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Stuttering wheel motor

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  • Lee Hart
    It s (finally) Spring in Minnesota! The grass is ready for its first mowing, so I fired up my Robomower 850. It works, and there are no error messages; but is
    Message 1 of 12 , May 30, 2014
      It's (finally) Spring in Minnesota! The grass is ready for its first
      mowing, so I fired up my Robomower 850.

      It works, and there are no error messages; but is doing something
      peculiar. As it moves, it stutters and hesitates. It may run normally
      for several seconds, then stop for a fraction of a second, then start
      again. I can also hear occasional the motors momentarily cutout for
      fractions of a second.

      I thought it might have a slipping pinion gear, or the plastic mounts
      for the motors may have softened and are allowing the motor to jump a
      tooth on the gear occasionally (both problems that others have had). So,
      I removed the cover to have a look.

      I can't see a thing wrong! The gears look perfect. There's no slipping
      or backlash to speak of. The motors are solidly mounted, and their
      pinions mesh well.

      The wires to the motors also look fine. Nothing loose, melted or discolored.

      What should I check next?

      --
      I view this year’s failure as next year’s opportunity. Failures are
      not something to be avoided. You want them to happen as quickly as
      you can, so you can make progress rapidly. -- Gordon Moore
      --
      Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
    • Austin Morgan
      I had a similar problem. It was caused by too much corrosion in my splices in the perimeter wire. After replacing the wire I have not had the problem since.
      Message 2 of 12 , Jun 1, 2014
        I had a similar problem. It was caused by too much corrosion in my splices in the perimeter wire.

        After replacing the wire I have not had the problem since.

        Austin

        On May 30, 2014, "Lee Hart leeahart@... [RoboMower]" <RoboMower@yahoogroups.com> wrote:
        It's (finally) Spring in Minnesota! The grass is ready for its first 
        mowing, so I fired up my Robomower 850.

        It works, and there are no error messages; but is doing something
        peculiar. As it moves, it stutters and hesitates. It may run normally
        for several seconds, then stop for a fraction of a second, then start
        again. I can also hear occasional the motors momentarily cutout for
        fractions of a second.

        I thought it might have a slipping pinion gear, or the plastic mounts
        for the motors may have softened and are allowing the motor to jump a
        tooth on the gear occasionally (both problems that others have had). So,
        I removed the cover to have a look.

        I can't see a thing wrong! The gears look perfect. There's no slipping
        or backlash to speak of. The motors are solidly mounted, and their
        pinions mesh well.

        The wires to the motors also look fine. Nothing loose, melted or discolored.

        What should I check next?

        -- Sent with K-@ Mail - the evolution of emailing.
      • Lee Hart
        ... Thanks Austin, But I have two zones, and the mower behaves identically in both of them. So it seems pretty unlikely to be the perimeter wire. I can confirm
        Message 3 of 12 , Jun 1, 2014
          Austin Morgan admorgan@... [RoboMower] wrote:
          > I had a similar problem. It was caused by too much corrosion in my
          > splices in the perimeter wire.
          > After replacing the wire I have not had the problem since.

          Thanks Austin,

          But I have two zones, and the mower behaves identically in both of them.
          So it seems pretty unlikely to be the perimeter wire. I can confirm this
          by laying out a temporary new loop in the lawn, and see if that makes
          any difference.
          --
          I view this year’s failure as next year’s opportunity. Failures are
          not something to be avoided. You want them to happen as quickly as
          you can, so you can make progress rapidly. -- Gordon Moore
          --
          Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
        • Austin Morgan
          If it was only one motor I would suggest the thermistor. On my 1000 there is one per motor and it is hard wired and will just cut power without notice. It
          Message 4 of 12 , Jun 2, 2014
            If it was only one motor I would suggest the thermistor. On my 1000
            there is one per motor and it is hard wired and will just cut power
            without notice. It would be unlikely for both of these to fail though.

            Austin

            On Mon, Jun 02, 2014 at 12:48:11AM -0500, Lee Hart leeahart@... [RoboMower] wrote:
            > Austin Morgan admorgan@... [RoboMower] wrote:
            > > I had a similar problem. It was caused by too much corrosion in my
            > > splices in the perimeter wire.
            > > After replacing the wire I have not had the problem since.
            >
            > Thanks Austin,
            >
            > But I have two zones, and the mower behaves identically in both of them.
            > So it seems pretty unlikely to be the perimeter wire. I can confirm this
            > by laying out a temporary new loop in the lawn, and see if that makes
            > any difference.
            > --
            > I view this year’s failure as next year’s opportunity. Failures are
            > not something to be avoided. You want them to happen as quickly as
            > you can, so you can make progress rapidly. -- Gordon Moore
            > --
            > Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
          • Lee Hart
            ... It does appear to be the right motor that is hesitating and cutting out. The left motor then immediately cuts back, as the mower tries to maintain a
            Message 5 of 12 , Jun 2, 2014
              Austin Morgan admorgan@... [RoboMower] wrote:
              > If it was only one motor I would suggest the thermistor. On my 1000
              > there is one per motor and it is hard wired and will just cut power
              > without notice. It would be unlikely for both of these to fail though.

              It does appear to be the right motor that is hesitating and cutting out.
              The left motor then immediately cuts back, as the mower tries to
              maintain a straight path.

              Where is this thermistor? I'll check it.

              The other thing I'm wondering is if the motor's brushes are failing, and
              making a poor connection to the commutator. I've had that happen on
              other old brushed DC motors, that developed corrosion so the brushes
              stuck in their brush holders.

              --
              I do not waste my life in friction when it could be turned into
              momentum. -- Frances Willard
              --
              Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
            • CZ Unit
              ... Possibly. Could it also be a flakey FET? You could try squirting a bit of penetrating oil into the brush area, don t ever do this on a running motor by the
              Message 6 of 12 , Jun 2, 2014
                On 6/2/2014 3:52 PM, Lee Hart leeahart@... [RoboMower] wrote:
                > The other thing I'm wondering is if the motor's brushes are failing, and
                > making a poor connection to the commutator. I've had that happen on
                > other old brushed DC motors, that developed corrosion so the brushes
                > stuck in their brush holders.

                Possibly. Could it also be a flakey FET? You could try squirting a bit
                of penetrating oil into the brush area, don't ever do this on a running
                motor by the way, the phrase "jet engine of flames" doesn't escape my
                lips too often...

                C
              • Danny Miller
                I don t know how it could be the thermistor. The firmware will either pass it, or cross the temp threshold and latch into a shutdown mode- disable ALL the
                Message 7 of 12 , Jun 2, 2014
                  I don't know how it could be the thermistor. The firmware will either
                  pass it, or cross the temp threshold and latch into a shutdown mode-
                  disable ALL the motors, and display an "overheat" error. Depending on
                  what the firmware is, it might have a "thermistor error" if the wire's
                  disconnected entirely, I couldn't say for sure, but it won't start/stop.

                  I don't see how you could have a case where the thermistor would make it
                  jitter, firmware simply doesn't work that way. If playing with the
                  thermistor wires fixed anything, it's probably gonna come down to having
                  unknowingly shifted and thus "cleaned" one of the motor's Faston
                  connectors, or anything else causing a problem really.

                  In my RL800, the Faston connectors on the motors didn't fare well. Some
                  have melted the rubber shield around them.

                  Danny

                  On 6/2/2014 2:52 PM, Lee Hart leeahart@... [RoboMower] wrote:
                  > Austin Morgan admorgan@... [RoboMower] wrote:
                  >> If it was only one motor I would suggest the thermistor. On my 1000
                  >> there is one per motor and it is hard wired and will just cut power
                  >> without notice. It would be unlikely for both of these to fail though.
                  > It does appear to be the right motor that is hesitating and cutting out.
                  > The left motor then immediately cuts back, as the mower tries to
                  > maintain a straight path.
                  >
                  > Where is this thermistor? I'll check it.
                  >
                  > The other thing I'm wondering is if the motor's brushes are failing, and
                  > making a poor connection to the commutator. I've had that happen on
                  > other old brushed DC motors, that developed corrosion so the brushes
                  > stuck in their brush holders.
                  >
                • Austin Morgan
                  My thermistor is glued to the side close to the bottom. It is inline on the positive wire. Austin
                  Message 8 of 12 , Jun 2, 2014
                    My thermistor is glued to the side close to the bottom. It is inline
                    on the positive wire.

                    Austin

                    On Mon, Jun 02, 2014 at 02:52:07PM -0500, Lee Hart leeahart@... [RoboMower] wrote:
                    > Austin Morgan admorgan@... [RoboMower] wrote:
                    > > If it was only one motor I would suggest the thermistor. On my 1000
                    > > there is one per motor and it is hard wired and will just cut power
                    > > without notice. It would be unlikely for both of these to fail though.
                    >
                    > It does appear to be the right motor that is hesitating and cutting out.
                    > The left motor then immediately cuts back, as the mower tries to
                    > maintain a straight path.
                    >
                    > Where is this thermistor? I'll check it.
                    >
                    > The other thing I'm wondering is if the motor's brushes are failing, and
                    > making a poor connection to the commutator. I've had that happen on
                    > other old brushed DC motors, that developed corrosion so the brushes
                    > stuck in their brush holders.
                    >
                    > --
                    > I do not waste my life in friction when it could be turned into
                    > momentum. -- Frances Willard
                    > --
                    > Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
                  • Austin Morgan
                    On my RL1000 the thermistor on the motor itself is inline and does not feed back to the IO on the motherboard/CPU. Therefore on my unit it is not detectable
                    Message 9 of 12 , Jun 2, 2014
                      On my RL1000 the thermistor on the motor itself is inline and does not
                      feed back to the IO on the motherboard/CPU. Therefore on my unit it is
                      not detectable that the motor cut out because of temperature. There is a
                      thermistor, I can't remember it's exact location without opening it up,
                      that does feed back to the motherboard that I assume will display a
                      warning but not the one I am referencing.

                      Austin

                      On Mon, Jun 02, 2014 at 03:57:03PM -0500, Danny Miller dannym@... [RoboMower] wrote:
                      > I don't know how it could be the thermistor. The firmware will either
                      > pass it, or cross the temp threshold and latch into a shutdown mode-
                      > disable ALL the motors, and display an "overheat" error. Depending on
                      > what the firmware is, it might have a "thermistor error" if the wire's
                      > disconnected entirely, I couldn't say for sure, but it won't start/stop.
                      >
                      > I don't see how you could have a case where the thermistor would make it
                      > jitter, firmware simply doesn't work that way. If playing with the
                      > thermistor wires fixed anything, it's probably gonna come down to having
                      > unknowingly shifted and thus "cleaned" one of the motor's Faston
                      > connectors, or anything else causing a problem really.
                      >
                      > In my RL800, the Faston connectors on the motors didn't fare well. Some
                      > have melted the rubber shield around them.
                      >
                      > Danny
                      >
                      > On 6/2/2014 2:52 PM, Lee Hart leeahart@... [RoboMower] wrote:
                      > > Austin Morgan admorgan@... [RoboMower] wrote:
                      > >> If it was only one motor I would suggest the thermistor. On my 1000
                      > >> there is one per motor and it is hard wired and will just cut power
                      > >> without notice. It would be unlikely for both of these to fail though.
                      > > It does appear to be the right motor that is hesitating and cutting out.
                      > > The left motor then immediately cuts back, as the mower tries to
                      > > maintain a straight path.
                      > >
                      > > Where is this thermistor? I'll check it.
                      > >
                      > > The other thing I'm wondering is if the motor's brushes are failing, and
                      > > making a poor connection to the commutator. I've had that happen on
                      > > other old brushed DC motors, that developed corrosion so the brushes
                      > > stuck in their brush holders.
                      > >
                      >
                    • Danny Miller
                      MOSFETs typically don t flake . They either fuse (usually short circuit) or work. Oiling the motor brush area is a no-no. This will do 2 terrible things-
                      Message 10 of 12 , Jun 2, 2014
                        MOSFETs typically don't "flake". They either fuse (usually short
                        circuit) or work.

                        Oiling the motor brush area is a no-no. This will do 2 terrible things-
                        one, it's oil and can insulate the brush/copper interface. Two, all the
                        carbon dust and dirty cooling air will form crud that will now stick to
                        things. It could short out the armature, or jam the brush in the holder.

                        Danny

                        On 6/2/2014 3:50 PM, CZ Unit cz@... [RoboMower] wrote:
                        > On 6/2/2014 3:52 PM, Lee Hart leeahart@... [RoboMower] wrote:
                        >> The other thing I'm wondering is if the motor's brushes are failing, and
                        >> making a poor connection to the commutator. I've had that happen on
                        >> other old brushed DC motors, that developed corrosion so the brushes
                        >> stuck in their brush holders.
                        > Possibly. Could it also be a flakey FET? You could try squirting a bit
                        > of penetrating oil into the brush area, don't ever do this on a running
                        > motor by the way, the phrase "jet engine of flames" doesn't escape my
                        > lips too often...
                        >
                        > C
                        >
                        >
                        >
                        >
                        > ------------------------------------
                        > Posted by: CZ Unit <cz@...>
                        > ------------------------------------
                        >
                        > Yahoo Groups Links
                        >
                        >
                        >
                        >
                      • Tim Wolff
                        Cleaning the motor won t hurt. Just use an aerosol electric motor cleaner. You should be able to find it in an automotive store, automotive dept. of a
                        Message 11 of 12 , Jun 2, 2014
                          Cleaning the motor won't hurt. Just use an aerosol electric motor cleaner. You should be able to find it in an automotive store, automotive dept. of a department store, hardware store, etc. One labeled safe for plastics would be a plus. But, keep even that off the plastic parts of the mower.

                          > To: RoboMower@yahoogroups.com
                          > From: RoboMower@yahoogroups.com
                          > Date: Mon, 2 Jun 2014 16:03:49 -0500
                          > Subject: Re: [RoboMower] Stuttering wheel motor
                          >
                          > MOSFETs typically don't "flake". They either fuse (usually short
                          > circuit) or work.
                          >
                          > Oiling the motor brush area is a no-no. This will do 2 terrible things-
                          > one, it's oil and can insulate the brush/copper interface. Two, all the
                          > carbon dust and dirty cooling air will form crud that will now stick to
                          > things. It could short out the armature, or jam the brush in the holder.
                          >
                          > Danny
                          >
                          > On 6/2/2014 3:50 PM, CZ Unit cz@... [RoboMower] wrote:
                          > > On 6/2/2014 3:52 PM, Lee Hart leeahart@... [RoboMower] wrote:
                          > >> The other thing I'm wondering is if the motor's brushes are failing, and
                          > >> making a poor connection to the commutator. I've had that happen on
                          > >> other old brushed DC motors, that developed corrosion so the brushes
                          > >> stuck in their brush holders.
                          > > Possibly. Could it also be a flakey FET? You could try squirting a bit
                          > > of penetrating oil into the brush area, don't ever do this on a running
                          > > motor by the way, the phrase "jet engine of flames" doesn't escape my
                          > > lips too often...
                          > >
                          > > C
                          > >
                          > >
                          > >
                          > >
                          > > ------------------------------------
                          > > Posted by: CZ Unit <cz@...>
                          > > ------------------------------------
                          > >
                          > > Yahoo Groups Links
                          > >
                          > >
                          > >
                          > >
                          >
                          >
                          >
                          > ------------------------------------
                          > Posted by: Danny Miller <dannym@...>
                          > ------------------------------------
                          >
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                        • Lee Hart
                          Thanks for all your suggestions, guys. I got it fixed! My RoboMower is happily mowing away as I write this. :-) I tried setting up a new small perimeter wire,
                          Message 12 of 12 , Jun 3, 2014
                            Thanks for all your suggestions, guys. I got it fixed! My RoboMower is
                            happily mowing away as I write this. :-)

                            I tried setting up a new small perimeter wire, but the mower still
                            stuttered along. That wasn't it.

                            The thermistor (or some kind of temperature sensing device) is riveted
                            to the side of the metal shroud around the right motor. It is not in
                            series with the motor; it just had small white wires that go back to the
                            main board. So that wasn't it.

                            Removing the shroud let me inspect the brushes. With the motor out, I
                            could also run it. I connected it to a 12v battery charger with a car
                            tail light in series; it ran smoothly. I attempted to hold it to see how
                            much torque it had, and whether there were any dead spots or torque
                            pulsations when rotated slowly, which could be caused by bad brushes.
                            There were none; so the motor is fine.

                            But I did notice that the quick-connects to the motors were a
                            surprisingly loose fit. It turns out that the 0.187" quick-connects have
                            a sub-standard thickness; so the standard female terminals they used
                            don't fit tight. With the motor back in and running, wiggling these
                            terminals caused the stuttering. Aha!

                            I pinched the female terminals a bit to tighten them up. I put it all
                            back together, and it works!

                            PS: This was my first look inside. Getting the cover back on is even
                            worse than getting it off! What sadist designed this thing? FIENDLY
                            Robotics?

                            I also get the impression that they know little about designing
                            electronics for outdoor use. Everything is built the same way as indoor
                            electronics. No moisture proofing, no conformally coated PC boards, no
                            allowance for bugs or dust, no wide-temperature-range parts.
                            --
                            I do not waste my life in friction when it could be turned into
                            momentum. -- Frances Willard
                            --
                            Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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