Newbie - Servo Control with Micro Maestro

Robotics and electronics discussion Electronics
1

On the face my project should be fairly simple, but I have a few questions.

I need to control a single RC type servo operating in a fixed arc, maybe 30°, based on voltage sent to a motor. So the basic layout looks like this …

12v DC power -> PWM motor controller with POT speed control -> DPDT on-off-on switch (wired to reverse the motor depending on the ‘ON’ position) -> DC motor.

I want the servo to actuate (move 30°) whenever the motor is powered regardless of the polarity of the voltage to the motor. (POT is sending voltage and DPDT switch is in either ‘ON’ position ).

Then the servo should return to it’s original position if the DPDT switch is in the ‘OFF’ position or the output voltage of the motor controler is reduced to zero.

From what I’ve read, I think the Micro Maestro may work using the analog input. So here are the questions:

  1. Am I on the right track?
  2. Is the analog input on the Micro Maestro polarity sensitive?
  3. I found the ACS724 Current Sensor Carrier which appears to fill the bill for sending the analog input to the Micro Maestro. Does the output of this sensor reflect polarity? (May not matter depending on the answer to question #2)
  4. Given the fixed arc of the servo, 30° out, 30°back, should I be looking at analog or digital servos?

Thanks in advance…

2

Hello.

I will address your questions one at a time.

  1. Yes, I think the setup that you are describing with the Maestro will be a good solution. There are just a few details to work out.
  2. Yes, the analog input on the Micro Maestro is polarity sensitive. Only positive voltages between 0 and 5 V can be applied to those pins. Negative voltages or higher voltages could damage the Maestro pins.
  3. The output from one of the bidirectional ACS724 Current Sensor Carriers will reflect the polarity, but it will do so while remaining between 0 and 5 V.
  4. The analog vs digital distinction probably doesn’t matter unless you need the arc to be extremely precise, in which case some digital servos might do a better job of that. For an application like that, you might consider one of our servos with feedback and use that to make sure it’s doing exactly what you want.

-Patrick

3

Thank you Patrick… that’s what I needed to know.

I can get around the issues by adding a separate ON/OFF switch upstream from the motor controller and replacing the DPDT ON/OFF/ON with a ON/ON switch for reversing the motor.

Then I can add the ACS724 Current Sensor Carrier between the motor controller and the reversing switch, so it will always see positive voltage.

Sweet! Order placed. Thanks again.

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