So, how do I start. Over the last year or so, since I finished the first iteration of RaceBro, I’ve been taking racing fairly seriously, been constantly upgrading my setup, trying to make it out to as many events as I could, and practice a lot. I’ve improved my riding skills heaps along the way, with just recently making it to the pro finals at esk8con on the most recent iteration of RaceBoi:
This journey of racing and building is well documented in the thread RaceBoi, which has by now grown itself to over 600 posts. That thread has also shown my lack of self control skills for building esk8s - I’m always striving for what I consider at the time the best thing that I can possibly have. And this brings us to the name of the board: PROJECT: ENDGAME. Firstly, this is so far, just a project. That has been going on for some time now and will continue to unfold over the rest of this year. Secondly, endgame. I’m hoping that by getting ahead of where every other setup is now, I can finally make a setup, that I just can’t upgrade anymore, because there’s absolutely nothing that can be upgraded on it, everything is top notch, even by my ever-evolving standards.
Since about last December, I’ve been working on a new project that’s much larger in scope which I’m hoping brings real innovation to the esk8 racing scene. The main idea with this project, is to take all the tire development that the kart racing scene has received, and fit them on an esk8. But you can’t just fit 10x4.5" tires on any esk8 and expect it to feel good, you’ll be standing way too high off the ground. You need a chassis designed from the ground up to make this happen in a way that’ll feel good on the track. Before we dive into it too deep, be aware, this WILL be a long read.
Trucks
First a little bit about trucks. I’ve tried all kinds of trucks over the years, and Dualities by @Titoxd1000 are the best ones that I’ve ridden on so far, hands down. They achieve a precise zero slop feel, they take any regular skate bushings (including WFB), they are easy to work on and can change bushing setups within minutes. So Dualities it is. But what width? Well, the kart wheels are so wide and so offset, that I want to minimize hanger width, so I went with 240mm for now. And tried to design all clearances around that.
Wheels
Now, lets talk about the wheels, as the whole project is centered around fitting them. Full size racing kart front wheels are most commonly 10x4.5-5, so that’s the target. It’s as small as the best kart wheels can get, unfortunately going any smaller would mean compromises in tire compound. Chronologically the exact tire choices were only decided later on, so for now lets talk about how to fit the rims.
The custom MBS pattern BRP hub development from @Ac53n has given me a good start with a wheel hub - the original plan was a chassis that can swap between BRPs and kart wheels in a fairly short amount of time, so I went for these. If you stack these fully with bearings, you end up with an insanely wide bearing spacing, and they are adaptable to many setups. More about my exact bearing setup a little later, but for now the important part is that the sheer size of these wheels require me to run a very wide bearing spacing, which these do support. Afterall, they were designed to run on 17-20mm shafts, not 12mm.
At around the same time these were being designed, I found a set of kart rims which have a fairly rare 55mm centering bore, instead of the much more common 40mm centering bore of 5" rims. This is important, because this is what we needed to be able to have the BRP pattern and the kart rim pattern on one part. Meet the Righetti Ridolfi KC70AL125-67. 5" wide, 5" diameter, 55mm centering, 3x67mm M8 bolt pattern.
So, these obviously don’t just bolt together, what’s up with that? Tommy designed up an adapter for me, which gives the rims the least amount of offset possible, so they stay supported as much as possible, while still having a little bit of the bearing left for the wheel spur. Huge thanks again! I’ve got two sets of these machined, hoping to be able to swap between different tires (for example practice and race tires) within a reasonable timeframe. Or for example if I get a flat mid race I don’t want to swap tires on rims between heats, I can swap them with the BRP pattern screws.
In the middle, this can also take bearings for extra support.
So a bit about that bearing spacing now. From hanger to axle nut, this is the plan:
hanger - 1mm speedring - 28x12x12 wide double row angular bearing 3001 - 6001 regular bearing - 22.2mm spacer - 6001 regular bearing - 6001 regular bearing - axle nut. There’s 1mm extra left after the nut for perfect nylock engagement, and the Tito Dualities 68.5mm axle length is pretty much fully stacked with 58mm total bearing spacing.
Another idea that I had just recently, but might require 270 hangers, is to mill a 30mm or 35mm bearing mounting interface for the 22^2 R6 motor mount part which would take an oversized gear bearing, and shift the wheel to the insides a bit, freeing up axle length on the outside of the wheel which could be used for extra bearings for an even wider total bearing spacing (including the spur’s bearing).
Everything was test printed when the tire arrived, and it went all together, signaling that these parts are ready to be ordered from metal.
Tires
Well, I have to talk about these too, even though I am yet to ride them. The main goal of this project was running top notch tires. For now I’ve got two sets of discontinued Bridgestone YPB softs to go through, as I’ve got an 83% off deal on them. These are close to what I’ve wanted to run anyways, but not the final tire choice. Given that my board is not as heavy as a gokart, and that esk8 racing is harder on my body than karting, I decided to go for super soft compounds, as I probably wouldn’t be able to overheat them anyways. The tire that I really want to try later on are Lecont LPM, they are the grippiest tire in karting right now, and they have stiff sidewalls, which I think is what we want in an esk8. Oh and I think this is the perfect place to throw in a size comparison to more normal tires:
Linnpowers (6.5") CST C190 slicks (9x3.5"), kart setup (10x4.5")
These kind of super soft compound tires are specifically made for the higher power karts, this one is for the 50hp KZ category, as they are known to bog down rental engines too much. Another reason for an electronics upgrade.
Also rest assured there will be custom gear drives in this project, but now lets get to the chassis itself, now that we know the constraints that I’m designing around - the wheels and the trucks.
The chassis
Well, a raceboard has to be stiff and rigid so that the inputs by the rider are translated directly to steering. That calls for an all metal chassis. Also I’m not super experienced with welding, but I can weld somewhat. This made me want to avoid the V5 style tubular steel chassis. Let’s come up with something new, what are cars made of? Sheet metal. Let’s see if I can make that work. I can design for the parts to be able to take most of the load without welds already, and then the welds just make sure everything stays in place and add strength - they aren’t as critical in my design as in a V5 or something like that.
The design work for this chassis started months ago already. I set out a couple goals in the beginning: adjustable ride height, by a large range, being able to go down as close to the ground that I can scrape. (Mostly) top mount, with space in the frame for a few components - ESCs, and a small part of the battery. Standing platform length that suits my stance. Then as time went on, I also added the goal of an adjustable standing platform length, which can be used to shorten the total wheelbase by a fairly large amount. This last goal might be scrapped if it turns out not to be strong enough in FEA (finite element analysis). Early stages looked something like this:
Then I realized how I can make those ugly square towers look better:
Then recently I decided to get rid of that ugly pelican while also making the standing platform adjustable length, and making the bellypan capable of taking the makerx G300 ESCs:
That’s where I currently am with the chassis, I want to confirm a few dimensions part fitment wise and get it through FEA, other than that, I think I’m happy with it. Oh and possibly trying to shave off some weight if I can. It’s gonna be HEAVY, enough so that it justifies an electronics upgrade.
Electronics
So, lets talk about electronics. It will start running on my RaceBoi electronics in the beginning, so 2x D100S, 21S4P P42A, 2x 6385, 2x 6395 reachers. Then, I’ve got a cruiser board planned which would need one of the D100S, and then 2x G300s would go in. Roughly at this time, I’d also build a 20S6P battery for this board, 15S6P on top in the middle, 5S6P under. Tabless cells of course. After that the remaining D100S would also be swapped to 2x G300 as funds allow.
Then, it will be time for new motors. But while I still run the reachers, let’s discuss the gear drive I designed up for the reachers.
Gear drives
Well, there were a couple design requirements. First of all, I wanted to be able to make everything cheap on a laser, the wheel spur was cut on a laser too. Secondly, ratio should be able to gear me down to 80 km/h or 50 mph. Thirdly, somewhat enclosed.
I ended up getting a set of clamps from Tito, designing my mounts around those clamps, which is just a lasercut aluminium plate, then designing a 3D printed cover and a spacer that mounts to the side of the gear. The gear itself is lasercut chromoly 4130 from sendcutsend, not as nice as hobbed gears, but it does the job and it’s cheaper. They do appear to have a different sounds profile and maybe even a bit louder compared to the stooge open gears.
There was another design requirement, and that’s quite a strange one: the kart rim needs to run inverted for the proper offset, which makes the valve stem face towards the inside, rather inconvenient. I designed the gears and the mounts so that I have plenty of space to pass a valve extender through the whole assembly, so that I can inflate my tires without having to disassemble the board.
Back to electronics - motor upgrade
So, all the cool guys are moving to inrunners nowadays. I’ve got a couple challenges - I don’t want to move below 20S, so 600ish KV is out of the question. And I also absolutely hate the look of staggered motors like the new stooge setups.
I’ve found these long boi SSS motors, that are nearly as long as the distance between my mounts, so I can print like 20mm spacer or whatever and then it looks like two full length cylinders.
At 330KV this motor is rated for 75V, so what could go wrong if I do 20S. I intend to only charge to maybe 3.8-3.9V or so per cell, so that hundreds of amps of regen won’t cause that much damage to the battery. So close enough to that voltage rating, and not like I’ll ever be riding top speed anyways. Rated for 14kW constant 20kW peak per motor I’ll be able to gear to top speeds I can never reach and still have infinite torque. Probably doing a ratio of 12:1 or somewhere in the neighbourhood of that, requiring the design of a new gear drive, more on that when I actually get to it. Rated for 266A (continuous (I think)). Hoping to be able to set 400-500 phase amps on G300s and never reach it due to not having enough grip with a 60 mph gearing. Hoping to have enough torque to not need to run any power to the front for maxing out total traction, and not need to run any brake to the rear. That would mean complete freedom for tweaking my bias, without having to worry about any power compromise. And hoping to set 400+ battery amps at 20S, and never reach it because I’m not that crazy (yet).
PS: I’ve decided to break this out from the RaceBoi thread, where it doesn’t really fit that well anymore, so it’s not burried under 600 ish posts. I’ll first try to fit the kart wheels on the old chassis just because I’m impatient and can’t wait for the frame to be made, but progress regarding the new chassis will all be here in this thread.
Timeframe: Hoping to be running the wheels in May on my current chassis. Hoping to order the new chassis sometime in May, probably after having done the first ride on the wheels. Hoping to build out the first iteration on the new chassis by mid July. First pair of G300s ideally during the summer, second pair and new battery probably autumn, new gears and motors late autumn/ winter.
I’ll be watching closely
and wanted to throw my experience out there. Best of luck with the build!
