Society of Robots - Robot Forum

Electronics => Electronics => Topic started by: StAnkys on May 20, 2009, 11:15:55 AM

Title: Control Servo with DC Analog Signal
Post by: StAnkys on May 20, 2009, 11:15:55 AM
I want to use a high-torque servo to "pull" the cable to apply a manual brake.  I have a DC signal that varies in level depending on input to it.

Most servos require a ~2ms square wave AC signal to apply constant maximum torque.  How can I apply this torque with just my DC signal?

Ideally I want:

(small 0-2.5V DC signal) --> if it exceeds 2V, trigger relay to allow 5V higher amperage DC current to power servo --> pull cable to apply mechanical brake

What I need help with:
1) What kind of servo could be used?  I need VERY high torque and cheap cost, but do not care at all whatsoever about precision/feedback/digital/etc.  Should I use something else to accomplish this goal?
2) How do I set up this "gateway" that only triggers the relay if a certain voltage input is reached (it will always have *some* voltage reading, so it can't just be run straight to the relay)?
3) How do I power the servo with a DC current, as described above?

Thank you,
SOR noob
Title: Re: Control Servo with DC Analog Signal
Post by: Webbot on May 20, 2009, 11:45:00 AM
You could feed the DC into an ADC channel to monitor the voltage and then use this to drive the servo. But servos dont tend to have a lot of torque - check the datasheet for the servos you are thinking of. Since servos are normally connected to the mcu output pin then it cant draw more than around 40mA - not a lot.
Depending on the torque required you may want to use a standard motor or stepper motor instead