Servo Re centering ?

[Finnsllc 917]

Hey all. Just wanted to ask the more enlightened. Im having some servo issues with the servo not bringing the wheels back to center. When i turn left the servo comes back about 8o percent so the wheels are still facing left. When turn full right the wheels come back to center. Servo adjustment combined with alignment trueing are and have always been an issue for me. I did start adjusting endpoints in order to make the steering better. Im currently trying to adjust a buggy. Thanks 

[DeadMeat666 1675]

I do not consider myself 'enlighted' by any means, but here's what I do with steering. After building the whole steering assembly, and before attaching the servo, I ensure that the steering has no binding throughout the suspension travel range of the buggy, and that the amount of force required is minimal to pull the steering (holding the tie-rod end which the servo horn will be attached to) in either direction. Then I center the steering servo by powering it up and zeroing the trims on the TX. I then attach the servo to ensure the wheels of the buggy are centered with minimal trim. If too much trim is required, I shift the servo horn one tooth over and try again. 

Once that's all set, I turn full left and reduce the endpoint until the servo doesn't sound like it's squealing for mercy, and then I turn right and do the same.

If you still have problems after doing all that, you may need a stronger/better servo.

I know all this is basic, but I hope it helped. If not perhaps it can help someone else who reads this in the future  

[sosidge 624]

As DeadMeat said, first thing to check here is that there is no biding in the steering mechanism it needs to be completely free moving when the servo is detached.

Second, always do these kind of tests off the ground.

If the linkages are free, check that the servo horn itself is a precise fit on the servo. If you are using a servo saver, check it doesn't have free play.

If all of the mechanical aspects seem fine then it could just be that the servo is bad and needs replacing.

[Mad Ax 9325]

Yep, as per above - if you've checked for play in the steering links (there will inevitably be some), then check in the servo / saver assembly.  There's nothing you can do about play in the servo besides replace or rebuild it if it's old or buy a better servo if it's new.  If there's play in the splines then check you have the right splined adapter and that it's not worn.  If there's play in the servo saver, the spring may be not tight enough - I often add a small ziptie around my servo saver springs to firm them up.

Another issue I wrote about on another thread recently - if you're using a Tamiya servo saver with a metal geared servo, there is a tendency to tighten up the machine screw that holds the servo saver onto the splines.  These servo savers were designed to work with self-tappers into plastic, but we instinctively tighten metal threads tighter (because they come loose otherwise).  This clamps the servo saver together and stops it from doing its job.

Then, if you have a knock, or your endpoints are not properly adjusted, the servo saver spring is forced open but doesn't have enough tension to close again.  My general solution is to use threadlock and not do the screw up too tight, although using a better aftermarket servo saver is a more reliable option.  Check your servo saver is working properly and always returning to centre before assuming a more serious problem or general Tamiya sloppiness

[Finnsllc 917]

so @DeadMeat666 @sosidge @Mad Ax No, there is no binding on the control arms at all, smooth as glass. its a mechanical thing. I know how to build. but i dont know how to perfect. This specific question lends itself to many of my 20 builds. i seem to just have problems with the steering adjustments. i know on road off road is a thing where it doesnt need to be perfect. but, i build more buggys than on road, meaning, i test the buggies on tarmac/asphalt. i really struggle to get them straight. i do all the free hand testing on the kit before the servo. i adjust the endpoints. i do the "work"  to preemptively fix the issue. but, 10 min ago my son ran my schumacher up the street. I ran it 3 hours ago straight as an arrow. he couldnt run a straight pass. i tried and it was nowhere near as alligned as it was earlier. im just trying to understand how to dial the steering in. i know a few spaceres will help with a shimmie. It s frustrating to know that i know that i built it correctly and its not correct.

[SupraChrgd82 1425]

Check servo mounts and linkage for any play.  Assure servo mounts are rigid and do not flex.  Tighten loose components and wax the pivot balls as needed. Set EPA such that max throw is right where bump stops make contact, then back off one more click on the TX so that there is a 0.5mm gap in the bump stop. If the EPA is past where mechanical travel stops, the servo mount will flex or the horn will twist on the splined hub. The steering will not return to center. Today’s high torque servos have the ability to force seemingly rigid mounts from their intended position.

Check toe-in and tie rod lengths to confirm left and right are equal. Add a dab of dielectric grease to electrical connections. Look for loose or missing components in the steering linkage and cantilevers.

When all else fails, remove the servo with horn attached.  Connect the RX and run thru its paces outside of the vehicle. Confirm it centers in the same position each time.  Add some resistance with your fingers and operate the servo.  Confirm it centers in the same position each time.

 

[Finnsllc 917]

Allof the parameters seem to be correct. This is one of those things. I dont spend money on servos. Ive only used futaba 3004/3003 since the 80s. However im now wondering if i need to move to a higher end or more quality servo. I just have a thinf about spending money on servos. Why? I have no idea. 

[silvertriple 3557]

As per my own experience, that happens sometimes with the tamiya high torque servo savers (and similar ones at lower cost): for some reasons, they sometimes don't get back to center once they made the job. I noticed this with my DT03. I never have this issue with the standard servo saver included in the kit. I thought the servo was the issue until I found out that the servo saver was the issue...

 

[TurnipJF 9192]

 

On 2/17/2021 at 9:26 PM, Finnsllc said:

Allof the parameters seem to be correct. This is one of those things. I dont spend money on servos. Ive only used futaba 3004/3003 since the 80s. However im now wondering if i need to move to a higher end or more quality servo. I just have a thinf about spending money on servos. Why? I have no idea. 

How confident are you that your "Futaba" servos are actually Futaba servos? I have come across quite a few fakes which appear convincing from the outside but lack the tolerances of the genuine items, making their centering very poor indeed. These days I use Alturn servos mostly - decent value and AFAIK nobody has tried to counterfeit them as yet.