IR Remote Interference

Some people have been worried about IR interference that would occur if two teams picked the same IR codes. The chances of that happening are so low that I don’t think it will ever happen, but I am worried about something else. I have been experimenting, and it turns out that if any two remotes are transmitting at the same time, neither of there codes will be received correctly. I have tested this with several combinations of TV remotes.

Understand that the IR board is not being triggered by other remote controls, but the presence of other IR transmissions causes the IR board to not react to the intended remote.

I am wondering what is going to happen when there are 6 remotes all going off at the same time and the IR lap counters are on, or when somebody realizes that they can cut off all communications with the other team’s robots by holding down any button on their remote. I don’t think I am going to be able to rely on the IR board to control the robot in the hybrid period.

Good experiments, and thoughtful concerns… however from my understanding, the robocoaches at any one corner are all from the same alliance. If you build your IR receiver to be directional, your remote control to be directional, and co-ordinate your transmissions with the other robocoaches on your alliance the chances of this happening should be greatly reduced.


P.S. Actually there will be up to 12 IR remotes on the field at any one time, as each alliance can have 2 robocoaches. So the potential for a problem exists, but perhaps that is an intentional complexity of the game.

Each team can only have one robocoach.
Taken from page 4, section 7 of the manual.
“ROBOCOACH: A pre-college student team member designated as the only team member permitted to provide external stimuli to the ROBOT from either of the two ALLIANCE ROBOCOACH STATIONS. There is one ROBOCOACH per TEAM.”

Each team is only allowed 1 robocoach. What they showed in the Human Robot game was 1 teams robocoach became the robocoach for another robot. Each team can only provide 1 robocoach, but one robot can take commands from multiple remotes.

Each alliance can have three, one from each team. Nobody said anything about how many robots they can control combined (other than you can have only one device per coach).

I stand corrected… one Robocoach per team, six remotes on the field.

However the important part is that each alliance has two robocoach stations because that means if there is any jamming coming from a station, it is the alliances own fault. Take turns, young robocoaches! Not everyone needs to transmit at once.

This also means that an alliance that got their act together in advance could place just one robocoach in each corner.

Red A would respond to buttons 1-4
Red B would respond to buttons 5-8
Red C would respond to channel up/down, volume up/down

Now I see why the IR boards were made to be so easily reprogrammed… it isn’t about the technology but about the teams working together. Sneaky GDC has done it again. * (see edit below)*


Well, darn… that won’t quite work out that way due to rule R65 that limits any one signalling device to using no more than four buttons during a match. Still, a clever designer could build a custom board that resulted in 12 different outputs from four different inputs, I would think.

Second edit… dang… R65 goes on for a while… no, you are only allowed four output states. So, technically, based on R65, a standard IR remote is actually illegal. This rule may need some clairification from GDC on the Q&A forum, as I doubt they meant to ban standard IR remotes, however not many of them fit into the “be able to switch between no more than four states or conditions” rule.

This will be more of an issue in the pits. I told my team that they might want an FLL “IR garage” used to program their FLL robots in the pits for testing.

This could well be a problem. But, it probably could be solved by “boosting” yhe signal from your remote. Ie. wiring more IR LED’s in series. (or is it in parallel?)

anyway, once more IR LED’s are soldered on your remote, it will effectively double or triple the range of your remote.

No little FLL box or tube is going to change what goes to the IR receiver on the robot. The problem is that all light disperses. IR is just a lower frequency light than visible. It disperses a lot over a few feet. Anyone who has played pointing their TV remote away or at an angle to bounce against a wall etc. and was able to change the channel can attest to this.

If you have two or more robot coaches on one end, both trying to control their robots at the same time, there is nothing to keep both IR signals from getting to both robots. As someone pointed out, it doesn’t even have to be a frequency issue, it’s the fact that both robots are going to receive both signals.

I personally think the frequency issue will be an issue. How are they going to handle a frequency interference issue at an event?

As well as a FIRST mentor I am also a coordindator for another robotics competition RobocupJunior which uses IR emitting balls to play soccer. We allow no cameras, even without flashes as the IR sensors on the cameras can be read by the sensors. The robots can only use passive IR sensors to see the robot and dont see them well (we even have teams tape up the IR emitter on the Lego sensors). If they used active sensors all robots would look like the ball. Competitions are in rooms without windows, no incandescent lights, etc. because of the IR issues. Yes the IR issues are a little different, but IMHO IR remotes are just too fickle.

I do like the idea of a hybrid period instead of autonomous.

The minute I got the unit, I cringed.


A suggestion to get rid of at least one type of interference:

Each team could use a programmable universal remote, setting the code to their team number.

The only problem is that then the other team will be able to easily know what frequencies you are using, and im not saying this will happen because of the GP in FIRST, but i would not like the other teams knowing what frequency i am using.

I suggested the FLL box for use in the pits as a safety measure.

Scenario: Team A is testing out their new arm code. They have stopped briefly and are waiting for something. One of their commands is “raise arm.” Unbeknownst to them, Team B across the aisle has the same remote and unintentionally has the same buttons to do different things. Team B is testing their robot and hits the button. Team A’s arm starts moving suddenly, catching a team member in the head.

In the pits, I would want the box over the sensor to block IR; I might even use the remote in it.

As far as I can tell, it is very unlikely IR interference will be a problem as long as the teams have remotes from different model TV/VCRs. Each IR signal is made up of 4 parts: a start command, the command itself, a device code (identifying the device to control by a certain binary number), and a stop command.

Check out this site:

It has a good explanation as to how IR signals are transmitted.

i just tired this at home. It appears this WILL be a problem… If two infrared commands are issued at overlapping times, even if they are difffeent frequencies they cancel each other out…

Think of this…

three teams on an alliance are driving down one side of the field. Team a issues a “ARM UP” via remote control by holding down the button they programmed with. team b during that time issues a comand to turn left, via remote control. It won’t work… The signals “collide”… even though they are different frequencies…

What are the chances that robots are in the vicinity of each other while numerous commands ae being issued… VERY HIGH

Couldn’t a team just use a protective hood on IR Sensor? The robot could us a compass or a gyroscope combined with a turret to keep the sensor pointing at the RoboCoach area.

the problem with IR, is that the further you get back from the intended target (our robots) the wider the spectrum band is. The year we were introduced to IR during a FIRST competition they suggested that we use a bic pen to focus the ir signal to the ball drop pedestals. This worked, only because we were seeking out the same signal. This year where we will be transmitting multiple signals at the same time, it won’t matter how we focus/defuse/ or “up” our signal. We will still be intefering by having multiple signals at thesame time…

That is a very cool idea.

The IR interference is going to be a problem. Dave did point out that sound and light are also options. If key is for a team to use a fequency that no other team would think to use.

If only for this reason, lets not use our remotes as joysticks in another tele-operated period! If your design calls for buttons to be held down, you may want to rethink it to give your alliance partners a chance to send commands to their robots.

If alliances split robocoaches between the stations, use tubes to make their remotes directional, and treat the signals as commands and not a direct controller (such as “investigate that rock” and not “drive forward while I hold this button down”), IR should work. Pretend your robot is like Dave’s, and on Mars. Another tele-operated period is not the intent of the hybrid period!

Having “start moving forward” and “stop” buttons would work better for everyone than moving forward while the button is held down, with the same effect. Let’s practice gracious professionalism with our hybrid control designs!

That said, other mediums for command transmission would be great fun and potentially less prone to interference. Let’s see the light and ultrasonic stimuli! (We might have to ask people to please not use flashlights or jingle keys near our robot :smiley: )

I have also tested this and found the same thing. Summary of my tests can be found in this thread: