MG996R Servo with NiMH 7.2V battery not turning door knob all the way

So I have an Arduino UNO with 4 AA batteries supplying it 6V into the Vin pin, and another power supply which is a Mangoo brand NiMH 7.2V 6 Cells 1.800mAh for the Servo. I have attached the servo to a door knob so that it spins it and opens the door.

The problem is that, from the intended 30 degrees of angles of spin that it has to achieve, it apparently stalls and goes back to the stationary position at about 20/15 degrees. This seems to be the servo/power supply not having enough strength (It does retry to spin again 2/3 times in a quick succession). Now to point something: I remember using the 4 AA batteries with a servo stripped out of it's control board (Only using the DC motor, no PWM no nothing) and it worked! So it's very odd that it doesn't work with an even better battery. It is worth noting anyways, that the other servo (basically a DC motor by then, not really a servo) had all of it's gear teeth grinded and rendered useless after opening the door 3 or 4 times. I don't know if it was because the knob is too hard or something else, but it might have been that.

The matter is, I saw a tutorial where some other people achieved opening the door knob. Maybe their knob was a lot easier to spin? They were using a 995 servo instead of a 996, maybe the 995 is much stronger?

Kind regards, Joaquin.

6V is not enough for Vin. It really needs 6.5V-7V.

The MG996R is slightly upgraded version of the old MG995. Certainly no weaker, though there are some cheap clones about that might be anything. That fact that moving the door knob a few times has destroyed a servo gearset suggests that the door knob is simply too difficult to move.

If you remove the connection to the door knob does the servo move the 30 degrees that you expect? Please post the code you're using at least for the servo part but preferably the whole thing.


I just solved it by loosening the knob a lot. It really was hard, and now it worked flawlessly.

I do have another problem though. After activating it 3 or 4 times and testing it successfully, the servo became stuck and very unresponsive. Sometimes it would spin a lot, and some other times it would not, and you'd hear a faint pulsating sound coming from inside the servo, as it was moving and stopping very briefly, even though no movement is seen. I have no idea as to why this may be happening. I have tried to put all of it on a single power supply, and the Arduino Uno keeps resetting everytime, something that didn't happen before even with the same power supply. Could there be a short circuit inside the servo? Did I burn the servo circuit board?

Kind regards, Joaquin.

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