Re: servos

"Arne Chr. Jorgensen" wrote:

> Jon is smart, he know that an old fashion tacho generator works,
> and what we are looking for is something that will behave like one.
> There is some PPL, freq->dc signal tachometer cicuits like ( LM2907)
> etc. But somewhere in the back of my mind, I have read something
> about designs that did not match an old fashion tacho. What I would
> like is something "stupid simple" - but it has to work properly. I
> wish I had some better knowledge about what was wrong with my own
> attempts, and Ray Henry has pointed out that there is other
> attempts, - that must have experienced something similar to what I
> have done.

Well, with a very nice DC tach available for US $7.95, and the problems
of a simulator using the encoder, I just don't see what the problem is.
Getting a bipolar pulse interval to DC converter (kind of like a freq-voltage
converter, but optimized for VERY low frequencies, too) to work just
looks troublesome to me. It needs to go from below 1 Hz to 40 KHz
or so, and have constant delay across those frequencies, and not give
bumps when pulses come in at the 1 Hz rate, but not have more than
a couple mS delay. I think that is HARD!!!!! Getting a couple KHz
bandwidth, with no ripple below 1 Hz input is a TOUGH PROBLEM!

<snip>

> How is the pico servos working ? How good are they.

Well, they have been working great for a full year, now. No failures,
quirks, or other problems! I'm VERY happy with the performance.
And, once I figured out the trick with the feedforward term, the error
is VERY small. Maybe I need to pull one of the graphs from EMC's
logging function out, and post it for you guys! Maybe that will convince
you how good it does. (I'll try to do this this weekend.)

Jon