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Topic: Need Help controlling a Weird DC Servo/Motor (Read 716 times) previous topic - next topic

JonMarkGo

So I've been playing with some DC motors on an RC airplane lately, and they work fine when interfaced with the L293D driver (http://www.ti.com/product/l293d)

But there's one motor on this plane used for rudder control that doesn't seem to work. Similar model here: http://www.wowhobbies.com/eflh1066replacementservomechanicsforblademcxmcx2msr.aspx

Anyone have an idea of how I would need to wire this up to control it from the Arduino? It acts like a servo but seems to be a DC motor...

johnwasser

You control it like a DC motor and use those metal brushes on the slider to get position feedback.  The motors are mounted on a circuit board and the brushes short contacts on the board to let the microcontroller know which position the servo is in.  These look like they would be better for retractable landing gear where there are only two positions needed: down and up.
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JonMarkGo

It's for a rudder - I tried controlling it with the L293D but it didn't work at all despite working with other DC motors I had around.

johnwasser

The red and blue wires appear to go directly to the motor.  Are you saying that voltage applied to those wires does not cause the motor to turn?
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JonMarkGo


retrolefty

#5
Aug 10, 2012, 09:06 pm Last Edit: Aug 10, 2012, 09:10 pm by retrolefty Reason: 1
I actually own a Blade Mcx micro helicopter (a very cool thing to learn to fly indoors) that uses two of those devices to manipulate the tilt of the rotor blades. These are low voltage motors as the battery is a single cell li-po, so 3-4.2vdc. The on-board electronics to sense position and drive the motor is built-into the single electronics module for the helicopter which also controls rotor speed and tail rotor speed and the radio control link. So to utilize this module you would need a H-drive to power the motor for variable speed bi-directional movement, and you would need to read the voltage of the feedback slider portion so your software would always know the existing position of the device. This is essentially a linear servo actuator minus all interfacing electronics. This would not be an easy module to get working, but certainly something possible to do, assuming enough knowledge and experience.

Lefty

JonMarkGo

Interesting, I actually got mine as part of this kit (http://www.amazon.com/Hobby-Zone-Champ-RTF/dp/B003DZ35GK) which I'm trying to hack up with the Arduino - got the propeller working with the L293D and I can run the little servo-style motors by just connecting them directly to a battery. I'm trying to use the servo motors with the L293D which is an h-bridge as far as I know, but it doesn't seem to work like a normal DC motor

retrolefty

Quote
I'm trying to use the servo motors with the L293D which is an h-bridge as far as I know, but it doesn't seem to work like a normal DC motor


However you did state that the motors operate as you would expect if you hook them up directly to a voltage source, so that would imply they are just small 'standard' DC motors, would it not?

Your source of error maybe in the wiring, configuration, or supply voltage/current source of the H-drive or in how you are commanding the H-drive command input pins?

Lefty

JonMarkGo

Right, they are standard DC motors just geared to act like servos (they only go so far in either direction)

The reason I don't doubt my wiring is that if I hook up a spare DC motor (not geared) to the h-bridge, it works fine with the Arduino. But when I swap out the wires to this "servo" it doesn't work.

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