Re: Axis Stall Problems

Dave:

> Looks good Wayne.. is there any reason why you settled on the L298 (
> a bit old in the tooth now) over the newer chips such as the
> lmd18245 which handles more current at a higher voltage? The L298
> was also a little 'delicate' and pwm noise was always an issue (as
> with most fixed off time choppers)

To date the L298 has been robust for me. At 35V, I am hardly
pushing it. I think I understand the PWM noise issue and my
design should be able to handle it.

The LMD18245's are great, but they are kind of pricy -- ~$13 each
and two required for each motor. I contrast this with the L298's
at $3 each (one required per motor) and the Schottky diodes
at $3/axis, I wind up with power electronics in the $6-$7/axis
range rather than $26/axis.

If I want to go to higher voltages, I would probably wind up
building an H-bridge out of individual transistors like the
IRF640 -- they are rated at 200 volts and can handle 18 amps.
At $.69/each, an axis would be $5.52, plus the additional
electronics to get them to turn on reliably.

I have to be a little careful here. Each board that I design
takes 1-2 weeks of my time. Even if I value my time at minimum
wage, I am certainly not saving any money by doing it myself.
It would be far cheaper to purchase a finished product. However,
I am having fun doing it myself, and I am learning more about
motion control, which I view as a "good thing". It is just a
habit of mine to try and design boards that get the job done
with a cost conscience selection of parts.

> Another idea for the next version might be to trash the old linear
> regulators for the power supply, and use a simple switched regulator
> like the L4970 etc which could be powered by the motor supply rails
> (up to 55V I think offhand). I base all my designs around these regs
> and they are brilliant for the price.

I agree that the linear voltage regulators are kind of stupid
looking, but they are dirt cheap. The lowest price L4970 I can
find is $12 (US).

> All up though, nice first design, very flexible and easy in the way
> it can be configured.

Thanks for reviewing the design. By the way, it is my third design,
so I guess I not as quick a study on motion control as I would like.

Thanks,

-Wayne

[snippage]