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9545Re: [solectria_ev] RE: surging/vibration

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  • Rex Allison
    Dec 6, 2013
      Skewed rotor bars are are generally used in line start AC Induction motors to minimize reluctance torque interaction between rotor lamination teeth and the teeth in the stator laminations. A typical 3 phase 4 pole AC induction motor will have 36 teeth and therefore 36 slots. If you imagine the rotor teeth ever lining up with the the stator teeth as the motor rotates, the motor will cog. This is usually minimized by picking a prime number of teeth in the rotor. A typical number I've seen is 17 teeth. To further minimize the cogging effect the rotor laminations are skewed by one stator tooth pitch. This lower magnetic coupling between the stator and rotor a bit reducing the torque density of the motor. I haven't taken apart a Force motor and I certainly haven't gotten a hold of a Tesla motor so I'm not sure if they are skewed.

      The typical instability that is found in a Force is when the current regulator runs out of voltage (field weakening as Wolf stated). The controller is basically transitioning from current motor to voltage mode. When I had Lead Acid batteries I found this to be around 22mph. With LiFePO4 batteries this has moved up to 30mph in my car most likely because the LiFePO4 batteries don't sag under load as severely as Lead.

      From: Wolf <wolf@...>
      To: solectria_ev@yahoogroups.com
      Sent: Friday, December 6, 2013 12:13 PM
      Subject: Re: [solectria_ev] RE: surging/vibration

      Not quite sure I buy that, sounds like Tesla needs to adjust their field weakening model...
      The jerking when moving at speed in Solectria vehicles is more likely to be a worn spot on the throttle pot, which tends to happen around typical cruise speeds.
      Giving more or less throttle moves you out of the worn spot.
      On Dec 6, 2013 10:12 AM, <joeboxbaytown@...> wrote:
      I read where some Tesla owners had questioned surging/vibration at a certain speed. their tech support said it was normal with induction motors. it was something about magnet motor poles jerking on  the rotor as the controller fires them off. Slanting the rotor bars in the induction motor design buffers this but  is less effective  at certain rpm because of some geometric anomilie between rotor  and controllers rotating magnetic field . The motor moving in step can jerk wheel back and forth such as it pulls one way aceleration and other engine brake.

      Tritium ws 200 manual says having wrong weight in programing can cause oscelation with control loop. dont know if it applys not familiar with your setup

      hope this helps

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