L297/298's

Hi,

I've just built up a driver board based on the L297/298 chips and I'm a bit
disappointed at the maximum motor speed I seem to be able to get from it - I
managed 300 rpm with one motor and only 200 with another. The motors are, I
believe, 3.2 volt, and 1.4 and 0.8 amp respectively (the 0.8 amp one went
slowest) and I was driving them in half step mode from a 12 volt 3amp supply
(L297 was set at motor's rated current output).

On the machine I'm building with a 1:5 reduction driving a 1mm pitch
leadscrew, the fastest equates to about 60mm or 2.5" per minute! - a bit
slower than you all seem to talk about!! That, of course, is also the
fastest I could expect - in G00 mode. Whilst I'm not too bothered about
speed, I wondered what typical speeds you were getting from L297/298 driver
boards and consequently whether mine are performing as well as I might
expect.

In this test I was pulsing the step input with a 555-based oscillator and
the motors ran really cleanly with plenly of torque up to the maximum speed
I got and then suddenly stopped and sat there buzzing loudly.

Ian
--
Ian W. Wright
Sheffield UK