Gear Lash & Criteria For Replacement
 

I have a bunch of metal geared servos and am wondering what the factory uses as the criteria for replacement of those gears? In the shop I've tried to set up several "jigs" so to speak for testing spank brand new servos against some used ones. The results weren't what I was looking for with what Ive done so far. I tried using a dial indicator but couldn't get consistent and repeatable information. Thanks for any ideas_bob

RE: Gear Lash & Criteria For Replacement
 

The rule that our service center uses for checking them is by uisng a 12" pointer on the servo, at idle, there should be no more than 4mm movement at 12" out. Generally they are 3-4mm.

Gear Lash & Criteria For Replacement
 

Thanks Danny! Is there any reason to check the lash at the extremes? I remember a "fix" posted on one of the boards/lists. It went something like this;
To check if there is wear at neutral, check the backlash by hand, power off at neutral. Then rotate the servo to the max left/right and re-check. If there is less backlash at the left/right position than there is at neutral, the gears have worn.
It also listed a litte trick to fix the problem. It was to rotate all of the counter gears 180° from their current position to move the worn spots off neutral.
What is your opinion of moving the gears around, and what exactly are the counter gears? Thanks alot_bob

RE: Gear Lash & Criteria For Replacement
 

The only reason to do that would be to check the gear lash at the extremes, such as if the slop was worse at the extremes than the center. That should be rare since the servo in not at the extremes as often as the center, but would still be possible. The slop check should be done power on to get an accurate reading, but not under any load. We have found that rotating the 2nd gear, the gear that meshes with the output gear, 180 degrees sometimes reduces the slop considerably when there is slop.

Gear Lash & Criteria For Replacement
 

I will make a jig like yours and do some testing. I have a couple of new 2721 and 8411 servos. As a baseline, what can I expect the lash to be on new and never used servos?

Thanks again_bob

RE: Gear Lash & Criteria For Replacement
 

At 12" you will likely see around 3mm or so, maybe a bit more, maybe a bit less. Anything over 4mm needs repair.