[kwlug-disc] OT: Below freezing cables ...

[Khalid Baheyeldin]

As some of you know, I had a telescope project that I finished during the
summer. It works. One of the requirements was to remotely control it so I
don't have to be outside with the bugs or the cold.

The remote control part works well.

But as the weather has cooled, a challenge appeared: intermittent behaviour
of the motors.

The current motors are steppers with 4 wires each. They are not high amp
(run at 0.67A per phase). The wiring from the control box (which has 12V
input, an MCU, and current chopping drivers) is RJ45. There are two motors,
and each has 4 wires. There is an RJ45 to each axis, with one pair as one
wire (less resistance, ...etc.)

You can think of the telescope controller as a 3D printer with only 2
motors. Same principle of operation. The motor housing moves as the scope
rotates around the sky, so the cables have to move too.

Here is the challenge: a few days ago I was out and it was around freezing.
The telescope would work for a while, but then strange things would happen.
Motor stalls, missed steps, ...etc. I am suspecting that the RJ45 connector
is contracting and losing connectivity.

So my current plan is to use something more robust, and my thinking is one
VGA cable (that is 15 pins, and I need only 8 for the motor and a few for
other logic stuff). On each end (controller, and telescope) there will be a
DB15 Female 3 row connector.

I want to connect the telescope's motors to the controller using a standard
VGA cable that has all the pins connected straight. The cable must not be
too stiff since it will stiffen more in the cold.

Ideally the cables would be silicone, not PVC, so they do not stiffen with
the cold, but those are expensive.

The DB15 3-row female connectors must be the solder type (not crimped), and
should have the hex nuts on the sides where the screws from the cable go in
to secure it.

If I can find those female connectors with the wires soldered onto them,
that would be a *great help*, since it will save me the agony of soldering.

Ideas welcome on powering stepper motors in low temperature without losing
connectivity.

-- 
Khalid M. Baheyeldin
2bits.com, Inc.
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