[Dale(294engr]]

Hi Tony,
High Power DC motor controllers are very complex and technical.

Your darlington bipolar TIP120 transistor 60v 5A continuous, 8A peak, is fine for small On/Off motor applications

..but NOT likely for a loaded CIM! (may work for unloaded CIM)

Note TIP120 has Vce sat of 4v @5A (Vdrop CE fully ON)
so 12.6-4v = 8.6v Max at motor.

TIP120 Power dissipation is an issue P=IV 5A*4v=20W*duty switch heat loss
(unavailable to motor) R=V/I 4V/5A = .8 ohm

FETs are easier to control and parallel to achieve very low 'on' resistance
.001 ohm achievable with a few paralleled. I^2 R = 25A*.001ohm =.025W*duty switching loss

Application detail determines design needs: how you intend to use CIM:
Fwd & Reverse? Just full or zero throttle=open or variable PWM?
Dynamic braking? Battery V supply for CIM? (12.6v as in FIRST?)

A simple switching transistor needs to safely handle a few hundred peak amps until your CB cycles without smoking plus handle inductive kickback from ~100-300 uHy inductance of commutating + PWM switched CIM, then when switch opens tolerate collapsing magnetic field of rotor's flyback voltage as it attempts to reach infinity Or until something breaks down from very high voltage else switch transistor will likely fail shorted!! Protective devices must be designed with ample margin to handle this repetitive energy stress. The TIP120 internal reverse diode provides some protection but requires an external fast supplemental diode for reliability.

Some considerations:

CIM zero to full throttle step draws 133A from 12.6V 18AH AGM.

The longer it takes to get up to speed the longer 133A load draw time

(Unloaded = shortest 133A instantaneous draw = ~.05s
then continuous current draw drops to ~3A NL forever)

(NL current draw directly relates only to mechanical friction loss = commutator + 2 bearings, [NL current is a measure of internal motor mechanical loss]

a zero mechanical friction CIM would spin at 5500 RPM drawing Zero current!)

Example: FIRST Robot Drive ~133A for ~.3 s in Low gear.. .5s high gear

Stalled CIMs draw 133A ea OR until 40A reset CB begins cycling at ~50A

circuit breakers by design HOLD at marked rating, opening/recycling after ~125% marked, opening quicker as over current amplitude increases, or fails to decrease (bi-metal thermal time constant) ref: CB data sheet

or ~2s at 133A & why many robots falter or 'pulse' when stalled or nearly so pushing against resisting robot or field barrier (or one side in stalled turn)

Victor contains reverse voltage protected low on-resistance 12 FET H-bridge

3 FETs are paralleled in each of 4 switched legs in diamond cfg,

Opposing corners wired to Batt +/- , remaining corners to motor +/-

Opposing switches act together, to provide fwd / rev,

then One "On" leg turns off periodically to coincide with PWM for speed control,
'Dynamic breaking' isolates battery while shorting motor in neutral
(or open motor for 'coast')

The Victor is a rugged, complex uControlled subsystem ~100 components converting a 1.5 millisecond 0-5v PWM control signal to 120Hz variable speed, high current, Reversible power to a high power motor at 13v 50A continuous allowing hundreds of amps peaks for hundreds of milliseconds for motor start-up from stationary, or full fwd to full Rev (= worst case stress as motor acts as generator adding to battery voltage, potentially drawing >133A for brief time)

Good luck Tony.

PM me if you have questions this degree of technical not likely to be of interest to general CD reader