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Old Nov 17, 2011, 06:29 PM
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Servo signal to DC converter

I'm looking for a device to convert the servo signal (digital or analog) from a receiver to a proportional DC level. That is, the more I move the stick the higher the DC level.

I'm suspect that such a gadget already exists. Does anyone know?
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Old Nov 17, 2011, 07:20 PM
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A 1 bit DAC is basically what you want, which is effectively a low pass filter. Similar to the way power supplies convert the AC output of a bridge rectifier to DC signal with a small amout of ripple.
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Old Nov 17, 2011, 07:21 PM
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Quote:
Originally Posted by JPMacG View Post
I'm looking for a device to convert the servo signal (digital or analog) from a receiver to a proportional DC level. That is, the more I move the stick the higher the DC level.

I'm suspect that such a gadget already exists. Does anyone know?
http://www.bpesolutions.com/bpemanuals/dmxtoanalog1.pdf
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Old Nov 17, 2011, 07:44 PM
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A brushed motor ESC will do that with a little filtering on the output.

Andy
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Old Nov 18, 2011, 02:43 PM
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take a look at the input circuitry on this esc.

http://www.stenulson.net/rcflight/sc7.htm

SteveH
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Old Nov 18, 2011, 09:11 PM
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Excellent information. Thank you everyone!!!
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Old Nov 19, 2011, 02:51 AM
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JPMacG

The principle as shown in the circuit diagram of the motor controler isn't the only one, Advatage is, it is the simpliest, but disadvantage is, little bit a-linear and slow. It's based on the charge and discharge (tau) curves of a capacitor (C2 in that circuit). and mean voltage level.

I do disign an build my own circuits and if I want fast response and ultra linear relationship (as for measured values) I use a priciple of a closed loop just like a servo.

Such a closed loop system translates the inlput pulse length in a voltage level of capacitor to compare with the feedback voltage of a position feedback potentiometer of a servo with the use of a "one shot". If there is a difference, the voltage is changed by charging or discharging.
It's faster than the first method shown in the circuit of the motor controller.

Fastest system and less components than second method is a sample and hold circuit, not used by me, but action is.
The pulse length is used to charge a capacitor (by a current source) and the value is hold until a new value is known of the next pulse, and exchanged, vastest system of all.

I think you can find examples on the WWW if you realy need speed or linearity

Cees
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Last edited by Taurus Flyer; Nov 19, 2011 at 03:05 AM.
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