Attached are two PPT slides in jpeg format from my workshops given at Chatsworth, CSUN, El Camino College and BCR Team 294
The V884 is an H-bridge
H-defined: 2 connections each to battery & motor forming an 'H' with a switch in each of the 4 legs
.. 2open+2closed opposite switches define motor direction by reversing battery connections to motor,
.. motor speed is set by the PWM input varying the ON time of selected ON switch from 0% motor stopped to 100% full motor current
.. note supplied to the motor is always full battery voltage
.. i.e starts at 12.6v (no load) dropping ~1v for every 50A drawn due to battery ~.02ohm internal resistance (Vdrop = 50A*.02ohm = 1v)
(example: for each CIM at start up =133A spec at 12.0v constant)
..for few hundred mS battery Vdrops ~2.6v ea CIM which in turn drops the stalled I in practice (spec Rcim= 12/133=.09ohm)
1 CIM at start up 12.6-2.6 = ~10v/.09=~111A for TBD mS
2 cims ~8v/.09 ea = 89A ea for TBD mS etc up to 4 or 6 CIMs used)
while in neutral (1.5mS PWM 127 +_5 deadband)
jumper selects either all switches OPEN for COAST
for BRAKE two ground side switches close shorting Rotor aka dynamic Brake
Spike switches are mechanical.. aka relay
In Victor & Jaguars they are FETS
(3 in parallel in each of 4 places to reduce ON resistance sharing current to reduce P=I^2R heating most of which occurs only during the fast <1uS rise & fall times between 0v & ~12.6v for the applied variable duty rectangular wave if the FET ON resistance is << .09ohm (like ~.009 ohm) It has a positive temp coefficient so it is essential keep the switches cool else they may smoke and burn
example: Team 702 at LA Regional smoked V884.. most likely from voltage breakdown 'punch thru' spike from highly inductive motor inductance upon switch OFF kickback, shorting the source to drain of a FET = tied directly to the Battery which caused one of the biggest smoke + fire event I've seen in 14 years serving FIRST.
Note: Victors & Jag's have good internal spike protection which rarely fail but when it does it's spectacular!! ++
DaleScience@aol.com