AVR-Chat

At 10:05 PM 1/31/05 -0500, ethan@bufbotics.org wrote:
>I saw in the articles how you described the current consumed at 50%
>dutycycle (motor stopped).  Is this ok? Or should the enable pin be
>disabled when you want to idle?


It depends on the motor (the PWM, frequency, the voltage, the ripple 
capacity of your capacitors...).  Generally if the frequency is high enough 
the ripple won't be enough to cause any problems.  Assuming, of course, 
that you can run at that frequency without large switching losses.

You get a couple of advantages running in this mode to offset the ripple 
losses.  The first is that since there is no explicit direction change 
around zero, there is no dead spot as you move from forward to reverse and 
vice versa.  The second is since you are driving the motor at zero rather 
than passively braking it by shorting it you have the potentially of much 
stronger braking around zero.  This second effect compounds on the first so 
that you don't get a fade in torque as you slow to zero and reverse 
directions.  Whether or not these effects are strong enough to notice, like 
the whether the ripple losses are significant, depends on a lot of factors, 
not the least of which is whether torque and control in all four quadrants 
near zero speed is important.

Robert

" 'Freedom' has no meaning of itself.  There are always restrictions,
be they legal, genetic, or physical.  If you don't believe me, try to
chew a radio signal. "

                         Kelvin Throop, III