Sonar Sensors legal

[cosato22]

If someone has already posted this, please direct me to the discussion.


My team does not want to use dead-reckoning during autonomous, and we're considering using sonar to find balls. We have two "VEX Robotics Ultrasonic Range Finder Kits." It is from VEX (http://www.studica.com/products/shoppingcart.cfm?productid=56151&productpriceid=271877).

It is an ultrasonic range module.

Do you think this is legal?

thank you,

Cosato22

[EricH]

I don't see anything in the rules against using them.

The rules in question would be the custom circuit/sensor rules.

[Al Skierkiewicz]

Cosato,
As long as the sensors are COTS items and not something you have on hand but is no longer available you may use them. Please be aware that the field is a loud place and the player stations have diamond plate on the front. The environment will differ from your shop or practice field.

[apalrd]

If your goal is to look for a ball, you already know where it is. You place it on a dot that is at a known place on the field, so as long as you put the robot in the right place you're OK. You can use a broken-beam sensor to tell you when you have it. All you really need to do is use your encoders to drive for x inches, then creep forward the last ~3 while checking the broken-beam sensor. Thus, you don't really need ultrasonic.

[Foster]

I'm really familiar with the ultrasonics and I'd like to suggest you try IR sensors instead.

I can recommend these:

Robodyssey.com IR sensors page (http://www.robodyssey.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=RS&Category_Code=S) They sell two different Sharp sensors that come in two different ranges. At the bottom of the page they have a nice mounting bracket that I've used with great success. Cables, sensor pair, mounting for under $50

The ultrasonics are sensitive to the materials around them, sounds don't bounce exactly like you think, carpet sucks them up and non-flat surfaces (like a ball) don't reflect the way you want. IR with the much shorter wavelenght has better bounce.

The Sharp IRs are my "go to" sensors for finding things 5" to 5' away.

[cosato22]

Thanks for all the responses!

Al Skierkiewicz, what is a COTS item?

Foster, do the sensors work with Labview code? About how long does it take for them to ship? I live in Hawaii.

Foster, it sounds as though one can use two infrared sensors without interference. Is that true?


thank you,
Colby

[EricH]

COTS: Commercial Off-The-Shelf.

Full and complete Manual definition (Section 8.2):COTS – A “Commercial, Off-The-Shelf” COMPONENT or MECHANISM, in its unaltered, unmodified state. A COTS item must be a standard (i.e. not custom order) part commonly available from the VENDOR, available from a non-team source, and available to all teams for purchase.
• Example 1: a team orders two robot grippers from RoboHands Corp. and receives both items. They put one in their storeroom and plan to use it later. Into the other, they drill “lightening holes” to reduce weight. The first gripper is still classified as a COTS item, but the second gripper is now a “custom part” as it has been modified.
• Example 2: a team obtains openly available blueprints of a drive component commonly available from Wheels-R-Us Inc. and has local machine shop “We-Make-It, Inc.” manufacture a copy of the part for them. The produced part is NOT a COTS item, because it is not commonly carried as part of the standard stock of We-Make-It, Inc.
• Example 3: a team obtains openly available design drawings from a professional publication during the pre-season, and uses them to fabricate a gearbox for their ROBOT during the build period following kick-off. The design drawings would be considered a COTS item, and may be used as “raw material” to fabricate the gearbox. The finished gearbox itself would be a FABRICATED ITEM, and not a COTS item.As for using mulitiple IR sensors without interference, it is possible. Back in 2004, there was an IR beacon on each side of the field. My team mounted 4 IR receivers in tubes that were wrapped in aluminum foil, cut the other ends at angles, and mounted the receivers in pairs on servos, with the angles facing away from each other in each pair. I don't know of any problems other than weight; they and their mounts didn't make it onto the final robot. (It was a pound or two all told; we had not that much available.)

I wouldn't be surprised if a sender/receiver IR unit could be configured in the same way, if needed.

[Foster]

I responded to Colby in a PM on how to get overnight shipping.

As far as many IR sensors go, it is possible to put a large number of sensors on the robot. You are limited by two things:

1) Number of analog ports available. These are very simple voltage devices (the closer the object is, the more light is reflected, the more light they see the higher the voltage) so it's not a load on the system.

2) Reflections from other IR sources. The beam from the IR LED that is illuminating the target is fairly narrow. But due to bounce patterns that light may be seen by another sensor. You can use this to your advantage by using the sin/cos formulas to triangulate the position. You can also narrow the focus by putting the sensor in a tube. (EricH's example)

It takes some experimenting, but it's pretty fast to make changes and figure it out. And since the hold back allowance has gone up 20 lbs it shouldn't be a problem keeping a few of the 1oz sensors to play with.

Good luck!

[cosato22]

Thanks for all the info.

I'm still wondering about code. Is there a VI I could find somewhere to program the infra-red? I've been looking around, and I found one for labview 9.0, but we only have labview 8.6.1 in this competition.

Should I write it myself? How do I do that?


thanks,
Colby

[Foster]

Treat it as an analog device. The value that the sensor puts out is higher the closer the target is. You'll need to do some minor testing: Put the sensor on the robot. Put the ball 5" away. Take a reading. Move the ball 6" away, take a reading. Move the ball, read, repeat.

From the data points collected you should be able to create a formula that will convert the value into distance. (like .1 volt ~ 1"). The formula will depend on the IR sensor that you use. If you buy the ones from the Robodyssey.com IR sensors page they come with a little BasicX program that shows the distance formula.

Good luck!

[cosato22]

so the basicx program shows up in Labview as a Vi? With open and close Vis?

[Foster]

Sorry to confuse you.

In the packet they give you a sample of code using Basic on how you would use the sensor. You can see how they read the value from the Analog to Digital Converter (like our cRio analog card) and convert it to distance.

The formula for the Sharp 2Y0AD21 sensor is:
DistanceToObject = (3027.4 / IRVALUE) ** 1.2134

In my prior message where I said to take a number of samples at different distances and create the formula what I was saying is at the end you'll have a formula like above to calculate the distance.

The sensor is easy to use, plug it into an analog port on your cRio. You'll need to make it work, so it's not 100% plug-and-go, but in under 15 minutes you should be able to figure it out.

Chapter 12 of the FRC Labview Manual has the VI information. You can use GetVoltage.vi, but you might be happier with the GetAverageVoltage.vi. (Dont forget Open.vi to open the channel!)

Good luck!