R/C Tech Forums - Corally Kronos XTR Thread

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- - Corally Kronos XTR Thread (https://www.rctech.net/forum/monster-trucks/1092328-corally-kronos-xtr-thread.html)

Well RC tech sure is quiet. Worse than that, it's also broken - actually and metaphorically.

Android users can no longer add images to posts from their devices. 🤔

What a shame.

To keep things objective and fair, I'm linking back to the Corally Forum that links here!

Anyone into Corally Rigs should visit it. It's generally more active than RCtech is these days.

Corally Forum

Enjoy!

Just to update - Using a new Onyx Graphene 6S, I beat my Kronos XTR 0-60mph time with a 3.79 seconds run - and it was wet!

Top speed of 64mph on 13t pinion and Corally ESC and motor.

https://cimg8.ibsrv.net/gimg/www.rct...3aee924f4c.png
https://cimg9.ibsrv.net/gimg/www.rct...9a4743d446.png

With these kind of basher rigs, upgrading occurs continuously. It's always a work in progress.

https://cimg9.ibsrv.net/gimg/www.rct...fb02ccf1a3.jpg
https://cimg0.ibsrv.net/gimg/www.rct...c2357b96ed.jpg
https://cimg2.ibsrv.net/gimg/www.rct...d563b4813e.jpg
Adding a more powerful motor, one which could turn bigger pinions, was a step towards finding higher top speeds.

https://cimg5.ibsrv.net/gimg/www.rct...68b624c3ef.png
On 19/52 gearing, the XTR hit 69mph on a 6S Graphene pack, which is very good!
https://cimg9.ibsrv.net/gimg/www.rct...16cf274a6e.jpg
https://cimg0.ibsrv.net/gimg/www.rct...9b424e4f16.jpg
The Rocket 1780kv 4292 motor generally keeps it's cool, but these runs pushed it to the max. Running it hotter risks failure.

I created a very accurate gearing and rollout spreadsheet that I plan on turning into an app. It works out theoretical top speeds very accurately. On my Sworkz and Baja, it worked out speeds to within 0.3mph of real world results, so I'm satisfied the spreadsheet works well. However, on the XTR, I got larger differences - more than 3mph.

The conclusion I came to was that the centre driveline works at such extreme angles, losses were occurring that my spreadsheet was not compensating for.

So, I wondered how much better the XTR might run with a more efficient driveline. To achieve this, the XTR would need an after market chassis.

Unfortunately, there isn't one. So long story short, the XTR went through another stage of modification with a chassis of my own design, which I'll briefly show here.

https://cimg1.ibsrv.net/gimg/www.rct...71d4d00996.jpg
The 3mm 7075 chassis is comparatively light. But whilst I'm never likely to bend it - people that send it to the moon have.
https://cimg2.ibsrv.net/gimg/www.rct...75f0db04d7.jpg
5mm Woven carbon fibre has been selected to upgrade the chassis, with a much stiffer, lighter material.
https://cimg0.ibsrv.net/gimg/www.rct...3cb5423be8.jpg
Straight off the bat - 46g saved, despite being 40% thicker and 10% wider.
https://cimg4.ibsrv.net/gimg/www.rct...2ecc7b621d.jpg
The steering plate required mounting at a revised angle, to compensate the new 0° kick-up angle.
https://cimg9.ibsrv.net/gimg/www.rct...ccd391f4a5.jpg
https://cimg1.ibsrv.net/gimg/www.rct...76a38b19b5.jpg
DIY milling with a Dremel isn't pretty, but it went as well as I could have hoped for!
https://cimg6.ibsrv.net/gimg/www.rct...14089640a8.jpg
Removing the mass of plastic, typical with RTR's and rollers, reaps lighter, stiffer and stronger results. This Scorched Parts steering servo mount makes for a much stronger, zero flex option. It's based on the Kraton mount, but it really doesn't matter for a custom build.

https://cimg8.ibsrv.net/gimg/www.rct...19bbcf67d1.jpg
Titanium shock stand-offs were supplied by Scorched. I'm not sure if he gave them to me by accident, but I really like them either way. Thank you Dave!

https://cimg4.ibsrv.net/gimg/www.rct...2bf9fd4b65.jpg
https://cimg5.ibsrv.net/gimg/www.rct...4c3c5f2b43.jpg
https://cimg6.ibsrv.net/gimg/www.rct...87796ae4c0.jpg
The chassis has been configured to bring the driveline into the centre, bring the weight forward and increase available mounting space.

https://cimg1.ibsrv.net/gimg/www.rct...6c70843b87.jpg
And so the XTR Wide Boy 'H' is born.

This rig is light. The new design eliminated most of the bracing - it's simply unnecessary with a chassis this stiff. The rear braces are retained, primarily because that's what the body mounts to!

Watch this space for incoming speed runs and 0-60mph times.
https://cimg7.ibsrv.net/gimg/www.rct...955b6313d2.jpg
https://cimg8.ibsrv.net/gimg/www.rct...3bc21296b8.jpg
https://cimg9.ibsrv.net/gimg/www.rct...d4c58b883e.jpg
M2C front and rear carbon shock towers are on the way!

What a rig this has been so far - the gift that keeps giving.

Corally Kronos XTR Thread

I’m really so intrigued by how detailed you have been since 2020 I guess i would like to meet and talk to you personally

Quote:

Originally Posted by Horatio (Post 16130672)

I created a very accurate gearing and rollout spreadsheet that I plan on turning into an app. It works out theoretical top speeds very accurately. On my Sworkz and Baja, it worked out speeds to within 0.3mph of real world results, so I'm satisfied the spreadsheet works well. However, on the XTR, I got larger differences - more than 3mph.

The conclusion I came to was that the centre driveline works at such extreme angles, losses were occurring that my spreadsheet was not compensating for.

I should probably point out that your spreadsheet probably does not take into account a bunch of other variables, but you might already be aware of this. Motors are notorious for not running at their claimed RPMs, batteries might be voltage sagging under load, aero becomes very important at such high speeds. Oh and tyre ballooning is almost impossible to account for. These variables might be the same for your Sworkz and Baja, but not for the Corally.:nod:

https://cimg6.ibsrv.net/gimg/www.rct...71b9040db1.png
It's this terrible drive angle that my calculator wasn't taking into account. It's this. The shaft also travels through a downward angle to the input drive - which itself normally goes through a 6° angle upwards, due to kick up.

Battery sag and tyre ballooning, whilst not technically calculated for, are mitigated by giving the user a range of inputs for each.

In my case I tend to test with belted tyres. Speed runs on unbelted tyres = disaster. :lol:

The only rig where my calculator was consistently giving 3mph over the real world results was the XTR.

Thus the new chassis layout.

Once I get some higher traction days, I can put all the theories to the test.

Despite a difficult first run, I can already feel how much punchier the rig is. This isn't just from the weight saving, but from more power getting to the wheels.

Fair enough. This driveshaft angle phenomena was noted upon years ago in 1/8 buggy, so I'm not saying you're wrong.

Have you run an identical electronics and tyre package on your other cars as a reference?

Quote:

Originally Posted by Sir 51D3WAYS (Post 16133367)

Now that the Kronos Wideboy XTR has been created, I can prove it - using identical batteries, motor, ESC, gearing and rollout.

I'm going to find those lost MPH - all of them. I can already feel the extra punch and acceleration, but I need much better conditions to beat my Kronos XTR personal bests.

If my theory is right, I will hit 73 mph on 17/46.

The Losi 8 nitro buggy proved the weight distribution Vs drive angle stuff. It jumped well and handled great - but the front drive angle was sub-optimal and robbed power and efficiency.

I'm hoping I've kept the weight forward, central and with zero angles on the drive. This rig is basically the best of a Kraton combined with the best of the Kronos.

It's basically what the Kagama wanted to be.

Quote:

Originally Posted by Horatio (Post 16133408)

The Losi 8 nitro buggy proved the weight distribution Vs drive angle stuff. It jumped well and handled great - but the front drive angle was sub-optimal and robbed power and efficiency.

Ah yes, it was famous for wearing out front driveshafts. Theoretically, this power loss should be negligible, at least on a circuit. But I'm not sure if anyone outside of factory test drivers have experimented with this.

It's oppo was the ill-fated Tamiya TRF801X. That one had completely straight driveshafts and was noted for it's acceleration. It got around the weight distribution issue by canting over the engine by 15 degrees IIRC. Not quite enough, but still.

You've also reduced the weight significantly, so that too would contribute to the punch, although probably not the top speed.(significantly)

Also, since you killed the kickup, be aware that this is going to handle VERY differently. The truck was designed to work with it as a non-negotiable......Probably very twitchy.

Mind you, I once gained hella punch by swapping Tamiya connectors to Deans....:nod:

Quote:

Originally Posted by Sir 51D3WAYS (Post 16133427)

The lack of kick up has reduced caster, although I now run the spacers in front of the upper arms to gain some of it back.

The truck has much more aggressive turn in and on-power steering, though oddly enough, off power steering has reduced.

My Sworkz has very little kick. So fingers crossed. 🤞