Angry_Arowana

Anybody ??

eunique

iTrader: (3)

I don't know of anyone using aluminum arms...the plastic stocks have been working good and even when they have been modified for KPI

EDIT: except for the custom ones that were fabricated by SKR8PN (Pickled uses those same fabbed a-arms)
(I had ordered some from him a while back but I had not received them yet and he has been MIA - hope he is ok )
they might have been stainless steel - can't remember for sure

Caseymacgyver

I'm very interested as well.

Particularly something aluminum and maybe 3-4 mm narrower at the (3mm) hinge pins so it could be shimmed fore/aft. Don't particularly care about the track width as long as there some meat to cut across and tap into. I'm sure there are a ton of touring/drift cars that fall in that range but I dont know squat WRT other modern touring/drift chassis.

eunique

iTrader: (3)

I had acquired aluminum arms from Broadtech.hk but have not tried to install them. They will fit. and will have a good amount of adjustment on them so you will be able to adjust your wheelbase (length between front and rear wheels?)
http://www.broadtech.hk/eagleshop/sh...px?id=3247V2P2


the arms for the R31 fit also...here
http://www.broadtech.hk/eagleshop/sh...?id=R31-04-LBL
if you are going to go this route..you will need to order the plastic set of R31 arms as well since the outer pins from the D3 won't fit and the aluminum set does not come with the pins...I used the outer pin from the plastic set (used the stock pins for the inner)
http://www.broadtech.hk/eagleshop/sh...?id=R31-01PLP1

Caseymacgyver

The first set might be just the ticket, thanks for the lead. Were you planning to use the pillow ball setup as is? How tight do they feel (quality-wise)?

eunique

iTrader: (3)

I Haven't tried it yet since I am loving the KPI mod set up
QUality looks very good.. im using the R31 aluminum arms on my Sakura Zero S that I have modified with 1.74 CS and those aluminum arms are good quality

Caseymacgyver

IMHO, if your setup can go to 60* and you get chatter at 45*, you have some room for improvement in your setup. I do not purport to be an expert here, but I have no steering angle limiters and have my EPA's set to push/pull maybe a hair or 2 before the shaft hits the rim of the CVD cup. Because I have so much front arm travel, I had to very carefully set my front roll center and bump steer to very closely maintain that CVD angle, even as the wheel moves up and down, and the outdrives stay fixed. This reduces the steering angle by design, but this is necessarily true for all cars running non-zero caster. Unless something has come loose, there is no perceptible chatter on smooth concrete, textured concrete or asphalt, but this was not without considerable effort. I haven't had a chance to try carpet, so I can't speak to that. I still can't post links, but I'll try to get a video at some point.

Chatter is not a fact of life. It's true that all single joint CVD's will exhibit velocity and torque variation while rotating whenever there is an angle between the input and output shafts. This fundamental variation will exploit any slop in the car's steering and suspension linkages, possibly causing chatter. As the steering angle approaches 60*, those variations become quite significant (~43% increase going from 45* to 60*) and take an increasing level of attention to every single interface in the front end to mitigate chatter. Needs lots of rotational stiffness at the hub, no slop throughout the steering, optimization of steering geometry, strong servo and minimal flex throughout. Also, to the point of why I posted sexy pics, a posican setup has several key benefits WRT chatter. More on that below.

Not all single joint CVD's are created equal though. Most of the cup style CVD's are self limiting, meaning the max possible angle is where the shaft hits the cup rim. This is very useful as it precludes shaft locking. Generally, the shaft is able to complete a full revolution while in contact with the cup rim, with only the unavoidable velocity/torque variation evident. Specifically for the D3, the stock CVD's do not allow this. The groove on the dogbone (ball side) is cut at a shallow angle, so it hits the cross pin and straightens the CVD joint by 5* or more, twice per revolution. With the steering angle set anywhere beyond that angle, this "Bump" will cause chatter period. No matter how tight the front linkages are, these will rip it apart. The D3 UWA's do not hit the cross pins and have a larger cup. This allows a wider unobstructed steering angle, but also comes with the fundamental increase in velocity/torque variation.

Double cardan joint CVD's, like the SSK's do not exhibit velocity/torque variation as they rotate. At this time, the available options are not capable of achieving the same steering angles as the available single joint CVD's. That said, the SSK's will compensate for a whole manner of setup sins and eliminate chatter with even the slopiest of front ends.

You're right about the geometry, but who says the geometry can't be changed? If the steering tie rod forms a straight line through the leading wheel's steering axis at lock, the effective moment arm goes to zero. But what happens if you move the steering axis inward, then tilt it in such a way that the steering arm actually moves rearward as the wheel turns in? This is one of the side-benefits of KPI, pushed even further with the offset adapter.

In a normal setup (modest caster, no KPI), the driver will generally increase their negative camber to achieve the biggest contact patch possible on the leading wheel at lock. Basically to try and avoid any positive camber through the steering range. But that caster still wants to turn that wheel over, and the sudden change in traction from a full patch to a thin strip as it goes up on the tread edge at lock, coupled with the velocity/torque variation of the CVD's, will, as you say, amplify any steering/suspension weaknesses into a cyclic chatter.

I posted details and pics of my setup because I personally own a D3 and have first hand experience with its idiosyncrasies. I gained a great deal of insight from the information, ideas and experiences of other D3 owners who have shared on this site. Having built upon some of those ideas, I came here to give credit to those who have shared by showing them what they have inspired, while at the same time hoping to inspire others to take this chassis even further.

Finally to the point and why I thought it was relevant here: KPI is very much related posican, which still seems to be a very misunderstood topic. Although the concept is simple, it was quite difficult to accomplish and I tried many, many different variations of front/rear suspensions and steering linkages before settling in on an approach to optimize. In application, each front wheel behaves more like motorcycle tires, rolling smoothly across the tread as it steers. Even though the left-right contact patches are not identical as it steers, traction is continual and changes are minor and gradual. People tend to think that this wheel motion would be harder on the CVD's, but with extreme caster and KPI, it's actually the opposite. By further rotating the hub rearward on the leading wheel, and rotating the hub forward on the trailing wheel, the CVD 'sees' less of the effective steering angle than without KPI.

For me, a posican setup made high speed drifting on asphalt MUCH easier and more controllable. It wasn't about sexy pictures or angle specs. I couldn't get it to do what I wanted it to do when I built it stock. So, I set out to 'Fix' it and this is where it is at the moment. There's still a lot of things I want to try, so I don't think it will ever be done.

Caseymacgyver

Cool, thanks, I just ordered all 3. They look inexpensive enough and I had to justify the EMS

Thanks again!

danb1974

I feel the the problem is not so much in the torque variation (probably greasing the cvs with the right stuff and not trying to get to full angle helps here), but in the velocity variation. Wheels off, there is no chatter at all because there is almost no weight after the joint. Wheels on, you are hit by the wheel mass - it has enough inertia to induce nasty chatter because at each wheel revolution the cvd has two complete cycles of velocity variation, to which the wheel opposes.

Normally while driving you will likely not notice much chatter because of the ambient noise (also on carpet it dampens the noise).

The chatter is particularly nasty with front spool, wheels fight each other being directly coupled. It's better with ball diff which can absorb some of the vibration and best with one way which allows any wheel to rotate faster without dragging the other one either way.

What I don't get is that almost everyone will tell you there should be no chatter, denying the simple fact that a simple cardan joint induces velocity variations when angled.

OTOH seems problem went noticed when onroad racers started to look at front spools, wanting to keep traction on both wheels while cornering. Therefore we now have those (very few) DCJ or ECJ as they are named. Think I read that latest tamiya ta chassis will come stock with such axles.

Caseymacgyver

That's a fair statement and I completely agree. I also think that there's a wide range of what people consider noticeable or acceptable chatter. I took the "Sexy pics" comment to imply that they didn't have technical relevance because the quest for more steering angle was futile due to the inescapable laws of chatter.

Generally speaking, recommending that someone get wider angle CVD's when they already have unacceptable chatter would be misguided advice. However, specifically on the Sakura D3, the stock CVD's are so poorly designed that they 'bump' the cross pin as they rotate, rather than being properly limited by the CVD cup rim. This bump will exhibit itself as the usual chatter, but it's really a different animal. Velocity/torque variation aside, the shaft physically hits the pin, and one way or another, the CVD angle must be reduced to cross over it. The recommendation to new D3 owners to get the Ultra-Wide Angle (UWA) CVD's is more about eliminating that bump than it is about obtaining more angle. That said, most new owners will immediately dial up their EPA's the minute they put them on, perhaps generating new chatter to replace the old.

pettyeagles

iTrader: (86)

I'm wanting to reduce the CS ratio. Do I need to replace the 13t rear pulley with a larger one? I tried an 18t but the center belt is too short.

Caseymacgyver

FWIW, here's some video to try and show realistic steering performance with extreme caster and KPI on the Sakura D3.

http://youtu.be/WZZY4T0PVHo

I originally mounted my iPhone to the car, but the video was crap due to the chassis vibration.

I ended up just clamping the front end to my work bench with a 5mm spacer under it to hold it in place and simulate the effective wheel loading at my set ride height. Not exactly 'Real World,' but better than floating in the air. The bench surface is probably comparable to lightly textured concrete. The rear wheels are elevated just off the surface.

I tried to run through a range of speeds while steering (Tough with one hand), and you can definitely hear the speed variation on the CVD's ramp up as they get towards lock. There's also a couple of resonances in the wheel that it crosses through. It's interesting to see the front springs ripple too.

Keep an eye on the hub though. At around :30, you can clearly see and hear the CVD load up at low speed and high angle, but the hub remains well damped fore/aft.

This is a new tire that's not broken in yet, but watch the contact patch as it rolls left to right in the first clip at full throttle. Also watch the swing shaft move in the direction to the turning wheel in the 2nd clip.

I also wanted to show the actual wheel contact angle to the ground while at the set ride height. Looks to be 58-ish on the inside wheel.

Exita

Looking good mate !!!
how much caster degrees you think you got there?

pickled

OK about chatter and my D3 the standard units are horrible I went to double cardins and the reduce the chatter to unnoticeable levels but also restrict the angle to about 45* when I decided to KPI this chassis I also had to then deal with the chatter that CVD's produce what I did to start with was buy Square R31 48mm 50* CVD's they worked but were slightly to short at the wheel axle but the dogbones are a great thickness for an UWA CVD so as I used MST knuckles I decided to buy the Wheel axles to fit them and graft them onto the Square 48mm dogbones with this setup I get around 60* with an incredibly low amount of chatter barely noticeable at full lock I would go as far as to say these CVD's have more angle left in them that can't be tapped even with the Alloy steering installed I should also mention the MST knuckles I use are the Front Uprights and the linkage holes are close to the hubs which is why I can get more than 55* out of the alloy steering system

Caseymacgyver

Thanks!

Running around 20* of caster and 12* of KPI there, but it's tough to measure accurately.

I've taken it as high as about 25* caster and 18* KPI and it drove amazingly smooth at higher drift speeds, but understeered too much at low speed for my taste. Perhaps more suited for large tracks where you need to carry a lot of speed. Tire wear on asphalt was another drawback for me, as it would lay the inside wheel over so far that it quickly wore through to the wheel lip, with a ton of meat still left in the middle.