Re: Low cost Servo Controller

Ian Wright wrote:

> ----- Original Message -----
> From: Jon Elson <jmelson@...>
> I made my own PWM servo amps, and a bunch
> > of people are building copies
>
> Do you have a circuit diagram of this or any web addresses which I might
> look at which would give me an insight in practical terms as to what is
> required.
> My finances won't allow me to go for commercial boards at present but, If I
> can understand exactly how these things work, I may be able to do a bit of
> 'home brewing' to allow me to try servos out - I have a servo motor
> gathering dust under the bench and it would be nice to see it going.

I have let a group of people use my design, and after signing a non-disclosure
agreement, I send schematics, board layouts, circuit theory and tune-up
procedures. I think for the next batch, I'm going to raise prices just a
little, to cover the mailing costs, which I underestimated the first time
around. So, the board, with some small components that would be hard to
get in small quantity, plus a pot core transformer and wire to wind it with
will go fo US $64 each. The total cost, including these parts, should come
to a little under US $200 per amp. Nothing is really very expensive in
there, but it all just adds up. There are 3 CMOS digital ICs, about 5
assorted op-amps, 2 LED bar graphs and their drivers, 2 FET driver
chips and 4 power FETS. I usually use IRF640s, but depending on
voltage and current requirements, others could be used. You could
also use IGBT transistors, although lowering the PWM frequency might
be required for them. I usually use 100 KHz as the PWM freq.
just to keep the filter components small.

The whole amp fits on a 4.5 x 6" (115 x 150 mm) circuit card, with
small stamped sheet metal heat sinks for the transistors.

Jon