Don..
I've been using a super convenient m/cheap & available ethod to measure robot (motor) currents since 1999..
(Harbor Freight DMM works fine, $1.99 w/9v batt on sale!)
Super easy & remarkably consistent considering CB "switch" action.
use any DMM on +_199.9mV scale
place it across the 120A main CB! (install permanent jacks for more ease)
120A CB has tightly controlled resistance of almost exactly 1 milliohm..
(~ .96 millohm)
therefore 1A drawn per 1 mV measured for a resolution of .1A
you will be surprised at subtle mechanical misalignment/friction this method reveals
the caveate here is current is definately relative for single closed CB test, &
MOST handy to gauge fine "unloaded" motor current draw directly proportional to mechanical load.. commutator &two bearings baseline for ea motor as removed from KOP, then with added gear (test shift if used), again w/chains, wheels/bearings.
keeping log between competitions warns long before driver can sense change.
off floor: log current: full speed fwd, reverse, each motor or side..
Quiescent current is ~1A (power up all motors neutral "off" no drift etc)
compressor can be similarly characterized.
I've seen abused breakers (thousands cycles or tripped often) exhibit up to 2 milliohm but will also trip below 120A (or sporadically) so should be replaced )
Do some tests to assure yourself.. multi cycle the breaker - measure delta under constant load.. One time Calib test: use Lab 1 milliohm shunt in series as Gold Standard.. or use DMM 10 or 20A scale with a known load (10A = 1.2ohm 1% resistor, do measure exact V as battery health &state &charge &age determine its internal Vdrop with load)
email me at
DaleScience@aol.com I'll reply with 50A constant load FIRST 18AH Batt curves demonstrating delta R with load time and workshop dwg of DMM across breaker for handy high current robot measurement
Many of you have heard this before in my workshops or as I RI at events (mini wkshops!)
in ATL I'll be RI on Newton and scootin around field on 3 wheels