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No tennis balls?....what? Can someone please explain, i thought that was a great idea...

AlphaTauri wrote:This year, the judges are allowed to pause the match if they see either of the bots experiencing radio interference, and the team is allowed to change their frequency.

Well, theoretically, that should work fine. But last year at states, we had to stop three of our matches for interference. Even though we had to ask to interrupt, we were able to prove it each time. Unfortunately, with a 2.4Ghz system there is no crystal to change, so the judge eventually just got fed up and banned us from asking to stop again .

Hopefully things go better this year.

That's really sad.

Primate wrote:Did anyone else have trouble using 2.4 at states last year? We had some serious interference against Vex bots. Kind of a shame... we had the lamest Vexer take out our custom built bot last year.

Doesn't vex use 27 MHz?

And yes, it is very easy to get interference if you're using a 2.4 GHz set. I think there are some more expensive sets that can manage interference really well with frequency hopping, but I've never tried one.

That is awful. I had no problems with 2.4Ghz last year, but the previous year I did. I don't know what was different- maybe the bots I faced were just the right choices...

ichaelm wrote:That's really sad.

Primate wrote:Did anyone else have trouble using 2.4 at states last year? We had some serious interference against Vex bots. Kind of a shame... we had the lamest Vexer take out our custom built bot last year.

Doesn't vex use 27 MHz?

And yes, it is very easy to get interference if you're using a 2.4 GHz set. I think there are some more expensive sets that can manage interference really well with frequency hopping, but I've never tried one.

Exactly! That's why we were so baffled. It was definitely the Vex bots, though. I built one for our C Team for invitationals, so we even did some testing outside of the competition. Within a minute or two of booting up the Vex microcontroller, our custom bot would start slowly drifting.

We're definitely going to be switching back to 27/75 MHz this year. Can anyone recommend a good radio system? We just graduated our R/C guy.

1. Vex uses 75 MHz (the 27 MHz Vex kits cannot change frequencies and therefore can't be used in Sumo Bots). The more likely culprit of the interference with a 2.4 GHz system is the local WiFi network.

2. The only way you can be assured that you won't experience interference with a 2.4 GHz system is to use one that binds the transmitter and receiver - once they are bound, the receiver will ignore signals from anything except the transmitter it is bound to, even if there are other devices using the exact same frequency.

3. This is all explained on the web page referenced in the Sumo Bots rules (http://www.newyorkscioly.org/SOPages/Su ... ncies.html). The information regarding possible interference on 2.4 GHz has been posted for two years. Students need to read the rules, including any web pages referenced by the rules. Keep in mind that no school or college will turn off their WiFi network just so a robot competition can be held, so selecting to use a 2.4 GHz transmitter/receiver that do not bind together is "at your own risk". The judges will do everything possible to eliminate interference, but there are some things out of their control, and the entire tournament cannot be held up because one bout has to be restarted over and over again because a team decided to risk using a transmitter/receiver pair that are not bound together.

4. Many of the bots at both the C Division and B Division State tournaments last year used 2.4 GHz, and this is the only incident I am aware of where there was interference with that frequency that could not be resolved by restarting the transmitter and the bot (same holds true for the National competition last year).

JBoyd-NY wrote:1. Vex uses 75 MHz (the 27 MHz Vex kits cannot change frequencies and therefore can't be used in Sumo Bots). The more likely culprit of the interference with a 2.4 GHz system is the local WiFi network.

Oh okay, I'm not up-to-speed on the different models of Vex. Either way, though, it's a narrowband system, and theoretically there's no way it would be interfering with 2.4GHz.

JBoyd-NY wrote:2. The only way you can be assured that you won't experience interference with a 2.4 GHz system is to use one that binds the transmitter and receiver - once they are bound, the receiver will ignore signals from anything except the transmitter it is bound to, even if there are other devices using the exact same frequency.

You'd think that would work perfectly, right? We were actually using this Spektrum transmitter, which does bind to the receiver. Sure enough, though, we were getting some serious interference, both at West Point and at home.

JBoyd-NY wrote:3. This is all explained on the web page referenced in the Sumo Bots rules (http://www.newyorkscioly.org/SOPages/Su ... ncies.html). The information regarding possible interference on 2.4 GHz has been posted for two years. Students need to read the rules, including any web pages referenced by the rules. Keep in mind that no school or college will turn off their WiFi network just so a robot competition can be held, so selecting to use a 2.4 GHz transmitter/receiver that do not bind together is "at your own risk". The judges will do everything possible to eliminate interference, but there are some things out of their control, and the entire tournament cannot be held up because one bout has to be restarted over and over again because a team decided to risk using a transmitter/receiver pair that are not bound together.

Sorry if I was unclear, but I am extremely familiar with that page. Other bots at the state competition had been using 2.4GHz without problems, and my partner and I decided the advantages outweighed the risk. (Obviously, we were wrong.) I'm in no way blaming our event supervisor, and it's certainly not West Point's fault for having their WiFi on. It was just extremely frustrating to watch a Vex bot take out our custom bot due to interference.

JBoyd-NY wrote:4. Many of the bots at both the C Division and B Division State tournaments last year used 2.4 GHz, and this is the only incident I am aware of where there was interference with that frequency that could not be resolved by restarting the transmitter and the bot (same holds true for the National competition last year).

Exactly. We obviously restarted the bot each match, and did the same whenever we stopped for interference. Yet no matter what, after half a minute, we'd start to have interference again. So with all due respect, I really don't think our issues resulted from not reading the rules carefully enough.

You certainly know your stuff, so I'd like to ask your opinion on which system you think is best for Sumobots. Right now, I think we'll use our existing 2.4GHz system for invitationals, and see how it goes. Even if we don't run into any interference, though, I'll be worried that we just got lucky. The way I see it, we have two options:

1. Upgrade to bigger and better 2.4GHz system. The cost to get a good system is a little more than I'd like to spend, though. Also, there's no saying we wouldn't run into the same issue again, in which case the upgrade would be pointless.
2. Switch to an old-school 75MHz system. This is the tried-and-true method, even though you have to deal with the hassles of crystals. My concern revolves around the fact that people upgraded to 2.4GHz in the first place--what else made them ditch narrowband?

What do you think is the best course of action for us?

I am into RC helicopters and have the Spektrum DX6i 2.4GHz transmitter and have never had any interference problem flying near wifi, cars, phones, and power lines. I'll be using that this year with the receiver that came with it, it actually has two connected receivers to completely eliminate interference. I have never used it at a competition though so I don't know for sure if it's better than the DX5e but it seems interference free. In terms of quality though the DX6i is a heck of a lot better and has full range 2.4GHz DSM2.

Primate:

The first thing I'd do is contact Spektrum and describe your experience. If you are using a transmitter and receiver that bind to each other, there should be NO interference problems, and it would be worth finding out what Spektrum has to say about the subject.

The second thing I would do is search for forums on using 2.4 GHz in competitions and interference problems. A year ago, when there were complaints of interference at the B Division States, I did so and found a number of forums where people who appeared to know much more than I indicated that what appeared to be interference on the 2.4 GHz systems was something else 99% of the time. Remember that your receiver has a battery to power it, and the forums I read indicated that when that battery gets weak, systems start to shut down on the receiver to conserve power. There were a number of other things that could cause problems that look like interference, and it would be worth finding those forums and checking each of those potential problems out.

Finally, if you do decide to ditch the 2.4 GHz system and go back to a 75 MHz system, I'd contact a place like The Robot MarketPlace and speak with a salesperson directly. Let them know what you are doing, what your price range is, and be sure to order the two sets of extra crystals when you order the transmitter/receiver pair. Don't try to purchase a system just by looking at a web page and ordering one you think will meet your needs. I've found the people at these places are very helpful and willing to help you find the best system for your needs that meets your price structure.

Jmmaroli wrote:I am into RC helicopters and have the Spektrum DX6i 2.4GHz transmitter and have never had any interference problem flying near wifi, cars, phones, and power lines... I don't know for sure if it's better than the DX5e but it seems interference free. In terms of quality though the DX6i is a heck of a lot better and has full range 2.4GHz DSM2.

I can't quite decipher Spektrum's website, but I think the DX5e has full-range DSM2 as well. I think we're stuck with our DX5e if we stay with 2.4GHz, though--the DX6i is just too similar to warrant an upgrade, and anything more powerful is overkill for sumobots.

@JBoyd-NY, you're convincing me that that maybe it wasn't interference. It looks like everyone gives the Spektrum equipment top marks for being pretty resilient, so you're probably right. I don't think the battery was necessarily the issue--we saw the "interference" occur right off of a fresh charge--but I'm sure there's tons of other reasons. I really haven't heard of anyone else having trouble at West Point.

I'll also get in touch with Spektrum for sure; maybe it's a known issue that just needs some configuration to resolve. I'll keep my fingers crossed that we don't end up needing to switch radios, but if we do, I'll make sure to checkout the Robot Marketplace. We've got a local hobby shop here I was thinking of, but they deal mostly with 2.4GHz these days, and I'm not sure how much surface FM equipment they've got left that's not the stupid pistol grip.

Thanks for the help!