Limitless How to reduce caster to improve steering?

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kaladeth

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Arrma RC's
  1. BigRock 4x4
  2. Limitless
Goal is to reduce (front) caster from stock 20 degrees, to 16 degrees, to improve steering on the track.

@Overkill

Some options:

1. Trim the stock arms on the front hinge pin area by about 5 mm, so the arms (and pillow ball) can be moved forward 5 mm.

AR330215 stock

1709323043731.png


AR330215 trimmed

IMG_5824.jpeg


2. Get a longer suspension mount that moves the rear hinge pin location outwards by about 2 mm on each side. This will swing the pillow ball about 5 mm forward.

Set to 61 mm eye-to-eye:
https://www.thingiverse.com/thing:6532459

AR330379 Font-Rear Suspension Hanger is second from the top:

1709323025900.png


Extended

IMG_5826.jpeg
IMG_5827.jpeg


3. Design and 3D print a custom front suspension arm that has the same hinge pin geometry, but sweeps the pillow ball forward by 5 mm.

One of the guys at the track did this, will check in with him for more info.

Are there any other options out there?
 
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Typhon TLR towers, ackerman, and hinge pin/suspension blocks will provide unlimited adjustments. Just cut the tower down and create the geometry hole for the shock mount.
 
I had to dial it down from 8 mm to 4 mm because going too wide interferes with the steering bellcrank. I got around 3-4 degrees less caster (not much). Was able to take the car out for a test run, using the same old tires as before. The steering feels better but hard to see if it has an impact on the track - will have to see on the next practice day.

Link to the STL for those interested:
https://www.thingiverse.com/thing:6532459

@CosmoM3 @Garcbomber - I will certainly read up on it (ackerman). Any quick pointers for me?
 
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@CosmoM3 - I will certainly read up on it. Any quick pointers for me?
If you need more steering, you could go down a hole (or two, preference really) on your ackerman bar (the silver bar where your steering tie rods are connect to). That's what they're for: lower holes = the inner wheel of the car will turn more during cornering.
 
Got it thank you! I put in a beefier steering rack. Will try the different holes. Right now it is setup connected to the “stock” position which on the below photo will be the lowest of the three.

IMG_0760.webp
 
Is it possible to increase steering response further by moving the top shock mount to the outer hole to make the shock more upright?
Negative on the shock angle (results in negligible change in spring rate/rebound), but if you replace those brass/bronze bushings with bearings that will most certainly help. IIRC they're 6x10x3mm
 
i feel like the onroad cars have so much caster for nothing. at full lock you only have the edge of the tire touching the ground. causes premature wear and funky steering like understeer. i printed the part in petg and see how it drives before i change the fluids
 
So I get about 1 breakage a month on the modified front-rear suspension hanger printed in PLA+. Hopefully with less crashes, that number improves.

@Surchaufeur how is the PETG printed one holding up?

I am giving Option 3 a shot. Black is the original Front Upper Suspension Arm. Red is the modified one, shifting the pillow ball mount forward by 5 mm. I suspect the failure mode for this will be the pillow ball mount area; will likely need to reinforce that area, or print in Nylon.

1718995822176.webp
 
M6 helical/threaded insert (y)

I've had them pull out from bad crashes with alloy hubs, instead of trashing the arm it's usable again and even stronger.
 
So I get about 1 breakage a month on the modified front-rear suspension hanger printed in PLA+. Hopefully with less crashes, that number improves.

@Surchaufeur how is the PETG printed one holding up?

I am giving Option 3 a shot. Black is the original Front Upper Suspension Arm. Red is the modified one, shifting the pillow ball mount forward by 5 mm. I suspect the failure mode for this will be the pillow ball mount area; will likely need to reinforce that area, or print in Nylon.

View attachment 374753
I tested it 2 times with my tpu tires have to say it drives very controllably. Is it the caster block or not i cant tell but its a lot harder to make the car spin on itself even if i try. Ran it with the normal tires once and it drove well also. Couldnt get the ussual 360 then drift that i could do before with the factory caster block. To be sure i will need to put the stock back on and run it. I was running 30k front and 50k rear but i haven't done any maintenance in a year, the front and rear feel to be the same thickness now. I was able to go full throttle on a straight at 75% with the tpu tires without losing any control.
 
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I experimented with this last summer, but gave up and went back to stock. I didnt report anything, but maybe I'll revisit.
I printed modified front caster arms and got a TLR ackerman bar to compensate.

I had the hubs vertical with the tires flat on the ground, but the biggest problem was the shafts would interfere with the shocks. I made another print with less extreme arms, but the caster was still lifting the tires. So I just went back to stock.

0805231513.webp


0804232246_HDR.webp


0805231538.webp
 
If I were going to pursue an avenue to reduce caster I would probably lean more toward the complete elimination of the pivot/pillow balls and utilize an existing C-hub with good bearing surfaces and redesigned (printed) upper and lower arms instead of just trying to “twist” the existing configuration to get better caster numbers in a very imperfect system.
Arrma should have done this already for the Limitless, and should certainly have done it for the 1/8 GT road race car that unfortunately doesn’t exist yet.
Just spitballing…
 
If I were going to pursue an avenue to reduce caster I would probably lean more toward the complete elimination of the pivot/pillow balls and utilize an existing C-hub with good bearing surfaces and redesigned (printed) upper and lower arms instead of just trying to “twist” the existing configuration to get better caster numbers in a very imperfect system.
Arrma should have done this already for the Limitless, and should certainly have done it for the 1/8 GT road race car that unfortunately doesn’t exist yet.
Just spitballing…

So, which existing C-Hubs do you have in mind?
 
If I were going to pursue an avenue to reduce caster I would probably lean more toward the complete elimination of the pivot/pillow balls and utilize an existing C-hub with good bearing surfaces and redesigned (printed) upper and lower arms instead of just trying to “twist” the existing configuration to get better caster numbers in a very imperfect system.
Arrma should have done this already for the Limitless, and should certainly have done it for the 1/8 GT road race car that unfortunately doesn’t exist yet.
Just spitballing…
I thought about that too as the ultimate option.

I have a ZD Racing EX07 (1/7 Hoonicorn knockoff) that uses a C Hub set up and it still has the same excessive caster. It and the Arrma are just modified stretched off road buggies, so I guess they didnt "correct" the caster either.

Fortunately ZD Racing has optional adjustable C Hubs, I might order some one day, they're less than $10.

The EX07 front suspension is on thingiverse, if someone had the time and skill to modify it....
 
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