Hang a current probe on the motor leads and the supply.  Something is not r=
ight.


Denny Esterline <desterline@gmail.com> wrote:

>Ok, I've got dents in my wall and lumps on my forehead. It's time to tap
>the collective wisdom of the list.
>
>I'm building a system to control a sensored NEMA23 size brushless motor
>based on a dsPIC33F128MC804.
>I've got the motor spinning and I'm working out my control loops (speed an=
d
>position).
>Earlier, when I was doing simple bench testing, the motor
>was noticeably smoother in one direction
>than the other. Now that I have the gearbox and a load connected to it,
>it's _much_ worse.
>Clockwise, it's smooth as silk and moves my load at about 1.5 Amps.
>Counter-clockwise it's noticeably
>noisier and draws upwards of 7 Amps. The load is very close to the same in
>both directions.
>
>I'm completely at a loss for why it would behave differently depending on
>direction of rotation.
>
>I'm using brand new, Electrocraft motors, (two different motors,
>from different production batches have been tried with the same results)
>
>The board is our design. I've run several tests on it and I'm confident
>that the FET drivers and FETs are operating correctly.
>I've got a small logic analyzer and I've looked at the halls (clean, well
>sequenced, uniform widths - both directions) and the control lines to the
>FET drivers (exactly the expected sequence).
>I've scoped the gates of the FETs and I don't see anything odd.
>
>The Hall sensors and commutation is managed with the CN interrupt.
>Assembled into a three bit value and used as lookup in a sector table.
>The sector value is then incremented or decremented (CW vs CCW) and used t=
o
>lookup the OVDCON value. This is all very much strait out of the appnotes.
>
>I'm fresh out of ideas. Any good suggestions?
>
>-Denny
>
>
>
>
>Here's some snips of the relevant code sections:
>
>//globals
>char SectorTable[] =3D {0,6,2,1,4,5,3,0};
>unsigned int StateLoTable[] =3D { 0x0000,  /* All off, guards from bad hal=
l
>data*/
>                                0x0204,  /* PWM2L -> 1, PWM1H -> PWM */
>                                0x0210,  /* PWM3L -> 1, PWM1H -> PWM */
>                                0x0810,  /* PWM3L -> 1, PWM2H -> PWM */
>                                0x0801,  /* PWM1L -> 1, PWM2H -> PWM */
>                                0x2001,  /* PWM1L -> 1, PWM3H -> PWM */
>                                0x2004,  /* PWM2L -> 1, PWM3H -> PWM */
>                                0x0000}; /* All off, guards from bad hall
>data*/
>
>
>
>
>
>//and in the CN interrupt
>
>tempC =3D PORTC;                                  //grab the pins as quick=
 as
>possible
>tempB =3D PORTB;                                  //according to stopwatch=
,
>assembly takes 15 cycles
>HallValue =3D (0x0007 & (((tempC & 0x0040) >> 4) | ((tempB & 0x0200) >> 8)=
 |
>((tempB & 0x0100) >> 8)));
>
>CurrentHallSector =3D SectorTable[HallValue];     //linearize hall reading=
 to
>sector number
>
>if (MotorDirection =3D=3D CW)                       //Calculate the next s=
ector
>based on current sector and direction
>    {
>    NextHallSector =3D CurrentHallSector + 1;
>    if (NextHallSector =3D=3D 7)                    //the numbers wrap aro=
und...
>        NextHallSector =3D 1;
>    }
>else
>    {
>    NextHallSector =3D CurrentHallSector - 1;
>    if (NextHallSector =3D=3D 0)
>        NextHallSector =3D 6;
>    }
>
>P1OVDCON =3D StateLoTable[NextHallSector];        //Load a value into OVDC=
On
>based on next position
>--=20
>http://www.piclist.com PIC/SX FAQ & list archive
>View/change your membership options at
>http://mailman.mit.edu/mailman/listinfo/piclist

--=20
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.