The "KRF" Build

[lukej 319]

As some of you know, I work in motorsport, and I've had the challenge of building a car to a set of regulations many times before. Extracting all of the performance from a rulebook, finding the grey areas, and coming out with something competitive is some of the most interesting work I can imagine. To have found an enthusiast in this hobby who has done the same then, well that's the very best thing!

Before I start with the build, I want to extend my deepest thanks to a member of this forum, someone who represents the best of us and who has demonstrated incredible knowledge, skill and talent to bring this product to market - Kevin Kreft.

There are few people I can point to who have had more impact on my love of this hobby than Marc Reinhard & Atsushi Hara, their battles in the mid 2000's made me fall in love with 1/10 on-road, but Kevin (@wtcc5) outranks them both.

I plan to have a TRF 415MRE and an HPI RS4 Pro 4 Hara Edition in my collection at some point, but they'll be joined in my perfect trio of touring cars by the KRv4.1, the ultimate version of the TT-02 with a few blue touches to make it the "KRF".

Let's get started then, with a large glass of chocolate milk, a clear workspace and a ton of excitement. Thanks Kevin!

Luke

[wtcc5 4900]

I need to screenshot your post and put it in a frame. Thanks for that great compliment! I just hope that the KRv4.1 conversion can fullfill that standard.

[lukej 319]

Things are properly underway now, and the build space is prepped!

I started by following the instructional videos, but deviated from time to time to check fitment of parts I have whilst I wait on those that I don't - HMRC interrupting play there...

And with the pressure relief holes showing under the tub.

From here, I started building up the suspension. Unfortunately I didn't do the cleanest job of grinding the carbon down for the two droop plates, but that's hidden so the perfectionist will have to pretend I didn't do a less than perfect job. Unless you want to file me a pair Kevin? 

I'm going to take the droop plates off again, but I'm using the assembly to check for flatness across the mounting points. At this point, I think I have approximately 0.5mm to remove on one side of the front plate as there's a little twist here.

Driveshafts being built up. @wtcc5 which blade drives and drive cups are you using in the videos?

Here's how I'm leaving it for this evening. A productive-ish night. More parts to order and hopefully I'll be away!

Luke

[Kol__ 3377]

Sounds like an exciting build mate. A bit in the dark about what this KRv4.1 is though and what @wtcc5 Kevin's involvement is, some sort of build created previously?

[lukej 319]

Kevin is the creator of the KRv4.1, a modified TT-02 for a GT class of the RC-Kleinkram series. You’ll have to forgive me if I get some bits of this wrong, but essentially the class rules mandated that you had to use a standard TT-02 bathtub & a few spec electrical components but everything else was free.

@wtcc5’s development and race reports thread gives a detailed insight into how the car came to be, all the trials and tribulations of making it what it is, and a brief foray into the world of Awesomatix style dampers. You can find it here.

The reason this was so impactful to me, is that I went down a rabbit hole on the internet one day and ended up of RCTech reading his build thread. As a new member of the forum, I got a frosty reception from some quarters, but Kevin was always polite and respectful, & when I saw that I could buy his upgrade parts kit I took the chance. He’s even supplied a carbon prop shaft and spool to me which aren’t parts of the regular kit.

Luke

[lukej 319]

A bit more progress today, though I'm rapidly running out of sub assemblies to build with the RC-Kleinkram delivery being delayed at customs. I think I'll reassess the screws I'm using too as the aluminium ones are getting chewed up a touch.

Anyway, I started off by modifying the front bumper mount, because the 3D print needs a little sanding to fit right and I decided that this would be better achieved before the sun warmed up my flat too much. Dremel and vernier callipers in hand, I set about reducing the post height to 9mm.

I've got two kinds of sanding wheels available to me, 60 grit and 240 grit, and I also laid a piece of 600 grit on a flat surface to level the posts and finish them once I'd made all of the progress I was comfortable with power tools. As a precaution, and in order to ensure I wasn't sanding unevenly, I used a sharpie to recolour the post tops and would then inspect where it was worn away by the Dremel.

Marking my posts to ensure a flat surface.

The results of a single pass. For reference at 5000rpm with a 240 grit wheel, the Dremel removes about 0.1mm/pass, switching to 60 grit and 10,000rpm removes about 0.35mm per pass.

When the heights of the posts were set to the required 9mm (I got them to 8.98mm, so a little under), I ran a 2.8mm drill through the inside of the post to clear the molten plastic and any swarf, and I trimmed to outside edge of the posts with a hobby knife before colouring the post tops in again.

Finally, when fitting the bumper I slid a 0.75mm shim below the carbon piece to level the bumper relative to the ARM mount it rests on. The whole assembly is then screwed together with 3x14mm countersunk titanium machine screws. These will shortly be replaced by 3x16mm versions of the same to ensure the thread bites into the nylon insert of the 51255 3mm thin aluminium lock nuts.

And here's how it sits as I break for lunch.

Luke

[wtcc5 4900]

Great work so far!

 I use Tamiya TRF420 spool steel outdrives and the blades (54934) for them.

[lukej 319]

3 hours ago, wtcc5 said:

Great work so far!

 I use Tamiya TRF420 spool steel outdrives and the blades (54934) for them.

They all come in one set, so I'll get them ordered up. Now to swap the rear diff out and build a spool!

Luke

[lukej 319]

So I've gotten as far as I can I think now, at least until my RCK delivery arrives.

It was shortly after this image that the video manual showed me an error in by build process. No idea why I flipped the diff, but that'll have to be undone when I take it the carbon top plate out to add the bearing shims. I might even swap to the 3Racing diff Kevin uses at the same time.

The moment the penny dropped.

This afternoon/evening's building started with the rear droop plate sub-assembly, which ultimately didn't progress very far because I don't have the OfficinaRC ball studs yet. Those were ordered this evening from MonacoRC, and the required pivot balls were sourced via eBay at the same time.

Baby steps.

The rear driveshaft build followed. I've ordered 54934 now too so that will sort me out for the TRF 420 drive cups and blade drives at both ends of the car.

A TT-02 oil diff was added in. @wtcc5 is the 3Racing diff you have necessary to accommodate the TRF420 drive cups?

As I built up the suspension mounts for the front and rear of the chassis, I had to compromise on perfection. Kevin's instructions state that the front set screws should be installed to leave 4mm out, and the rears with 3mm showing, but I can only get so close...

Finally, using my spec racer for reference, I pulled the kit diff cover off and snapped the head straight off an aluminium screw in the process. I'll extract that tomorrow!

Luke

[wtcc5 4900]

The TRF420 spool outdrives are for the spool in front.

The 3Racing diff comes with strong outdrives and can be used with blades. But if you have the TT02 oil filled gear diff already, just use it. At least for the first runs I wouldn’t buy a second one. I just went for the 3racing diff, because I had no other alternative in 2018.

[Nicadraus 6201]

Nice project! Looking forward to this KRF car. I've followed Kevin's builds and have seen the progress and updates. Fantastic engineering and design of parts.

As you mentioned HPI Pro4, I loved that car. I had one in 2005-2007. It started as the 2005 version and modified it fully to every hop-up available that time. I still wish I kept it. 

[lukej 319]

3 hours ago, Nicadraus said:

Nice project! Looking forward to this KRF car. I've followed Kevin's builds and have seen the progress and updates. Fantastic engineering and design of parts.

As you mentioned HPI Pro4, I loved that car. I had one in 2005-2007. It started as the 2005 version and modified it fully to every hop-up available that time. I still wish I kept it. 

That’s a work of art! Might pick your brains on building one after the KRF is finished!

Luke

[lukej 319]

Small update to bring you on this one, but after some conversations with Kevin I've decided to ignore the build rules and put more blue bits on (sorry Kevin!).

I was having some issues with the Awesomatix ball nuts binding in the cups, and the OfficinaRC items are available to me through MonacoRC, but not without a hefty shipping bill so I've raided the spares tray and will do my own "KRF" interpretation here because Tamiya would add more blue right?

Despite working to free the Awesomatix parts up, I had some problematic resistance in the suspension arms, and have opted for Tamiya's finest blue 5x5mm and 5x8mm ball studs & their 5x5mm ball nuts. These are 0.1mm smaller at the ball than the specified parts, and the ball nuts 0.4mm taller due to a thicker hex but using the same parts top and bottom should keep the suspension geometry the same whilst lowering the COG by 0.4mm overall - a competitive advantage this is not, but I'll claim it regardless.

Some discreet but very necessary blue components I'm sure you'll agree.

I also took the opportunity to add an additional 6x0.1mm shim to the underside of the ball cap because I felt some play in the arm once everything was positioned, and we don't want that slop in the car if it's to drive predictably.

Once fitted, you will not see the extra shim, but the small amount of play I did have between the ball caps and suspension arms is now completely removed.

Luke

[lukej 319]

A few extra bits arrived today, now to work out which hardware I'm missing and then I can finish the rolling chassis!

Luke

[wtcc5 4900]

@lukej: Regarding purchasing more sets, please check your mailbox 

[lukej 319]

11 hours ago, wtcc5 said:

@lukej: Regarding purchasing more sets, please check your mailbox 

Yes, I need to pay you 😊

Edit: Sent