

[yash101]

I do not have any ideas on how to shield against light, except to create an enclosure around the sensor. However, you could use some different technology, like hall-effect or mechanical

[philso]

Originally Posted by Daryl Vogel

In the last competition we had a number of IR and other optical sensors on our robot. Due to the halogen lights however, we kept getting a true when it shouldn't have detected anything. Are there any sensors that you guys use that aren't affected by them or how do you get around that.

People here will be better able to help you if you describe what you are trying to do with the sensors.

[MrForbes]

we got around it by designing our robot so it doesn't need any sensors other than the compressor pressure switch. It's amazing what you can do with mechanical design, to eliminate the need for software

[yash101]

Closed-loop programming is good enough for most cases. However, when you are building a robot that will be in a different scenario at most times, you cannot rely on closed-loop. Open-loop seems like it would be slower, but it would be trustworthy. Would you rather shoot 100 frisbees into the goal at a 60% accuracy, or would you shoot 60 frisbees and make all 60 into the goal? The latter would be more impressive because that is a 100% accuracy compared to a 60% accuracy of the first one. Also, these numbers above are sarcastic. It would be more of a 7-9 or 8-9 ratio of made goals.

[MichaelBick]

Originally Posted by yash101

Closed-loop programming is good enough for most cases. However, when you are building a robot that will be in a different scenario at most times, you cannot rely on closed-loop. Open-loop seems like it would be slower, but it would be trustworthy. Would you rather shoot 100 frisbees into the goal at a 60% accuracy, or would you shoot 60 frisbees and make all 60 into the goal? The latter would be more impressive because that is a 100% accuracy compared to a 60% accuracy of the first one. Also, these numbers above are sarcastic. It would be more of a 7-9 or 8-9 ratio of made goals.

I don't see how open loop would be slower. It actually should be much faster than closed loop. In response to the OP we used banner sensors that could be tuned based on light.

[Gdeaver]

We had a similar problem in 2012 with sharp IR sensors from Pololu electronics.
http://www.pololu.com/catalog/product/1134
They are inexpensive and worked very well at first to control the indexing of the balls in our pick up. Between the 1st and 2nd competition we change the robot covering for a couple of reasons. That's when we started getting false positives. At that point for many reasons we could not go back to a robot covering that shielded the sensors. The human operator ended up being the controller. A tough lesson. So in the future we would use them again but design shielding in to the robot.

[otherguy]

Originally Posted by Gdeaver

We had a similar problem in 2012 with sharp IR sensors from Pololu electronics.
http://www.pololu.com/catalog/product/1134

The SHARP IR sensors can be GREAT if used in the right application, but here are my lessons learned.

• The version linked above is affected by long wire runs and supply voltage fluctuations. You can remedy this by putting a capacitor 'backpack' on the sensor, across the supply voltage pins (VIN, GND). I think we used soemthing around 300uF electrolytic cap. This significantly reduced our intermittent detections due to supply voltage fluctuation.

• There are quite a few different models of these sensors available, they are each tuned to work at different distances. Make sure you get the right sensor for the job. You need to know the minimum and maximum distances the object you are trying to detect will be from the sensor. This page has a good break down of ranges supported by different models.

• The larger versions that are mounted within their own plastic housing MUST be mounted so that the plastic is isolated from the chassis. I know it sounds crazy, but the plastic shroud on these is conductive.

[Alan Anderson]

Originally Posted by yash101

Closed-loop programming is good enough for most cases. However, when you are building a robot that will be in a different scenario at most times, you cannot rely on closed-loop. Open-loop seems like it would be slower, but it would be trustworthy.

Can you explain why you say this? It's pretty much the opposite of my experience.

[yash101]

The robot will not be in the same place very often. It needs to adapt by itself to it's surroundings. Also, yes, open-loop can be faster, or it can be slower depending on how you tackle it. In the case that I was thinking about, it would take time to read sensors and joysticks, process that information and then move the robot. That would basically have very little impact, unless you are doing complex processing (like vision). So, you are right. The impact of speed would be very little.

[Alan Anderson]

Originally Posted by yash101

The robot will not be in the same place very often. It needs to adapt by itself to it's surroundings.

I still don't understand your previous post. You seem to be saying that closed-loop control is not capable of dealing with dynamic situations, and that open-loop programming is necessary in such cases. Again, that is completely opposite to my experience. Please tell us what you mean by open-loop and closed-loop in this context.

[Joe Ross]

Originally Posted by yash101

Closed-loop programming is good enough for most cases. However, when you are building a robot that will be in a different scenario at most times, you cannot rely on closed-loop. Open-loop seems like it would be slower, but it would be trustworthy. Would you rather shoot 100 frisbees into the goal at a 60% accuracy, or would you shoot 60 frisbees and make all 60 into the goal? The latter would be more impressive because that is a 100% accuracy compared to a 60% accuracy of the first one. Also, these numbers above are sarcastic. It would be more of a 7-9 or 8-9 ratio of made goals.

I'm confused. A few weeks ago, you said:

Originally Posted by yash101

Our team wants to start PID, because we properly designed our robot last year, but didn't use sensors. If we did use sensors, we would have probably won the championships.

You seem to be contradicting yourself.

[MichaelBick]

Microcontrollers can respond to input much faster than a human could. The lag in reading input is barely noticed compared to the time taken off repetitive tasks. For example closed loop code on a shooter could reduce down time between shots and increase reliability. This makes the action of shooting much faster.

Also, open loop relies on human feedback or constants. Humans make mistakes and constants aren't as accurate as battery voltage decreases. Closed loop properly programmed will always be better than open loop code.

[magnets]

To address the open/closed loop control issue-
The confusion probably comes from the fact that the poster isn't too familiar with implementations of closed loop control in FRC. It's really hard to make blanket statements about one method being faster than another, or one being more reliable than another unless you have spend a significant amount of time working with both.
I do agree that a well-written closed loop control (PID, bang-bang, take-back-half...) is much superior to an open loop version, but in some cases, a team with little programming resources may not need to have PID control on their arm, but instead have two end of travel limits.
My recommendation to the poster is to spend time in the offseason experimenting with different control methods before commenting on their effectiveness.

As for the optical sensors, our team uses the banner IR sensors. We've used them on our drive wheels, our shooter wheels, and to detect the bump in 2012. We've found that with high speed control, we'd sometimes see that the speed reported would get cut in half when we went to competition, due to false positives. We fixed this by making sure that when we did high speed sensing, the black and white parts of the shaft that the sensor looked at were equal lengths. This makes it harder for the sensor to skip over one of them and report the incorrect speed. We also turned down the sensitivity as far as it would go without loosing the signal.