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ActivityBot: board no longer works with servos connected — Parallax Forums

ActivityBot: board no longer works with servos connected

elahavelahav Posts: 7
in Robotics
The robot worked fine until yesterday, when any attempt to load new programs (either to RAM or EEPROM) started failing with "no propeller chip on port". I disconnected all devices, one at a time, and found out that the servo connections are the deal breakers. Once disconnected, the board is working again.

Any advice?

Thanks,
--Elad

Comments

  • ercoerco Posts: 20,257
    New batteries.
  • elahavelahav Posts: 7
    I actually thought of that, but couldn't possibly see how that could be related to the symptom.
    I'll give it a try.

    Thanks!
  • Duane DegnDuane Degn Posts: 10,588
    edited 2017-04-10 14:59
    Servos suck a lot of power. When the batteries get low they can't source enough current for the servos and the voltage of the pack ends up dropping too low for the microcontroller to work properly.

    It is very common for people new to robotics (including myself a few years ago) to underestimate the amount of power required by servos.
  • elahavelahav Posts: 7
    I am by no means underestimating the energy requirements of the servos, but something still seems wrong here. I disconnected the battery pack from the board, set the three-way switch to position 1 and still see the problem as long as the servo cables are connected to the board. A potentially-related problem is that even when the three-way switch in is position 1, both the #1 and #2 green LEDs are on. I am pretty that it used to be that only LED 1 would turn on when the switch was in position 1.
  • Duane DegnDuane Degn Posts: 10,588
    Do you know how old this Activity board is? I think some of the earlier boards had bad switches.
  • Duane DegnDuane Degn Posts: 10,588
    I'll add, I've had trouble with an Activity board when I powered the board from a battery while also connecting to USB.

    I suggest unplugging a battery whenever you program the board. I don't know if the newer boards have this problem but I burned out an older board this way.
  • elahavelahav Posts: 7
    Thanks Duane. I don't know how old the board is, but it came in as part of an ActivityBot purchase in December. For the record, it is the WX variant, which I believe is fairly new.

    The tests I ran were with the battery pack disconnected.
  • Ken GraceyKen Gracey Posts: 7,395
    I'm asking our Tech Support staff to visit this thread.
  • Miguel RodriguezMiguel Rodriguez Posts: 24
    Hi Elad,

    When you get 2 green power leds turning ON when you have the switch set to position 1 is a common symptom to a shorted board. One of the logic transistors is blown. The board can still potentially work, however you won't be able to turn off the servo headers. They will always remain ON.

    There had to of been a short on the board if it was not working until you disconnected the servos. Either the servos themselves were connected wrong or another circuit you built may have been causing it.

    Also if it seems like the servos are sluggish check that the jumper next to servo port P12 is jumped to Vin and not 5V.

    Miguel Rodriguez
    Parallax Tech Support


  • ercoerco Posts: 20,257
    BTW, welcome to the forums, Elad. Hopefully Miguel's comment helps you sort out your issue.

    Looks like you joined a few months ago and I'm sure you've noticed that this is a very friendly and helpful place. How great is it that Ken (the President of Parallax) personally responded to your post and got Tech support involved?

    Keep us updated on your progress, Team Parallax is here to assist.
  • elahavelahav Posts: 7
    Thanks, Miguel. The interesting part is that everything worked well (including the servos and the various circuits my son and I built) up until this weekend.
    Is the situation hopeless, then?

    erco, I will do my best to keep the forums friendly and helpful ;-)
  • [Deleted User][Deleted User] Posts: 0
    From what you describe it sounds like the board is still functional the only thing is that the servo headers will have to always be ON. Its not necessarily a show stopper. Whenever you load a program that involves moving the servos prop the AB up so that the wheel do not touch the ground. This will keep it from taking off when you load a program that involves motion.
  • Miguel RodriguezMiguel Rodriguez Posts: 24
    Hi Elad,

    Having an issue with my account however the last comment coming from ELEV-8 Flight Crew is actually from me.
    Please let me know if you have more questions.

    Miguel Rodriguez
    Parallax Tech Support
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