Bob et al,

<<I tested a variable power resistor, but reducing the voltage significantly reduces the power of the trim motor>>

 

You really don't want to put a resistor in series with a trim servo motor for speed control.  The voltage level seen by the motor will vary with load and time.  Say for example you do a ground test and find a resistor size that gives you a nine volt drop across the resistor and five volts across the motor. This is not the same as having a 5V regulated source for the motor.  As soon as you apply some loading to the servo, current will go up increasing the voltage drop across the resistor and your motor can stall.  If you control the voltage either with a regulator or pulsing, the voltage will not crash when more load is encountered and more current is drawn.  I used pulsed power for my hefty avionics cooling fans because they draw far more current.  (model airplane motor speed controls are a good source)  Pulse control is also more efficient since voltage regulators dissipate the excess voltage a heat.  This is not an issue for the milliamps of a trim servo, but it can be for bigger power consumers.

Chris Zavatson

N91CZ

L360std