View Full Version : Frequency Reservations

09-18-2008, 07:26 PM
Ok, so I have been looking a lot at wireless video systems, doubting that my poor 200MHz Hammer can encode a webcam in real time.

I think one thing we need to do before too many people buy a camera setup, is allocate frequencies, due to their limited nature (especially in wireless video devices).

I'll start with the requests, and I guess Tyb or another organizer can deny or grant them.


For my bot, I am looking at two frequencies:

While my bot is operating, I am requesting exclusive access to:
910MHz +/-4MHz for video transmission
(exclusive as much as we can make it at least... amongst the mechwarrior people only if thats all we can get. The reason I am asking for exclusive is because I am having a hard time finding a 'cheap' video transmitter that offers multiple channels.)

While my bot is operating, I am requesting shared access to:
2.4GHz for a Zigbee link. (I believe Zigbee is spread spectrum. what I don't know is if we need to start assigning "channels" for zigbee like WiFi has.)


I may be way off base with this post. Maybe the contest comes down to "She with the biggest transmitter sees video" or something.

09-18-2008, 08:16 PM
As far as I have seen there are some wireless camera systems that have two channels. But for 30 bucks there wont be to many options. The one with two channels is about 100 bucks. Who knows what could come by the time of the event.

I havnt played with the Zigbee But I believe uses some sort of network encryption and I assome it wouldnt matter how many people are using them as long the network your on is secured.


09-18-2008, 09:36 PM
This is a good idea Sienna. In the very least we should all be communicating as to what frequencies and channels we'll be using and try our best to work around each other. We also need Dave Calkins to weigh in here and give us the lowdown on what Robogames' RF policies are, and what we should expect. He has more experience in this area than any of us by far.

Personally I'm going to stick with Wifi as we have 14? channels by default to work with. I've heard people have had good results with the Zigbees as well, they do indeed use a channel system (more than even Wifi I believe) so they aren't as prone to interference. We can also adjust them as needed.

Bluetooth is another option, don't believe it shares any channels with Wifi even though its on 2.4ghz.

I think we should shy away from 2.4ghz cameras, ps2 controllers, and RC radios as much as possible though.

09-18-2008, 11:42 PM
There's no way to get unrestricted access to any freq. Not going to happen.

We have freq. control tables which allow you to check freqs in an out for short times. But anything in the 900 range is liable to get interfearence from any number of sources outside of RoboGames...

Things like XBee allow for digitally encoded signals, eliminating the need for freq control.

In the end, any off-the-shelf 900 or 2.4 Tx/Rx is liable to have problems due to the countless consumer goods using those freqs.

09-18-2008, 11:52 PM
Rc radio equipment is okay they have those new radios that are pcm im probalbly wrong on that but they dont worry about frequencies anymore since they jog around. I remeber going to the track in high school and trying to get that pin with your freq on it to race cars.

Bluetooth is what i was thinking about but the majority is for cell phones not much in the camera department besides that. If it its most likely its expensive. I saw one for 1600 a secrurity system camera setup but thats insane in the brain dude.

09-19-2008, 05:11 AM
There's no way to get unrestricted access to any freq. Not going to happen.

We have freq. control tables which allow you to check freqs in an out for short times. But anything in the 900 range is liable to get interfearence from any number of sources outside of RoboGames..

Ok, how fine grained are the frequency tables in the 75MHz, 400MHz, 900MHz, 1.2GHz, 2.4GHz ranges? Is scheduling them an impromptu thing, or are all the competitions coordinated with regards to wireless?

And I am not worried about transmitters outside of RoboGames so much, as the building itself acts as a shield of sorts, and I don't think us pilots are going to be *too* far from the transmitters (right Tyberius?)

09-19-2008, 11:58 AM
There's a freq table with a channel master. What happens is, you have a clip with your name and pit table on it. When you need that freq, you go get the freq clip, turn in your clip, and can use your Tx. People can ONLY use their Tx when they've checked oujt the freq. If the freq is checked out, you find the person who's checked it out.

It's not elegant, but it works.

09-19-2008, 12:11 PM
As Dave mentioned, there is a freq check out. With 75 MHz, there are channels 61-90. Also the combat folks are all on 2.4 GHz or something custom, so they aren't a problem with the 75 MHz stuff.


09-19-2008, 04:59 PM
That doesn't really help answer my question.

I am well aware that the 75MHz R/C stuff is easily allocated.

What I am not clear on are the ISM and amateur bands. Is there any plan in place to control the 420MHz, 902Mhz, 1.2GHz, 2.4GHz, and 5.8GHz bands? (To name a few common ones.)

For instance, everyone is familiar with the 2.4GHz band (2390MHz to 2450MHz I believe.)
What could be on that band:
Bluetooth devices.
Wireless Cameras
High end R/C controllers
Wireless game pads
Baby monitors
And a lot of other random crap.

How does RG manage this 2.4GHz band? Some items are completely dumb (wireless video), some hop over a few channels (802.11), some have more channels (zigbee), etc.

I think we can all agree that simply handing out a clip that says "2.4GHz" is meaningless. (Unless such clip is simply an indication of how many devices are on the 2.4GHz band.)

Does RG manage each connection type (802.11, zigbee, etc), which channels they occupy (3, 6, 22, etc), and hand out clips for each protocol/channel pair? Does RG manage spacing to ensure that the hopping protocols don't tromp on the dumb protocols (like wireless video) (or vice versa)? Does RG ask that viewers turn off their Bluetooth and Wifi connections on equipment they bring inside?

Or are the ISM bands simply a wild west, where its the person with the best protocol and strongest signal gets to control their bot?

09-20-2008, 01:11 AM
Have you attended?

When I was there, I wasn't observing any jammed bands. They didn't instruct people to turn-off their bluetooth headsets, and I didn't notice any of the 300lb robots capable of shredding humans into instant pizza topping go berserk. (If it happened, I'm bummed I missed it...)

09-20-2008, 07:01 AM
No, I hadn't attended. Which is why I was trying to get clarification before I do!

09-20-2008, 12:09 PM
Ok - then I can help:

No killer robots were observed to turn people into instant pizza topping during my visit.

09-20-2008, 12:29 PM
Ok - then I can help:

No killer robots were observed to turn people into instant pizza topping during my visit.

I'll back that observation.
...Although two years ago I saw a titanium bar shoot accross the arena and gouge 1/2" into the 3/4" thick lexan wall at eye level right in front of the panel of judges! That was just physics though... nothing to do with radio freqs. I bet most of them were checking their shorts right after :happy:

I do remember that some of the humanoid operators using zigbee experienced some communication dropouts that same year... it was only in one area (30' or so section) and lasted for only an hour. Don't know what that was about.

09-20-2008, 01:04 PM
>> some of the humanoid operators using zigbee experienced some communication dropouts

I almost made a snarky reply, and then realized that I'd be enabling some scriptkiddie to ruin everyone's fun, so I'm going to let it go. ;)

09-21-2008, 09:49 AM
So... what is the message here? We are great at controlling the 75MHz R/C Band, and everything else is a free for all?

I guess I fail to see what combat robotics has to do with all of the other competitions that are using wireless. Especially with MechWarriors, where we are not going to know what our bot is doing unless we have a wireless link.

09-21-2008, 11:19 AM
Because they have the highest vantage point, hence best reception of spurious signals?

And a combat robot that gets spurious signals is NOT going to be pretty.

10-03-2008, 11:27 AM
So I am going to resurect this thread again...

Am I the only one so far that has purchased a wireless video system? Or does everyone else just not feel like sharing what frequencies they are on?

10-03-2008, 11:49 AM
If you already have a system then you are ahead of a lot of us. I guess I'll be using a wifi signal to transmit from a webcam on my robot to my other computer. But that is me. I'm not sure what channel that is, or if it matters. I'll also be using an RC transmitter to control my robot at 74 something. I'll probably have to have a couple crystals for that part to ensure I don't interfere with, or get interference from anyone else.

Not sure what everyone else is doing because I dont' think anyone else really knows. Some are going for the Zigbee deal, and hoping to use tyberius' wifi camera solution.

I suggested previously that we collectively get four cameras that we know will not interfere with eachother, and swap those in and out. Tha idea was shot down though.


10-03-2008, 12:40 PM
I'm browsing various wifi cameras, which wouldn't interfere with much. Hoping to find something suitable for all to use.

Really its just a matter of finding a good price on them, I've found good ones but they're in the $200-300 range.

I'll be using Zigbee for my control solution, so interference isn't an issue. Can't speak for everyone else, but I doubt they're keeping it a secret for the sake of irritating you.

10-03-2008, 12:55 PM
Did that new round of cameras that I pointed you towards not work out? I can go for "round three" if you need...

And I am keeping it secret with the sole goal of being an irritant. :tongue:

10-03-2008, 01:02 PM
Oh, I know people wouldn't do it deliberately (except Adrenalynn :P). I was just a little surprised at the lack is all.

FWIW, my wireless TX/RX pair cost $110 (thats the cheapest set I could find that would perform reasonably well). The camera I am looking at is another $145. The composite studio monitor to display the signal on cost another $50.

So, $200 to $300 for a WiFi system isn't too bad in comparison.

10-03-2008, 01:27 PM
I'm still in the dark as to which camera setup to use.. Probably it will be Wifi.

For control, I'm going totally paranoid. I know that R/C radio is not all that good with my particular robot controller. Sooo I will have a Bluetooth to my laptop connection and/or something Zigbee, and/or the current PS2 wireless lashup I am using at the moment. All 3 will be usable and changing from one to another will be relatively quick and painless. All will be something in the 2.4Ghz range though.

Just call me Mr Paranoid

10-03-2008, 04:13 PM
I think the word you are looking for is "prudent" not "paranoid". I think it is very smart to have backup control schemes.

I was looking at using a 433MHz radio as a backup system, but will be evaluating zigbee first to see whats its faults are.

10-03-2008, 04:34 PM
OMG... I think I just had a hot flash... not bad for a 64 yr old guy.. Actually Siennas mention of a composite monitor just gave me a brain flash. Instead of using my laptop (which doesn't have a video in) for the video, I still have my old composite monitor from the Commodore 64 (still have the C64 too). So I could use a cheaper camera setup. Hmmmm