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Old 08-03-2010, 07:55 AM   #1
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Default Servo Arm Centering - Subtrim vs Linkage?

Whats the best practice for setting up a servo arm on the losi 8ight 2.0 or 8ight-t 2.0? I have both a buggy and truggy and it seems the servo arm on steering is never exactly at 90 degrees like it should be. So do you use subtrim to correct it and get it at 90 degrees or do you adjust the linkage so the wheels are straight even though the servo arm is slightly off center? I know either method can be used to get the vehicle running straight but which is the better method and why?

Last edited by jwm2; 08-03-2010 at 09:39 AM. Reason: Changed title to reflect the discussion.
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Old 08-03-2010, 08:14 AM   #2
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ive ran into that problem also, always seems the servo horn in 1 tooth in front or rear of being at 90deg. i like to use linkage to adjust, adjusting trim limits the travel on servo in one direction.
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Old 08-03-2010, 08:20 AM   #3
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Yeah i'm thinking thats probably the best way to go as well. I got a buggy about a month ago and set it up using the subtrim, but now that i'm setting up my truggy i'm thinking that setting the linkages might be the best option so i don't mess with the servo too much as lots of subtrim can have adverse effects, so i've read.
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Old 08-03-2010, 08:46 AM   #4
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ive ran into that problem also, always seems the servo horn in 1 tooth in front or rear of being at 90deg. i like to use linkage to adjust, adjusting trim limits the travel on servo in one direction.
+1 use the linkage ..it may take you a minute to get it just right ..but dont take the easy way out ...i try and get mine as close to zero on the subtrim as possible ..i see to many people that have like +30-30 on there subtrim because they were to lazy to make the mechanical adjustment
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Old 08-03-2010, 09:34 AM   #5
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Ok but i just read an article in rccaraction from the general manager of ko pro that said to use the subtrim to get the servo arm centered. So which method is the best practice? I realize the end result is the same but which way is better and why? Could the general manager of a well known radio company be wrong? Of course he could be, but i'm not in a position to say otherwise.

I can see the advantage of setting up the linkage but i can also see an advantage to having the subtrim set to center the servo.

On the linkage side i see that the servo will have equal throw in either direction. So thats definately a plus.

But on the subtrim side i also see an advantage if i had to change the servo at a track for instance. If the linkage is set so the servo arm is exactly at 90 degrees then if i have to change servos i just have to adjust the subtrim so that its back at 90 degrees and i'm all set to go. However if i change brands of servos the location of the spline might be slightly off, so that would require adjusting the linkage once again to get it back to straight.

So which method is right or which method is best?
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Old 08-03-2010, 10:16 AM   #6
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Ok but i just read an article in rccaraction from the general manager of ko pro that said to use the subtrim to get the servo arm centered. So which method is the best practice? I realize the end result is the same but which way is better and why? Could the general manager of a well known radio company be wrong? Of course he could be, but i'm not in a position to say otherwise.

I can see the advantage of setting up the linkage but i can also see an advantage to having the subtrim set to center the servo.

On the linkage side i see that the servo will have equal throw in either direction. So thats definately a plus.

But on the subtrim side i also see an advantage if i had to change the servo at a track for instance. If the linkage is set so the servo arm is exactly at 90 degrees then if i have to change servos i just have to adjust the subtrim so that its back at 90 degrees and i'm all set to go. However if i change brands of servos the location of the spline might be slightly off, so that would require adjusting the linkage once again to get it back to straight.

So which method is right or which method is best?
It depends from car to car. With my losi I've always used a little subtrim to get the arm pretty centered. Your left and right epa adjustments should be relatively close. So you don't want the right epa to be at 100% while the left EPA is at 40%.

Honestly, the subtrim vs linkage tradeoff is wayyyyy more noticeable with onroad cars. Making sure that you have correct EPA adjustments is a lot more important.
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Old 08-03-2010, 10:31 AM   #7
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i just turn the servo adapter, one tooth so the arm is straight enough i dont mess with the linkage or the sub trim.

i just leave my throttle trim at 0.
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Old 08-03-2010, 10:35 AM   #8
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Well on a losi 8 i've heard that 20% difference on the EPA is not uncommon. But what i'm wondering is what the torque curve is on servos. Do they have the most power closest to center or is it pretty even throughout the throw. This imo would be the determining factor in which i would go with personally.

If the servo is strongest closest to "its" natural center position (no subtrim) then by all means using the linkage would be the way to go. But if the torque curve is the same for true center and virtual center then subtrim would be the way to go.

Its kind of an interesting topic and i've not been able to find too much online to suggest one method over the other.

The gm from ko pro says to use subtrim to center the arm once its at its closest position to center on the spline, but i've also read on the web that using too much subtrim can have adverse effects.

Whats too much subtrim? In order to get the arm straight i was up into the 20-30 range one direction or another when trying to center the arm. To me this seems like its getting into the too much category. I can see 0-15 would be alright, but any more than that and it seems like you are getting carried away with subtrim.

I also think subtrim should be used only to get the car to track straight down a runway, so a couple notches in either direction once the linkage is setup would be ideal, but then again a quick turn of a wrench can get you back to 0 if you really dialed it in.
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Old 08-03-2010, 10:40 AM   #9
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i just turn the servo adapter, one tooth so the arm is straight enough i dont mess with the linkage or the sub trim.

i just leave my throttle trim at 0.
Ok but are you getting the most torque and throw with those settings? Is it optimal for everyday use?
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Old 08-03-2010, 10:48 AM   #10
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Ok but are you getting the most torque and throw with those settings? Is it optimal for everyday use?

i dont know it has 133 @ of torque at 6v , im talking about my throttle servo
yea its fine for everyday use.
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Old 08-03-2010, 11:04 AM   #11
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Originally Posted by jwm2 View Post
Well on a losi 8 i've heard that 20% difference on the EPA is not uncommon. But what i'm wondering is what the torque curve is on servos. Do they have the most power closest to center or is it pretty even throughout the throw. This imo would be the determining factor in which i would go with personally.

If the servo is strongest closest to "its" natural center position (no subtrim) then by all means using the linkage would be the way to go. But if the torque curve is the same for true center and virtual center then subtrim would be the way to go.

Its kind of an interesting topic and i've not been able to find too much online to suggest one method over the other.

The gm from ko pro says to use subtrim to center the arm once its at its closest position to center on the spline, but i've also read on the web that using too much subtrim can have adverse effects.

Whats too much subtrim? In order to get the arm straight i was up into the 20-30 range one direction or another when trying to center the arm. To me this seems like its getting into the too much category. I can see 0-15 would be alright, but any more than that and it seems like you are getting carried away with subtrim.

I also think subtrim should be used only to get the car to track straight down a runway, so a couple notches in either direction once the linkage is setup would be ideal, but then again a quick turn of a wrench can get you back to 0 if you really dialed it in.
It's not a very interesting topic at all for offroad. Like I mentioned earlier, all these subtrim/linkage issues are a lot more relevant in on-road applications. In my opinion, your time would be a lot better spent working on shocks, diffs, etc. The fast guys are not beating you because they spent hours on their linkage and radio settings. I promise. They get their radio settings fairly close and wheel it.
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Old 08-03-2010, 11:05 AM   #12
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I like to use the sub-trim. If you use the reg trim it will change the center and then the servo will throw more one direction than the other. With the sub trim it keeps the throw equal on both sides. You can use the linkage but why not do it the easy way and just use the sub trim.
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Old 08-03-2010, 11:07 AM   #13
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I use both subtrim and adjust the linkages. Subtrim doesn't affect the the EPA settings, that's the beauty of it, normal trim does however. I put my steering horn on as close 90 degrees as possible and then adjust it to 90 with subtrim, then I adjust the linkage to get my wheels centered while making sure the two steering arms are equal length. Last step is adjusting the EPA, I hold the steering at full lock and add EPA till the servo starts buzzing, then back off till it doesn't buzz anymore. This gives me the most amount of steering without overworking the servo.
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Old 08-03-2010, 11:24 AM   #14
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Originally Posted by 071crazy View Post
It's not a very interesting topic at all for offroad. Like I mentioned earlier, all these subtrim/linkage issues are a lot more relevant in on-road applications. In my opinion, your time would be a lot better spent working on shocks, diffs, etc. The fast guys are not beating you because they spent hours on their linkage and radio settings. I promise. They get their radio settings fairly close and wheel it.
I'm not worried about getting beat, i haven't even entered my first race yet. Thats not my question. I realize driving & setup skills are more important for racing and thats fine.

What i'm asking is do you adjust the servo linkage or the subtrim when the servo arm is not completely centered? Do you get it as close as possible with the servo arm and adjust it to be centered on the subtrim or do you just adjust the linkage so the wheels are straight?

I realize you can do it either way and in the end most likely some subtrim may be needed. But does the servo arm need to be straight (90 degrees) in correlation to the servo itself?

I still have yet to hear any advantages of doing it one way over the other and vice versa.

So which is it, subtrim or linkage adjustment?

I realize its much more pronounced in onroad racing, thats obvious. But whats the answer for onroad racing?

What i'm doing right now is getting my 8ight truggy set up how i want it. I just got the radio tray installed with my servos and am working on getting the servos, arms and etc adjusted to how i want it. But as stated before on my 8ight buggy i just put the servo arm as close to center as i could and subtrimmed it to center in correlation with the servo itself. But as i set up my truggy i'm starting to think that putting the servo arm on there and adjusting the linkage may be the best method to solve the problem. I have a day or 2 before my engine shows up so i figure why not discuss this now and get it setup right from the beginning?
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Old 08-03-2010, 11:29 AM   #15
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I like to use the sub-trim. If you use the reg trim it will change the center and then the servo will throw more one direction than the other. With the sub trim it keeps the throw equal on both sides. You can use the linkage but why not do it the easy way and just use the sub trim.
Thats exactly what i did with my buggy. But now when setting up my truggy i'm wondering if i should go the other route instead. Both will accomplish the same end result which is a straight line when not touching the wheel, but which method has an advantage once i turn the wheels? Thats assuming one has an advatage over the other.

I like to read and search google (since the search here doesn't work anymore) to find the answer to my questions and problems when i run into them. I'm sure alot of us do the same thing. But i've run into conflicting results. Some say adjust the linkage, some say to adjust the subtrim and others say to buy 8 servos and find the one thats the closest to dead center and take the rest back for a refund, LOL. Some even suggest buying hitec servos with a programmer so you can manually change the center point in the servo itself. The last 2 options seem like alot of hassle and wasted money. But if people will go to those lengths to find or make a servo dead on center with the servo arm, then there must be some sort of advantage of it right?

I realize i may be over analyzing it, but even within this thread you have some who prefer subtrim and others who prefer linkage adjustment. But neither has stated a very solid arguement one way or another.
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