I just noticed today that the HS-5645MG servos on my AeroWorks Yak 54 1.20 are overshooting when centering. This happens when the control is centered quickly. This was surprising to me for servos as expensive as these. I have never seen this before on any other servos, and it may influence whether I buy Hitec servos in the future. Is there an explanation for this? Thanks.

How long have you used these servos? Is this centering overshoot something that is just now occuring but didn't happen before on this model?

I'm having similar experiences, but in a different format. I have the servo set up as a single steering servo for my E-Revo Monster Truck. Last week, it sideswiped a light pole going about 40 MPH. It ripped the left front wheel, A-arms, axle, and blew the bulkhead into 6 or seven pieces. It was UGLY! I chalked it up to operator error. After rebuilding half of the truck, and getting it operational again, I noticed that I couldn't set the trim correctly. If the last turn I made was a left, when I let go of the steering control, the truck had a left list to it's course. If my last turn was a right turn, the truck veered slightly to the right. I could set the trim, but the next right or left turn I made brought the same problem back. In the troubleshooting section, the problem was blamed on the servo saver, but I didn't have this problem with the stock Traxxas servos, or the Spectrum servo that I used, before replacing it with the Hitec servo. I'm afraid I have to agree with LarryB, my upgrade feels like a downgrade, last weeks operator error is looking more like faulty servo error. AND, it hums while the truck is just sitting there, it stops when I physically lift the front of the truck and set it back down. That tells me that it lacks the power to pull the wheels back to the center position. Digital servos have 3 times the torque? And the dish ran away with the spoon, right?

So you crashed your vehicle ripping off the left side of the truck and now it won't steer straight? With that sort of impact you could have damaged the servo or you still have some damage/bent parts on your truck. Disconnect the linkage from the servo (so it's just the servo with the horn on it) and check its operation and centering. If it doesn't center this way then the servo is damaged and you need to send it in. If it does center, then the problem is not the servo. You have something else in the vehicle that is bent or broken.

The hum is normal for digital servos. I take it you are new to this technology. It's just the digital circuitry refreshing to hold center (300 times/second). There is nothing to worry about there.

for the guy who demolished his car. take the steering servo horn off and check for binding if your steering is binding then the servo will have a hard time centering.

After the crash, I replaced both A-arms, the axle, the toe link, both front shocks, installed P3 rockers, and the rocker arms that are suggested for it. The crash ruined the Tekno swaybars, so I removed them. and I changed wheels and tires all around to Proline Road Hogs, I even replaced the hinge pins, because it had snapped the long one in two places. Also, the cross member that the servo saver connects to was broken in half, so I replaced it and the hinge pin retainer that bolts on in front of it. I also replaced the front bulkhead, because it blew into 6 or 7 pieces, rebuilt the tranny with hardened steel Robinson Racing gears, and put a whole new differential in the bulkhead, including 90 weight Losi silicon shock oil in the carrier. I'm not saying that the servo got damaged by the impact, I'm saying the servo may have been the reason why I hit the light pole, because it wasn't tracking accurately. I re-installed the Spectrum Racing Servo, and it tracks great again. As far as the servo hum and my experience with servos, a hum means that if you have two or more servos doing the same job, as in twin servos for your steering, they are fighting each other to stay centered. With one servo as the steering servo, it means that the servo does not have the power to center itself, and so it hums as it constantly tries to center itself. And, if you have any other explanation, I'd like to know where you got your knowledge from, it for sure wasn't from RC experience.

digital servos hum... thats a fact of life.. its normal. get over it..
the fact that its not centering right. you obviously messed up the gears during the crash.. go buy a new gear set
install lightly lube them up . and have another great experience until it gets demolished again..
the fact that the servo humms is its constantly trying to center..
every one of my digital servos do it. none of my analog servos do it..
i have around 10 digital servos.. all from hitec

That pretty much sums it up.
In a 2 servo setup where the servos are ganged to each other the only true way you can see if they are fighting each other is to measure the amperage draw. Simply listening to the servo will not tell you 100% if your setup is ok or if the servos are binding.

As for my knowledge, it comes from my 17 years of experience in this hobby. I can understand how light poles seem to jump out of no where though.

man youve been in the hobby 17 years.. you got me by six years..been in it 11 years and it feels like forever.. hopefully hitec will continue to put out great servos..

Yup it has been a long time. I started in planes/sailplanes and then also got into the car part of the hobby about 7 years back for a change of pace.