Kronos XTR Rocket RX 4292 1780KV Motor -Quest 4 Quickness

[Horatio]

My XTR has been cleaned and serviced. The diff screws were loosening again and just beginning to leak. All the screws were degreased and re-threadlocked.

This just goes to show how important regular cleaning and inspection is. Prior to cleaning:

Tell tale signs of diff oil on chassis.

Diff service - all 8 screws removed and threadlocked with loctite 243.

Despite running on tarmac, because it was wet - look at the crud on the POS mudguards!!

Full cleaning complete, the 4292 is now fitted with a 16t pinion. Next dry day we'll see what it can do.

The POS guards are really helping protect the shocks and other components from projectiles thrown up like bullets from the front tyres. After cleaning, I noted all the craters in them!!

 

[Horatio]

I've just ordered these:

Sweep Racing VHT Crusher Slick Belted Tyre Black 17mm Wheel 1/2 Offset (2)

Whilst I am happy with the Jetko Supersonic tyres, according to Modelsport these Sweep tyres are just 274grams each. My Supersonics on the other hand are 441 grams each.

That's a saving of 167grams per tyre and a combined saving of 668grams of rotating mass.

This has got to see an improvement in both 0-60 times and overall top speed.

I eagerly await their arrival.

 

[Horatio]

So, the Crushers arrived today from Modelsport - less than 12 hours after my order!!!

These are super light, belted tyres. 274grams (pre-balancing).

Tyres dressed and balanced - ready to go!

They balanced up really nice - no more than 2.5grams and 1 wheel didn't require any weight.

The wheels are vented at the heavy spot, so sweep clearly make an effort to provide the wheels reasonably balanced.

This time of year, I'll need to tape over the vents - it's always wet - and I don't want water ingress into the insert.

 

[Horatio]

They're on. Now all I need is:

• Time
• Daylight
• Weather

 

[The Stig]

They're on. Now all I need is:

• Time
• Daylight
• Weather

View attachment 4842

Lol. Kronos on steroids Looks fast.

 

[Horatio]

So today's weather was a 9°C day, with a drizzle as I left for the strip.

Gearing was 16/52, and to begin with, I went with the Gens 6S.

It turns out the new tyres were a 2 edged sword. They were definitely more controllable, but because they were brand new and likely still had mould release on them, I could light them up at pretty much any speed. This was loads of fun, but it wasn't helping me go faster.

After 5 minutes of hooning 'to scrub the tyres' I went for a quick pass. Off the line, the tyres still spun, the car was squirming. Punching the throttle from half - the tyres still lit up, so this motor has a lot of power.

Sadly, whilst I'd geared up by 2 teeth, these lighter tyres had come down in diameter. Would you believe, I ended up at the same rollout, thus identical speed. 56 & 57 mph.

Getting ready for the Onyx RC pack, I noticed my transmitter down to 9.5v, so clearly my Tx pack had decided to croak. In fairness, it's only the 2nd pack I'd bought for it in 18 years and it owes me nothing. Clearly, NiMH still has a place in RC - they last forever - and don't spontaneously combust.

Next, I decided to give the truck a quick temperature check. The motor was......93°F. Honestly! Just below body temperature, despite all the hooning around. This was with the Dusty Motors Shroud on.

Checking the new Yeah Racing pinion, I was horrified to see that the grub screw was backing out, but the pinion was solid to the motor shaft. Turns out, the M5 hole was oval, so the grub was not actually lining up with the flat on the motor. Drilling it back out with a 5mm drill seems to have helped (not easy, because it's hardened steel), but it's definitely a duff one. The 17t I replaced it with though is fine.

I guess at £4.99 per pinion, I shouldn't be too surprised.

So, 18t and 19t Tekno pinions are on the way M5 Mod 1 with 5mm grub screws. £13.99 per pinion. They ain't gonna move though. Knowair suggested I got them, but the UK supply was poor at the time. Now I've got them, I suppose I'll end up getting a full (very expensive) set.

To run with the 19t, I'll probably have to fettle the sliding motor mount.

Despite another very mediocre sub 60mph run, the tyres track perfectly and don't 'snap' away when they let go - it's more progressive. I just wish they were slightly larger diameter.

There's some more onboard footage, including some catching and passing a car. It's on a private stretch, so for the record - no laws were broken and the driver wanted me to race.

So, whilst this was lots of fun, from a speed point of view it was poor. I'm £50 lighter. And waiting on Royal Mail.

 

[Horatio]

16t coming out -

New Tekno 18t M5 5mm pinion in it's place.

I'm very impressed with it. Thank you Knowair - this was definitely the best pinion choice. Over time, my selection of 8 pinions will all be these. The 5mm grub screw seals the deal. Much better.

Note the very small clearance for 2.5mm hex driver. Even then, you have to hold the pinion between the magnetic 'notches' to line the grub screw up.

18t is the largest pinion you can use before the mount requires opening up with a Dremel.

The remainder of the week is dry and cold, so I'm definitely taking it on another run.

Gotta beat 64mph this time.....

 

[BashingBrian]

Are you using a 52T spur.?? if so, get yourself the 46T one, that way you can go much bigger with the pinion.
Where did you get the Tekno pinions, you should use www.rprcdistribution.com if you're in the UK

 

[Horatio]

Are you using a 52T spur.?? if so, get yourself the 46T one, that way you can go much bigger with the pinion.
Where did you get the Tekno pinions, you should use www.rprcdistribution.com if you're in the UK

I'm using the 52t spur with the XTR 2021. Excellent idea!

Using the 46t spur, there'd be no going back to the 825.

I got the Tekno pinions from RPRC, along with the Leadfinger Bruggy body for the S35 T2E.

The pinions are £13.99, which is nearly 3 x the price of the Yeah Racing pinions. But at least they're round!

 

[BashingBrian]

Can't go wrong with Tekno pinions..
I still think you would be ok with the 825 with the 46T spur, my Radix still runs stock motor with that setup, and I think I'm at 17/46

 

[Horatio]

Can't go wrong with Tekno pinions..
I still think you would be ok with the 825 with the 46T spur, my Radix still runs stock motor with that setup, and I think I'm at 17/46

Thanks for letting me know - that's encouraging. I'm cautious because I nearly smoked my 825 when I first ran it 'bareback' ie no fans or shroud etc - on the 13t pinion.

It's much better with fans to be fair and mighty quick even on 13t. Very impressive stock setup.

This 4292 is running very cool, so it seems to be begging for taller gearing. I need to gear it around low 60mph and see if it can beat the 825. If I can't beat 3.79 secs, I'll carry on gearing up - it's got to beat 64mph. It's 4200watts - it has to, right?

If not, it's a very cool running motor with loads of mid-range grunt for easy driving.

The 825 may be destined to end up in the S35 T2E. Bruggy body on the way!!

 

[Horatio]

Well seeing as the weekend is nearly upon us, along with crisp, frosty weather, I am thinking about more speed runs. By afternoon it should be frost free and dry!

Between gearing, tyre and motor options - there's a lot of variables. This time of year, there are losses that are difficult to calculate, but having a theoretical top speed (that doesn't take into account losses) at least serves as an optimistic guideline.

So, what I needed was a gear chart, one that shows ratios between 12t - 19t pinions, on 52t or 46t spurs. The final drive ratio. And the Roll out in mm/rev for 2 different tyre sizes. On the same chart, a motor comparison section where you input battery voltage, motor KV and your rollout to calculate potential top speeds. It's a tall order. There wasn't anything - so I sorted out my own!

If I'm running smaller tyres and shooting for 0-60, using the 4292, now I can see exactly where I need to gear to.

On a good day, with decent temps and grip, I got to within 4mph of the theoretical top speed for the 825. Using that as a benchmark, I will anticipate needing about 7-10mph more during colder temps.

From my spreadsheet - I now know 17t pinion on 52t spur should get me to 60mph comfortably, given a theoretical maximum of 71mph. So likely best for 0-60.

The 18t should help me beat my top speed, with a theoretical maximum of 76mph.

In a way, I feel bad taking all the mystery out of it, but on balance - given the small windows of opportunity in Blighty at this time of year - it will be an advantage knowing what to expect given so many different possible combinations.

So, 19/46 on the Jetkos.....97.64mph - in the summer, that has to mean 93mph is possible on the 1780kv.

The 825, if it could survive pulling the same gearing on 150mm tyres.....a blistering 112.45mph!! Hypothetically. I suspect there'd be a trail of

 

[Horatio]

Chilly 2°C air temp, surface temp 0°C. Batteries were freshly charged and the strip was dry.

62mph was as good as it was going to get speed wise on 18/52.

0-60mph were decent attempts, given that it was cold.

Attempt 1

Attempt 2:

Attempt 3:

Dead heat!

Using the new gearing & rollout tool, I can also work backwards from real world data. There are mechanical losses and aero related things that I'm not accounting for at all, but I think the main issue at this time of year is voltage sag. There's no way of gearing or driving around it. And I suspect a realistic loaded voltage is around 22v with a freshly charged back at 0°C.

Even if I had all the voltage in the world, cold tyres aren't going to cut it anyway!

I keep seeing this big, icy, gravel pit - it's calling me away from speed runs...


Frosty

Even after multiple passes, the highest temp I saw at the motor was 102°F.

 

[BashingBrian]

Try and get yourself some GRP's the old R1's, they are designed for wet and cold but they get super sticky once you get some heat in them, don't use them in the summer though as you'll glue the car to the road

These...

 

[Horatio]

Try and get yourself some GRP's the old R1's, they are designed for wet and cold but they get super sticky once you get some heat in them, don't use them in the summer though as you'll glue the car to the road

These...

View attachment 4917

I'll take a look. They sound like just the ticket! Thanks for letting me know.

Sworkz arrives today - ahead of schedule!

It would be rude not to try them on that as well!