Hexcrawler R/C Question-batteries

DonWDonW Posts: 37
edited 2004-12-02 - 12:06:38 in Robotics
I am just getting started on the R/C Hexcrawler project..using the Tower Hobbies R/C controller, with wireless camera.

As I dig into laying everything out, I am trying to come up with a way to charge batteries without having to remove them, or even, preferably, charge them one by one.

I am thinking of a few possibilities, be it just having a "charge/run" switch, or possibly an inline jack that does the switching for me when I plug it in...

Before·I reinvent the wheel, wanted to toss the question out there to see what has already been made to work.


  • Ken GraceyKen Gracey Posts: 6,865
    edited 2004-11-30 - 06:29:57
    Hello Don,

    The power supply I used in my HexCrawler is shown on page 5 of this document: www.parallax.com/dl/docs/prod/robo/HexCrawlerRC.zip.·I used two 7.2 V batteries in parallel for the wireless video transmission (required 12-14V) with a center tap for the BOE/BS2/Servos at 7.2V. As it works out the current draw drains both batteries at about the same time (1.5 hours of use). I put a nice power switch on the top of the Boe-Bot to turn everything off easily without making a bunch of disconnects. I bought the "charger side" connectors (I think they are called Standard Tamiya style) from Tower Hobbies so that I could quickly disconnect the batteries from the BOE/RF devices and charge them.

    A copy of the schematic is shown below, plus a picture of the robot with the power switch.

    There is no need to remove the batteries from the HexCrawler to charge them if you keep their R/C connectors. Simply disconnect, hookup the charger and away we go. . .no tricks here but I think the key lies with having the·male conenctors for a wiring harness which·mate with the "standard Tamiya" style connector on the batteries.

    Hope this helps.

    Ken Gracey
    Parallax, Inc.
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  • DonWDonW Posts: 37
    edited 2004-11-30 - 11:23:46
    Thanks...what you describe is my "default" plan...just swap connectors.

    Long ago, I built a crawler from a company called Mekatronix, which used something like 6 D sized NiNH batteries, and used a charger jack which switched to charge when you plugged the charger in, and then went into run mode when you unplugged it. I still need to find the schematic for that and see if it makes sense to duplicate.

    Challenges there are the two batteries in series, with the center tap. I'd have to do some digging to see if the Pirahna charger can really handle the two at the same time (assuming not..) which means individual charging for the two..

    More and more I think about this, I am beginning to think the way you describe (similar to what Alex at CrustCrawler suggests..) is the easiest way to go..
  • Joe FishbackJoe Fishback Posts: 99
    edited 2004-11-30 - 17:30:19

    I am following this topic with hopes of using it as guide to controling my Boe-Bot with R/C.
    On the Stamp connections on page 6 of www.parallax.com/dl/docs/prod/robo/HexCrawlerRC.zip, I have some questions.

    1. The connection of CH1 & 2 to Pin12 & 13. Is this done by plugging the 3 wire connector from the receiver to the Servo ports on the BOE?
    2. How is the ground of the receiver connected to the BOE? Is it thru the 3 wire cable?
    3. If you use this 3 wire cable, do have problem with the power to the servos from the batteries on the BOE bucking the power from the R/C Receiver?

    Joe Fishback
  • allanlane5allanlane5 Posts: 3,815
    edited 2004-11-30 - 17:46:02
    1. Yes, P12 and P13 are hard-wired on the BOE to the signal pin of the servo port on the BOE.

    2. The 3-wire cable is signal (white), power (red), and ground (black). You *can* use this to connect the receiver ground to the BOE.

    3. The servo's *can* 'buck' the power to the BS2, as you put it, if there is insufficient capacitance on the power pins of the servo's, or if the servo's pull too much current through the regulator. If this happened, the BS2 could 'reset' whenever it tried to control the Servo's. However, the BOE-Bot uses this configuration all the time without problem.
  • Kenny GardnerKenny Gardner Posts: 169
    edited 2004-11-30 - 21:03:20
    Here are some pics of my older HexCrawler.

    I installed a Charging Jack and use my 7.2V charger to charge the battery without having to disconnect anything or take the battery out.

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  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2004-12-01 - 00:52:17

    ·· Where's your BS2???· tongue.gif

    Chris Savage

    Knight Designs
    324 West Main Street
    P.O. Box 97
    Montour Falls, NY 14865
    (607) 535-6777

    Business Page:·· http://www.knightdesigns.com
    Personal Page:··· http://www.lightlink.com/dream/chris
    Designs Page:··· http://www.lightlink.com/dream/designs
  • DonWDonW Posts: 37
    edited 2004-12-01 - 01:29:28
    Kenny..looks like what I was envisioning...

    With the R/C system, it is two batteries to deal with, so that gets a little trickier.

    I assumed you used a switched jack so you could plug and unplug the charger without any needed switches, right?

    I am also impressed by the neatness of your wiring...definitely makes it easy to see what you are doing from a picture.

    Oh, and I'll be on the lookout for your BS2..it's missing..smilewinkgrin.gif
  • Kenny GardnerKenny Gardner Posts: 169
    edited 2004-12-01 - 21:29:53
    Where's your BS2???

    It's there! Under the LCD Appmod! tongue.gif

    Those first pictures were taken right after assembly. Had to make sure the power supply was working so as to not burn anything up!

    I assumed you used a switched jack so you could plug
    and unplug the charger without any needed switches, right?

    Err, umm.... Switched Jack? hummm.

    No. Just a regular two terminal power jack. There is a switch, which you can see better in the attached pics. It's a 3 way: Off, Electronics Only, Electronics and Servos. The plan was to not charge it up while it is on so there won't be any damage to the servos due to excessive voltage.

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  • DonWDonW Posts: 37
    edited 2004-12-02 - 12:06:38
    Good to see your BS2 is home safe and sound.

    What I am referring to re switched jack is...you could do (and it is easier with one battery) a charging jack that when you plug the charger plug into the jack, it connects batteries to charger, as opposed to battery to electronics. The other way is as you did it there, with a switch, which ultimately is probably the easier way. As much as I like things "automatic", I'll likely take the switch route...

    With the R/C system, you have 2 batteries in series, so it gets a bit trickier trying to split them, especially since they are in series. I had visions of charging both at the same time, but I don't think that is easily done.

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