It turns out that both the TowerPro SG90 and the metal version, MG90S are both too under powered to move Winnie-the-Pooh’s head. However switching to the large and more powerful TowerPro MG945 resulted in a much more positive outcome. This did however result in having to remove the plastic pan-tilt head that housed the micro servos and instead replace it with my own solution that provided the same movement.
The other discovery made was that the initial housing I had made for the electronic components was a little too large and therefore was restricting movement of the head as the fabric was putting up too much resistance even for the MG945 servos. So a smaller housing for inside the body is now required.
Below is a video of a basic test of the head and neck movement of PiBear. Using the TowerPro MG945 servos and the original housing.
The ServoSix happily drives these larger servos, which was really good news. They are still powered by the same 6v battery pack. The servos themselves however have some annoying characteristics, mainly that they do not always return to the same position when the same angle is provided. 90 being the centre point. If turning the servo to 0 degrees then back to 90 all is good, the return position is the same as the start. However if turning to 180 degrees and then returning to 90 degrees, the motor stops at about 120 degrees. Instructing the servo to move to 90 again result in no movement, but tell it to go to 70 degrees and it returns to the centre location of 90 degrees. This can be worked around in code but shouldn’t have to be. Both servos are the same so maybe it’s a feature of the servo, or I have factory seconds or fakes… ah the joy of buying off ebay.
The MG90S servos will still be put to good use. Driving the arms and mouth movement. That’s to come in the next installment.