mBot Servo Pack not working properly

#1

Hi,
I recently bought for my daughter’s mbot the extension Add-on Pack - Servo Pack . We built the “Dancing Cat”. Additionally, we installed the LED matrix and the sound sensor. Everything went fine, all the sensors tested were working properly. However the servo pack itself its not behaving as I expected. I have a two main issues:

  1. When I turn on the mbot, the servo pack is always rotating about 30 degrees, until it reaches 180 degrees plus about 30 degrees. E.g., If the original angle is 50 degrees when the mbot is off, when I turn it on it moves automatically to about 80 degrees. If i turn it off and then on again, it moves until about 110 degrees, and so forth until it reaches about 210 degrees, then I can turn off and on and is not moving anymore.
    Why is this behaviour? I supposed when I turn on the mbot the rotor should no move, and if its moving it should try to reach either the 0 or 180 angle as starting point. This behaviour is annoying because I cannot make the correct angle to leave the horizontal bar having enough angle from both sides to move equally (to make movement like weaving).

  2. When I start to play with the angles, after setting different values, suddenly the mbot starts to move randomly (run forward or backward or in circles) or stop responding.

I tried attaching the horizontal bar in different angles but the behaviour is always the same.

I am thinking either something is connected incorrectly or the servo pack itself is damaged.

Can someone please help? To make it easier, I attach the picture of the current construction of the mbot. And then I also attach a video of what the mbot does with a very simple program that sets the rotor in 180 degrees and decreases 1 by 1 until 150, shows the value in the matrix, and repeat (forever)
The mbot:

IMG_0184.jpg1935x2580 830 KB

The program:
IMG_0185c.jpg2931x2093 863 KB

The video executing the program:
https://box.psnc.pl/f/b357b9a99f/

Thanks,
Raul

#2

Hi rapw3k,

From your description, it should duo to the original degree of the servo is not o degree, please refer to the following steps to calibration the angle for the servo.

  1. Remove the servo pan (white) as well as the cuttable linkage from the servo.
  2. Connect the mBlock software to the mBot. Upgrade firmware for mBot first. Then run the following program to set the servo angle to 0 degree.
  3. Attach the servo pan to servo. The servo pan should be level to the servo. Show as below:
    blob.jpg1337x830 260 KB
  4. Attach the cuttable linkage.
    After the calibration, please check if it works normal by testing the following program:

As for the mBot function abnormal like reboot by itself, please kindly remove some other electronic modules like the me matrix and sound sensor have a try in case the load are too heavy for the main board.

#3

Thanks for the suggestions.
Regarding the first issue (calibration), I removed the servo white arm, and cuttable linkage from the servo, and I run the program to set the servo angle to 0 degree. The strange thing is that when the servo moves to 0, it keeps making a buzz (sound) - please see video link below. Is this normal?
Then I tried attaching the arm + cuttable linkage and run the program in step 4 (you suggested). I tried different positions of the cuttable linkage and it keeps hitting the board, as the movement is too broad.

video available at: https://www.icloud.com/sharedalbum/#B0M532ODWtOMJi

I tried moving from 45 (instead of 135) to 0 and works more or less normal, but always keeps buzzing at 0 degrees, and every time I start the mbot the servo tries to move the cuttable linkage about 30 degrees (as before) - see second video link below.
Can you tell me if this is normal, or something is wrong?

second video also available at: https://www.icloud.com/sharedalbum/#B0M532ODWtOMJi

Regarding the second issue (automatic rebooting or moving), I disconnected for the testing the matrix and the sound sensor, and the issue was almost gone. Still one time rebooted/moved automatically after the servo couldn’t move beyond (hit the board). In any case, does it mean that is not possible to have the four rj-25 connected? Or perhaps is my servo the faulty one?

thanks,
Raul

#4

Hi rapw3k,

The servo keeps making a buzz when set servo to 0, please kindly test again after removing all the other electronic modules from the mCore have a check either.

Yes, it is better to set 45 degree since the cuttable linkage is long so it will hit the cover when set the degree large.

For the phenomenon that every time start the mbot the servo tries to move about 30 degrees, here I tested it and this is normal.
As for how may load the mCore can handle, it may determined by various application and the quality of the battery.

#5

I also have this problem after installing a new Servo Pack. The servo makes a buzzing noise when set to angle 0. (All other angle settings move the servo arm appropriately and don’t produce any noise after the arm comes to a stop.)

#6

Hi nu-bo,

Which Main board did you connect the servo to?
Normally, there is sound produced by the gear inside the servo while the servo rotating to any different angle.

For your situation that there is only sound when set angle to 0 but no sound when set angle to others, is it possible for you take a video to show your operation and the behaves on the servo (please record the voice in the video too), thanks!

#7