2007 Radio link reliability problem

[Dave K.]

Although there has been some discussion of this issue in this thread, I wanted to highlight the fact that for those teams experiencing radio communication problems, that you need to contact IFI... don't just sit and wait for a solution.

This past Saturday our team had enough of the robot completed to start some inital testing of the drive train and control system. We immediately began seeing dropouts in communication every 60-90 seconds.

Monday, we took a closer look at the issue and found that the problem is at its worst when motor electrical noise is at its worst. Although much easier to reproduce when the motors are under load, we were able to reproduce the problem with the robot up on blocks by making frequent directional and speed changes in the motors.

Testing showed that the problem appeared to become a bit worse as the primary battery discharged. Realizing that at some point, the sudden current demands placed on the primary battery may cause the control system and radio to fall back upon the NiCd battery, I substituted the NiCd with a bench supply set to ~7.2V and noted that that this substantially reduced the number of communication errors. So something as subtle enough as slightly lower power supply impedance on the backup battery input seemed to have an effect on the problem.

Throughout all of the testing, we swapped in previous years radios and had absolutely no communication problems. As soon as the 2007 radios were reconnected, the problems returned.

The problem we noted manifests itself in this manner:

- The Robot Controller's "Radio Modem" LED will flash yellow. As it does, the robot is not receptive to Operator interface input.
- Usually, but not always, the communication link itself may be lost for 15-20 seconds while the OI and RC resync. During that period the "Radio Modem" LED may alternately change color between yellow and green more than once.
- Towards the end of the syncronization process, the "No Data/Radio" LED on the OI will change to red briefly, and after it turns back to green, the link is re-established.
- On the RC, when the link re-establishes, the "RC Mode" LED on the RC will change from green to Yellow (disabled) and then back to green.
- The link is now re-established.


Monday night, after verifying that the problem was tied to the 2007 radio, I sent a note to Corey at IFI along with the details of my observations. When I asked if they wanted the radio's overnighted to them versus a ground shipment, he indicated that they have only received complaints from 4 other teams, and to date have only received 2 radio pairs back at their facility for analysis.

I shipped our radios back last night and Corey confirmed receipt today and that they are taking a look to see what they can do.

My intent in posting to a new thread is not to create any sort of panic, because it appears that this problem may not affect everyone. My intent is to highlight the fact that of the 4 teams that had notified IFI of a problem, apparently only 2 have returned their radios. Our pair would make it 3 out of 5.

If there are other teams experiencing problems that have not yet contacted IFI, please pick up the phone or send them an e-mail, and work with them directly so that this issue can be resolved as soon as possible.

IFI's contact information can be found here: http://www.ifirobotics.com/

Thanks,