Range Finder?

[Wzup4021]

I'm not sure if this is the right category, but I hope I can find some help. For this years competition we're looking at possibly using a range finder, however the one we have tried in the past (Not sure the exact model, it used radio waves is all that I know) didn't work out very well and wasn't consistent. Has anybody had luck with a good (Possibly infrared?) range finder that isn't very expensive? Looking for around a $100-$150 range. Any help would be greatly appreciated.

PS: Also, what makes a range finder legal/illegal for FIRST FRC?

[jwfoss]

A number of teams have used the VEX one with success in the past.

[Wzup4021]

I believe that was the one we tried before, but as it got farther out it became very inaccurate unless you had perfect conditions.

[otherguy]

Originally Posted by Wzup4021

I believe that was the one we tried before, but as it got farther out it became very inaccurate unless you had perfect conditions.

It's range is 1.5" to ~9.5'. Were you operating outside this window.

We used it in 2011 to detect our distance from the wall in autonomous. We were looking for relatively close distances, somewhere around a foot away. I think we missed a total of two tubes in auto at our two competitions that year. So depending on application it can work quite well.

I've also had good luck (outside of FRC) with the Parallax PING sensors.

I haven't used them myself, but there is quite the range of options available from maxbotix. They have sensors that supposedly can measure to the cm resolution at a range of up to 35ft, which is pretty amazing. You have a $30 voucher for this company in your kit of parts.

There aren't any rules specific to the use of range finders in FRC. Read the robot section of the manual for electrical rules and custom circuits.

As far as what you should use. Nobody is going to be able to tell you that unless you describe your application. When are you envisioning using this sensor. What range of distances will you be from your target. How large is your target. What material is your target made of?

In general ultrasonic sensors will be used for lower resolution higher range applications. Infrared is typically limited in range, but can provide good resolution over that range.

[wireties]

We have good luck with these...

http://www.maxbotix.com/Ultrasonic_S...ngefinders.htm

[Wzup4021]

Well, this is second hand information from a mentor (my first year on the team). He said that after they got to a certain distance (I assume not to far out of range) the cone of the radio waves became big enough that it had a half second delay, along with it not being accurate enough to pin point the target, and was picking up things farther away and occasionally registering them.

[wt200999]

Originally Posted by Wzup4021

Well, this is second hand information from a mentor (my first year on the team). He said that after they got to a certain distance (I assume not to far out of range) the cone of the radio waves became big enough that it had a half second delay, along with it not being accurate enough to pin point the target, and was picking up things farther away and occasionally registering them.

As long as you are in range of the sensor you shouldn't have much of a delay. The ultrasonic sensors use sound waves, which travel ~1116 ft/s

For the maxbotix sensors the max range is 255 inches or 21 feet, so at the max range, the sound travels a total of 42 feet for a travel time of ~37 ms.

If you look at the maxbotix datasheet they show approximate detection fields based on various targets. For long distance they use a 12" wide target and can detect it within a 2' variation side to side. For closer range they use small dowels to show the side to side bounds of where the sensor can detect. Different sensors from them have different side object detection ability.

Originally Posted by otherguy

It's range is 1.5" to ~9.5'. Were you operating outside this window.

I've also had good luck (outside of FRC) with the Parallax PING sensors.

I haven't used them myself, but there is quite the range of options available from maxbotix. They have sensors that supposedly can measure to the cm resolution at a range of up to 35ft, which is pretty amazing. You have a $30 voucher for this company in your kit of parts.

I would highly recommend either of these. With the maxbotix sensors you get a much wider range of sensors to choose from, and they also have a higher resolution product line which may be useful. Their standard sensors have a resolution of 1 inch, and their high resolution sensors claim to have a resolution of 1mm. Definitely use the KOP voucher at least.

[Al Skierkiewicz]

Ultrasonic range sensors may give unpredictable results if aimed at the player station. The diamond plate gives unusual reflections. There are laser sensors as well and the rule that comes into play for those is the one covering Class I lasers only. I believe Digikey has some ultrasonic that are inexpensive and easy to use.

[Nzoner]

In the 2014 Aerial Assist game my team and I tried to use Ultrasonic sensors, but with no luck. The Ultrasonic sensor could not get a constant reading, and would often jump from 15ft to only a few inches which would triggers safeties and our launch system. So unless we were just unlucky with our three sensors ( all failed) I would say to avoid them. Maxbotix was the brand, I'm interested to see if the VEX Range Finder works better, and will pitch it to my team.

[timytamy]

Originally Posted by Al Skierkiewicz

Ultrasonic range sensors may give unpredictable results if aimed at the player station. The diamond plate gives unusual reflections.

Are the unpredictable results consistent with:

Originally Posted by Nzoner

The Ultrasonic sensor could not get a constant reading, and would often jump from 15ft to only a few inches which would triggers safeties and our launch system.

Our software team had similar spikes, and think that it is due to noise on the analogue signal.

Could those of you who used the Maxbotics sensors successfully provide some more info on how you did so? Which signal did you use (analogue/PWM/UART)? If you did anything non-trivial in reading the input (such as filtering), could you also provide some sample code?

We are also at a loss on how to read in the PWM signal (to get over the analogue noise above) directly into the cRIO (and probably roboRIO), if anyone has experience with reading in PWM signals it would be great to hear.

[pastelpony]

Originally Posted by timytamy

Are the unpredictable results consistent with:



Our software team had similar spikes, and think that it is due to noise on the analogue signal.

Could those of you who used the Maxbotics sensors successfully provide some more info on how you did so? Which signal did you use (analogue/PWM/UART)? If you did anything non-trivial in reading the input (such as filtering), could you also provide some sample code?

We are also at a loss on how to read in the PWM signal (to get over the analogue noise above) directly into the cRIO (and probably roboRIO), if anyone has experience with reading in PWM signals it would be great to hear.

We used a Maxbotix ultrasonic sensor this year. We wired it directly to our cRIO's analog breakout and it worked well for detecting how far away the goals were. What language are you programming in and how many other devices are plugged into your analog breakout?

[timytamy]

We currently use Java.

Last year we had two sensors connected, the Maxbotics ultrasonics sensor (the one from the KoP a season or two ago) and a sharp infrared sensor (to channels 4 and 5 respectivly).

[lamk]

This year we use the Vex ultrasound for our autonomous and to guide manual shooting; it worked very well for us. The only problem is you'll fry it if it get subjected to too much vibration. We mount it at a spot where it get subjected to large amount of shock from our shooter arm. We fried three this season: during practice, regionals and St Louise. Try the Maxbotix in our practice robot while we wait for replacement Vex ultrasound and it did not work for us. Reading jump all over the place even with averaging. We're using Java and we use the analog when we wired the Maxbotix.

Originally Posted by Nzoner

In the 2014 Aerial Assist game my team and I tried to use Ultrasonic sensors, but with no luck. The Ultrasonic sensor could not get a constant reading, and would often jump from 15ft to only a few inches which would triggers safeties and our launch system. So unless we were just unlucky with our three sensors ( all failed) I would say to avoid them. Maxbotix was the brand, I'm interested to see if the VEX Range Finder works better, and will pitch it to my team.

[kaliken]

We looked at the dt50 as well. Looks like our performance was similar to yours. The dt50 was out of stock at the time we ordered. Thanks for the info.