Voltage regulating transistor

Hey,
Another electrical question, can I use a voltage regulating transistor to slow down the trim motor speed on the Ray Allen servos? I have the Infinity Aerospace relay panel, and don?t want to spend the money on the safety trim system, but from what I have read on this form the servo speed is to fast.

Thanks Matt

Yes, but...

This will also reduce the torque - perhaps to the point where the trim tab it powers won't move against aerodynamic forces. The best way to regulate the speed of a servo is to use PWM, or pulse width modulation, which in basic terms rapidly switches the servo on and off using full voltage. The width of the "on" pulses is used to adjust the speed, and the servo torque is almost unaffected.

Needless to say this takes a lot more circuitry than a simple adjustable voltage regulator, but works a LOT better.

Mark Olson N407V RV-7A N16XV F1 EVO Rocket

Trim circuit

Here's one way to accomplish this; I know because I made one several years ago. There's an interesting trick you can do with a DC motor that makes use of putting a small resistor in series with the motor to get a voltage proportional to its armature current. Based upon the motor equation of the motor voltage, which is the sum of KeS, the EMF generation, and IR, the current through the motor times its armature resistance, you can set up a bridge circuit that will give a voltage proportional to the motor's rpm. Feeding those two bridge-voltages to an op-amp to get the differential voltage, then feeding that to one input of a simple pulse modulator, such as an LM2578, and having the other input from a temperature-compensated and amplified voltage from a differential pressure transducer, such as a Freescale MPX5010DP, you will have a trim control that always moves the trim tab at the correct speed for the TAS. Get one of your electronic whiz buddies or even Jim Weir to build one.

You should be able to use a voltage regulator circuit on the trim servo's. I'm pretty sure that's what the Ray Allen speed controller is. It states in the install instructions the Servo will maintain sufficient torque down to about 9 volts and at that setting the speed from min to max goes from 19 to 31 seconds. See his documentation http://www.rayallencompany.com/RACmedia/instructionsSPD.pdf

Like Mark said, with a PWM you have more speed control without losing torque. Here's what I used (one each for pitch and roll trim): http://www.matronics.com/governor/