The reason CVD's are breaking

[wrightcs77]

When someone breaks a CVD, take a small screwdriver or something small and try moving the drive shaft up and down. The axles have no outer bearing support, letting the axles are flexing slightly due to this. I do not know how Losi can have support at the worm drive and then not until the steering knuckle.

Seems pretty obvious, but maybe I am over/under thinking it.

 

[DiEzel]

I assure you that's not the reason they are breaking.

 

[Harley]

I assure you that's not the reason they are breaking.

Don't be so sure, with a fixed input at the "diff" side it puts an awkwards stress on the shafts. If the "diff" side were a dogbone then there is a much better chance they would survive.

But they are way under designed as well. I can't believe they put those CVD's in this truck, really makes me question the designers.

 

[sddill]

Anybody figured out how to get some 1/8th scale buggy cvd's in there yet :mrgreen::mrgreen:

 

[WrenchHead]

So I see they are made from the same paper like material they made the MRC cvd's from and with the same crappy workmanship.Just venting,I have now been through 3 sets and only one set ever made it to the rocks.:evil:

 

[IDnewcrwlr]

i dont own a losi, but you would have thought they would have caught those little glitches when they were out "testing" the rig. .. . almost makes you think that the "test" rigs were made with better and or stronger parts :|

 

[gunnar]

Anybody figured out how to get some 1/8th scale buggy cvd's in there yet :mrgreen::mrgreen:

Your on the right track. I think the only way for CVD's to survive is they need to be made larger. The C and knuckle must be larger to hold a larger joint. It would really have to be a whole kit that bolts to the axle, increasing size and strength to all areas of the joint. Really big would be great, like minimum 1/2" CVD ball diameter, 3.5 to 4mm diameter pin. That should last for awhile.

 

[Robbob]

i dont own a losi, but you would have thought they would have caught those little glitches when they were out "testing" the rig. .. . almost makes you think that the "test" rigs were made with better and or stronger parts :|

im not speaking for them but sometimes things like that come from the vendors. first run protoype parts are made to the spec you request, once production starts the supplier starts looking for ways to save .003cents per piece and start playing with materials.

[e]: by suppliers/vendor im talking the people Losi used to machine their CVD's - Not Losi themselves.

but i agree, cant see why they wouldnt put an outer bearing on the axle tubes. :|

 

[kikcaffine]

I noticed before mine broke, that there was a good amount of slop/play on that side. Hum......

 

[big geo]

i doint know bout u guys but i wheel 1:1 and my dana 60 doint have a bering out there and its just fine. if you look close at the shaft as it turns in the axle it actuly moves forward and back in the tube beacuse of how mutch steering it has. i think if you put a bering there your gonna limit the stering throw i had this problem when i changed my wheely king to maxx cvds.

 

[eron]

Everyone is saying that Losi does this to save money. If Losi had made the crawler with to notch parts, they can raise the price. I would much rather pay more for a reliable crawler, than pay cheaply and have to buy all these upgrades.

 

[Code454]

Also who tested them and what did they test them on because they would have had the same problem that everyone is having.

 

[bustedcrawler]

Two things I see are: 1) the neck down by the ball is too sharp creating a weak point, and 2) its made in China, what did you expect? There is a reason why my company doesn't get fabrications made there for jobs here in the USA. We don't want to deal with the lawsuit WHEN not IF it fails.

But everyone looks at ways to save $$ when going into production, and a company overseas that has a labor rate to them of maybe $0.35/hr total is hard to beat.

 

[renoirbud]

I believe that having a bearing supporting the inside shaft of the CVD closest to the knuckle would reduce the forces on the CVD joint greatly. The current design causes the cvd joint to be in tensile stress as well as rotational stress.

If the CVDs are properly aligned with the kingpins, steering angle should not be decreased by the additional bearing.

I think that Losi is well aware of the design flaw, but they need to add a thicker feature on the CVD shaft so that you can get a bearing onto the shaft. Then it would be possible to redesign the knuckle to accomidate a bearing. The current CVD is fat on either end, so it is not possible to install a bearing where it is needed, unless you use a two piece spacer (clam shells).

 

[bustedcrawler]

I believe that having a bearing supporting the inside shaft of the CVD closest to the knuckle would reduce the forces on the CVD joint greatly. The current design causes the cvd joint to be in tensile stress as well as rotational stress.

If the CVDs are properly aligned with the kingpins, steering angle should not be decreased by the additional bearing.

No bearing would put a bending stress on the axle not a tensile load. The fluctuating bending load, plus torsion on a shaft with a sharp taper (ie too high of a stress concentration factor) would create a nasty stress riser and weak point.

 

[dkf]

Two things I see are: 1) the neck down by the ball is too sharp creating a weak point, and 2) its made in China, what did you expect? There is a reason why my company doesn't get fabrications made there for jobs here in the USA. We don't want to deal with the lawsuit WHEN not IF it fails.

But everyone looks at ways to save $$ when going into production, and a company overseas that has a labor rate to them of maybe $0.35/hr total is hard to beat.

When I was in school to be a machinist they touched on machining radiused corners whenever possible especially on heat treated parts. Using radiused corners greatly reduces the chance of the part cracking during heat treating.

 

[bustedcrawler]

When I was in school to be a machinist they touched on machining radiused corners whenever possible especially on heat treated parts. Using radiused corners greatly reduces the chance of the part cracking during heat treating.

Yup! The larger the radius the better, to a point. It lowers the cracking, because it doesn't create a stress riser. Basically it makes too sharp of a change in size and the stresses concentrate there.

 

[fwilly]

On top of the sharp neck down, the slots for the pin cut even farther down into to same area. The radiuses in the bottom of the slot are very sharp. The slots don't even need to be cut that far. The pin stops well short of getting into that part of the slot.

EDIT: I was comparing my broken axle, to the one thats OK, and the slots are definetly cut deeper on the broken one. Wish my camera could take a decent picture of it.

 

[APESHAT]

'They' definitely overlooked the Stress factor on the machining of these shafts! 4.5 mm inner shaft necked down to 3 +/-mm ? obviously the 45* steering spec got in the way of fixing that from the start. . .
If you look at the manual- ALL the part #s are ' LOSA ' = made here, U.S.A. + assembled overseas. . .it's not China's fault.
Plenty of talented minds are @ work on this- just a matter of time.

 

[dkf]

Don't let anyone fool you. Even if a product has the "Made in USA" sticker on it doesn't mean it was made here. The company I used to work for got the main part of the item from an overseas manufacturer and added some things to it and slapped the US sticker on it. Not to mention India and China are putting out some garbage steel and aluminum stock and products.

They could have over hardened the parts also, leaving them not only thin but brittle as well. Put some twist on it and it shatters like glass.