When is it time to replace dog bones?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
D

danl

Well-known member
Messages
209
Reaction score
175
Points
193
Corally RC's
  1. Kagama
  2. Spark
This still has a few more hours left, right?


IMG_0349.webp
 
No, I think you may have needed to change them a month ago. 😅🤭

When the dogbones start getting sloppy in the out drives etc, it's a good idea to change them.

Speaking of which - what do the out drives and axles look like?
 
The out drives on the center diff are not great. Most of the wear is between the center and front diff, possibly due to bleeding off power and super high rpm?

I've been waiting for the tool from A main to put new pins in for 6+ weeks. I finally ordered new bones from Jenny and will use those to get me by. I'll do new pins and out drives where needed as soon as I have the tool from A main. I know the worn out drives are going to eat into the new pins but I want to drive the truck.

The rear dog bones and front universals are not as bad, but I have been rotating spares in if I bend one and then I straighten the old one and have it ready for next time I bend one.
 
The front centre has sub optimal alignment 100% of the time AND like you said, it's always the front that lights up when you give it the Beanz during acceleration. 👍

It's a vicious circle once the inputs/outputs start wearing.

If you haven't already, it's well worth getting the spring steel HD input/outputs. 👍
 
If you have the tool press for the pins - that's great. But dogbones are cheap enough to replace usually.

The OP has been waiting > 6 weeks for the tool already - so perhaps just changing the driveshafts is a good short term solution till the tool arrives.
 
It’s the kagama LE so it’s got the spring steel outdrives. I’ll be ordering new outdrives next time I place an order. I would have ordered them already if I had noticed, but they are tucked away pretty good and harder to inspect.

I was thinking of using a ptfe spray lube, but not sure if that would help at all.
 
danl said:
It’s the kagama LE so it’s got the spring steel outdrives. I’ll be ordering new outdrives next time I place an order. I would have ordered them already if I had noticed, but they are tucked away pretty good and harder to inspect.

I was thinking of using a ptfe spray lube, but not sure if that would help at all.
Click to expand...
They need to design an outdrive cup with a replaceable POM sleeve so that the pin isn't directly riding on the metal cup. Metal on POM lasts far longer than metal on metal that's why large R/C helicopters use steel pinions with a POM maingear. And a 700 size heli is swinging a 1.5M rotor with a 12S power system and a 5KW~7KW motor. The gears are typicly helical MOD1 and 12mm thick
 
It looks like I’ll be going through out drives every 6 months. Perhaps I can get more if I replace the dog bone pins more frequently. I also bought a second corally but all that happens is my bash sessions go longer because I want to drive all my cars. So my junk doesn’t see less time, it’s the same. Oddly the maxx slash upgraded out drives and dog bone pins are in great shape. I think they are larger diameter, so maybe that’s a reasonable compromise?

I’m not a TRX fanboy, I just like having different brands around so that I can see what works better. That truck has many flaws.
 
Corally used 'Blades' on their touring cars at one point. Schumacher use these:

22338.webp


I adapted my Yokomo MR4 TC SD SSG with these in 2003:

14524.webp

Delrin is the better variant of POM - ideal for this application.

There isn't a design reason why these can't be used.

However, the output drives and axles would all need a wider slot and thus a different design.

Once done, these are a million % better.
 
In other news - RCTech is down. This is a shame, because I wanted to show the modifications I made to my diff upgrades on the Yokomo.

14040.webp


You can see the wear from the standard dogbone end from previous use. These outputs were machined with a wider slot to accept the blades. All slop disappeared.

14034.webp


So much better.

This is what our 6S and 8S rigs need. Proper 'pin cushions'.

Edit: if you're wondering why the diff is so skinny - it's a ball diff. 😅
 
Will they handle the high torque of bashing? Like when people land on power panic revving trying to get that last rotation in? I don’t do that half a dozen times a day, but some people might.
 
danl said:
Will they handle the high torque of bashing? Like when people land on power panic revving trying to get that last rotation in? I don’t do that half a dozen times a day, but some people might.
Click to expand...
Yes, they would handle much more abuse and reduce wear. Delrin is self lubricating and perfect for this application.

Corally would need to change the slot size of the outdrives.

And start making bigger versions of their old blades. It could happen. 👌👍
 
Maybe I need to finish this shed I have been working on so that I have space to put a small table mill in my small workshop. It is my understanding that Delrin needs machined? That is unless Corally beats me to it.
 
Horatio said:
In other news - RCTech is down. This is a shame, because I wanted to show the modifications I made to my diff upgrades on the Yokomo.

View attachment 10401

You can see the wear from the standard dogbone end from previous use. These outputs were machined with a wider slot to accept the blades. All slop disappeared.

View attachment 10402

So much better.

This is what our 6S and 8S rigs need. Proper 'pin cushions'.

Edit: if you're wondering why the diff is so skinny - it's a ball diff. 😅
Click to expand...
I like this design a lot!
I ‘ve found Team Associateds ones, but not the Schumacher ones. Are the Schumacher ones stronger?
https://60years.associatedelectrics.com/rc10b74-2-ft-center-dogbone-blades/

Team Corally’s Swiss Steel outdrives are very good, but I’d be willing to try and make them wider once they have some wear on them. Doing that and replacing the dogbone pins, together with those blades should extend the lifespan of the outdrives quite a lot I’d guess.

When using these blades with the center and rear drivetrain dogbones, there is no longer a need for using o-rings to li it dogbone travel.
 
Horatio said:
Delrin is the better variant of POM - ideal for this application.
Click to expand...
Not necessarily, delrin is a trademark of DuPont and is a specific patented formulation of POM but whether it is "better" than other variants depends on the application (if it's going to be exposed to heat a lot then POM-C might be better) EDIT I think the patent on POM-H (which is what delrin is) may have expired in which case you could get chinese knockoff POM-H, it just won't be called "delrin"

EDIT: Perhaps a PTFE (teflon) insert might work better, less friction less wear.

Then again Corally might like selling everyone a new set of expensive drive cups every 6 months.


One of my big RC helis (KDS Agile A7) uses a POM drive cup at the ends of the tail drive shaft, not sure how well that would hold up on an R/C car though. The tail rotor typically handles about 25% of the total power system output and it's running a 5000W motor on 12S. For size reference those are MOD1 gears. This is actually a wierd over engineered design for a tail rotor drive most simply use a + shaped aluminum spline on each end of the shaft that inserts into the back of a bearing supported POM gear.

agile_a7_tail.webp


agile_a7_tail_front.webp


a7taildrive_01.webp


EDIT: I forgot to mention that the "cups" don't have slots like metal cups on an RC car, it's a cylinder of POM with a bore and a slot for the pin machined into it, externally it is enclosed. Maybe that plus a thin metal external shell of aluminum would be strong enough?
 
Last edited:
Blades or pucks are the way forward. There's no need to re-invent stuff that's already been well proven on 1/10th scale buggies and touring cars. It just needs to be replicated for 1/8th.

MOD speed have been using 'pucks' - which are essentially the same thing. They're made for centre driveline and axles.

20210315_181849.webp


This means the shafts can be made from lighter material. Ditto the input/output cups.

Lower rotating mass.
 
Back
Top