Servo arm fixed link to bellcrank arm length question Long or Short

[332_RC]

The link that connects the servo horn arm to the bellcrank steering arm is called the fixed length link. My question is, most all I've seen are short, fixed links. I've seen some that are adjustable. On my build, I mounted the servo with the horn to the rear of the chassis. This is a Talion chassis, & they mount longways. Stock, they are mounted to the front with a short link. I made a custom adjustable long link. I've read contradicting views that longer is less precise & longer is more precise. Anyone got any ideas or input? I'm close to finishing this project & I'm hoping this is a good setup.

My Talion chassis with the servo mounted like so.

I made this long link. Is longer better? Or will it affect throw & cause poor steering or make it more controlled?

It will be 90° to the servo horn arm & flat with the chassis plane when installed.

This is how my Kraton is setup. Servo the other way & short adjustable link.

This is a stock Talion with the servo longways, horn towards the front & short fixed link.

I asked this on another thread but didn't want to derail it & get everyone's ideas.

 

[jimdavis577]

i think in my opinion, the only deviation or change in the way it works is if you installed a longer servo horn. The further away from the shaft of the servo you get the further the tip of the horn will travel through the servos sweep. Thus the longer horn will give it "more throw" as a shorter horn will not travel as far therefore limiting the length of throw. The length of the connecting link i don't see or think it would make any difference, same as the orientation of the servo, horn in front or back , but i could be wrong

 

[Littlemotor]

See my post I made over at the other spot lol.. well hell-I’ll just be a lazy-

-and copy/paste it over here..

The way I’ve been doing it, and was learnt was that while yes; there can be deflection (as NOTHING on this planet is 100% efficient), but so long as your centerline of the mechanical master, and slave are the same, and the distance from that centerline to the mechanical connection; IE-the servo saver hole position, and the servo HORN hole position) are equidistant from said centerline, then as long as the servo HORN is properly “clocked” to be parallel with the servo ARM, then your arc will be the same, and therefor correct.

I should mention that I cannot STAND how Arrma does this. They do it in order to utilize a single non-adjustable steering link across the board to work with literally ALL of their vehicles (more or less-within the same scale platforms at any rate).

The problem with this is that when you cannot achieve what @WickedFog, @jimdavis577 , and myself are talking about mechanically due to servo spline TEETH, or that there’s a minute difference in those measurements, your vehicle will ALWAYS have more throw to one side than the other; mechanically speaking. It’s a piss-poor way of doing it imho. If I were doing your caliber build on an Arrma, I’d have done the exact same thing you are doing. Much better way of setting it up IMO.

*edited because Apple autocorrect SUCKS BALLS.

 

[332_RC]

Gotcha-
Thanks & that's been an issue building my Arrma rigs. All my 6s bashers have adjustable links & custom end points to achieve proper L & R full throw steering. I even clearance the bulkheads for more. Right to the very point the knuckles are in the pillow ball spheres & rod, still no bind or hyperextension of the steering turnbuckles.

 

[332_RC]

I've played with the servo arm hole position & noticed a difference on my SWB Noto but not the LWB Kraton. Further out on the Notorious & adjustable link set that thing on rails. Didn't notice any change in the K6.

 

[Littlemotor]

I've played with the servo arm hole position & noticed a difference on my SWB Noto but not the LWB Kraton. Further out on the Notorious & adjustable link set that thing on rails. Didn't notice any change in the K6.

That’s just mechanical advantage. You can use that to tame down, or make it more of a “nervous” or “twitchy” drive.

 

[Littlemotor]

This is what you want in order to have the same throw left to right at the wheels, mechanically.

 

[Littlemotor]

The above exhibits ever so slight NEGATIVE mechanical advantage, or mechanical “disadvantage”, and will calm the drive down a bit. With a longer servo arm, you would have neutral, or advantage; mechanically. (As long as my last 3 brain cells are functioning correctly )

 

[332_RC]

This is what you want in order to have the same throw left to right at the wheels, mechanically.

View attachment 215071

Technical pics- I love em. I will definitely have them parallel to one another. I've worked it out, I believe, just right with the link I made. The arm will be 90° to the chassis & the bellcrank arm also. I'll connect the link in the center hole on the servo arm & the link will be parallel to the chassis. OCD is real but it's geometry!

 

[Littlemotor]

See post #6. I don’t know wtf language my autocorrect was speaking when it hijacked my words for no reason, but I remedied it..

 

[Littlemotor]

Technical pics- I love em. I will definitely have them parallel to one another. I've worked it out, I believe, just right with the link I made. The arm will be 90° to the chassis & the bellcrank arm also. I'll connect the link in the center hole on the servo arm & the link will be parallel to the chassis. OCD is real but it's geometry!

Best way to do it is to locate absolute center with your Ackerman plate beneath your steering top plate. Pay no attention to your wheels, as your steering rods/links will need to be adjusted AFTER.

Then where ever your servo saver arm is positioned, is where you determine your servo horn position. -even if the splines F you up, you can just rotate them with the horn, and take care of that in your trim, and endpoints AFTER all of your mechanical stuff is correct.

THEN get your measurement for your steering link that ties the horn to the servo saver arm, and install.

THEN set your toe, and make sure your steering rods/links are the same length by measuring the amount of exposed turnbuckle between your rod ends.

Vehicle should be at full weight, on a level surface ON the tires. Battery should be in the vehicle for this, but body isn’t necessary unless it’s got 19.428lbs of shoe goo, and drywall tape under it lol..

 

[332_RC]

Best way to do it is to locate absolute center with your Ackerman plate beneath your steering top plate. Pay no attention to your wheels, as your steering rods/links will need to be adjusted AFTER.

Then where ever your servo saver arm is positioned, is where you determine your servo horn position. -even if the splines F you up, you can just rotate them with the horn, and take care of that in your trim, and endpoints AFTER all of your mechanical stuff is correct.

THEN get your measurement for your steering link that ties the horn to the servo saver arm, and install.

THEN set your toe, and make sure your steering rods/links are the same length by measuring the amount of exposed turnbuckle between your rod ends.

Vehicle should be at full weight, on a level surface ON the tires. Battery should be in the vehicle for this, but body isn’t necessary unless it’s got 19.428lbs of shoe goo, and drywall tape under it lol..

I actually got that metric in my mind for that process. Perfect. And I have old school screw type machinist inside mechanical calipers to measure the inside of the turnbuckle rod ends, then take a digital caliper & measure over that. Get them the same. This Talion is gonna be a race style basher no doubt.

 

[Lumikko]

I cannot STAND how Arrma does this. They do it in order to utilize a single non-adjustable steering link across the board to work with literally ALL of their vehicles (more or less-within the same scale platforms at any rate).

The problem with this is that when you cannot achieve what @WickedFog, @jimdavis577 , and myself are talking about mechanically due to servo spline count, or that there’s a minute difference in those measurements, your vehicle will ALWAYS have more throw to one side than the other;

I don’t think the servo spline count is a factor in this equation. You can always choose the closest spline position and fine-tune it with the sub trim. Steering geometry won’t be affected.

What you do need is an adjustable servo link so that the arms on the servo and bell crank can be adjusted to be parallel. Should the arms happen to be of the same length, then the link length (center-to-center) will be the same as the distance between the servo axle and bellcrank spindle.

 

[RustyUs]

You like using the outer most hole on the horn? What is the three distances (center to center) of the holes on that servo horn?

Just curious I am.

 

[332_RC]

You like using the outer most hole on the horn? What is the three distances (center to center) of the holes on that servo horn?
View attachment 215204
Just curious I am.
View attachment 215205

I am going to use the center one.

 

[332_RC]

I don’t think the servo spline count is a factor in this equation. You can always choose the closest spline position and fine-tune it with the sub trim. Steering geometry won’t be affected.

What you do need is an adjustable servo link so that the arms on the servo and bell crank can be adjusted to be parallel. Should the arms happen to be of the same length, then the link length (center-to-center) will be the same as the distance between the servo axle and bellcrank spindle.

It's adjustable, the one I made. I wasn't concerned with the spline count. Just the effect of the geometry or effort of the system when using a longer link.

 

[332_RC]

Luckily my transmitter has sub-trim if needed.

 

[Littlemotor]

I don’t think the servo spline count is a factor in this equation. You can always choose the closest spline position and fine-tune it with the sub trim. Steering geometry won’t be affected.

What you do need is an adjustable servo link so that the arms on the servo and bell crank can be adjusted to be parallel. Should the arms happen to be of the same length, then the link length (center-to-center) will be the same as the distance between the servo axle and bellcrank spindle.

I literally said all of this to a tee sir…

 

[RustyUs]

I don’t think the servo spline count is a factor in this equation. You can always choose the closest spline position and fine-tune it with the sub trim. Steering geometry won’t be affected.

What you do need is an adjustable servo link so that the arms on the servo and bell crank can be adjusted to be parallel. Should the arms happen to be of the same length, then the link length (center-to-center) will be the same as the distance between the servo axle and bellcrank spindle.

For the steering setup OCD folks, why I only buy/recommend radios with that must-have feature.

 

[332_RC]

You like using the outer most hole on the horn? What is the three distances (center to center) of the holes on that servo horn?

I'll measure them all 3 in just a bit. I just got in from grocery store. Gotta eat! I got you!