Given the context of the question, robotics, OP seems to be looking
for "accurate effort diagnosis", e.g.. force/torque required.

Given that the robot geometry and masses are known, the required
torques for a given motion/position can be computed (or measured by moving
slowly through the range of motion envelop and recording 'static' currents
as a starting point).

Measuring the actual currents on your BLDC motors will give your torques pr=
etty
much directly.

Not sure how you can measure force/torque output of a stepping motor
from the input side. Perhaps with a precision position sensor, and seeing h=
ow
far the commanded position deviates from 'expected' because of torque
pulling the pole off step center, and knowing what the coil current is
at that exact
moment.

Since most motors are geared in robotics applications, the only 'good' meas=
ure
of 'effort' is with a force transducer. e.g. load cell.

Robert

On Sun, Mar 8, 2015 at 4:57 PM, IVP <joecolquitt@clear.net.nz> wrote:
>> Would you need designated hardware, or could it be done all
>> electronically via given wires (Stepper or bldc servo)?
>
> A driver like the L298 has low-side sense resistor in series with
> the motor coil. The voltage across the resistor is passed back to
> eg an L297, which is commonly used with the L298. The L297's
> comparator uses the coil voltage vs a Vref to determine the coil
> current, for chopping etc. Vsense is available to any IC
>
> http://www.uni-kl.de/elektronik-lager/419182
>
> As Jason shows, a discrete circuit can be used to deliver Vsense
> to an ADC
>
> I'm not sure what you mean by "Resistance" in the Subject. Do
> you mean the amount of current needed as the motor tries to
> move against a load ? If the coil is being chopped or PWMed,
> then the start of a drive cycle can be used as the start point for
> gathering data to track the increasing coil current
>
> Joe
>
>
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