regenerative motor driver ?

I don't know anything about the Sabertooth in particular, but yes,
that's generally what the term "regenerative" means when applied to a
motor.  This is how regenerative brakes work in a (good) electric or
hybrid car, for example.

I'm skeptical that you'd get any noticeable benefit from this in a
robot, however.  A car will coast a considerable distance without
braking; that's all energy the brakes can recover.  But a robot usually
doesn't coast; it doesn't have all that much momentum to begin with, and
friction quickly brings it to a stop, so what's to recover?

Best,
- Joe

Yeah that's kinda what I thought, too. I could really care less about the
regenerative part ... just trying to
understand things, though.

Thanks !
JCD

Almost any mosfet motor driver is capable of regenerative braking under
the correct circumstances, that is, when pwm duty cycle is reduced
below the motor's current speed.  (but not to zero and not reversed)

As Joe mentioned it may be unlikely that the amount of energy recovered
is significant.  However, if you want to use your motor and drive
electronics for braking, you're going to have to get rid of that energy
somehow.  It is better to dump it into your battery than into the drive
transistors and *much* better than to let the motor coils ring it off.
For that matter, it's also important that if you're going to do this
with a big motor your power system can handle it; rapidly stopping a
large motor can result in a nontrivial power surge.

-chris

pogo wrote:

latest Servo magazine. I am curious about

. How exactly do the batteries get

keeps the bot moving after current is cutoff,

The regenerative topology means that your

reverse."

Sorry, but that's not true. If the maximum motor voltage is
say 12V, and the motor driver is driving full ahead, then
goes open circuit, the motor will generate *less* than 12V,
which won't be enough to regenerate into the battery even if
there had been a current path (like a diode).

If the driver uses locked anti-phase, and the driver switches
negative, some regeneration may be possible. But in general,
motor drivers do not provide 4-quadrant control unless they're
specifically designed for that purpose.

During the off phase a mosfet pwm driver output is essentially a dead
short.  During that period current begins to flow backwards through the
armature coil, storing the motor's rotational kinetic energy in the
coil's magnetic field.  When the driver switches to the on-phase, the
current continues to flow, because the armature coil is an inductor,
and that is what inductors do.  The battery voltage is indeed greater
than the motor emf, but the energy stored in the armature coil's field
is drained during the on phase to make up for that.  In effect, it
functions like a dc-dc upconverter.

-chris.

Clifford Heath wrote: