You have a short circuit !!

You are assuming that things are as you believe.  There is a fault (short circuit  -  pcb or component) and such faults are not shown as a feature of schematic drawings.

Suggest you have a look at Force Sensitive Resistors such as shown here http://www.openmusiclabs.com/learning/sensors/fsr/

That'll work OK but at what voltage is your 44volt battery charged.  If it's a rechargeable battery rated at 44 volts then the charge voltage could be as high as 60.  As to the zener diode for protection, you could eliminate it by placing a resistor of say 10k connecting the junction of R1/R2 and your analogue input.  This resistor will limit the input current and so prevent damage.

Not too expensive I hope ?
http://www.ebay.co.uk/itm/12V-to-12V-1W-DC-DC-Converter-isolated-single-output-New-Qty-1-/121013364355?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item1c2cf56683

Data sheet here :  http://www.datasheetcatalog.org/datasheet/candd/NME0515S.pdf

Or use an isolated DC - to - DC module which will operate off 12 volts and give 12 volts out.   You can then connect the 12 v output to the common 0volt line and the output 0v pin will now sit at -12 volts.

If you use a non-isolated version then you must use one which is designed to give -12 volts output.  ie you connect the 0v output pin to the common 0volt line.

You misinterpret my the intent of my comment.  The use of curly or square brackets generally makes things easier for "humans" to read.  Machines, being somewhat short on cognitive-power use the standard curved bracket. 

An expression can't have too many parentheses, can it?

In your case ,  yes it can.  You have one set of redundant parentheses.  Good equation writing uses the minimum necessary.  In the case of a computation the same form is generally used but using different forms will make it a little easier for a reader to interpret

RG = R3 / { (V_out / V_in) + [ R2 / (R1+R2) ] } - R3

Scotty's concept is the ideal system and is often used in industrial tension monitoring systems.  The main benefit of it is that it monitors tension in the actual cable and totally ignores winch drum effects caused by increasing winding radius as the drum fills.  (As the radius increases the torque on the motor increases, so motor torque is not a reliable measure of cable tension).  The system often uses 3 rollers, 2 to act as guides for the cable with the third located between the two guides.  This middle roller is spring loaded such that the cable has a slight offset in it.  As tension increases, the roller is deflected against the spring -  in effect the cable endeavours to straighten out the offset.  The deflected roller then operates a microswitch at a pre-determined pressure.  The attached site shows a typical example  http://www.checkline.com/tension_sensors/TS2H

You need to reverse the polarity on the detection wires periodically (several times per second ?)  In effect you apply AC to the detection wires.   This can be achieved in a DC circuit by setting one probe to 1/2 the supply voltage then switching the other probe between supply voltage and ground.

Some info here if you understand German
http://www1.extrahertz.de/moorhuhn/daten/VRDM36x-DE.pdf

Clocks do NOT use their supply voltage to regulate their speed.  Previous posts give you all the links you need to hack the oscillator and get you there.  As to the continuous movement, if you used a high speed camera you'd see that the continuous movement was actually the integration of lots of small steps.  The human eye is pretty useless at high speed step discrimination - it wasn't necessary as part of the evolutionary process so simply didn't happen.  Nature is pretty good at avoiding unnecessary complication.

Battery clocks are timed by either a conventional escapement wheel or a crystal oscillator.  Neither of these can be altered without being extensively "re-engineered".   What you need is a "slave" clock that is driven by timed pulses originated by some master clock.  These were generally used in industrial situations with one master clock feeding numerous slave clocks around the site.  The slaves were simple solenoid driven ratchet mechanisms with the solenoids being pulsed, typically once per second, to drag around the indicating mechanism.   The attached link shows an example 
http://en.wikipedia.org/wiki/File:Slave_Clock_Inside.jpg
You can set the pulse rate to suit your application.

why are you using an arduino to switch power to a raspberry.  Can't you use the one processor to do both tasks (that of the arduino and that of the raspberry)

You talk about 2-phase.  Do you mean 2 phases plus a neutral from a 3-phase system or do you mean 220 supply rather than 110 as the USA uses.  If the latter then I'm sorry to advise that it's still single phase even if running at 220.

such as ?