Competition Radio Interference Solution?

[FIRST JerseyKid]

I was thinking about the IFI lib file. I know how at competitions there can be issues with robots in the pit using their radios interfering with robots on the field.

I was wondering why IFI doesn't add to it's .lib a check for a packet, that the field would transmit, indicating what teams are "in the round". If no packet is received don't do anything but if a packet is received than check the team numbers to the RC's team number and if the team isn't "in the round" than disable the radio.

Just an idea... What do you think?

[DonRotolo]

That might make it hard to use the radio, say, at your school.

And, if it can be disabled, it will be.

I think the issue is less being one of interference, and more one of safety. Pits are crowded, and the LAST thing anyone needs is one inadvertent motion by the robot, causing an injury.

Don

[Stuart]

the problem isnt on a logical layer but on a physical layer. while Im not sure how many channels are used for the first RC I am sure that it is less than 384(thats close to the number at nats). and youll just have teams transmitters stepping on the toes of the field transmitters.

in short that special packet you want to send would just be drowned out.

now what they could do is make the recievers dual band(75mhz and 900mhz) and have the field transmitters be one and the teams be another, but thats just over complicating things.

[Jon Jack]

Originally Posted by Stuart

the problem isnt on a logical layer but on a physical layer. while Im not sure how many channels are used for the first RC I am sure that it is less than 384(thats close to the number at nats). and youll just have teams transmitters stepping on the toes of the field transmitters.

in short that special packet you want to send would just be drowned out.

now what they could do is make the recievers dual band(75mhz and 900mhz) and have the field transmitters be one and the teams be another, but thats just over complicating things.

There still wouldn't be enough channels to allow everyone that's not in a round to run their robot via the radio.

If you just want to sit in you pit and test your robot, use a tether cable. If you're on a practice field and want to drive around a far easier solution than making switching to dual band radios would be to buy a long tether cable from sandrag (http://www.chiefdelphi.com/forums/member.php?u=2022).

[JohnBoucher]

From the 2007 Manual.

3.14.3 Pit and Competition Safety
Robot Operation: Operate robots on tether only in Pit area.

I like the suggestion of the long teather for pratice field.

Originally Posted by Stuart

the problem isnt on a logical layer but on a physical layer. while Im not sure how many channels are used for the first RC I am sure that it is less than 384(thats close to the number at nats). and youll just have teams transmitters stepping on the toes of the field transmitters.

in short that special packet you want to send would just be drowned out.

now what they could do is make the receivers dual band(75mhz and 900mhz) and have the field transmitters be one and the teams be another, but thats just over complicating things.

In news I work with a lot of radio receivers and transmitters and wireless mics and all that....from a radio operations perspective I would simply have a set of frequencies/channels set aside for use in the pits only...and clearly posted, those of course would not be used out on the field and that would solve the problem of units keying up ontop of each other, I suppose another solution would be to add CTCSS/DCS squelch and you can look that up on www.radioreference.com but still even with PL/CTCSS tones you can knock someone else off the air by stepping on their channel if you are too close....

just an idea.....separate and set aside channels for the pit would be my fix.

[Andy Grady]

Does anyone know what the frequency range of the radio's is? I am assuming it carries a VHF range similar to that used on wireless microphones at the events...another problem which may or may not become more of an issue. I just remember last year at Championships having to switch mics and change frequencies often as my microphone kept taking frequency hits and cutting out. I wonder if this problem is cause for some of the unexplained robot issues we see at offseasons and beyond.

Originally Posted by Andy Grady

Does anyone know what the frequency range of the radio's is? I am assuming it carries a VHF range similar to that used on wireless microphones at the events...another problem which may or may not become more of an issue. I just remember last year at Championships having to switch mics and change frequencies often as my microphone kept taking frequency hits and cutting out. I wonder if this problem is cause for some of the unexplained robot issues we see at offseasons and beyond.

All depends on what wireless mic system you are using, alot of the Sony camera mics are in the 700 mhz range, mine is the senheisser G2 kits and i'm in the 518.mhz range+ and then I guess there is some stuff up in the 900mhz range now....

when you say "hits", unless I can hear it, it is hard to say if perhaps you're mic was just going a touch out of range or perhaps the signal was multipathing which at such low power than these units run it actually happens.

if a robot or other radio keyed up on you're mic freq you should have been knocked off the air good! not just hits here and there

another wireless mic can also knock you off the air. I use this site in canada to look up frequencies http://sd.ic.gc.ca/pls/eng_alpha/web...see_name_input

you might have a similar site in the states with the FCC, Industry Canada is our version of the FCC.

[Alan Anderson]

Originally Posted by STORMCENTRE

just an idea.....separate and set aside channels for the pit would be my fix.

There aren't enough channels to do that.

The radio modems provided to us have 40 channels. They are apparently not quite selective enough to be able to use adjacent channels at close range without risking interference; I think I remember someone saying that only 14 of the channels are really usable at the same time in the same area. The user-selectable channels are 04, 13, 22, 31, and 40 (a spacing of 9), with 01 added a couple of years ago.

Each field requires six channels, one for each robot. Some regionals have two fields. Championship has four fields running simultaneously, but the opposite corners are probably far enough away that interference isn't a real problem between them.

However, there are dozens to hundreds of robots in the pits. You do not want radios interfering with each other when teams are trying to work on their robots. The "no radios in the pits" prohibition is a good safety rule even if you can keep field interference from being an issue.

[Andy Grady]

Originally Posted by STORMCENTRE

if a robot or other radio keyed up on you're mic freq you should have been knocked off the air good! not just hits here and there

The mic that i use personally is a Shure brand radio. According to the website you posted, it ranges in the low VHF range of around 152.820 MHz. I know from my work expertise in radio that alot of mobile radio frequencies operate at this range. In a large city like Atlanta, its very possible for alot of frequencies to be jumping all over each other. When you have many VHF frequencies popping up in a small band of frequencies, they tend to raise the noise floor on the VHF spectrum, particularly around the interupting frequency. Often this will cause for radios to squelch off the tones. More than likely, the problems with the microphones at the competitions has more to do with that than robot frequencies. But chances are that the robot radio's frequency range would be in a different area than that of wireless mic's or mobile radios would carry.

Also keep in mind that power of a signal can make a big difference in how a piece of audio or radio equipment squelches. Often if you have two frequencies sitting on top of each other (and they have to be directly on top to really cut something out alot) there will be massive amounts of intermodulation. Instead of the absolute cutoff like you are suggesting would happen with a robot frequency sharing a mic frequency, what you would get would be the higher power frequency winning over, with alot of interuptions, though not quite a complete cutoff. This is an effect we often run into with pager frequencys intermodding over our company radio frequencies. I find that it is very rare for two frequencies to be quite that dead on to be that destructive to a signal.

I am still curious however to find what frequency the radios run at. There are tons of radio signals that run rampid in a city...any one of them could cause an issue. Not to mention noise problems from exsisting robot radios that may have damaged parts from all the collisions robots take.

Essentially...radio control is a plecomplicated thing!

[DonRotolo]

Originally Posted by Alan Anderson

You do not want radios interfering with each other when teams are trying to work on their robots. The "no radios in the pits" prohibition is a good safety rule even if you can keep field interference from being an issue.

Absolutely right, Alan.
Again, folks: It's not logistics - interference can be addressed. It is a safety issue, plain & simple.

Don

[Dave Flowerday]

Originally Posted by Andy Grady

I am still curious however to find what frequency the radios run at.

The radio modems used up through last year were 900MHz (who knows, they may be different this year). Same band as 900MHz cordless telephones.

Originally Posted by Don Rotolo

It is a safety issue, plain & simple.

I won't disagree that the rule is probably in the interest of safety, but from a technical perspective interference from other robots shouldn't be a safety concern really. There's several mechanisms built in to make sure that interference from other robots doesn't inadvertently operate your robot: 1) RCs will only respond to data coming from an OI with their team number, and 2) each data packet is protected with a checksum and if that is not valid it is discarded. With these two safeguards in place it should be essentially impossible for multiple robots on the same channel to interfere with each other and mis-operate each other's robot. If this were not true then I would expect FIRST to take this one step further and confiscate each team's radio modems to guarantee no interference (like they did back in the days of the RNets).

[Billfred]

Originally Posted by Dave Flowerday

There's several mechanisms built in to make sure that interference from other robots doesn't inadvertently operate your robot: 1) RCs will only respond to data coming from an OI with their team number, and 2) each data packet is protected with a checksum and if that is not valid it is discarded. With these two safeguards in place it should be essentially impossible for multiple robots on the same channel to interfere with each other and mis-operate each other's robot. If this were not true then I would expect FIRST to take this one step further and confiscate each team's radio modems to guarantee no interference (like they did back in the days of the RNets).

1293 had an experience with this during build in 2005. We had both Ockham and Hockham (the practice robot) running at the same time. Ockham had its team number set to 1293, Hockham was set to 1294--but we had forgotten to switch the channel on one of them. Both would barely even twitch while on the same channel (we finally came to our senses and flipped one around).

While it would seem to be good that neither robot moved on the same channel (given that the field channels are inaccessible by teams), I fear for the time when someone pegs the joystick and the other team using that channel powers down the robot.

[Kingofl337]

Based on the trend we are seeing with most devices. They will probably be around 2.4GHz range.

[Pavan Dave]

Originally Posted by Don Rotolo

That might make it hard to use the radio, say, at your school.

And, if it can be disabled, it will be.

I think the issue is less being one of interference, and more one of safety. Pits are crowded, and the LAST thing anyone needs is one inadvertent motion by the robot, causing an injury.

Don

This happened at our pits at LSR without the radio when someone forgot to turn off the OI and when we went to make an adjustment, someone leaned over the OI and pushed a Joystick and the robot fell off the cart.

Think of what would happen if someone forgot to turn the OI and RC off when it was radio. At least when there is a tether it is a bit safer and helps prevent some of the stuff that happened.

Pavan.