Re: [CAD_CAM_EDM_DRO] Advice on moving forward

paulk6158 wrote:

>Hi folks, I've spend some bleary hours tolling the archives (LOTS of
>good stuff there) but haven't found a directly applicable post so, if
>I may ask.
>
>I've spent about 3 months tinkering with stepper drivers designs
>based on pic micro's. With acceptable results.
>Recently I bought a larger (400oz) motor rated at 3V 4A.
>I just can't seem to get this thing to work at more than 150PPS!
>At 100PPS it's fine. Really good torque, no problems.
>
>

This sounds like a typical resonance problem. If you have no electronic
damping, you are going to get a strong resonance, and 150 PPS on an
unloaded motor is right where I might expect the first one to pop up.

The first thing to try is see if the motor performs a bit better if you
wrap a rag around the shaft and hole it tightly. This is providing
mechanical damping, which will also absorb the resonant energy.
If so, that confirms the diagnosis. You can try developing a simple
RC damper, with a few Ohm resistor in series with a pretty large
capacitor. I come up with something like 10 Ohms and 2.6 uF
These values are VERY rough, anything within +- 50% would produce
strong damping at this speed. (I'm calculating based on 150 pulses/sec
in full step mode = 37.5 Hz on the actual pulses on each winding.)
You would put the dampers between the far ends of each winding.
This should work for both unipolar and bipolar drives.

Most modern stepper drives use more advanced electronic methods
of providing this damping. I've used the Gecko G201A drive, and it
has adjustable damping, which works AMAZINGLY well!

Jon