Competition Radio Interference Solution?

[Astronouth7303]

Originally Posted by Pavan

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.

Of course, the way to deal with that is to build a cart such that the wheels don't touch anything solid. (Highly recomended.)

IMHO, the minor convenience afforded by being off the tether is offset by the technical complexity of such a system. The fields last year had enough issues without the pits (the Ypsilanti regional comes to mind). Even with Hatch Technologies out of the picture (IIRC), I think the entire control system needs less complexity, not more.

[Andy Grady]

Originally Posted by Dave Flowerday

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

900 MHz radios are widely used in the electrical industry. As a matter of fact, most of our radio controlled devices out in the field use 900 MHz frequencies to operate. In a big city, there may be a 900 repeater at the top of a large building (say for instance the Westin Building) that would be sending out signals at fairly high power. It would be very easy to cause intermod with a robot signal which isn't even close in terms of power to a repeater. You would need some sort of PL or similar encoding to prevent massive issues, but you would still be at a high risk for intermod.

I think what it comes down to is...radio frequencies are everywhere, we might just have to live with the nuances of interference for a while.

Dave, do you remember when RNETS would cause for many rematches in FIRST as a result of the radio being on the same frequencies as Orlando International Airport? God I miss the old days.

[Dave Flowerday]

Originally Posted by Andy Grady

Dave, do you remember when RNETS would cause for many rematches in FIRST as a result of the radio being on the same frequencies as Orlando International Airport? God I miss the old days.

Absolutely. Anyone who complains about the current radio control system clearly never experienced the days of RNets. I remember that back in those days every field had a frequency analyzer sitting next to it with someone watching it during each match to scan for interference, and I remember lots of rematches (and more importantly, several matches that I'm sure we lost due to interference that they did not replay ).

To be honest I'm quite amazed that the current radio system seems to work so well at so many different competitions over the course of so many years. Like Andy said before, radio control is hard to get right, and between IFI and the makers of the radio modems I think they succeeded.

[Jimmy Cao]

Originally Posted by FIRST JerseyKid

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?

I believe that IFI included something that would compare the team numbers on your OI with the RC. It should only let you control the robot in competition mode when the 2 numbers match, if i'm not mistaken.

[mtaman02]

We all know that the IFI Control Systems alows -X- amount of channels to be used by the teams and the rest to be used by the Field Control System. My next quetstion is why can't more channels be added to the current set that already exsists (instead of 40 channels why not make it 80 or more. Is there a reason behind only having 40 channels to use with only 5 / 6 of them to be selected by the team. I know the system is complex already but how about a Tri-Band System with one band for the Pits another for Competition and the last to be used for Team use and then 40 channels for each.

I remember that back in my days of being in H.S. that our robots use to go nuts reguardless of having different channels & team numbers set and no one at the helm, As a matter of fact the robots use to react to Walkie Talkie uses back in my old H.S. (which is why the Walkie Talkies are not allowed at competitions - since robots do tend to stop performing / preform poorly during a match when that device is in use.)

[Al Skierkiewicz]

OK, some weird data coming through in this thread.
The 900 MHz band that the radio modems use in a part of the shared Amateur and FRS band just above 900 MHz. Although close to cell phone frequencies they are not exactly crossing but, any high power transmitter close to or adjacent to your frequency can produce spurious signals on your frequency. Common wireless microphone frequencies in this country are designed to operate in the VHF TV band or on the now unused channels at the high end of the UHF band, ch 65-69. I have seen some in the 900 MHz band but they are pretty scarce at this point. However, second and third harmonic radiation from these radios can occur in the 900 MHz range. In particular, wireless microphones in the presence of metal produce out of band response as the RF is affected by the rectification of the metal to metal contact. Often, hanging jewelry, metal belts, even metalized fabric places havoc with wireless mics. (not to mention brush noise from DC motors) Regardless of the error checking that takes place there is still so much in the way of interference that can affect modem communications and since we can control it by not using the radios in the pit let's do it.
I am a big fan of adding a tether extension so that the tether can be connected to the outside of the robot, not directly to the RC. (Don't use the locking hardware for this when you connect to the outside tether.) When using the tether in the pit, should the robot act erratically, you just yank the tether out. Robot comes to an immediate stop, simple and effective. Also highly recommended is the use of a disable switch on the OI port. These are easy to build and you need one to enable the robot and autonomous mode during build. Info is on the IFI website.
If you think you can get away with using your radio in the pit, be advised that the IFI monitor at the field table, can tell every robot that is fired up and what the status of things like battery, backup batt, etc. They know when you are sleeping and they know when you're awake.

[Astronouth7303]

Originally Posted by Al Skierkiewicz

OK, some weird data coming through in this thread.

Too much metal in the server.