Servos Misbehaving

[Shadycrisp]

Hi!

I am currently using a teensy 4.1 and I am trying to control two servos. Since the voltage requirement for the servos(Tower Pro GM90S) are 4-6v, I am using a voltage step up to power them. This of course increases the current as well. I am having problems controlling the servos, using the sweep example program with both the Arduino Servo Library and PWMServo library. The Servos preform extra rotations before changing direction. Could this be because of the current, or could it be a software issue?

#include <PWMServo.h>

PWMServo servo1;

int pos = 0;

void setup(){
  servo1.attach(14, 500, 2400);
}

void loop() {
  for(pos = 0; pos < 180; pos += 1) {
    servo1.write(pos);             
    delay(15);                       
  }
  for(pos = 180; pos>=1; pos-=1) {   
    servo1.write(pos);             
    delay(15);                       
  }
}

 

[MarkT]

Servos take a lot of current, please describe in more detail how you are powering them, the current ratings of the parts etc. Also which servos are you using?

 

[Shadycrisp]

The Servo is the Tower Pro MG90S. They are connected to a 3.7V 2000mAh LiPo battery which goes through a voltage stepup to 6V

 

[MarkT]

please describe in more detail how you are powering them than

goes through a voltage stepup to 6V

Part number, current rating, that sort of detail is essential. A diagram is helpful so we are on the same page.

 

[Shadycrisp]

Operating current is 120-250mA, The part number from the vendor I got it from is WHS15024. The circuit is part of a larger project. The Motors represent the servos. It's voltage rating s 4.8-6V.

 

[PaulS]

Now I'm not familiar with the Tower Pro MG90s, but when you power them with 6Vdc, is the 3V3 output of the Teensy sufficient amplitude to reliably drive the PWM control signal?

Paul

 

[Shadycrisp]

The current is not coming from the teensy. Do you mean for the signal pin? If you mean current from the battery I believe it is sufficient if not in excess.

 

[PaulS]

Do you mean for the signal pin?

Yes, I do mean the control signal pin. The specs of the Tower Pro MG90S do not mention a minimum voltage for the control signal amplitude.
I also did not find any specifications of the WHS15024 boost/step-up converter. Do you happen to have specs or a link to that part?

Paul

 

[Shadycrisp]

Yes that's what confuses me is the lack of a min voltage for the control signal. Sorry the step up is here:

Μετατροπέας DC-DC Step-Up 5-24V 2A

Μετατροπέας συνεχούς ρεύματος μικρός σε μέγεθος για χρήση σε πλήθος εφαρμογών Με αυτό τον μετατροπέα μπορείς να αυξήσεις την τάση εισόδου χρησιμοποιώντας την μεταβλητή αντίσταση που έχει ενσωματωμένο η πλακέτα Η τάση εισόδου μπορεί να έχει εύρος 2 - 24 VDC και η τάση εξόδου μπορεί να ρυθμιστεί έως

grobotronics.com

 

[PaulS]

Μετατροπέας DC-DC Step-Up 5-24V 2A

Μετατροπέας συνεχούς ρεύματος μικρός σε μέγεθος για χρήση σε πλήθος εφαρμογών Με αυτό τον μετατροπέα μπορείς να αυξήσεις την τάση εισόδου χρησιμοποιώντας την μεταβλητή αντίσταση που έχει ενσωματωμένο η πλακέτα Η τάση εισόδου μπορεί να έχει εύρος 2 - 24 VDC και η τάση εξόδου μπορεί να ρυθμιστεί έως

grobotronics.com

More commonly known as XY-016 module. But still very limited in specs.

Paul

 

[PaulS]

Looking at your code I noticed this line:

servo1.attach(14, 500, 2400);

Is there a reason why you deviate from the standard values of 1ms and 2 ms, like so?

servo1.attach(14, 1000, 2000);

Paul