Exactly! Yes, the two on the left are the ones that went bad. The one on the right, labelled "TIANKONGRC", seems to be much better.
It would not fit the keyhole slot, so I had to use a small rat tail file and relieve it a bit.
But works fine. I'll be sure and post some negative feedback to the seller on Amazon for the first two - though since I've cut then leads I probably can't return them.
Thank you again - Richard
I'm an avid RC model guy with a box of servos of all kinds. There must be a hundred of them. Some are dirt cheap and some are on the expensive side. NONE of them are dead reliable. Quite a few are dead on arrival and it's not uncommon for them to fail in use. So think about servos like a bunch of grapes; most are OK but a few are not up to par. I would suggest that everyone building a servo damper buy at least one spare servo because you can never tell when yours will shoot craps.
The most ordinary servo is a 9g size. To add to the confusion, the nine gram designation is just a suggestion of the weight and doesn't refer to the torque of the servo. Furthermore, they all seem to be different in size and the splined drive shafts aren't standardized. The servo arms aren't the same size either.
Most of the damper designs for our use rely on sealing properly only when the vertical dimension from the mounting surface of the servo to the top of the case just below the drive shaft is exactly correct. Too tall and your damper leaks air. Too short and you have too much friction. In practice, it makes substituting a different servo tricky. You MIGHT sand or file your way to happiness or you might find that the servo you have on hand simply won't work.
I know all this because I figured with my box of 100 servos, I could just pick through them until I found one which would work with the damper components I made on my 3D printer. Those slightly differing dimensions have no consequence for RC model builders, but I learned, as you did, that BBQ dampers are a different story.
Since I have so many servos, I decided to redraw and re print the upper part of my Adapt-a-damper. For many people, simply buying the EXACT recommended servo (and a spare) is a good solution.
As for some servos being "counterfeit", that might be something of a stretch. These things are all made in China and it's hard to tell if a particular servo is a knock off or simply a new batch that Tower Pro (or any other company) contracted from a different source. Even within brands, things are complicated. Take a look at this link: https://servodatabase.com/servos/towerpro
It shows a bewildering variety of Tower Pro servos ranging in price from two bucks to thirty bucks, each slightly different in size and performance.