Yamaha Truly Unlimited UTV - Rustfish Racing 2921

kornfed

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May 13, 2015
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As some of you know, the Rustfish Racing team has been looking at the options around a truly unlimited UTV. No compromises...! Our plan is to use the best fabrication techniques and racing technology we can assemble to make the ultimate 1 liter off-road race car.

We started with a plan to create a car that would take the best 1 liter powertrain on the market and then build a purpose built race car for BITD and eventually SCORE. We all knew that we were not going to have a belt driven power plant and we purchased our donor car. The Yamaha YXZ.

We took some of the things we learned with the original Rustfish 1992, the collective brain power of group of racers that have over 30 titles, sat down with Jerry Penhall and started to design the ultimate UTV. Kent Pfeiffer, Craig Gregory and Jerry Penhall started with the baseline Penhall Class 1/10 chassis to create a cab and rails that was functional and safe. From there, it was all about powertrain layout and designing the suspension. The front suspension is completely CAD designed to give travel and stability to the car. It came out insane. The rear is a combination of several elements. Some UTV parts, some completely new ideas/parts.

We are using Dual KING shocks on all corners including external bi-passes, custom hubs, spindles, CVs, Axles, drive lines, alternator and arms. At this phase we are going to focus on the suspension, durability and drivability for the UTV World Championships. Once we have this sorted, we are going to start working on more power. First things first.

Below are some of the pictures of the build. We have made some good progress since this phase and will send out other photos as we progress. IMG_0850.jpg IMG_0859.jpg IMG_0865.jpg IMG_8981.jpg IMG_0860.jpg IMG_9385.jpg IMG_0866.jpg
 

kmb760

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Mar 28, 2013
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Awesome to see a build like this happen. I hope it's everything you guys wanted and more. Maybe it'll push the manufactures to build a more custom race vehicle.
 
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badassmav

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Jun 11, 2013
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Jamul
This looks like the beginning of an epic thread. It's refreshing to see you exposing your build to the extent that you are. There is so much that forum members, and fellow racers alike can learn, when following such a comprehensive build thread as this appears to be.
Will you be entertaining technical inquiries along the way? I know I already have a mouth full of questions based on the first few pics. It would be awesome if this thread would not only chronicle the build, but also the teething pains and evolution of the chassis throughout the first season. Win, break, or crash, there is no such thing as bad publicity! It is unfortunate that there aren't similar builds in your class to compare to, and race against. Once dialed in, your "UTE" may very well be the first one to consistently challenge class 10 times at any given event.
Hoorah, it's AFT.
Now that I've got you all buttered up, on with the show!
 
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kornfed

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Awesome to see a build like this happen. I hope it's everything you guys wanted and more. Maybe it'll push the manufactures to build a more custom race vehicle.
Agreed. The UTV platform is great but it is fragile. We want to show what they could be and perhaps get the manufacturers attention.


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kornfed

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This looks like the beginning of an epic thread. It's refreshing to see you exposing your build to the extent that you are. There is so much that forum members, and fellow racers alike can learn, when following such a comprehensive build thread as this appears to be.
Will you be entertaining technical inquiries along the way? I know I already have a mouth full of questions based on the first few pics. It would be awesome if this thread would not only chronicle the build, but also the teething pains and evolution of the chassis throughout the first season. Win, break, or crash, there is no such thing as bad publicity! It is unfortunate that there aren't similar builds in your class to compare to, and race against. Once dialed in, your "UTE" may very well be the first one to consistently challenge class 10 times at any given event.
Hoorah, it's AFT.
Now that I've got you all buttered up, on with the show!
Nice. We will for sure share the pains and how we are building it. The processes involved are tried and true for the C10 and C1 world. The tricky part is mating this platform to a UTV powertrain and weight. The front end is pretty simple. Think 10 car with a front diff. Little tricky to get the clearances, but in CAD it was pretty straight forward. We aren't going crazy on power yet so we should be fine with our hardened CVs and axles.

The rear is the tricky part. How do you keep from granading the rear diff...? Where do you make the failure point? There is some secret sauce in that area that Jerry and Kent are working on now. It is close. Once we have it nailed, we will showcase it. It is pretty trick and it tracks perfectly through the stroke. But will the custom combos and CVs hold up, stay in, not bind, not break and and and and. This is the area that we need to nail.

Hit me with questions and I will get with Kent and Jerry to get the answers. Might take a day or two, but we will get back to you on it.

Also if you see something, say something.. We are looking for input. Bring it on...! :)


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tatum

Hans Solo - 2009 UTV Baja 500 & 1000 Winner - UTVU
Feb 10, 2009
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I have a couple of questions. Are the trailing arm pivot points going to allow the arms to "scrub" so you dont have to run dual plunging cv's? Also how much deliberation over one or two shocks per wheel.

BTW thanks for doing the build thread as I agree with everything Reid said.
 

kornfed

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I have a couple of questions. Are the trailing arm pivot points going to allow the arms to "scrub" so you dont have to run dual plunging cv's? Also how much deliberation over one or two shocks per wheel.

BTW thanks for doing the build thread as I agree with everything Reid said.
We are going double plunging to keep the track consistent. It stays pretty neutral camber top to bottom. Much less than the normal UTV trailing arms.

The two shock layout was always in the plan. We think this car will be really fast, like 10 car fast in phase 2, so we want the fine tuning/multi stage dampening and heat advantages of the external bypass with reservoirs. Weight is the disadvantage but we really want to have the flexibility when we start getting more speed.


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badassmav

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Jun 11, 2013
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Jamul
Thanks for the invitation. Ok, so here it comes:
I do have a few observations on the dynamics of running a semi trailing arm suspension in the rear. Assuming there are no toe links to help maintain the forward direction of the rear tires throughout the travel, wont there be excessive bump steering? Judging by the skew of the pivot axis, and an approximate arm pivot length of 42", I'm guessing maybe 1/4"-3/8" toe change throughout 20" of wheel travel (a good thing that comes from this is that the tires will toe inwards instead of outwards as the suspension bumps, which adds some desired stability if kept under 1/8" total inward bump). Also, because of the pivot motion/direction of the (semi) trailing arm, the wheelbase will grow/shrink up to 2" (again, based on a trailing arm pivot length of 42") throughout the full motion of travel, introducing a compound working angle on the cv joints due to longitudinal displacement of the stub axle. When I was building UTE's, 31 degrees deflection in one plane is about what our modified cv's could reliably handle, with stock horsepower being just above 100 bhp or so.
Also:
Where the rear wheel bearing hub plates bolt onto the trailing arm, it looks like the thickness of the plate and gussets that make up the "business" end of the trailing arms is no more than .160" thick. Although differently loaded, my experience on a Polaris RZR XP1000 "trailing arm" shows that due to the minimal amount of metal surrounding the holes in the hub bearing plate welded onto the end of the arm, a plate thickness of 3/8" was necessary to avoid fatiguing, and ultimately failure of interface between the bearing plate and the end of the arm.
So, I guess in a nutshell, I'm concerned about the rear cv joint /axle integrity, strength of the interface between the rear wheel bearing hub and the trailing arm, and the ass end wandering around as the rear suspension moves throughout its full range of motion.
Just 2 more questions. When mounting the front a-arms, will you be introducing any "anti-dive" into the front suspension, and are you building positive ackermann into the steering geometry? Thanks, and please don't take my inquiries as a personal attack on your build. It's all about the learning, brother. Anyhway, I'm sure I will be corrected more than once during our correspondence(s). Or, is that "correspondii" Haha!
 
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///Airdam Clutches

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Nov 14, 2014
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it appears with a longer upper arm, the unequal arm should camber in during full droop but depending on the spindle would likely be on a level plane at ride height and bump. obviously ackerman and dive come into how the arms and positioned and their adjustability and with heims on both upper and lowers in front and rear locations with misalignment spacers one would assume that he should be able to get all the tunability he wants correct?



edit : just looked at pix... the front lowers are solid mounted.
 

kornfed

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May 13, 2015
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it appears with a longer upper arm, the unequal arm should camber in during full droop but depending on the spindle would likely be on a level plane at ride height and bump. obviously ackerman and dive come into how the arms and positioned and their adjustability and with heims on both upper and lowers in front and rear locations with misalignment spacers one would assume that he should be able to get all the tunability he wants correct?



edit : just looked at pix... the front lowers are solid mounted.
Yes solid lowers with spindle handling the level with oversized Uni balls for the front.


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kornfed

Active Member
May 13, 2015
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Thanks for the invitation. Ok, so here it comes:
I do have a few observations on the dynamics of running a semi trailing arm suspension in the rear. Assuming there are no toe links to help maintain the forward direction of the rear tires throughout the travel, wont there be excessive bump steering? Judging by the skew of the pivot axis, and an approximate arm pivot length of 42", I'm guessing maybe 1/4"-3/8" toe change throughout 20" of wheel travel (a good thing that comes from this is that the tires will toe inwards instead of outwards as the suspension bumps, which adds some desired stability if kept under 1/8" total inward bump). Also, because of the pivot motion/direction of the (semi) trailing arm, the wheelbase will grow/shrink up to 2" (again, based on a trailing arm pivot length of 42") throughout the full motion of travel, introducing a compound working angle on the cv joints due to longitudinal displacement of the stub axle. When I was building UTE's, 31 degrees deflection in one plane is about what our modified cv's could reliably handle, with stock horsepower being just above 100 bhp or so.
Also:
Where the rear wheel bearing hub plates bolt onto the trailing arm, it looks like the thickness of the plate and gussets that make up the "business" end of the trailing arms is no more than .160" thick. Although differently loaded, my experience on a Polaris RZR XP1000 "trailing arm" shows that due to the minimal amount of metal surrounding the holes in the hub bearing plate welded onto the end of the arm, a plate thickness of 3/8" was necessary to avoid fatiguing, and ultimately failure of interface between the bearing plate and the end of the arm.
So, I guess in a nutshell, I'm concerned about the rear cv joint /axle integrity, strength of the interface between the rear wheel bearing hub and the trailing arm, and the ass end wandering around as the rear suspension moves throughout its full range of motion.
Just 2 more questions. When mounting the front a-arms, will you be introducing any "anti-dive" into the front suspension, and are you building positive ackermann into the steering geometry? Thanks, and please don't take my inquiries as a personal attack on your build. It's all about the learning, brother. Anyhway, I'm sure I will be corrected more than once during our correspondence(s). Or, is that "correspondii" Haha!
Awesome. Ok you are obviously way beyond my level of understanding, let me answer what I can and get with Kent and Jerry later today on the rest...

On your first point about bump steer, the guys have a plan to deal with this directly. There was a lot of talk about this. I will get you the details on how this is handled.

Yes the wheel base adjusts through the stroke and the angle is below 31. I think way below, but will check.

On the rear bearing hub plates, yes they are .160 and have an external plate on the arms. This area is our major concern. It has custom dual plunging CVs that allow the stroke to stay within tolerance and we are adding more gusseting at the plate and arm. But yes this is the section that we worry about the most. I will bring this up with the guys and get back to you.

On the anti dive, yes this was considered in the design. Let me get back to you on the Ackerman.

Great questions...




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kornfed

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Ok talked with Kent, who talked to Will Ritzman(the ninja fabricator), the steering is rear based and accounts for Ackerman and anti bump steer and anti dive. He said it is spot on. He will send me some pictures later today.

On another note, the design in the front actually can use the stock spindle. I though we decided to go with the custom ones, but Will found a way to make the stock ones work. Hopefully that will work so others can use this design.

I am a bit over my skis now so I am going to talk to Will today and get additional details. So look for a post tonight with pictures and a description from the man himself...


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kornfed

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Looking forward to all the pictures you post on this thread! I got another question. What's up with the paint on the lower part of the frame?
Kind of a funny story so we thought that a proper race car is bare metal. Hence the name Rustfish for our 1992 car. Then we realized that after every testing day or every race we had to take the car all the way down and treat it. This got really old. So we decided to paint the lower sections to avoid having to take the car all the way down every time it saw dirt. So we compromised. ;-)


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jajl22

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Jun 5, 2015
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Looks like this is going to be a good thread with some interesting conversations...going to have to stick around a bit...i will probably learn something...always enjoy when i get to learn the easy way!
 

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