> What kind or motor are you using?  brand? model? voltage?
> current?  what
> speed you got actually?

I have been working with small 55mm 7.5 degree 12V , 30 ohm unipolar motors,
20 ohm 12V unipolar, and also some 5V bipolars @ 5.2 ohms.

I have several bench supplies  - up to 40V.
Ihave the actual load assembled, and have been using it for motor testing
over the past few weeks.

I have run the 12V 20 ohm motors OK at between 60 - 100 RPM. I was able to
get approx 4X the speed out of 12V 30 ohm motors by running them over the
rated current, but, of course they don't like that very much.
>
> Also, it is good to remember, that low voltage and high
> current motor gives
> you more torque and faster response.

That's why I went to 5V motors for next tests. Also Bipolar.

>High voltage and low
> current motors
> are to be used where low torque and low speed is required, so
> low current
> drivers can be used, small transistors, etc.  It will be
> difficult to drain
> high torque and speed from a 12V motor, you can start to hope
> this when
> using 5V and below motors.  Best results you can get with
> motors around 2V
> @ 4A.
I have a feeling that this may be more than I need for this application -
the torque isn't very much. I don't have a small enough torque wrence to
measure it, so I don't know exactly how light it is, but consider that all
of the small unipolar motors drive it fairly well already. I spent a fair
amount of time reading, listening, and slowly trying thigs to get this far
already.

>
> I have some projects using Allegro chips, they work pretty
> well, but they
> require good heatsink and they don't drive higher currents.
> You really
> need to implement discrete high current transistors.
Will I really need this for < 1A?

  8 x
> IRF530 is a good
> solution for a 4 to 6A motor, but of course, it requires a current
> management, using  0.05 ohm resistors, a LM339 and a
> reference voltage, you
> can produce a current limiter or chopper and keep the motor
> working at its
> limit.

I have a good assortment of IRF devices handy - can you think of where I
might find a simple circuit to try?

At < 1A, would it be worth the effort? - The Allegro choppers are <$10 per
axis.....




>
> One of the tests you can do for "missing steps", is just
> programming your
> microcontroller to do several back and forth steps,

I have done exactly thi, except with much larger numbers of steps. I can
lose steps if I try to step too quickly now, but slow rates as I mentioned
never lose steps in two bytes worth of back and forth...
>
> When you find out the motor limits for torque and speed,
> never make it work
> more than 85% toward those limits.

Perhaps this is why I'mnot happy with my results yet...

Thanks....

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