Interference

[Jeremiah Johnson]

OKay, so this is really annoying. My robot just acquired a problem with interference, I assume. The controller always used to turn the channel on the tv when the battery was fully charged but now it doesn't do that. Frequently when the robot is running the gripper motor, and it does it with that motor the most, just goes crazy. Opening and closing seemingly randomly. When the arm is at its peak it seems like it does this the most. Is there anything I can do to stop it from doing this?

[Al Skierkiewicz]

Jerimiah,
I am not sure what you are asking. Is the robot interferring with the TV or the TV remote is interferring with robot operation?

[Jeremiah Johnson]

Neither, actually, the Vex controller has always interfered with the tv and does now. But that really had nothing to do with it... sorry. I was unclear about what I was trying to ask.

My robot is getting extreme interference from something or some how and it just started. I've taken it outside and it does it out there, too. It's gotten really bad. I have the original crystal in it and have made sure they are tight and secure. I've replaced the controller, the micro controller, and I have raised the antenna up. It was serpentined in a 5x15 plate b/c I don't have the antenna sleeve so I used a pen and wrapped and zip-tied it to it. But nothing has been working. I've tried turning all of the electronics off.

Everytime there is interference the light blinks in the micro controller. I don't know what else it could be. Maybe I should try a different reciever. Maybe that could be it. I have two kits so I can interchange these but it doesn't seem like they work.

And btw, it seems like it does this only after I tell it to do something and then stop. Then it goes crazy like. But if I leave it sit it doesn't do anything.

[lukevanoort]

That sounds a lot like this. Since that strange behavior was caused by using a Vex servo that needed a constant PWM signal on a FRC controller that doesn't give one all the time, is it possible that your PWMs are loosing power? Maybe a bad solder in the cable or internal power issue? And, given that the controller used to work before the ccurance of this issue a stress related issue like connections coming loose makes sense, at least to me.

[KenWittlief]

Originally Posted by Budda648

And btw, it seems like it does this only after I tell it to do something and then stop. Then it goes crazy like. But if I leave it sit it doesn't do anything.

This sounds like a bug in your SW. Is that possible? Is there some default code you could download to see if it does the same thing?

I dont know what frequency the RC system is on. If you had a scanner or wide band radio receiver that could tune to the radio control frequency, you might be able to determine if someone or something else is on your channel.

Maybe one of your neighbors installed a baby room monitor, or some other device that is on the same frequency?

[Al Skierkiewicz]

Jerimiah,
I checked the Quad Cities listings and unfortunately for you Channel 4 is likely causing the interference. They may have changed transmitters or they might have a transmission problem. Although the band in which the VEX controller is designed (75MHz) is supposed to be protected it is close enough to channel 4 to be a possible problem. Channel 4 has a channel edge 4.75 MHz above the carrier of 67.25 or 72MHz. If they are having a problem with their output color filter there would be a out of band carrier 3.58 MHz above that which makes it right in the center of the VEX Band. Do you know where the channel 4 transmitter is in relation to your house? I know that channel 8 is in East Moline but I am not familiar with the other transmitter sites.

If you have cable running through the backyard, especially above ground, the critters may have eaten through the coax and it is now radiating cable signals. Since cable is not intended to radiate, it can and does have signals throughout the band including the protected space between TV channel 4 and 5. You can check this if you have a portable TV. Take it out in the yard with a whip antenna and see if you can pick up cable signals. If you can, the cable company is required by the FCC to come and correct the problem. Under FCC rules, there may be no stray energy radiated by the cable system. Even if you were to purchase the alternate crystal kits, they all appear to be in the 75MHz band.
I am not aware of any military equipment operating in this band, that also may be a possibility if you are near a base. That I cannot help you with.

Since I haven't really been close to VEX this year, I can't remember this part. Doesn't VEX have a tether? Does the robot repsond the same way with the tether?

[Jeremiah Johnson]

Wow... that would have been the last thing I would have thought about. Channel 4 is in Rock Island, and that could be why I get interference in Milan at the robotics center also. I don't have cable though, just basic television. Hm... I guess I'll check the lines tomorrow. This is awefully weird. I do live by a military base also, the Rock Island Arsenal.

I guess I could try the tether, that would give me a definite idea of what is wrong whether it be the channel or the software or like.

Thanks a lot Al.

[KenWittlief]

if it is channel four then all you need to do is wrap your house in about 8 layers of aluminum foil - that should give you about 60dB of attenuation :^)

[Al Skierkiewicz]

Jerry,
If you are near the arsenal, then you are also near the river. At this time of year, the traffic is pretty high trying to get things moved before the freeze. You might just have an overload from all the navigation equipment on the river. Don't go cornering the market on aluminum foil just yet.