do the R2 and R4 resistor limit current to protect the motor or the LMD? I thought it was to protect the LMD but if thats the case why not set it at somewhere above 6.6k and leav it at that?
The reason I ask is I am sizing mine for a 2.8A motor which comes out to
20000/2.8 = 7143 Do I set it for a 7.15k resistor or should I provide a buffer and set it higher?
Any help would be appreciated.
Too much current thru a motor can lead to demagnitization.
Too much current thru the controller can fry the pass elements.
In a word, YES, you're protecting BOTH.
The motor maker should provide a peak current rating. First calc the resistor that will provide a tiny bit less or equal to max.
Then see if the pass elements (fets or transistors) in your drive can handle that much current. If they can, you're done, if not, figure out what they need to protect them and live with less torque from motor or get a stouter drive.
Or, get something close with a SWAG and see if it smokes.... but don't butch (sic) if it does or if the thing doesn't run well if you SWAG'd in the wrong direction.