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Old 12-18-2006, 01:19 PM   #1
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Default Unequal steering throw

What are the possible culprits in having unequal steering throw left and right? The radio has both end points set to 100%. The servo arm is not straight up and down, but is as close as possible with the closest spline. The link from the servo arm to the steering saver / bellcrank is not perfectly in line, but close as can be with way the servo and factory servo arm are supposed to be installed. The links from the steering saver to the wheels are unequal length. Not sure how you get the steering saver / bellcrank perfectly straight, other than resetting the steering links to factory specs (60.5mm and 62mm for an Fk05).
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Old 12-18-2006, 01:35 PM   #2
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there are a ton of assymetrical parts to a touring car steering system, starting with the pushrod itself. the best answer is to set your dual rate to the value you typically run at. set your epa's, at this point, to create symetric circles.

then adjust your pushrod (shorter/longer) while compensating with sub-trim (remember; subtrim pulls the epa's with it), until your epa's for that size circle (throw) are the same. note that larger or smaller circles (change in dual rate) will require new epa's to keep the circles the same left to right.

it's the nature of the beast. the only symetric linkages are those coming straight off the servo like a 12th scale (kx one, fsr bullet, xpress mk2 )

note also, that every linkage has an inherent mechanical exponential funcion (whether + or -), and that is assymetric as well.
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Old 12-18-2006, 04:48 PM   #3
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Actually, having the servo horn straight up in most of the modern cars is not the best method..... let me explain (I only figured this out recently, thanks to some guys on the Evo5 thread).

Effectively, the best postion, is when the servo link is perpendcular to the horn at dead centre. Usually as the links are at an angle (ie not perfectly horizontal), you need a little bit of angle in the horn to get the 90degree angle for the same steering throw each side.

Quick pick of what I mean... on my evo 5 the steering link is quite angled (high horn, very low steering rack) so the horn is quite a way off centre to get the perpendicular angle. However, this does give equal steering throw.

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Old 12-18-2006, 04:54 PM   #4
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first i put on the servo horn. i make sure it moves w/o hitting anything. i set my dual rate for 100%. i center my servo / steering linkages. then turn the wheels left, and set my expo to where the knuckle is just at full lock, but w/o the servo buzzing. i do the same for the right. then i adjust my dual rate for the certain track conditions. i always have equal throw left and right.

-Zac
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Old 12-18-2006, 05:10 PM   #5
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Quote:
Originally Posted by TryHard
Actually, having the servo horn straight up in most of the modern cars is not the best method..... let me explain (I only figured this out recently, thanks to some guys on the Evo5 thread).

Effectively, the best postion, is when the servo link is perpendcular to the horn at dead centre. Usually as the links are at an angle (ie not perfectly horizontal), you need a little bit of angle in the horn to get the 90degree angle for the same steering throw each side.

Quick pick of what I mean... on my evo 5 the steering link is quite angled (high horn, very low steering rack) so the horn is quite a way off centre to get the perpendicular angle. However, this does give equal steering throw.

HiH
Ed
Yes, that makes sense. The linkage is at 90 degrees to the servo arm, but not necessarily is the arm straight up and down. Thanks for the suggestion.
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Old 12-18-2006, 05:29 PM   #6
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also check that your steering turnbuckles are equal lengths if they are symetrical left to right
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Old 12-18-2006, 05:40 PM   #7
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Quote:
Originally Posted by protc3
also check that your steering turnbuckles are equal lengths if they are symetrical left to right
This part is screwy in the Xray manual. It has a drawing which it says is 1:1 scale. It shows the left turnbuckle as 62mm and the right as 60.5mm. So I adjust the turnbuckles using the drawing, and then measure them with a micrometer. The drawing is screwy.

Its says: Left 62mm, but when measured, the two lines are 60.5mm apart.

Its says: Right 60.5 mm, but when measured, the two lines on the drawing and the turnbuckle illustrated as 1:1 is 62.0 mm.

What gives? Equal length them, or offset them? If offset in length, do I follow the numbers given in the drawing, and ignore the supposed 1:1 drawing?

Anyone know FK05 assembly and what to follow, the number or the drawing itself?
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Old 12-18-2006, 06:23 PM   #8
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on my cyclone the steering turnbuckles are identicle lengths.if they are different left to right,your steering geometry will be different from left to right.
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Old 12-18-2006, 06:40 PM   #9
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Quote:
Originally Posted by protc3
on my cyclone the steering turnbuckles are identicle lengths.if they are different left to right,your steering geometry will be different from left to right.
I looked in the old FK05 thread on this site, and it sounds like the agreement was that the manual had a misprint in matching the wrong drawing to the numbers. No one disputed the unequal lengths. Not sure why they are not equal. The mechanism looks centred to me, and the difference is only 1.5mm. So you got me wondering what the story is behind it. Too bad the Xray site doesn't seem to have as good of a search engine as here. Here you can search within a thread. Saves reading hundred of pages to find the relevant post within a thread.
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Old 12-18-2006, 08:20 PM   #10
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The XRAY bellcranks on the FK'05 and T2 are not placed in the center of the car, they are offset for belt clearance...this is why there is a requirement for different L and R steering links.

To align the steering properly on an XRAY:
1) Set up the servo horn so that it is 90deg with the servo link going to the bellcrank (as TryHard posted). Simultaneously as you do this, set the length of the servo link so that the bellcrank is pointed straight forward with the radio at 0 trim.
2) Keep the bellcrank pointed straight forward, and set the length of your L and R steering links so that you have the desired amount of toe on each wheel. Do each wheel seperately.

With this setup, you shouldn't have to set your L/R steering EPA more than 5% different to get equal throw.

Some other cars do not have the unequal steering link requirement. This is because they either have a more offset belt (as on the HB Cylcone) or a dual-post style bellcrank (as on the Tamiya 415 series).
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Old 12-18-2006, 10:22 PM   #11
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Thanks.
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Old 12-18-2006, 11:07 PM   #12
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Quote:
Originally Posted by Nexus Racing
The XRAY bellcranks on the FK'05 and T2 are not placed in the center of the car, they are offset for belt clearance...this is why there is a requirement for different L and R steering links.

To align the steering properly on an XRAY:
1) Set up the servo horn so that it is 90deg with the servo link going to the bellcrank (as TryHard posted). Simultaneously as you do this, set the length of the servo link so that the bellcrank is pointed straight forward with the radio at 0 trim.
2) Keep the bellcrank pointed straight forward, and set the length of your L and R steering links so that you have the desired amount of toe on each wheel. Do each wheel seperately.

With this setup, you shouldn't have to set your L/R steering EPA more than 5% different to get equal throw.

Some other cars do not have the unequal steering link requirement. This is because they either have a more offset belt (as on the HB Cylcone) or a dual-post style bellcrank (as on the Tamiya 415 series).

there's your answer right there ...
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Old 12-19-2006, 07:05 PM   #13
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Does this apply to TC4s?
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Old 12-19-2006, 08:01 PM   #14
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the tc4 steering rack is not offset so you want the turnbuckles equal lengths.
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Old 12-19-2006, 09:19 PM   #15
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...Ive fought a couple of my cars in adjusting the rods to get the equal turning..and gave up...just not worth the effort.

Instead, I just go ahead and adjust the End Points to create an equal turning radius.

I make a U turn at crawl speed so there is no push or tire spin, note the width of the radius, then make the u turn the other direction equal it. Adjust the EPA until it does. When the subtrim is adjusted, these EPA's seem to still stay the same ratio and it's usually still MORE than ample steering angle.
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