Re: Motor box cable


Prasad
 

Hi Mark

I did some more research on the cables. Digikey cables are of only two types - Polyvinyl Chloride (PVC). or Polypropylene (PP). Both are not the best (no, Digikey site does not say this) for low-temperature environments we normally run into during the winter months. From what I see both these plastics begin to harden as the temps go down. I am not sure now. 

Prasad

   


On Wednesday, September 15, 2021, 02:20:18 PM EDT, Prasad <ad_prasad@...> wrote:


Thanks, Mark, 

I found them on Digikey. They have several of them and are a bit confusing too. Still looking at specs in detail. 

Prasad




On Tuesday, September 14, 2021, 01:38:16 PM EDT, Mark Christensen <mjcw500@...> wrote:


Prasad,

The modular flat, coiled, cables at DigiKey are exactly what Losmandy uses on the 492 Digital Drive. You can get them in 8 conductor models and pair the wires up to get more current with 4 conductors if you need it. If you don't then all eight wires are available. The old 492 drive used 6P6C connectors with flat coiled modular cables for the old Hurst/SAIA unipolar motors since those have six wires to the motors.

For our friends with CGEs and other mounts, alas, they do not make 9 wire versions, so for something like the CGE Pro you're kind of stuck unless you're willing to run a separate wire for either the RA limit or RA home switches. Or just give up on one (like the Home) and use the Park function. Since the RA housing doesn't move that is not a big deal (in fact you really don't need a flex cable for that one). The DEC really does need a flexible cable but isn't a problem since it only needs 4 for the motor, 1 for Signal Ground and 1 for Home and, again, the Home is expendable in my opinion since the Park function give more flexibility. The other 3 pins (in the original Celestron cable) aren't needed. Unless you spend a lot of time adjusting the Home microswitches by hand you won't get close to polar home anyway.

The older, original, CGE (modified to use circular connectors by TPI-Astro previous to me working on it) got around the problem by using the housing as signal ground for the RA. Not a good practice in my opinion. I've mod'ed both CGEs and CGE Pros but the original cables were available. I sure didn't worry about the color! If anything, for visibility at night, I wouldn't use black, red, or orange.

By the way, while ethernet signals are high frequency (in terms of bit rate), it is high frequency digital (as opposed to an analog sine wave) and hence has a very broad spectrum going all the way down to DC. Just ask C. Fourier and J.W. Gibbs. So ethernet cables have to be able to pass low frequencies without excessive loss and the spec requires them to be tested down to nearly DC (0 Mhz). Take a look at:

"Why Not Test at the Frequency of the Ethernet Signal?" -- Blue Jeans Cable

Best regards,

Mark Christensen

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