Please :Controlling DC brushed motor for dummies


I love flying!
Dec 9, 2016
First, let me explain that I know very little of electronics. Thus, please, forgive me if I am asking something very obvious or abstract. I have tried to Google this but I am obviously not using the right words as I find very little.

The problem: I have an auto-pilot that is supposed to control a hydraulic pump for a ram which will actuate a rudder. Well, I would like to use an electric 12 vDC brushed motor to control such rudder instead of the ram. The motor has a reduction and is connected directly to the output power for the hydraulic pump, which is 12 vDC, up to 25 amp and reverses the polarity when it needs to actuate in different directions. It works more or less and I would like to get rid of the 'less'.

Is it possible to have an interface between the output of the autopilot and the motor? that:

It fades the voltage of the output. When the autopilot decides to apply power to the motor, it does it straight away. I would like to have some dumping on it so that the motor starts and stops smoothly. I have put some capacitors attached to the motor but am not sure is doing much; probably just absorbing peaks and filtering noise?
It brakes the motor when there is no voltage applied (by shorting it?) So, when the autopilot does think that the rudder is in the right position and does not provide power to the motor, the motor cannot spin freely.
In short, the power is 12VDC and reverses on demand of the autopilot. The motor is 12 VDC and there is no need to alter voltage or amp in the power.

I have seen many motor drivers but I believe there must be something simpler? This motor driver can do what I want but I would then need to transform the -12/+12 output from the autopilot to 0/2.5/5 in order to use the analogue input of the driver. I am sure it must be simpler than this.
KHN4NX1RC pdf:
I obviously appreciate very much a full solution but I am very much willing to do my homework. Please, any advice or heading so that I can research further in the right direction?
It seems I didn't explain well. The autopilot is a controller and is fed by many sensors -heading, rate of turn, wind, rudder angle, GPS. It basically can follow a track or maintain a heading compensating for any forces. The problem is that it controls the rudder with a +/- 12 VDC, which is actually activating a DC motor is both directions. What I would like is to improve that signal and brake the motor when there is no current out of the autopilot, by shorting the motor I guess, and to apply those +/- 12VDC progressively, let's say with a period of 1/4 of a second, so that the motor starts and stops smoothly.

For a soft start. Could I use a simple circuit with a resistor, a capacitor and a MOSFET? Initially, the MOSFET is off and the current goes through the resistor, once the capacitor is charged, the MOSFET turns on and the resistor is bypassed.

And for braking it. Could I use a high power resistor in parallel with the motor controlled by a MOSFET?


Hang on! I've got an idea!
Nov 29, 2015
You don't say whether you are using a Dynon EFIS to control Dynon AP Servos.
If you are not then you are probably on the wrong forum.


Dynon Staff
Staff member
Jan 14, 2013
Woodinville, WA
So to be clear - Dynon servos can only be controlled by Dynon EFIS systems. They operate over a fully redundant data link, and the actual techniques we use to drive the servo motors are proprietary.

There might be other enthusiasts that may chime in though!