[Amps] "Best" limit indicators for multi-turn, shaft-driven gadgetry

[Jim Barber]

Hi Mike,

Thanks for the reply.

My current plan is to drive the stepper controllers with an onboard 
processor. That processor may or may not talk to a PC, but I want it to 
be able to run stand-alone for a few reasons. The biggest reason is 
probably just that I've been doing PC-based motion control for many 
years, and I'd just like to do something different. ;-) Other than that, 
I'd also like to have the amp run stand-alone with tuning "presets". I 
may not ever get to making it fully auto-tune, but there's also that 
possibility as well.

 From your comments it sounds like you're using a "smart" RS232 stepper 
board. Those do work well, but I've actually found it easier to use the 
simpler TTL-input stepper controllers (like the Gecko units) with either 
an onboard PCI I/O card, parallel breakout card or USB GPIO interface. 
That comes from my CNC motion-control background, of course and probably 
doesn't apply to anyone with better sense. :-)

My current pet peeve is limit switches. I don't like the mechanical 
complexity of the more primitive lashups, although using timing belts 
and optical interrupters isn't too bad from that point of view. I've had 
expensive failures with screw drives and microswitches in the past, so 
am somewhat prejudiced against that approach.

Anyway, thanks for the reply and if you come up with a simple, reliable 
and precise way of implementing limits, please share! :-)

Best 73,
--jim

Jim Barber, N7CXI


On 8/9/2011 5:25 PM, W5CUL wrote:
> Jim,
>
> I have a similar project that I have been working with off and on for some
> time now.  It is a Balanced to Balanced Antenna Tuner feeding a loop antenna
> with open wire, with coax to the station antenna switch.  The tuner is
> currently deployed in the attic, and is attached to the house LAN with its
> own IP Address and port.  The Stepper Controller I use is capable of
> controlling two motors, and has been provisioned with a granularity of 1600
> steps per 1 full revolution.  And as with Stepper Controllers, you need to
> talk to them via RS-232 or Ethernet or some other means in order to operate
> the motors.  One gentleman mentioned using a PIC processor as persistent
> memory which could store the location of the motor during powered down
> periods.  That would definitely work, and I too have thought about that
> method.  I also played around with the idea of using precision resistors
> geared up to the motor shafts using 5Vdc, feeding the subsequent voltage to
> 10 bit A/D converters.  That method will work as well.  But if wanting to
> use the KISS method, and since you have to talk to the controller anyways,
> why not write a simple GUI interface to control the motors as well as store
> their location and the controller configuration data.  That is where my
> project sets right now; learning curve in using VB 2008 Express. So while I
> still struggle with writing the GUI software, I am still able to talk to the
> controller via command line.  Now before placing the tuner in the attic I
> did run some tests to determine upper and lower bounds for both the
> inductors and the capacitor in terms of steps.  And the motors are powerful
> enough not to skip, even at that granularity.  So I am reasonably assured
> that the step location for each motor as reported by the Stepper Controller
> is accurate.  So for the time being I manually control the stepper motors,
> and write down the location of where the motors sit before turning the
> system off. My Stepper Controller board has the ability to accept and act
> upon the input from "hard limit" switches. I may still use that feature as a
> fail safe.
>
> 73,
>
> Mike
> W5CUL
>
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com] On
> Behalf Of Jim Barber
> Sent: Sunday, August 07, 2011 4:45 PM
> To: Amps at contesting.com
> Subject: [Amps] "Best" limit indicators for multi-turn, shaft-driven
> gadgetry
>
> I've reached the point where I need to decide whether or not to make my
> YC156 project amp "remote". Because of other interests, I already have a
> good selection of larger stepper motors and drive electronics, and a
> good feel for how to put it all together.
>
> What I don't have is a good, simple limit stop/reference concept for the
> vacuum caps and (possibly) roller inductor. I've used drive screws and
> leaf switches in the past, but don't like the mechanical sloppiness and
> complexity. I've also seen optical interruptors used in place of the
> leaf switches, but still don't like the mechanical complexity of the
> whole drive screw, platform and guide assembly.
>
> My favorite candidate at the moment is a high-quality 10-turn pot in the
> timing belt path for each shaft, "gearing it down" so that (for example)
> a vacuum cap that rotates 13 turns end-to-end would run 8 or 9 turns at
> the pot shaft. Using regulated 5VDC, I could then apply the output of
> the (pot) divider to a 10-bit ADC. Note I already have ten 10-bit ADC
> inputs at each control processor, so that isn't as much of a
> complication as it might seem.
>
> Any thoughts or suggestions?
>
> Thanks,
> Jim N7CXI
>
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