Steering Servo and Rod question

[Colbstromer]

I have a Savox (1238 I think) and I have adjusted the steering horn to allow for the best possible and equal turning and caster, but when I turn all the way to the right it seems as if my servo locks out and it won't turn the wheels back from the far right locked out position without some throttle and simultaneous steering manipulation to get it back to steering properly. My drag and tie rods, nor my rod ends are catching on anything, it simply just locks out. Could this mean I have something adjusted incorrectly or I need a higher torque servo?
Thanks for any help.

[redsawacs]

Double check the servo and get back to me. If you have the specs, that would be better. You may just have some adjustments incorrect ...happens.

[Colgout]

disconnect the servo horn , check if the servo operate properly. if yes, your linkages and steering maybe over-centered. take some pic on the steering at neutral and at extreme ends.

[Colbstromer]

Originally Posted by redsawacs

Double check the servo and get back to me. If you have the specs, that would be better. You may just have some adjustments incorrect ...happens.

It's a Savox SA-1283SG, got the numbers flipped:p

Heres a link to the servo:

Savox SA-1283SG Super Torque Steel Gear (better than titanium) Full Metal Case Digital Servo #SA1283SG (416.6 oz-in @ 6V) (Comparable to Hitec HS-7950TH) - The Crawlers Store LLC

Servo is good and operational. Here's some pics:




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Locked out side


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Good side


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[redsawacs]

Unless it's a defective servo, it has plenty of power. Quite possibly the linkage overextending. Have you checked end points and link geometry?

[Johnnysplits]

Looks to me that the geometry is all wrong causing the steering to lock up. I'm just looking at the relationship of the servo horn to the steering arm on the knuckle.

[Colbstromer]

I did some work on my EPA and tested several different positions, I think my geometry is the best it's going to be given my knuckles and shafts (according to dlux), looking at making it perfect for about 200 dollars. My front end is just a little dicy. I wish it were better.


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[Erik D_lux]

Do you have another servo you can try? To me, it sounds like it could be a gear or something to do with the servo itself. Even if it is high enough torque, it could have a problem and not work.

If you can disconnect the servo horn and turn the steering back and forth, all that stuff should be good.

Did you clock the chubs backwards again? If so, there may be some binding since that linkage was setup with it clocked down to the original holes.

[Colbstromer]

The steering servo is good and I left everything the way you had it set up, except bumped the horn a notch over for more equal left right turn and caster but otherwise it's the same. I really can't figure it out. I got it pretty close with EPA but otherwise I think it's the best it can be.




I'll post some more pics soon.

Everything is turning smoothly, and still clearing everything. It just seems that the servo hits maximum extension and then because of the angle can't pull the steering system back, if that makes sense.

[Erik D_lux]

Its going to be pretty hard to tell without being there. Only other thing I could guess that you could look for is the rod end on the servo horn hitting the servo horn at full turn. The servo horn was clearanced right there for that reason though so it should be good. The steering felt really smooth when turning by hand, does it still?

[Erik D_lux]

I see what youre saying.

I would think thats a servo issue though because mine gets really crazy like that and can return just fine? I would see if there were a servo you could borrow and try it. It would answer a lot of questions.

[Colbstromer]

I will try and get my hands on another servo, not many people in my area have comp crawlers so it will probably be pretty slim picking. Maybe just buy a new servo, just not sure if that's necessary, lot of money to spend. I am thinking after the new year do new shafts and knuckles and if necessary a new servo too.


I wish I could upload some videos of it, I have my EPA at left 100 right 80 so it doesn't lock out. Here are some shots:
The side that usually locks out, very little caster because any farther it locks.

Not locked side: a lot of caster.




These are a few general shots with the settings that don't allow the steering to lock out, Erik, you can see kind of, the button head off the servo horn catching at various points on the tie rod, but I don't think that's the cause.


Here is a close up of the steering totally locked out, it's like the drag and tie rods have no leverage at a certain point, again videos would help :/

[nharkey85]

Originally Posted by Colbstromer

From the angle of this picture, it looks like when the steering reaches full lock you develop some geometry issue. The point on the knuckle falls too far behind the servo horn so when trying to center up the servo and link are trying to push the knuckle even further into the axle housing

[Colbstromer]

I am beginning to agree, I think the rods reach the farthest point, which happens to be the point I need to achieve for best turning radius and caster, and don't have the geometry/leverage to pull the wheels back to zero. Not sure what my next move should be.

By "back to zero" I mean center up

[Erik D_lux]

Yeah, its just that side camming over.

I think youre just going to have to run less EPA for that side. The proper fix is like we talked about, zero ackerman knuckles that wont do that.

One thing you could look at is moving the servo horn to the other side. It will make it a tiny, tiny bit better but you will have the same issues.

[Charlie-III]

Originally Posted by Erik D_lux

Yeah, its just that side camming over.

I think you're just going to have to run less EPA for that side. The proper fix is like we talked about, zero Ackerman knuckles that wont do that.

One thing you could look at is moving the servo horn to the other side. It will make it a tiny, tiny bit better but you will have the same issues.

+1.

Alternative would be to make a new mounting hole in the hub steering arm a little closer to the axle. This will require less movement from the servo to get the same throw.
Or, get a longer servo arm, same affect.

[Colbstromer]

That might be a good short term fix. Would I make the holes on both the left and right arms, closer to the axles?

Erik: I think I will take you up on the zero Ackerman knuckles and new shafts around the first of the year. I'll make sure I shoot you a message. Thanks again for the help my man.


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[Charlie-III]

Originally Posted by Colbstromer

That might be a good short term fix. Would I make the holes on both the left and right arms, closer to the axles?

Erik: I think I will take you up on the zero Ackerman knuckles and new shafts around the first of the year. I'll make sure I shoot you a message. Thanks again for the help my man.


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Yes, the arms on each side, make a new mounting hole so the distance from the steering hole to the knuckle pivot is smaller.

Edit..... post 21 (last picture) looks to show you already have extra holes, use those. Yes, the tierod may hit the case a little bit, but you will fix the other issue.

[Colbstromer]

That sounds like a good deal right there, should I leave my drag arm in the forward hole and move the tie rod back one hole or leave the drag arm and tie rod stacked as they are just back one hole (closer to the axle)?


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[Charlie-III]

Originally Posted by Colbstromer

That sounds like a good deal right there, should I leave my drag arm in the forward hole and move the tie rod back one hole or leave the drag arm and tie rod stacked as they are just back one hole (closer to the axle)?


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Leave them stacked and move both ends back one hole.