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RWD M-Chassis, 1/12th inspired

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RWD M-Chassis, 1/12th inspired

Old 11-12-2022, 12:28 AM
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h2e
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Default RWD M-Chassis, 1/12th inspired

To brighten up my local track in Dagmersellen (CH) with some self made stuff I decided to give the M-chassis class a go.


First Pan-M concept sketch and space allocation.



The differences to a Tamiya M08 are not overly crazy.

Yes, it's more of a pan car than a touring car. But hey, some mix and match should be allowed!

Basic Idea
- Compete with M-Class guys (much more experienced than me) with a home built chassis
- Keep the same tyres, motor top speed, wheel distances and bodies as all others

But capitalize on the fact that it's a home build

- Chassis should be simpler, lighter and more robust, but adaptable enough to tune to my driving style

The current working plan is:
- Buy Pan car chassis
- Adapt wheelbase, track width and ride height
- make new wheel adapters
- make new bumper and body mounts
- use sweep or rush rubber tyres and M chassis body


​​​​​​Anybody got thoughts or recommendations?
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Last edited by h2e; 11-27-2022 at 10:30 PM.
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Old 11-12-2022, 03:21 AM
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Originally Posted by h2e
To brighten up the local track with some self made stuff I decided to give the M-chassis class a go.


first Pan-M concept sketch and space allocation.


The idea is as follows:
- Buy Pan car chassis
- Adapt wheelbase, track width and ride height
- make new wheel hexes
- make new bumper and body mounts
- use sweep or rush rubber tyres and M chassis body


​​​​​​Anybody got thoughts or recommendations?
I recall kawada and yokomo having similar mchassis sized cars. The kawada is a lot more drivable with the ability to use regular mchassis wheels (12mm hex). The yokomo uses their own wheels and tires.

Have fun!
p.s. lowest possible roll centre is best
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Old 11-12-2022, 03:36 AM
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Originally Posted by foampervert
p.s. lowest possible roll centre is best
Thanks for your remarks. Found the GT500 already. Looking for the Kawada... Thinking about using V-Link or single joint. Especially as I will move the ride height to 5mm (that's what the M guys have to run).
- Single joint has the advantage of simplicity and less play
- v-links give all freedom...

what to choose?
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Old 11-12-2022, 04:04 AM
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What is your overall goal? The MST TCR-M is already pretty close to what you're describing.
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Old 11-13-2022, 01:20 PM
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Originally Posted by gigaplex
What is your overall goal? The MST TCR-M is already pretty close to what you're describing.
The overall goal is to have a less destructible M-chassis compared to what I see on my local track. The Xpress and Tamiya versions keep breaking C-hubs. I want something at least comparably fast to the Xpress or Tamiya Chassis, so I opt for the Pan car design (lighter and lower CG for the chassis). As we have no weight limitations, I hope that the lighter Pan-car style chassis will give me good steering and traction for being a 2wd (which everyone on the track uses). Using a gear diff or spool on the rear axle should give me enough choice in traction vs. steering.
As my body choices are all RWD with the MX-5 (Tamiya, 225mm), Seven20 (Bitty, 201mm) and Porsche 911 (Supastox, 201mm), I will try to have a chassis wheelbase between 200 and 225mm. And as it is an indoor fun thing, I hope that my bump capability will be good enough. For outdoor I will try and see in the future.

As for the TCR-M, I like that chassis for its versatility and corner design that allows for crazy servo, motor or battery positions. I don't particularly like the limited tuneability of that chassis. Or what levers do you think one has for tuning under- and oversteer in corner entry/exit? And to change gearing you need to buy an alu motor mount? What about the outdrives? They don't have blades or ball bearings, so wear will be worse after a few hits?
For the Pan-car chassis I see caster (initial steering, exit steering), pod damping (reaction in chicane), droop (off power behaviour), gear diff oil or spool. I see super durability for impacts, and virtually no drivetrain wear (if I protect the rear axle from impacts via carbon bumper plates).

Am I missing something, or can you speak of experience with the TCR-M that it is a more versatile chassis that one might think?

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Old 11-13-2022, 01:37 PM
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The Xpress plastics are fairly durable. I've hit a wall at around 100km/h with the FM1S at a Velodrome speed run and only popped off a turnbuckle, the C hubs survived. If those are breaking regularly at your track, I don't think a pan car will be any stronger.
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Old 11-15-2022, 12:20 PM
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Google search for the Kawada M300GT2 and M300GT2R....you'll find what you're looking for
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Old 11-15-2022, 02:02 PM
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Thanks for the tip. Looks like it's not made for 5mm ride height. The front wheelhub looks interesting and I might copy that. The T bar looks not adjustable though. Maybe it needs a bit more refinement.

After reading about rc chassis dynamics I decided to allow for a v-link rear pod, because with the 5mm ride height I might mess up with the antisquat with just a normal ballcup/ballhead link.
Also it looks like I will have an issue with steering Ackermann... lets see how that can be solved.
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Old 11-15-2022, 03:33 PM
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Originally Posted by h2e
Thanks for the tip. Looks like it's not made for 5mm ride height. The front wheelhub looks interesting and I might copy that. The T bar looks not adjustable though. Maybe it needs a bit more refinement.

After reading about rc chassis dynamics I decided to allow for a v-link rear pod, because with the 5mm ride height I might mess up with the antisquat with just a normal ballcup/ballhead link.
Also it looks like I will have an issue with steering Ackermann... lets see how that can be solved.
I don't see how ~5mm ride height would be hard to achieve. Step 13 of the manual shows the ride height settings. If you really need exactly 5mm (it can do either 4.5mm or 5.5mm) then you should be able to shim the bulkhead above the chassis by 0.5mm to compensate. Stock setting is for 5.5mm.

http://www.kawadamodel.co.jp/manual_...anual_m333.pdf
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Old 11-17-2022, 03:34 PM
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TCR-M is really a beast. I've tried to perform some modifications on the TCR, but TCR-M was already so agile out of the box, I had nothing to change: https://photos.app.goo.gl/cFFXQShSfGMBqA579

That said, I've tried the TCR in MR motor position instead of FF, and it is waaaaaaay slower...
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Old 11-17-2022, 11:04 PM
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Well the TCR-M may definitely be a plan B if my already purchased base car plus my mods show to be slow.
I want it rear mid motor as my Bodies will be rwd cars. Don't want to spoil it all too much this time...

The rear pod on pan cars seems to create way too much anti squat (typical >200%, my M-class prototype: 166%), so I am thinking of making a 3 link rear pod attachment like the "Pantoura" that can be found on rctech too, to create less anti squat.

typical anti squat geometry on pan cars (centre ball and two side links).

Where I am unsure is what front wheel suspension I should choose, and where the rollcenters should be lying. Many rollcenter decisions on pan cars seem to exist just to counteract other weird effects (foam tyres hooking suddenly etc.). As I will run M chassis rubbers the starting point may as well be completely different.
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Last edited by h2e; 11-18-2022 at 01:30 PM.
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Old 11-18-2022, 01:33 AM
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What are the class rules? Seems odd that you're allowed to run pan cars vs the Tamiya minis.
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Old 11-18-2022, 01:45 AM
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Originally Posted by gigaplex
What are the class rules? Seems odd that you're allowed to run pan cars vs the Tamiya minis.
5mm ride height, track width, m class body, max 40kph, sweep tyres.
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Old 11-19-2022, 01:47 PM
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No minimal weight? TCR-M will dominate that without even breathing lol.
17.5 with a TS50 and a 3800 LCG shorty lipo, you should be around 800g with a light body lol
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Old 11-20-2022, 03:22 AM
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That's exactly what I am aiming at. but don't tell anyone.
Unfortunately it's going to cost dearly to mod a 1/12 car, as the front wheels need to fit a 12mm hex. So I will need to use 1/10th steering knuckles, and so a full blown front suspension. So weight wise I might go to 900g.
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