Kronos XTR Will droop screws eventually puncture through the chassis?

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DaniC

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Corally RC's
  1. Kronos XTR
Hi guys,

I recently took the front and rear gearbox and shock towers off the chassis and noticed that the droop screws have created engraved marks on the chassis as seen on the pictures below and I'm wondering if with time this will eventually puncture through the chassis?
PXL_20220824_165224676.jpg

PXL_20220824_165234340.jpg

PXL_20220824_165242874.MP.jpg


Is this something I should worry about? I'm not sure what can be done about this.... perhaps a locking nut at the end of the droop screw so that it creates a bigger contact surface against the chassis. Maybe there's nothing to worry about...?
 
Got the same on my Sketer. It is even wors then yours. Maybe i have to change them 2. Anyone have a clue where to get titanium ones in Europe?
 
look on ebay for titanium droop screws
I don't understand, how would titanium screws would prevent this from happening?

Got the same on my Sketer. It is even wors then yours. Maybe i have to change them 2. Anyone have a clue where to get titanium ones in Europe?
I've bought titanium screws from eurorc.com, I've bought a few from aliexpress too. But I don't see how this would fix this issue...

  • Mugen Schraube für Ausfederwegbegrenzung

Mugen

Mugen Schraube für Ausfederwegbegrenzung​

Artikelnummer: E0183
Oh this is very interesting, button head screw, but has a hex at the tip like grub screws do. So the button head goes facing down, with a bigger surface area and less chance of markings through the chassis.
 
I'm surprised at how hard it was to find these screws, but finally found the following 2 options which I think are best value as they're 8 screw packs:
- Arrma ARAC9870 M4x10mm 8pcs Double Socket Button Head Screw: https://www.ebay.ie/itm/185029599263
- Tekno TKR1238 M4x10mm 8pcs Droop Adjustment Screws: https://www.ebay.ie/itm/185506004930

They're both pretty much the same thing. I'll buy one of these.
 
Hi guys,

I recently took the front and rear gearbox and shock towers off the chassis and noticed that the droop screws have created engraved marks on the chassis as seen on the pictures below and I'm wondering if with time this will eventually puncture through the chassis?
View attachment 2909
View attachment 2910
View attachment 2911

Is this something I should worry about? I'm not sure what can be done about this.... perhaps a locking nut at the end of the droop screw so that it creates a bigger contact surface against the chassis. Maybe there's nothing to worry about...?
It's not ideal, is it? The XTR chassis is 7075 aluminium, so should be harder than regular aluminium, but clearly not as hard as the steel droop screws.

Titanium is harder than Aluminium, so I suspect this won't solve anything.
[Edit: Actually, grade 5 titanium used on quality screws is 41 on the Rockwell hardness scale vs 53.5 for 7075 Aluminium - so Titanium makes good sense for droop screws - hard enough to be functional, but soft enough not to wear the chassis]

Perhaps for this application, 7075 droop screws would be the solution?

Titanium is a great choice for turnbuckles because they are lighter than steel and still very resilient to bending.

The divot, once it's bedded in, is unlikely to get much worse unless you attempt to significantly reduce the droop or increase preload.
 
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It's not ideal, is it? The XTR chassis is 7075 aluminium, so should be harder than regular aluminium, but clearly not as hard as the steel droop screws.

Titanium is harder than Aluminium, so I suspect this won't solve anything.

Perhaps for this application, 7075 droop screws would be the solution?

Titanium is a great choice for turnbuckles because they are lighter than steel and still very resilient to bending.

The divot, once it's bedded in, is unlikely to get much worse unless you attempt to significantly reduce the droop or increase preload.
As you can see from previous comments, the solution seems to be double side screws, with a hex at the tip of the screw and the head is like a button screw but more mushroom-like, with a hex on it to. This will have a bigger surface area that touches the chassis and much less of a penetrating shape.
 
As you can see from previous comments, the solution seems to be double side screws, with a hex at the tip of the screw and the head is like a button screw but more mushroom-like, with a hex on it to. This will have a bigger surface area that touches the chassis and much less of a penetrating shape.
It will definitely help spread the load, but the button head will reduce the maximum droop you can have. And steel is harder than 7075, so it will still wear, it will just be the size and shape of the button head.

I guess it depends what range of droop people want as well. When you try and increase droop, you'll only be able to go as far as the button. 👍
 
It will definitely help spread the load, but the button head will reduce the maximum droop you can have. And steel is harder than 7075, so it will still wear, it will just be the size and shape of the button head.

I guess it depends what range of droop people want as well. When you try and increase droop, you'll only be able to go as far as the button. 👍
Yeah I'm not terribly worried about maximum droop. The way I have it set allows plenty of space for the button. We'll have to see, it might be the perfect solution, or it might no be. But it will certainly be better than a plain grub screw, of that I'm sure.
 
See for yourself. Mugen Truggy 8 months old and about 300 batteries used (competition)

View attachment 2927
View attachment 2928
View attachment 2929
That's a noticeable groove. I suppose as the groove gets deeper, you get more droop, so you screw the set screw in some more - rinse/repeat.

It's not been an isuue on my XT8 - only got about a gallon through it though, on very bumpy grass track.

Button heads on that would certainly reduce the droop from how it is set now.

On the XTR, I'm fairly certain that amount of button would alter my current droop setting.

I still think the simplest solution would be to find droop screws which are made from softer material than the chassis. Then as and when wear occurs, replace the alloy droop set screws - screws being cheaper and much more readily changeable. 👍
 
In the interest of objectivity, I looked up some of my old BRCA hardcore racer pals up and asked what they all did. Here's what I had back:

  1. Glue-in feeler guage steel onto the chassis where the droop screws dig in.
  2. Use the appropriate button head screws, with the buttons against the chassis - it does reduce the wear rate, so you guys are right!
  3. Round off the droop screws with a dremel, so they don't have pointy right angles where they touch the chassis.
  4. Remove droop screws altogether and limit down travel from inside the shock instead - just like 1/10th buggy racers always used to.
  5. Change the chassis every time the droop screws no longer make consistent changes to droop - because you're a team driver and your chassis is all scratched up now anyway.
I swear down that if the screws used were made from softer material, the source of the problem would be solved at source, then some of the above methods could be used in conjunction. 😊
 
In the interest of objectivity, I looked up some of my old BRCA hardcore racer pals up and asked what they all did. Here's what I had back:

  1. Glue-in feeler guage steel onto the chassis where the droop screws dig in.
  2. Use the appropriate button head screws, with the buttons against the chassis - it does reduce the wear rate, so you guys are right!
  3. Round off the droop screws with a dremel, so they don't have pointy right angles where they touch the chassis.
  4. Remove droop screws altogether and limit down travel from inside the shock instead - just like 1/10th buggy racers always used to.
  5. Change the chassis every time the droop screws no longer make consistent changes to droop - because you're a team driver and your chassis is all scratched up now anyway.
I swear down that if the screws used were made from softer material, the source of the problem would be solved at source, then some of the above methods could be used in conjunction. 😊
Wow nice comprehensive list of possible solutions! Thanks for taking the time to ask around and put it together!
I did think about number 1 but I felt that whatever I put there would fall very quickly.
 
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