Re: does anyone have OI and RC radio issues
 

It was Saturday we tested them, and we did not meet Sunday. Not sure how much we will run them tonight. We spent over two nights trying to resolve the problem before we got replacements, so we're playing catch up. I'll let you know how it goes.

I shipped the old modems back today.

Maynard

Re: does anyone have OI and RC radio issues
 

From another thread on this subject...
Any merit?

Re: does anyone have OI and RC radio issues
 

I am not sure how many people are having problems with the OI and RC, but from what I can tell we are one of the few unlucky ones. I think we will be contacting IFI soon about our glitches. Namely, the robot running several seconds after it drove into our makeshift player station. It's nice to see that they are doing something about this though.

Good Luck to all of you and I hope that not everyone is affected on this one.

Re: does anyone have OI and RC radio issues
 

cell phones are not the issue that's for sure. However, we have yet to try our new radios yet since we were powdercoating parts of our robot.
We will try it today and see if IFI has fixed our problem.
Again, I will keep it posted once we find out.

Re: does anyone have OI and RC radio issues
 

I wonder if this problem only affects random radios, or if it's every single radio.

Re: does anyone have OI and RC radio issues
 

Team 1511 has experienced the OI/RC radio issues as well for the past 2 weeks. Same symptoms of cutting in and out for a period of a few seconds, as well as the master disable switch on the competition port NOT killing the robot as it should.

I contacted IFI over this past weekend, and spoke with Corey Chitwood, who was extremely helpful. We had a discussion regarding potential RF interference issues, internal vs. external antennas, and we tried a few of his suggestions. From our discussion on Saturday morning, there is not a mass recall or swarm of teams reporting problems (yet). He mentioned the teams who have posted above this, and said that they found and fixed a clear hardware problem on the very first team to have sent their radio back. At that time, he had not received the other radios that were RMA'd, and couldn't provide any additional info.

We tested extensively on Saturday and Sunday, both in autonomous and manual drive modes, and continued to experience radio cutouts. After nearly squashing a mentors foot with a speedy autonomous (and un-killable) robot, we reverted to last years radios. I obtained a RMA from IFI on Tuesday afternoon, and our modems ship out Thursday morning.

When we receive our new ones I'll post an update regarding their performance.

--Eric

Re: does anyone have OI and RC radio issues
 

Well, our team has not yet contacted IFI, since we usually order an extra set of radio modems we were going to wait to see if those worked. But they have been out of stock for quite a while. Our problem from what i have seen and heard does not happen all the time it is quite random. But having a robot with no control even for a few seconds can be bad.

I'll post if i have any news

Re: does anyone have OI and RC radio issues
 

We decided to do a double process tonight. We broke in our transmissions and tested our modems. We had the controller on one side of the class room and the RC on the other.
We used the trim on one joystick to drive both motors via the "single stick" drive mode.
Randomly the motors would just stop and restart, indicating that the data comm. had dropped for a sufficient amount of time to cause a timeout. While observing the RC, it became obvious that the Radio Modem light would flash RED when ever the motors would stop.

We will be contacting IFI in the morning to report the problem and await further instructions.

Re: does anyone have OI and RC radio issues
 

While cell phones do not operate on the same frequency as the modems, they are capable of some high signal levels that could cause local inteference which could cause the radio modems trouble. It is one of the reasons that wireless communication is not allowed at the playing field.

From section 3.14.3 Pit and Competition Safety

Two-way radios: Not allowed in the Pit or near the playing field since they may interfere with robot operation and cause accidents.

Re: does anyone have OI and RC radio issues
 

If our new radios continue to have problems, I plan to run a poor man's RS103 test (1 V/m, 30MHz-9GHz) in a 3m shielded room to see if I can cause the problem to crop up at a specific frequency range. I might be able to push the field strength with some hacking up to 5 V/m from 1-8GHz, which includes the cell phone band.

For the interested reader, RS-103 is part of a battery of tests performed under MIL-STD-461D (the new E is very similar) for military qualification of electronic products. Commercial products rarely need to meet a susceptibility requirement, other than the generic FCC Part 15 statement for intentional radiators that says they "must accept any interference caused by the legal operation of other radio services".

I suspect no one is really interested in EMI though :( :(

Re: does anyone have OI and RC radio issues
 

Esqaured,
The modems operate in the 918MHz FRC band. So most cell phone interference is from cell phones operating just under 900 MHz and obvious FRC radios and Ham operators in the adjacent band. I suspect you might find that interference is not as big a problem as the AGC overload caused by nearby signals forcing the input gain down.
Please check for EMI as well, I think it will prove to be useful data.

Re: does anyone have OI and RC radio issues
 

I should have been more specific in my previous post, the medium power amplifier I will try out has a spec'd frequency range of 1-8GHz, but continues to exhibit reasonable gain and output power specs for another 2-300MHz below it. The 5V/m is my best guess at effective radiated power at these "unspecced" frequency ranges.

You've got an excellent point about AGC (Automatic Gain Correction, which in RF systems is intended to avoid saturating your receiver, which leads to data that all looks like the same, far too high level). To test this, I'd have to crack the case on the modem, and somehow I doubt our team leader will go for this :ahh: Anyone void their warranty and see how they implemented this year's radio?

Another possibility: I've seen front-end bandpass filters that had poorer than expected rolloff outside the band, resulting in a susceptible front-end. Since the hardware repair to the first team's radio was relatively quick, replacement of a poor quality filter would fit into this category. Additionally, it may not be an issue with all filters, so some teams could be operating just fine.

In the end, I expect this to be similar to last year's 8.2V problem where some teams had it, some didn't. Very similar in that both resulted in non-responsive or potentially destructive robots!

Re: does anyone have OI and RC radio issues
 

That's interesting. How about the old radios? Is there something in its makeup where cell phones dont have a strong enough signal to affect them.
I made that statement earlier based on an earlier post, then had our whole team use their cell phones near the robot with our old radios. It didnt encounter any loss signal between the OI and RC.
What's different internally with these new radios?

Re: does anyone have OI and RC radio issues
 

E,
I kind of doubt there is great filtering on these radios due to the low cost of the item. My guess is the T/R filtering is about all there is with a little additional low pass to cut the 2nd harmonic down to spec. What we don't know at this point is how great the shields are inside and your testing might show that.

waialua,
We don't know enough about these radios yet to answer your questions. The reports of failures from teams on CD do not tell the whole story. There are far too many variables to point to one thing. Let's just hope that IFI will take care of this as they have in the past.

Re: does anyone have OI and RC radio issues
 

Eric,

Pictures of the radio's internals are part of IFI's FCC OET, EA public file as is the emissions test report performed on a prototype unit.

Based on my own observations of the problem, an Electrical Fast Transients test, such as EN 61000-4-4, might be more revealing than an RF succeptability test, but certainly a lower frequency, 100% AM modulated signal can reveal problems that an EFT test would also expose.

Again, without motors running, we saw no indication of packet loss.

Our build location is surburban with no close field radiators, let alone any dynamic radio transmission that would be tightly coupled to motor actuations.