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Re: Robomower lithium

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  • beekilher
    Dan you may need to take the front counter weights off with less weight in the battery compartment. Since the RM s battery pack is to the rear of the axle,
    Message 1 of 6 , Mar 30, 2008
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      Dan you may need to take the front counter weights off with less weight
      in the battery compartment. Since the RM's battery pack is to the rear
      of the axle, changing this weight or position will alter the load on the
      front wheel. Those weights keep the mower from bouncing as it cuts but
      with a lighter rear end the front may bog down. You may need to play
      with weight distribution.

      BeeKilHer Buzz!! Swat!! Splat!!


      --- In RoboMower@yahoogroups.com, <dannym@...> wrote:
      >
      > Well, yes and no. See the tire itself doesn't NEED as much traction to
      move if it weighs less. Climbing a hill can be done with less traction.
      However, the force required to get the front castoring wheel out of a
      bump in the ground won't change because the nose of the machine still
      has the same weight.
      >
      > I took some actual measurements by popping the top off the Robomower
      battery, taking off one of the interconnects and inserted my Fluke
      ammeter. Then just stick the ammeter in cradle where the hand controller
      goes and drive around.
      >
      > Saw a surge of I think 14 amps as the blades sped up, but it only
      takes 1.5 amps to keep them running with no grass underneath. Running
      the drive motors, it makes a LOT of difference with even a slight grade.
      1.5 amps to drive "downhill" and 3 amps "uphill", even though the "hill"
      is something almost imperceptible. I did a little driving around with
      the blades mowing and saw like 3-5 amps driving around, sometimes 6 amps
      briefly. Actually letting it run against an obstacle and spin the wheels
      brought it up to 7 amps and occasionally spiked to 9 amps. This was with
      a low battery though, it might register a bit higher with a fresh one.
      >
      > I think the mower weight probably penalizes its uphill current more
      than it benefits its downhill current, but maybe it's just me. If so it
      would use less current overall if it were lighter.
      >
      > I think I do have a deal on some lithium cells now, where I can build
      a 14.4 amp-hr pack for just under $100 for the cells. Making the
      charger, low voltage cutoff, and even the battery tab welder to build a
      pack out of these (soldering will destroy the cells for sure) is gonna
      run more. The cells will take much less than 1/2 the available volume
      inside the batt case.
      >
      > And I do need a batt. I have 2 packs and the second one just crapped
      out on me after way too little time. Actually I checked on them after
      running them both down and each one had one batt at 10.5v and one at
      12.7V so I can make one decent long-running pack out of this by
      combining the best ones into one pack. So I've got a free case and I'd
      be spending a bundle on a normal batt anyways.
      >
      > Danny
      >
      > ---- wild_bill_howell wild_bill_howell@... wrote:
      > > <Remeber that the weight reduction would also increase the run
      time.>
      > > ---------------------------------
      > > With the trade-off being a corresponding loss in traction.
      > > May not be a consideration for some, though.
      > >
      > > WB
      > >
      >




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