[Dale(294engr]]

Don hope I'm not too late with this for you to use else good for future ref.!

Contrary to what many here may have reasoned
120A CB is a great poorman's 1 milliohm shunt!! (actually ~.96milliohm)

consider if Rcb was not tightly controlled trip, current would vary likewise!

(caveate: defective breakers internal R varies significantly =poor candidate)

I've been using 120A CB shunt yrs, include it in my FIRST wkshops & demo's
(previously 60A =bit over a milliohm so calibration factor req'd incr absolute accuracy - but relative current stability is quite good enough, in practice)

Using any DMM on 200mV scale place it across the 120A CB terminals

(best = install jacks to accept DMM pointed probes for competition ease use)

(Harbor Freight DMM works fine w/ 1Meg Rint on 200mV scale)

(when CB is open DMM reads overrange but csuses no harm [i sprotected])

when closed read the DMM +_199.9 A / mV full scale
polarity useful for drain/ batt charge current monitor if batt charged in robot

resolution is .1A!!

convenient to keep track of Robot quiescent current draw ~2A

useful to run each of 4 CIMs noload off floor as gauge of overall drive friction
.. motor, motor bearings& alignment, brush/commutator, gearing, chains, wheel bearing alignment, keeping in mind at zero friction current draw is Zero!

.. so keep log ea motor out of kit I-noload 12.6v reg pwr supply best cntrl
burn in to stable lowest full speed current draw. Future comparison will indicate: worn brush/commutator, bearings and shorted/open rotor windings

In competition = good quick test of left Vs right tank drive (or ea of 4 if 4WD)
do one at a time, subtracting quiescent draw, log result

It is remarkable just how sensitive this test is!!

NL current increase is measurable predicts a problems developing well before driver becomes aware of it!

and all Robot loads.. simply run each alone and subtract quiescent constant

using on-board A/D, a dynamic history may be recorded!!

with a little ingenuity ext. variable mechanical load constitutes handy dyno!

or with locked shaft and careful pre-set control of Victor / Jaguar
can test at any desired constant current up to 40A CB cycling which occurs at ~50A for each motor (for 3 motors tank cfg ~150A max ea side (~300A total) may be attained for a few seconds! - wise to monitor motor temp in this mode!)

.. great for finding resistive connections in wire, connectors, CB's, aging SLA's

also as dynamic 18AH SLA constant load battery characterization test:
use 50A, expect 9 minutes recording Vbatt every 10 sec
use Excel to produce Vbatt-at-terminals Vs Time for true batt discharge characteristic enlightenment!