Jittery servo

[stelar]

Hello,

I had built the “Makeblock Robot Tank With 2-DOF Robot Arm”. It runs great, except the servo motor (NOT the one for the gripper). The servo motor “sometimes” work as intended and “sometimes” does not work (i.e. very jittery or not functioning at all)…

I’ve tested the servo separately, in which case it seems to run normal. However, when it is attached as per “Makeblock Robot Tank With 2-DOF Robot Arm”, it gets jittery most of the time. Not that the gripper is not gripping any objects and therefore there is no load.

Is it possible that the servo motor’s torque is not enough to lift the gripper & the gripper motor?

[evan]

When the gripper is gripping object, the servo motor current is very big. Usually you need to set up a position, ensure servo motor rotation angle in the gripper within the scope of activities. This will reduce working current and reduce the jitter.
Because the “Makeblock Robot Tank With 2-DOF Robot Arm” has 5 motors, if the power supply current is not enough, it will gets jittery. We recommend that you replace the current larger battery, such as Ni-MH or Ni-Cd battery.
Thank you…

[stelar]

In my test, there is NO load on the gripper. In fact I did a test just now and took out the DC motors, leaving only bluetooth and the servo motors attached to the Me-shield. The jitters are still there for the servo motor, but the servo for the gripper IS OK. If I took out the servo for the gripper, the other servo is not jittery.

In addition, I tested with wall socket power adapter set at 9V with the above settings (only servo motors and bluetooth connected to the Me-shield) and the jittery issue remains…

[stelar]

Hi,

After some further testing today, it seems that the jittery is caused by small increments? Makeblock’s TestServoDriver has position 30 and 150 in the code. If I just change the values to 100 and 150, the jittery occurs…

[stelar]

umm…can anyone confirm that this happens? I tested with the other digital servo motor and it is also having the same issue.

[Eric]

Hi, stelar,

Could you paste your code here, and I will use you code to test. So sorry about the delay of replying your question. I will try my best to help you. And if there are any questions about our products, contact with us. Make a topic in the Makeblock Product Questions forum or send me a email. My email address is :
eric@makeblock.cc
We will try our best to solve your problems as soon as possible.

Thanks for your support stelar!

[stelar]

Hi,

I understand you’re very busy Thanks for the reply!

I reduced the test code to the TestServoDriver from Makeblock, but changed the value to be 100 and 150. The code is shown below. Just changing the value causes the servo to be jittery. I’m not sure why…

#include <Me_ServoDriver.h>
#include <Me_BaseShield.h>
#include <Servo.h>
/*
Class Me_ServoDriver has most of the functions from class Servo,
see Me_ServoDriver.h for more details.
*/
Me_ServoDriver servoDriver(PORT_1);//can ONLY be PORT_1,PORT_2

void setup()
{
servoDriver.Servos_begin();
}

void loop()
{
servoDriver.writeServo1(100);
servoDriver.writeServo2(100);
delay(1000);
servoDriver.writeServo1(150);
servoDriver.writeServo2(150);
delay(1000);
}

[leo]

Hi,

I can confirm the jittery if you use “smaller” angels. When you move the servo by 5 or 10 degrees it seems to have problems to reach the desired position and does some correction (at least it looks like this). When you move 50 degrees it hits the target directly…

[lertulo]

FWIW, almost all servos will do this to some extent: they get very picky about trying to be in the right spot, and just fighting gravity is enough to make them continually readjust their position…

[Eric]

Hi,

I understand you’re very busy Thanks for the reply!

I reduced the test code to the TestServoDriver from Makeblock, but changed the value to be 100 and 150. The code is shown below. Just changing the value causes the servo to be jittery. I’m not sure why…

#include <Me_ServoDriver.h>
#include <Me_BaseShield.h>
#include <Servo.h>
/*
Class Me_ServoDriver has most of the functions from class Servo,
see Me_ServoDriver.h for more details.
*/
Me_ServoDriver servoDriver(PORT_1);//can ONLY be PORT_1,PORT_2

void setup()
{
servoDriver.Servos_begin();
}

void loop()
{
servoDriver.writeServo1(100);
servoDriver.writeServo2(100);
delay(1000);
servoDriver.writeServo1(150);
servoDriver.writeServo2(150);
delay(1000);
}

Hi stelar,
Sorry about the delay.
We’ve tested the servo driver and found that this issue may be caused by the power supply.

So we changed the design and added a switching power supply on the servo driver. After that the servo may work well.

The new design of the servo driver is in producting now. We will send all the Kickstarter backers the new designed servo driver for free. And will make a update about this to the Kickstarter backers soon.

Thank you for you support stelar and sorry about the problem on the servo driver.

[Eric]

The new servo driver.

[system]