Battery Power Issue Resolved

WonderCon was last weekend, and it was my first real test of Artoo since the rebuild. I’d mentioned that both Gerard and I had problems with our batteries. We’d figured it much be the carpet, but I hadn’t had the problem at Celebration 4 – and in the back of my mine I had a niggling theory what was causing it.

For Celebration 4 I’d used 3 7Ah 12V batteries, two dedicated to powering the NPC-2212 drive motors, and one for the body electronics like the sound system, dome drive and speed controllers. But during the rebuild before WonderCon I’d decided to consolidate all 3 batteries into one block to make charging easier. I’d had issues with power before, but thought the problem was resolved and I could consolidate my battery sub-system. Runtime at WonderCon was approx. 60 minutes vs 180+ minutes at C4 – which is a huge difference.

Unfortunately, while I was redesigning my electronics and adding the charging system, I’d forgotten that the RoboteQ speed controller really likes a solid 12V supply, so last weekend as my batteries ran down and when the NPC motors first start-up they were eventually pulling the supply well below the minimum 10.5V required by the controller. It’s “intelligent” and shuts down if it thinks it doesn’t have enough power to control the MOSFET drivers. It’s only for an instant, and starts back up almost immediately as power is cut to the motors – which resulted in the very slow and slightly jerky movement.

RoboteQ AX3500

So today to prove my theory, I reinstalled the the “dead” batteries from last week without recharging them, and added a separate 12V battery to the Power Control lines on the RoboteQ – Bingo! Worked first time. The issue was totally gone.

I’m kinda embarrassed that I went through this, because I should have remember that there’s a know “design feature” with low batteries and high current draw on this type of speed controller.

I’m now confident that I can pretty much run Artoo for multiple hours on a single charge – but I will have to reconfigure my electronics system again – making it harder to charge batteries in place.

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Posted by Chris on March 1st, 2008 in Electronics, RC | 2 Comments

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2 Responses

  1. Calvin Thomas remarks on

    That’s all your running 2 7ah batts and getting 180 minutes?
    That’s pretty good.
    I stuffed 2 12ah batts in mine and thought they were too small. I was trying to figure out how to get bigger batts in there cause I thought mine were too small.
    Good to know this.
    Calvin

  2. Chris remarks on

    Don’t forget, you’ll not be driving solid for 2-3 hours, at most events you’re more likely to drive to a location and hang out with the droid, then you’re just moving around in one area posing for photos, moving occasionally to a new spot.

    If anyone was at C4 they’ll know how far away the Droid Games area was from our Builders Room. It couldn’t be any further away – from one end of the huge convention center to the other, we had to drive over all sorts of terrain and winding corridors to get there. Well, I was able to drive my droid there, compete in the games, hang out and entertain the crowds during other people challenges and on the way back take detours etc. All on one set of batteries. I did this two days running while others struggled to haul their stuff over on carts.

    I love my NPC-2212 and JAG drive setup.

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