The shaft encoders look cool... bet they're pricey!
I was thinking about a similar remote control project but to operate a
cap and roller inductor for my balanced tuner (AG6K) at the bottom of
the garden for my 88ft doublet...
I concluded that the best approach (for me) was a mixture of
technologies but still based on the KISS principal...
1. position encoding - use 1K precision wire wound pot (direct on the
cap, geared down on the roller inductor)
2. absolute end stops - take a leaf out of what the rotator
manufacturers do... use a DC motor with a limit switch (micro switch) at
each end across a diode. Once the limit switch opens all you can do is
go the other direction. This stops you driving the vacuum variable all
the way through the front panel of your amp and in to next door if you
have a control fault!
How you then display and process the position encoding (simple analogue
meter, ADC in to uP, etc) is personal preference.
Mike G8TIC
On 08/08/2011 23:19, Jim Barber wrote:
> Very interesting, Martin. Thanks!
>
> This leans back more toward what Al was talking about, but keeping track
> of the states becomes Someone Else's Problem. :-)
>
> I'll check these out.
>
> 73,
> --jim
>
> Jim Barber, N7CXI
>
> On 8/8/2011 2:46 PM, Martin A Flynn wrote:
>> Jim,
>> Have you considered using an absolute position encoder on the stepper shaft?
>> This particular family will track up to 192 shaft turns, sending a a unique
>> code for each position: http://www.stegmann.com/product/absolute/hollow.html
>>
>> Money permitting this is what I will be using on my GS35B project.
>>
>> Martin
>>
>>
>> -----Original Message-----
>> From: Jim Barber
>> Sent: Sunday, August 07, 2011 4:45 PM
>> To: Amps@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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