Loading ...
Sorry, an error occurred while loading the content.

Re: [RoboMower] Robomower drive motor observation

Expand Messages
  • Robert Silva
    Is it a planetary gearhead? What is the stock final drive ratio? -Bob ... [Non-text portions of this message have been removed]
    Message 1 of 6 , Jun 4, 2011
    • 0 Attachment
      Is it a planetary gearhead? What is the stock final drive ratio?

      -Bob

      On Jun 4, 2011, at 7:34 PM, Danny Miller <dannym@...> wrote:

      > In looking at possible replacements for a motor, I was doing all sorts
      > of calculations and found something very "odd" about the drive motors.
      >
      > I'm trusting that the 0.5m/sec forward speed, and 5800 rpm blade speed,
      > are accurate.
      >
      > I am fairly certain these motors are identical. They look the same, and
      > for cost reasons I can't imagine Robomower bringing in two different
      > types of motors.
      >
      > To generate that forward speed, with that wheel size and that gear
      > ratio, I get 2150 shaft rpm for the drive motor.
      >
      > That's way below HALF the speed of the blade motors! I can guess why-
      > the side gears are already at about the limit of geometry, and there is
      > simply no room for more stages. So they ran the motor below its normal
      > speed, I think.
      >
      > That's very significant. DC motors can always be fed lower voltages (or
      > PWM'ed, same thing) for lower speed, but at a cost, the heating
      > increases and the ability to air-cool decreases.
      >
      > My mower's disassembled and inoperative right now, otherwise I'd test
      > and see if they are actually using like a 50% drive waveform or what
      > here. This would explain a lot about the whole "gearframe melting" thing.
      >
      > But yeah- I'm coming up with a once-and-for-all replacement for the
      > Robomower gear drive system. It should be a lifetime, maintenance-free
      > "fix", if not perfect as hoped, well, replacement parts are
      > off-the-shelf items. No, I don't have a price yet.
      >
      > Danny
      >
      >


      [Non-text portions of this message have been removed]
    • Danny Miller
      Well I don t have an answer yet, only possibilities. The lack of a tachometer output on most of these setups is troubling. I do have some possibilities. The
      Message 2 of 6 , Jun 4, 2011
      • 0 Attachment
        Well I don't have an answer yet, only possibilities.
        The lack of a tachometer output on most of these setups is troubling. I
        do have some possibilities.

        The motors being run at half-speed, if true, could be improved at this
        point by just working with a gearbox with a higher reduction ratio.
        That's assuming the mower can drive it up to a higher duty when it sees
        the tach is below its target- which is a big "if". The firmware
        designer may have included a check for seemingly unnecessarily high duty
        cycles.

        The stock ratio is 60.0505. But the target would be 35 rpm at the wheels.

        The tachometer rate is important. If it's not consistent with the
        expected ratio- apparently 4203 pulses per second- it'll increase or
        reduce drive until it meets the target pulse rate. While it may seem
        "fun" if the mower went faster, the expectations of what it takes to
        make it turn a set number of degrees will be off. That could lead
        "drunken mower sydrome" (waggling when it should be going straight) or
        an inability to figure out how to back away and go around an obstacle.

        Danny

        On 6/4/2011 9:19 PM, Robert Silva wrote:
        > Is it a planetary gearhead? What is the stock final drive ratio?
        >
        > -Bob
        >
        > On Jun 4, 2011, at 7:34 PM, Danny Miller<dannym@...> wrote:
        >
        >> In looking at possible replacements for a motor, I was doing all sorts
        >> of calculations and found something very "odd" about the drive motors.
        >>
        >> I'm trusting that the 0.5m/sec forward speed, and 5800 rpm blade speed,
        >> are accurate.
        >>
        >> I am fairly certain these motors are identical. They look the same, and
        >> for cost reasons I can't imagine Robomower bringing in two different
        >> types of motors.
        >>
        >> To generate that forward speed, with that wheel size and that gear
        >> ratio, I get 2150 shaft rpm for the drive motor.
        >>
        >> That's way below HALF the speed of the blade motors! I can guess why-
        >> the side gears are already at about the limit of geometry, and there is
        >> simply no room for more stages. So they ran the motor below its normal
        >> speed, I think.
        >>
        >> That's very significant. DC motors can always be fed lower voltages (or
        >> PWM'ed, same thing) for lower speed, but at a cost, the heating
        >> increases and the ability to air-cool decreases.
        >>
        >> My mower's disassembled and inoperative right now, otherwise I'd test
        >> and see if they are actually using like a 50% drive waveform or what
        >> here. This would explain a lot about the whole "gearframe melting" thing.
        >>
        >> But yeah- I'm coming up with a once-and-for-all replacement for the
        >> Robomower gear drive system. It should be a lifetime, maintenance-free
        >> "fix", if not perfect as hoped, well, replacement parts are
        >> off-the-shelf items. No, I don't have a price yet.
        >>
        >> Danny
        >>
        >>
        >
        > [Non-text portions of this message have been removed]
        >
        >
        >
        > ------------------------------------
        >
        > Yahoo! Groups Links
        >
        >
        >
        >
      • Dan Barclay
        Where did you get the 5800rpm for blades? I don t think that s right. I remember a number around 2000 or 2500, which would put it in the speed you re looking
        Message 3 of 6 , Jun 4, 2011
        • 0 Attachment
          Where did you get the 5800rpm for blades? I don't think
          that's right.



          I remember a number around 2000 or 2500, which would put it
          in the speed you're looking for.



          Dan





          From: RoboMower@yahoogroups.com
          [mailto:RoboMower@yahoogroups.com] On Behalf Of Danny Miller
          Sent: Saturday, June 04, 2011 6:35 PM
          To: RoboMower@yahoogroups.com
          Subject: [RoboMower] Robomower drive motor observation





          In looking at possible replacements for a motor, I was doing
          all sorts
          of calculations and found something very "odd" about the
          drive motors.

          I'm trusting that the 0.5m/sec forward speed, and 5800 rpm
          blade speed,
          are accurate.

          I am fairly certain these motors are identical. They look
          the same, and
          for cost reasons I can't imagine Robomower bringing in two
          different
          types of motors.

          To generate that forward speed, with that wheel size and
          that gear
          ratio, I get 2150 shaft rpm for the drive motor.

          That's way below HALF the speed of the blade motors! I can
          guess why-
          the side gears are already at about the limit of geometry,
          and there is
          simply no room for more stages. So they ran the motor below
          its normal
          speed, I think.

          That's very significant. DC motors can always be fed lower
          voltages (or
          PWM'ed, same thing) for lower speed, but at a cost, the
          heating
          increases and the ability to air-cool decreases.

          My mower's disassembled and inoperative right now, otherwise
          I'd test
          and see if they are actually using like a 50% drive waveform
          or what
          here. This would explain a lot about the whole "gearframe
          melting" thing.

          But yeah- I'm coming up with a once-and-for-all replacement
          for the
          Robomower gear drive system. It should be a lifetime,
          maintenance-free
          "fix", if not perfect as hoped, well, replacement parts are
          off-the-shelf items. No, I don't have a price yet.

          Danny





          [Non-text portions of this message have been removed]
        • Dan Barclay
          OK, I see references to 5800rpm using Google searches on it. I don t recall where I saw the 2xxx rpm reference either. It s hard to understand why they d need
          Message 4 of 6 , Jun 4, 2011
          • 0 Attachment
            OK, I see references to 5800rpm using Google searches on it.
            I don't recall where I saw the 2xxx rpm reference either.



            It's hard to understand why they'd need that kind of speed,
            but if that's what they're using the numbers sure can be
            confusing. The motor could still be the same though, as
            you are suspecting.



            2xxx rpm with three cutting blades is a lot of slice and
            dice. 5800. is a lot of battery usage.



            Dan



            From: RoboMower@yahoogroups.com
            [mailto:RoboMower@yahoogroups.com] On Behalf Of Danny Miller
            Sent: Saturday, June 04, 2011 6:35 PM
            To: RoboMower@yahoogroups.com
            Subject: [RoboMower] Robomower drive motor observation





            In looking at possible replacements for a motor, I was doing
            all sorts
            of calculations and found something very "odd" about the
            drive motors.

            I'm trusting that the 0.5m/sec forward speed, and 5800 rpm
            blade speed,
            are accurate.

            I am fairly certain these motors are identical. They look
            the same, and
            for cost reasons I can't imagine Robomower bringing in two
            different
            types of motors.

            To generate that forward speed, with that wheel size and
            that gear
            ratio, I get 2150 shaft rpm for the drive motor.

            That's way below HALF the speed of the blade motors! I can
            guess why-
            the side gears are already at about the limit of geometry,
            and there is
            simply no room for more stages. So they ran the motor below
            its normal
            speed, I think.

            That's very significant. DC motors can always be fed lower
            voltages (or
            PWM'ed, same thing) for lower speed, but at a cost, the
            heating
            increases and the ability to air-cool decreases.

            My mower's disassembled and inoperative right now, otherwise
            I'd test
            and see if they are actually using like a 50% drive waveform
            or what
            here. This would explain a lot about the whole "gearframe
            melting" thing.

            But yeah- I'm coming up with a once-and-for-all replacement
            for the
            Robomower gear drive system. It should be a lifetime,
            maintenance-free
            "fix", if not perfect as hoped, well, replacement parts are
            off-the-shelf items. No, I don't have a price yet.

            Danny





            [Non-text portions of this message have been removed]
          • Danny Miller
            I found an old email where someone apparently had the part number of the Robomower motors, because it s quite specific: 1) no load current (without the blade
            Message 5 of 6 , Jun 4, 2011
            • 0 Attachment
              I found an old email where someone apparently had the part number of the
              Robomower motors, because it's quite specific:

              1) no load current (without the blade attached) = 0.673 amp @ 6106 rpm
              2) stall current = 18.23 amp @ 621.11 m-Nm
              3) motor diameter = 51.09
              4) motor length = 85
              5) motor weight = ???

              Naw, the blade speed isn't too fast. Ever notice what happens when the
              mower's battery slows down? Much poorer cutting there. And that's only
              with like a 15% depression in voltage (which is an accompanying ~15%
              loss of RPMs).

              Danny

              On 6/4/2011 11:36 PM, Dan Barclay wrote:
              > OK, I see references to 5800rpm using Google searches on it.
              > I don't recall where I saw the 2xxx rpm reference either.
              >
              >
              >
              > It's hard to understand why they'd need that kind of speed,
              > but if that's what they're using the numbers sure can be
              > confusing. The motor could still be the same though, as
              > you are suspecting.
              >
              >
              >
              > 2xxx rpm with three cutting blades is a lot of slice and
              > dice. 5800. is a lot of battery usage.
              >
              >
              >
              > Dan
              >
              >
              >
              > From: RoboMower@yahoogroups.com
              > [mailto:RoboMower@yahoogroups.com] On Behalf Of Danny Miller
              > Sent: Saturday, June 04, 2011 6:35 PM
              > To: RoboMower@yahoogroups.com
              > Subject: [RoboMower] Robomower drive motor observation
              >
              >
              >
              >
              >
              > In looking at possible replacements for a motor, I was doing
              > all sorts
              > of calculations and found something very "odd" about the
              > drive motors.
              >
              > I'm trusting that the 0.5m/sec forward speed, and 5800 rpm
              > blade speed,
              > are accurate.
              >
              > I am fairly certain these motors are identical. They look
              > the same, and
              > for cost reasons I can't imagine Robomower bringing in two
              > different
              > types of motors.
              >
              > To generate that forward speed, with that wheel size and
              > that gear
              > ratio, I get 2150 shaft rpm for the drive motor.
              >
              > That's way below HALF the speed of the blade motors! I can
              > guess why-
              > the side gears are already at about the limit of geometry,
              > and there is
              > simply no room for more stages. So they ran the motor below
              > its normal
              > speed, I think.
              >
              > That's very significant. DC motors can always be fed lower
              > voltages (or
              > PWM'ed, same thing) for lower speed, but at a cost, the
              > heating
              > increases and the ability to air-cool decreases.
              >
              > My mower's disassembled and inoperative right now, otherwise
              > I'd test
              > and see if they are actually using like a 50% drive waveform
              > or what
              > here. This would explain a lot about the whole "gearframe
              > melting" thing.
              >
              > But yeah- I'm coming up with a once-and-for-all replacement
              > for the
              > Robomower gear drive system. It should be a lifetime,
              > maintenance-free
              > "fix", if not perfect as hoped, well, replacement parts are
              > off-the-shelf items. No, I don't have a price yet.
              >
              > Danny
              >
              >
              >
              >
              >
              > [Non-text portions of this message have been removed]
              >
              >
              >
              > ------------------------------------
              >
              > Yahoo! Groups Links
              >
              >
              >
              >
            Your message has been successfully submitted and would be delivered to recipients shortly.