Kronos XTR Horatio's XTR Build

[Nelson.81]

Have you decided on an esc motor combo yet?

 

[Horatio]

Have you decided on an esc motor combo yet?

Well, I've decided on a TP motor. I haven't decided what size or what ESC, but will probably roll with Castle.

 

[Sandracer_NL]

@Horatio are you still running the stock (52T) spur gear? I’m wondering if Corally’s 46T will work work with the stock sliding motor mount when looking at the two mounting screws openings. Those opening seem pretty limited, but a 46T with give a lot more gearing options. I’m on first first TC car and haven’t checked what the max pinion size with the stock 52T spur is, but I’m thinking on going to a bigger /lower kv motor.

FYI: a 4050TP (4082 size motor) with Arrma’s 150blx esc with lead the esc going into thermal shutdown from time to time.
Caste esc’s are best for speedrunning while they have no limit on amps (which is also a potential fire hazard if you push it too far).
For bashing and occasional speedrun, maybe a tp4060 and Max6 g2 (a max5 g2 is quite a lot heavier)?

 

[Horatio]

@Horatio are you still running the stock (52T) spur gear? I’m wondering if Corally’s 46T will work work with the stock sliding motor mount when looking at the two mounting screws openings. Those opening seem pretty limited, but a 46T with give a lot more gearing options. I’m on first first TC car and haven’t checked what the max pinion size with the stock 52T spur is, but I’m thinking on going to a bigger /lower kv motor.

FYI: a 4050TP (4082 size motor) with Arrma’s 150blx esc with lead the esc going into thermal shutdown from time to time.
Caste esc’s are best for speedrunning while they have no limit on amps (which is also a potential fire hazard if you push it too far).
For bashing and occasional speedrun, maybe a tp4060 and Max6 g2 (a max5 g2 is quite a lot heavier)?

Hi, with the speed runs on 6S, I ran 19/52 on the 4292 1780KV motor.

The spur has been swapped for 46t, primarily to clear the chassis (I hadn't milled the chassis to clear initially when I was trying to line stuff up), but also I had hoped to lower the diff by about 3mm. I need to change or modify the motor mount to make that happen. A job for future Horatio.

I run an MMX with 1515 in this:

The TP series motors look pretty powerful, but I'm reading up to ensure that they are safe to use with Castle ESC's.

Castle link is a useful feature for speed running.

Otherwise, I might try Hobbywing. For now, I plan on using the Torox 185 for comparison purposes - a direct before and after - old chassis Vs new chassis on 6S.

I'm confident the new arrangement will be significantly faster, but there's only one way to find out!

19/52 is an overall ratio of 1:9.05
17/46 is an overall ratio of 1:8.95

So I'll use the 17 tooth pinion to begin with for the closest ratio. That way, an objective comparison can be made.

Meanwhile, I'll continue to scope new centre drive shafts etc.

For now, I'm set to take the rig to 100mph. I hope it can stay on the ground, that's all. The truck body is like a sail!

 

[Sandracer_NL]

The spur has been swapped for 46t, primarily to clear the chassis (I hadn't milled the chassis to clear initially when I was trying to line stuff up), but also I had hoped to lower the diff by about 3mm. I need to change or modify the motor mount to make that happen. A job for future Horatio.

I read somewhere TC made new motor and center diff mount when they changed the spur to 52T in the bigger cars.
Maybe you use the’ lower’ motor and center diff mount of the Spark which has the 46T spur. It’s not that expensive on Jennysrc.
With 19/52 gearing I assume you not using both motor mount screws. with 13/52 the outside screw is already close to its’ max.

 

[Horatio]

I read somewhere TC made new motor and center diff mount when they changed the spur to 52T in the bigger cars.
Maybe you use the’ lower’ motor and center diff mount of the Spark which has the 46T spur. It’s not that expensive on Jennysrc.
With 19/52 gearing I assume you not using both motor mount screws. with 13/52 the outside screw is already close to its’ max.

View attachment 6992

Great info - I'll check it out. If I can do away with the spacer underneath the nylon part of the centre diff mount, I could lower the diff by about 3-5mm I reckon. This would be a desirable thing to do, not only because it would lower the CoG, but it will perfect the front drive.

When you think about how it was every shade of wrong (well 3 shades at any rate!) in the stock set-up, these simple steps eliminate the power robbing nightmares that the front dogbone would normally have to go though.

Thinking about it, when the rear loads up and the center diff front off loads to the front - it's even more critical that the front drive line should be sensibly aligned!

The Kronos fell into the same trap as the original Losi 8 buggy it seems.

Yep! Definitely I use 2 screws and had to lightly relieve the motor mount to run 19/52.

With the 46 tooth spur, there is ample room in the milled out chassis to lower it with a revised motor mount. I don't need the center diff at the same height. 3-5mm lower would be perfect.

 

[Sandracer_NL]

Yes, TC uses pretty aggressive drivetrain angles, not only in height, but also sideways. Sideways, probably to create the left-to-right balance they are looking for. Height, no idea as I’d imagine you’d want that as low as possible.
Interested in the speed results of your build!

 

[Horatio]

Yes, TC uses pretty aggressive drivetrain angles, not only in height, but also sideways. Sideways, probably to create the left-to-right balance they are looking for. Height, no idea as I’d imagine you’d want that as low as possible.
Interested in the speed results of your build!

Radio is in. 1 antenna for my Controller, the other for NASA.

The massive shift of the centre diff over to the right was purely to cram the mass of plastic battery mount and ESC onto an (expensive) 7075 chassis that was too narrow to mount anything. The side guards weren't ideal to mount anything to, and took up 50% of the space. However, they prioritised keeping the weight forward - on that point they succeeded. That's why people say they prefer the handling of the Kronos over the Kraton.

With everything closer to the centre of mass, any difference in weight between the motor/servo/radio side Vs the battery/ESC side minimises the weight difference at the wheels AND lowers the polar moment of inertia, which should result in the car being able to change direction quicker. Double win.

That being said, my Kronos now has a 3mm longer wheelbase, which should aid stability.

 

[Horatio]

Just weighing up with all electronics - 3.5kg (7.7lb) and with a 600g 6S battery - it weighs a lithe 4.1kg (9.1lb).

I hope to shave a few grams off that with the M2C carbon shock towers.

So now we need the money shot.

I hope to run the "Wide Boy" XTR 'H' variant tomorrow, weather permitting.

I'll be running 17/46 on 150mm belted rubber slicks, 6S, for a shakedown run.

 

[Horatio]

In typical blighty fashion, high wind and wet weather hit today, this putting the kybosh on any RC car running.

So, just some pictures of the completed rig. There are some more goodies in the post.

Body had to be re-drilled to account for longer wheelbase.

I'm certain Autumn will afford some nice days, so for now, I'll just have to exercise some patience.

 

[VaporTrail]

@Horatio are you still running the stock (52T) spur gear? I’m wondering if Corally’s 46T will work work with the stock sliding motor mount when looking at the two mounting screws openings. Those opening seem pretty limited, but a 46T with give a lot more gearing options. I’m on first first TC car and haven’t checked what the max pinion size with the stock 52T spur is, but I’m thinking on going to a bigger /lower kv motor.

FYI: a 4050TP (4082 size motor) with Arrma’s 150blx esc with lead the esc going into thermal shutdown from time to time.
Caste esc’s are best for speedrunning while they have no limit on amps (which is also a potential fire hazard if you push it too far).
For bashing and occasional speedrun, maybe a tp4060 and Max6 g2 (a max5 g2 is quite a lot heavier)?

with the 52T spur, the biggest pinion I ran was a 16 or 17. I've since swapped out the 52T with my Python's 46T. If all you're doing is a diff swap, you'll have no problems with the smaller spur. If you want to run the 52T truggy spur on the Python, you need the complete truggy diff mount. Gear cover, front and rear diff mounts.

I used to run a 39xx size TP motor with a Max6 gen 1. It actually did ok as long as you didn't gear too aggressively. Power delivery was another story. TP motors and the stock 52T spur was a recipe for insane torque. I've since replaced the TP with a HS 4274 motor and the Max6 with a MMX 6S. I've also toned down the throttle EPA to help keep it smooth in the infield.

 

[Horatio]

The parts keep arriving!

7075 front shock tower.

M2C Carbon front tower. 12.2grams saving!

7075 Rear tower.

M2C Carbon rear tower. 20.3grams saving!

32.5 grams total saving!!

The M2C rear tower appears to offer slightly lower mounting positions, changing the geometry of the rear shocks. Almost like the Kagama rear shocks are shorter than the XTR?

Either way, they fit nicely and I now run the rear shocks further out on the arm, and with a lot less pre-load, to achieve the same ride height.

Quality of the parts is excellent. Prior to fitting, I used Sharpie and sealed all the edges with super thin Cyano.

Running total weight save so far: 235.5g (8.3oz) (0.52lb).

It adds up. Weight is now closer to the centre, further forwards, lower down and with less weight at the ends of the truck.

Now all we have to do is get some 6S shake downs. I have selected a rollout that's identical to my last outing, so we can see just how much the weight loss and more efficient driveline angles have improved things.

Then, we increase power and reduce rotating mass.

Obviously the wheels and tyres have to go.......

 

[Horatio]

The XTR lives!

5mm thick chassis is thick enough to apply UHB hook velcro to for the shroud. I did wonder if Dual lock sticks to the loop material in the shroud. Bizarrely, it did - but it attached to it too well, because unfortunately, it doesn't let go!

So, 8 pieces of 50 x 5mm now hold the shroud in place perfectly. With this arrangement, the side guards are really no loss whatsoever.

Whilst I am not in a position to speed run just yet (the 1/4 mile strip is in use at the moment) - the truck was given a run at low speed on 17/46.

I lost front drive after just 2 minutes, because I hadn't tightened the grub screw for the front input drive. I had a word with myself, then carried on. School boy error.

It's super quiet. Much quieter than before. I've always thought Kronos 6S rigs sounded good compared to other offerings - I credit that to the quality, hardened steel, CNC, precision cut gears.

I was half expecting to hear a different sound, a different resonance or tone from the car, but there's just less volume of noise - period. It's silky smooth, which I suppose you'd half expect following a complete rebuild.

As for handling, well whilst the car was far from it's limits, I was running it on narrow pavement adjacent a road, barely wider than the car itself.

Nipping onto the road, blasting into my drive and back onto the pavement - inch perfectly - certainly demonstrates that the car is extremely responsive. Steering at low speed is very aggressive, but then it has less caster and is riding slightly higher at the rear.

The truck has more steering and feels sharp. Bear in mind I'm comparing it now to an Sworkz T2E and an Xray XT8.

Watch this space.

 

[Horatio]

It's a tough call. The weather sucks but it's your day off. Slick tyres on cold wet tarmac = no grip. But surely - just a little straight line running? What could possibly go wrong?!

OPS charged and ready to go. Car has unbelievable punch and response. Barely able to touch full throttle without severe consequences.
Wind, driving rain, puddles. Annoyingly, I still had to share the 1/4 mile strip with a significant amount of traffic, despite no events.

Just darting around, drifting and finding the limits. Nice!

On this run, before full throttle, all rear traction was lost and the XTR spun. Instinctively, I caught the spin, but the trouble is: now I was driving the rig at 60mph across the strip - towards concrete.

Despite the high speed collision, the truck held up. Nothing broke. I think the big old Jetkos took the majority of the impact.

The crash was caught by the onboard camera!

Now realising the XTR was an absolute handful, I was tentative with the passes.

There's definitely 70+ mph on the cards with this setup on 17/46. Just not on a day like this.

The truck drives amazing. It has very aggressive, responsive steering at lower speeds and less off-power steering. However, there's good on-power steering and hooning around is confidence inspiring.

Using the same motor and esc, I was surprised that the truck is so quiet and feels much punchier. The tyres can be lit surprisingly easily, at any speed. Center diff was very warm after the first pack. Motor needed several minutes to cool down too.

Alas, the amount of steam coming off the rig tells a story. The 1/8th scale driver inside the rig couldn't see through the windscreen! No wonder he crashed!

This rig needed less rear pre-load and I added some front pre-load.

All things considered, I'm very pleased with the results but I'm under no illusion that hitting 70+mph requires decent conditions.

There's definitely more hp at the wheels now, so it's going to happen.

The handling of the rig would make it perfect for track use now. It feels light and responsive - not dissimilar to a full-on race Truggy on 4S.

Despite horrendous conditions, the shroud kept out 95% of the debris and moisture. Steering was removed and clearances checked.

I'll up the video of it crashing soon.

 

[VaporTrail]

Marvelous! Definitely interested to see how it's going to perform on a track. As for speed, I think you'd easily be able to hit 70+, with as light as it is now. Perhaps some canards on the body to help push it down some?

Kick job, H!!

 

[Niekname]

Nice speeds! Good to know it holds up without the braces, I have to admit I was skeptical about that. What speed are you aiming for?

Also which onboard camera do you use? I was also thinking about getting some sort of action cam, partially for RC.

 

[Horatio]

Marvelous! Definitely interested to see how it's going to perform on a track. As for speed, I think you'd easily be able to hit 70+, with as light as it is now. Perhaps some canards on the body to help push it down some?

Kick job, H!!

I'm certain it will sail past 70mph on 6S. I run the car fairly low, but at 60 - 70 mph, I haven't needed to worry too much about the rig taking off or flipping over.

I think there's genuine need past about 100mph to use aero on the car to help it stay 'stuck'.

Nice speeds! Good to know it holds up without the braces, I have to admit I was skeptical about that. What speed are you aiming for?

Also which onboard camera do you use? I was also thinking about getting some sort of action cam, partially for RC.

The braces the car had were 100% necessary with the 3mm chassis.

Now though, with the chassis being so much thicker, and because of the material properties of the carbon fibre - inherently, it's so much stiffer and stronger.

I could, if I had any concerns, brace from the front and rear transmissions to the centre diff mount - but honestly - it's tough as old boots!

My 60 mph excursion into concrete should have killed the car, yet it lives. I don't plan on making a habit of it, but I'm confident the rig can take some knocks.

The speed runs have happened almost by accident. If someone said to me years ago that I would derive great pleasure from driving in straight lines, I'd have thought they were losing the plot.

But once I realised I could hit 60, then 64, then 65, it started becoming a mission to beat the previous speeds. 68mph then 69mph left me so tantalisingly close to 70mph that I'm determined to breach it.

So at the moment - my goal is to get past 70 mph. Even just a 1mph gain is a win.

I fully appreciate that these rigs do not make great speed run machines, but in a strange kind of way, that makes it really interesting to see how far we can take them.

There's a channel on YouTube (Innovation RC) with a speed runner 1/5th scale Kraton, running on foam tyres. I'm pretty sure he gets over 100mph with that one on 8S.

Dave from Scorched parts likes the build - but asked me 'what's an XTR'?'

 

[VaporTrail]

I remember one night I was running a RC10L in an empty parking lot. Absolutely ridiculous setup; 1st Gen Mamba Max, Tekin Redline 7700KV motor, 3S. Yes, 3S. That girl would leave darkies on take off. Edit: IF she could actually keep her rear end straight.

I was running the lot diagonally to give the car a chance to get up to speed. On the 4th run I gave too much throttle too early (is 50+ yards too early?) and I lost the back end. When she turned sideways, the wind forced it's way under the pan body and she instantly became a parachute. Needless to say, I tucked her in for the rest of the night.

I'm glad your XTR isn't suffering the same.

 

[Nelson.81]

Only catching up with this build now awesome job, you mentioned Kronos body like a sail, try your sworkz body on it, sleeker and hugs chassis better, dementor rear body posts on front to fit it. I’ve fitted the original body posts on the front of the shock towers so can run both bodies, 1 for bashing try keep other good.

 

[Horatio]