Intermittant control with radio
 

Sympton: When using the radio to move the robot around we experience intermittant motor activity; cuts off and on but not in a consistent pattern. Very erratic and causes the robot move in a very herky-jerky motion and is nearly useless.

These symptons do NOT appear under autonomous mode or when tethered; motor runs very strong.

So, I have two questions. First, anyone else ever experience this? Second, any ideas what may cause this?

Thanks!

Re: Intermittant control with radio
 

One question, did this happen at a compitition while on the playing field?

EDIT: *points to below post* dez beat me 2 it

Re: Intermittant control with radio
 

replace the cables that connect your radio from the RC and also radio to the oi, sometimes they can get damaged from constant use and also see if there might be any visible damage to the oi, rc or radios.

Re: Intermittant control with radio
 

My team experienced this at competition. If this is not your first year as a team, then make sure that the radio transmitter and receiver you are using are from THIS YEAR. We accidentally had last year's transmitter hooked up, which cost us a lot. This year's radios should have blue text on them.

Re: Intermittant control with radio
 

Yep, it was during the Houston Regionals. I'll have to check which radio was on the robot; we did experience the problem with two different radios. But, that still doesn't mean the wrong one was on the bot.

Talk about a frustrating day!

Sean

Re: Intermittant control with radio
 

Innovation FIRST representatives monitor radio signals. They are also very helpful in fixing problems like these. You may want to have one of the reps stop by your pits at nationals if you are unable to determine the problem. MY experiences with them have been very positive.

Re: Intermittant control with radio
 

if this happened somewhere besides an event I would say that someone else is using your frequency - one thing to keep an eye on is the radio link LED on the OI

if it keeps turning red, you are losing your link - either someone else is on the same channel, or something is wrong with your transmitters (could be at the OI or on the bot, either one)

Re: Intermittant control with radio
 

This happened to our team during the first qualification match at the Canadian regional. It's too bad too 'cause we would have won the round easily: it was two vs one, and both of our robots were disabled from the getgo. Our alliances had an untested autonomous which gave them a code error (probably an infinite loop) so they were immobile for the round. And we had that radio problem. To the best of my recollection, the "receiving" light would blink for a few seconds, then cut out for a few seconds. It was very aggravating; couldn't really do anything.

We tested everything before the match, and the radio worked fine in the practice area setup in the pits. But when both of our robots got on the field, BOTH of us seemed to have the same radio error lights come up. I don't know if our alliance partner would have had the same error while driving around though 'cause of that code error. We took the robot back to the practice area after the loss, had the same problem, and the Innovation FIRST guy couldn't figure it out. I think we just tightened our connections and then it was working fine.

What cheeses me off the most though is that when both of our robots were having the same error lights when we were setting up on the field, the FIRST employees tried to fix things... they had us setup our tether (for some reason beyond me) and we both still had the same radio error lights coming up and they decided to start the match anyways when it seemed as though it was a FIRST error. I understand there's a schedule to keep to, but it hardly seems fair to me that teams should suffer because of a silly problem like the radio transmissions. If I remember, Simbotics had a radio error too and they were going to start the match anyways, but then their field mentor ran out and was adament about delaying the match until they fixed it (which they did) Good for you!

Of course... we all know it's hard try and make the competition fair... just easier to remember the bad luck you get than the good luck :P

Re: Intermittant control with radio
 

if they fixed the problem by tightning the connections ON YOUR BOT then it wasnt a FIRST problem, it was loose connections inside your bot

you cannot hold up a match if something is wrong with YOUR BOT - there are no timeouts in the qualification rounds.

Re: Intermittant control with radio
 

This happened to our team as well. We ran a simple autonomous that was programmed about 10 minutes before our match, and we only tested that the autonomous worked. However, in the switch from autonomous to controlled, a loop or something kept us from driver control so the robot just sat there. It was an agonizing two minutes because I knew that I was the acuse of the problem with the faulty code, and my drivers just sat there trying everything to get it to work. To add insult to injury, the match was replayed because of a problem with the field, so I had to watch this happen twice.

Re: Intermittant control with radio
 

If your robot will boot and run at all, then you can escape code error problems very easily. Simply hit the reset button on your OI after autonomous has ended, and your robot will start back up without the auto mode bit set and you'll be able to run as normal. I know Chief Delphi had that problem in their last elimination round at SVR and didn't get reset until about 20 seconds left, and it was painful to see such a good robot go down because of a very fixable problem.

Re: Intermittant control with radio
 

We had a few radio problems on Friday of the Canadian Regional. During our first match of the day, on three separate occasions we lost communication with the robot. Luckily, we only lost the connection for a few seconds and were still able to cap and hang.

After setting up the controls for our second match we noticed that the No Data/Radio red LED was flickering on and off. So as Blair was doing his introductions, I ran over to the Innovation First rep to report the problem. He supplied us with a temporary radio, and the problem was solved.

My advice to any teams who notice these types of radio problems is to go straight to Innovation First. Their staff is extremely knowledgable and helpful. They will go to great lengths to solve your problem. Also, make sure you check all of your connections. Many teams at the Canadian Regional reported radio problems, which ended up to be caused by loose connections. (Our team included)

Re: Intermittant control with radio
 

The Innovation First rep. was incredibly useful not only with our robot on the field, but with troubleshooting our (now-defunct) IR guidance system. Back in Pittsburgh he was checking the beacons every time our team was up, and was gving us info on telemetry he was getting to help us out after many of the matches. As usual, he was very helpful at the Canadian Regional as well. And yeah, we got our radio cable knocked out because someone forgot to use the thumbscrews. Good thing we won that match anyway.

Re: Intermittant control with radio
 

That would have been good to know, thank's for the information.

Re: Intermittant control with radio
 

We had this problem last year and a bit again this year. Then we wisened up. Theres three things:

A) Keep the radio away from any motors. They create interferiance (yes, I know I can't spell).

B) If you have a shell or a cage of some sort made out of metal, put the reciever outside that (the metal in the frame will create a ferridite cage thereby weakening or blocking most electormagnetic waves).

C) Make sure the two antennae (the transmitter and the reciever) are parallel. If they are perpendicualr, it harms the quality of reception.

-Kesich

P.S. And it did hurt when chief del phi didnt reset. We (1097, 114, and 47) could have won that match and probably made it to the finals. But you know what, it was still fun and it was just a simple mistake. No hard feelings.

Re: Intermittant control with radio
 

I am the lead sponsor for the team which started this thread.

The discussion about the reset button on the RC brings up possibly a related issue we had at the competition in addition to the erratic performance on the field. When the round ended or even in the pits on tether, after shutting down power to the robot the team color LEDs would continue to blink. They would shut off after one hit the reset on the RC. Are these problems related??? The back-up battery and LEDs being new this year leave me with little experience in their operation.

Thanks,

APS :confused:

Re: Intermittant control with radio
 

when you turn off the main battery the backup battery continues to power the RC (and team color LEDS)

think about it - thats what the backup battery is for, to keep the RC running when the main power dips

so how does the RC know you actully wanted to turn the main battery off?

ans: you hit the reset button.

Re: Intermittant control with radio
 

We found our that reset turns off the RC by accident. Before, we would pull out the back-up battery to cut off power, which led to a loose connection in the back-up battery.

Re: Intermittant control with radio
 

As someone said before, the problem might be in someone else on your frequency. That sounded exactly like what happen once when we were running two robots in one room without realizing it.

Re: Intermittant control with radio
 

The frequency problem affected us last year. About 10 seconds into the match the robot stopped suddenly. No matter what we did, it would not move. An IFI representative said that the OI was sending data, but the RC was not getting it. Turns out that either someone was running a robot on the practice field or in the pits with a radio, or some other radio signal (RC cars were running around everywhere)

Re: Intermittant control with radio
 

If the IFI guy did not explicity tell you that there was interference, then there most likely wasn't. FIRST runs frequency scanners which will detect anyone using the radio modem when they shouldn't be (i.e. they aren't playing currently).

Matt

Re: Intermittant control with radio
 

This may be related to your problem.

We noticed our robot was chattering quite a bit after uncrating it at the Plametto Regional. What I mean by "chattering" is that the motors seems to be pulsing instead of having a smooth operation. The symptoms disppeared when we connected our laptop to the PROGRAM port.

The problem was discovered to be caused by printf statements left in the code. Removing these calls solved our problem.

Many thanks to Tom Watson (Innovation First) and Ed Sparks for your help in solving this!!

Re: Intermittant control with radio
 

ya my team had the same problem, but it turns out that first of all our receiver was too close to all of our electronics creating interference. and that there were so many radio waves bouncing around in the stadiums that i'd say would be impossible to find a place in there where there wasn't any interference. but we ended up solving this problem by just moving the receiver higher up the bot away from the electronics and we just used a tether while practicing because it also seemed that the competition transmitters are much more powerful than the ones given in the kit.

Re: Intermittant control with radio
 

after cutting the main (12 volt) power to your rc, with the back up battery at a high charge connected will continue to run for 255 seconds. In that time, the leds do flash, the rc leds should stay lit and the radio modems will try to continue to "talk" with each other.

Re: Intermittant control with radio
 

Did they say why this could be a problem only with the radio and not when connected with the tether or to the program port?

Andrew: We do have a couple debugging printf statements in the code as it stands. I know it's too late to really be much help; but it would be very valuable info for next season's robot.

The programmers at the school know what files the statements are in and how to get rid of them. Might be worth testing.

Sean

Re: Intermittant control with radio
 

In the past we've had problems with the radios cutting out on us. The problems have ranged from low voltage(when we loaded all the motors at once), bad/loose radio wire, and errors in our code (infinate looping and that sort of things).

Re: Intermittant control with radio
 

Furthermore, when plugged into the competition port, the OI is opened up to a number of competition-only frequencies, which are very unlikely to be duplicated out in the pits or practice field (unless someone has a dongle on their OI to enable them).

Another thought that crossed my mind reading this thread: programming. I've heard from a number of people that floating point math slows the PIC procesor to a crawl. It's possible that the RC is processing too much code, or too many operations, where it can't meet the time requirement to loop properly. I see a number of warnings in the code saying "warning: bad things may happen if _____." Could this symptom be one of the bad things referenced?

Re: Intermittant control with radio
 

Indeed that problem could occur. While we never use floating point math, it is very very slow, but a worse problem existed for us. Our encoders were digital, counting gear teeth passed, and were linked into interrupts on the OI. We found out that they were firing at about 2000 times per second at full speed, which was interfering with the datastream between the master and the user (the IFI guys told us to protect our variables, but I still don't see the chance for desynchronization in the code we had--we just overtaxed the system, I think). It caused the robot to be jerking and nigh on uncontrollable, as well as to fall in and out of autonomous. Oddly enough, the problem only occured on radio, not on tether, but we were 99.99% sure it was not a radio interference problem.

Watch how many interrupts you fire, if I may throw another warning into the mix!

Re: Intermittant control with radio
 

Next question is where does one legally test radio communication problems at a competition? We wanted to test if our radios where bad by switcing out with spares and also if moving the radio from inside a angle brace to outside. Can one leave the building and test on the sidewalk...
I appretiate hearing some of the more specific ideas regarding code issues that may be causing issues.

thanks,


APS :confused:

Re: Intermittant control with radio
 

I hear a lot of teams talking about interference- someone being on your frequency, causing your robot to go out of control.

It is simply imossible for this to happen- unless there was malicious intent. You set the team number on the OI and RC for a reason. The RC won't accept a packet (radio information) unless it originated from an OI with the same team number as itself. So unless someone set their OI to your team number, you're getting your own data.

It's possible that if someone is on your frequency, that too much "information" is in the air. However, during competiton, the controllers use channels that are not the default for the control system. They are avaliable, but a team would have to directly set their control system to use it. Malicious, if done at a competition if you ask me.

Re: Intermittant control with radio
 

IFI will allow you to test in the pit. However, if they see you doing it for long periods (2 minutes or more) they will come talk to you. If you're using a competition channel and not the default channel, you should expect IFI to stop the competiton and come talk to you immediately.

Re: Intermittant control with radio
 

Page 5 of the "At the Event" rules clearly state otherwise:
Just because teams have done it successfully without getting yelled at doesn't mean it's a good idea. All these complaints of suspected interference are even more reason to only use the tether in the pit area. How would you feel if you lost a match due to radio interference, only to find out that someone was operating in the pits and may have caused the interference?

Re: Intermittant control with radio
 

I would agree it's against the rules- however, it does go on and if a team feels their radio is not working how else are the supposed to test it? You often can not remove your robot from the building.

Also, it wouldn't bother me in the least if we were told we caused a robot to lose a match, if I'm using the default channel with my team number set correctly. At that point it was a failure with IFI, not my team.

EDIT: Ohh, if my team lost because of radio interference? It depends on the situation. If they were using a competiton channel, I would be furious with the team. If they weren't- I would think IFI was trying to hide something.

Re: Intermittant control with radio
 

IFI keeps records of all occurances that teams function. More or less from the time your bot is powered on, IFI knows what channel you may be on, thethered or not and even as much as they can check your battery levels. Now i knoiw that when i was helping out IFI in NYC, there was one occurance when a team had to test radios and they were brought outside supervised and assisted by the IFI representative on site. If you ever need to test radios please get an IFI rep to help you as they normally can figure out the problem in under the length of a match. Also they will then know if you need a donor or a replacment unit while at the competition.

Re: Intermittant control with radio
 

I've had a chance to talk to Tom Watson of IFI at length during both the Peachtree and Palmetto Regionals. During the match, IFI has a scanner on all four channels. They watch very closely to montior the data rate and packet losses. All too often, teams blame the radio communicatoins first, even thoguh it is rarely the culprit. It is mainly for this very reason that IFI has a representative at each event - to cull misguided perceptions.

Re: Intermittant control with radio
 

You need to talk to the IFI representative at your competition. Their scanners will give a lot of information about any interference that goes on during the matches. They can also give you tips on what else might be causing problems.

Re: Intermittant control with radio
 

At SBPLI we had a damaged RC tether connector that caused us to have intermittent radio broadcasts of garbled data only while on tether.

IFI had a special dongle they loaned us temporarily for the competition port that put us on a frequency no one else was using so we could close our arms without using the tether.

We were fine on the field, but couldn't use tether in the pits. We repaired the connector after the competition.

Re: Intermittant control with radio
 

With IFI being such a small group, and spread so thin, I find it suprising they have the time for that kind of personal attention. Kudos to IFI.

EDIT:
I feel a little harsh to Dave Flowerday on post #33 of the thread, so let me first aplogize.
For me, IFI presents us with a control system that I believe has almost no faults. When they have different channels, I assume that teams can use different non-competiton channels and have no worries. I also assume, that IFI produced a radio system that can shift through the garbage and grab your own packets by team number, even if others are on the same channel. This belief is even further enhanced when at Annaplois, a full practice field setup, including radio control was setup about 100 ft from the competition. They have done such a great job with the control system, I feel that any interference anyone is receiving is the result of an issue with your robot, or malicous by another team.

Re: Intermittant control with radio
 

Not sure if this was posted before, if it was, I am sorry.

We had this same problem at our regionals where we had some packet loss. After some talks with the innovation first guy, he told us that our problem could be caused by having our radio right next to the main circuit breaker. We moved our radio farther away from it, and havn't had this kind of problem since. Try moving your radio away from all other electronics, and have the ifi guys run a check for you every time you go up (if you are going to atlanta). They can detect packet loss, and see just how much data your robot isn't getting.

Re: Intermittant control with radio
 

So here's the deal: first of all, IFI does not manufacture the radio modems. They simply resell them (they're made by Ewave (unless Ewave is a division of IFI, but I doubt it...)). Second, when there are multiple fields in operation, IFI carefully selects the channels used by each one to minimize any chance of interference. Notice I say minimize: I work for a company that happens to dabble a little bit in RF, and one thing I can tell you for certain is that RF interference is very hard to predict and understand. IFI can reduce the risk, but they cannot eliminate it. These radio modems work on the same frequencies as 900MHz cordless phones and a million other things. Additionally, as you have mentioned, IFI protects their data stream with both a team number and checksum to prevent a robot from reacting to invalid or corrupted signals (those who were around in the Rnet days really appreciate this!). However, all that does is cause the RC to ignore corrupted packets. Meaning, if you're transmitting something on the same channel as an OI, the robot won't go haywire, but it will lose radio contact and just sit there, disabled. If two teams are on the same channel, the RCs cannot simply pull each team's stream out based on the team number. More likely, neither RC will get a valid signal, and both will be dead. This is affected by how far each OI is from it's RC and from the other RC, etc.

The bottom line is that I personally would feel really bad if we were using our robot wirelessly in the pits and later found out that while doing that, someone was sitting dead on the field. Sure, the likelihood of us being the cause of the interference is low, but no one can be certain. My advice, and the way our team operates: only operate on tether in the pits, unless specifically instructed or otherwise granted permission to work wirelessly. Don't just fire it up thinking it will be OK. FIRST made the rule I referenced earlier for a reason.

Re: Intermittant control with radio
 

the radios used are FM - which have the characteristic of 'capturing' the strongest signal, and ignoring all weaker signals on the same frequency

so if you are on the field and your bot is right next to your OI the link will work, even if someone in the pit is on the same channel

but once you get some distance between your OI and your bot, which transmitter will be hitting your bot with the strongest signal, and which bot will be pinging back to your OI depends on a lot of factors (where you receiver is located in your bot for one thing, which way the antenna is pointing...)

it would be very easy for an OI in the pit to capture your Bots link, then since the team numbers dont match up, the link will go dead and your bot will do nothing.

Re: Intermittant control with radio
 

I took a look at the Ewave site. We definately use there radios. The Screamer422 , is my best guess.

The base and remote use 2 different frequencies to achieve full duplex. Which means each "channel" is actually 2 frequencies being used. The base broadcast range is 926Mhz - 928Mhz. The remote broafcasts at 902MHz - 904 MHz. Frequency spacing is 50 KHz. THe range on the modems is approximately 300ft.

EDIT: I'm so concerned with looking at the spec sheets I failed to notice the following paragraph:
Ewave's SCREAMER422™ RF Modem is designed specifically for use with the Innovation First Robot Controller used in the US First Robotics Competition and, unlike all other Ewave RF Modems, the SCREAMER422 features a RS422 interface.

Re: Intermittant control with radio
 

Lots of interesting discussion but my question still remains, where does one legally test radio communication at a regional? I knew that the rules are require tethered control in the pits but .... At the Lonestar regional it would be simple enough to roll outside the front door except I don't know where one would get power for the OI... We were at a loss of where to test and just made a change and had to use the next round as a test which is not ideal.


Thanks to all you experienced posters who can quote the rule book


APS :rolleyes:

Re: Intermittant control with radio
 

There is no "Legal" place to test your radio modems, except during a match. But if you do need to test them, find an IFI Representative on the field, explain your situation and they normally will help you out.

Re: Intermittant control with radio
 

Okay if anybody is still lurking and watching this thread. Our team apeared to have some control issue at the Lone Star Regional. Drivers reported dead stick type of complaints. Lots of good ideas for troubleshooting have been posted as well as an interesting discussion of the Ewave radios ....
An update,
I have tested the robot in a gym on radio and students conducted a similar test in the courtyard in the weeks following the competition. We have made no changes since are last few rounds at the competition.


Does this rule out any of the suggestions and seem to implicate others? I have never experienced this in the previous three years at the regional.

I trust my drivers when they tell me it wasn't working but now I wonder if maybe it was a mechanical issue with our wheels and the carpet. The gym and courtyard test obviously where not on carpet.... :confused:

Re: Intermittant control with radio
 

Most robots, especially those without casters, perform VERY differently on carpet. Motor currents are much higher during turns, causing problems with breaker tripping and current limiting software algorythms.

Take this scenario, a 4 wheel tractor steer robot tries to turn. Without good slippage, one motor stalls causing the breaker to trip. The other motor tries to go it alone, but can't, so it trips. The driver fails to recognize whats happening so he still there with the stick fully deflected. Now, the breakers aren't going to reset at the exact same time. One resets, it trys to go it alone, then trips again. Then, the same happens for the other motor. You get the picture?

The same thing can happen in a shoving match, or just by running into something.

ALWAYS TEST YOUR ROBOT ON CARPET. If you dont have carpet, check with the field manager at your next regional event. They usually give the carpet away after the event, if a team will stick around to help dismantle the field. It helps to make arrangements for that before the event.