Bearings!

[Jonathon Gillham 4605]

@Juggular that got your attention didn't it?

My sons HB D413 chews bearings and I'm wondering why and if anyone can help. Last race day i noticed a lot of vibration at the rear end when holding the car in my hand and applying throttle, it wasn't just the usual kick it was vibrating.

Today I stripped the car and did all bearings and oils and also took the universals apart and cleaned those out too which I hadn't done before. I should've done this ages ago but only just got a .05" driver which meant I couldn't take the diffs apart, dumb eh. I have changed the bearings in the hubs a few times before though.

The rear hubs have a 1510 inside and 1150 outside. I got the car secondhand and the hubs were completely seized up so I replaced the bearings. Now every 2 - 3 club days they are knackered and sometimes seized. The fronts wear quickly too but not as badly as the rears. I'm using Yeah Racing rubber shielded bearings but have run out so need to order more.

Would better quality bearings help? Protek are about 3 times the price but worth it if they last a year.

I got the car secondhand, it had done a season in mod and I don't think it had been well maintained. My Kyosho's just haven't needed any kind of maintenance like this car does and no one else at the club has this problem with their HB cars.

Any other ideas?

[Superluminal 3750]

Bent drive shafts causing uneven bearing wear or are they not seated in the hubs squarely? I hve had this on an aftermarket alloy c-hub, in that the counter bored hole for the bearing wasnt straight. Swapped it for the original tamiya plastic one and the vibrations went away.

[MadInventor 3884]

You could also look at whether the drive shaft yokes are lined up correctly (Assuming they are telescopic sliders). They should look the same at both ends. However, malformed hubs causing twisting of the bearing sounds like the most likely culprit, unless the bearings are being over-revved and getting hot.

It might also be worth getting the sub axles out and rolling on a perfectly flat surface to ensure they are all straight.

 

[nbTMM 433]

How much can the universal shaft move axially in the hub with the wheel attached? If wheel/shaft can move in and out of the hub more than 0.5mm that's a problem because when shoved sideways it can shock load the bearings - if this is the case add shims between the universal shaft and inner bearing so there is only about 0.1mm movement. Similarly if there is zero movement, the bearings are preloaded which will cause premature bearing wear. If it's too tight with no shims, try sanding down the back of the wheel hex (or just try different hexes, they all have slightly different tolerances). 

And yes there is a big difference in the life of bearings due to their quality. I have had quality ABEC 7 rated bearings last 10x as long as cheap ebay ones, and i'm only paying 2-3x the price for them. 

[Juggular 4961]

Oh, yes, I was leisurely watching "NASA's Dragonfly mission to Titan" on youtube.  "Bearings!" got me stopping the video immediately.  lol...the whole world now knows what gets me into Pavlov-mode.    

As everybody mentioned already, that might not be the bearings, I'm afraid.  

I would check to see if there is any play or vibration. (hubs and shafts)  Get the buggy moving at 1/4 speed and move the suspension up and down and steer.  If there are vibrations like below, that's a bearing destroyer.  

I am a bit suspicious of the "universal on one end and dog bone on the other" setting.  I don't know how the phasing works in that case.  This could be due to me lacking mechanical understanding.  Given an option, I'd prefer simpler dog bones. (But dog bones also have a problem of getting too deep into one side, which is why one-universal set up is popular at higher speed application)  

Many drivers use double cardan joints to increase the steering angle.  But it could also could alleviate the vibration problem. There is no phasing issue if two opposing universals are canceling in one housing.  (though, I'm still worried about phasing created by the dog bone side not being canceled, if there is any)

On to the practical matter.  

If only one leg is giving you more trouble than others, I'd replace that hub.  If possible, arms and universal as well. 

A second hand DT03 came with a bent thread. 

I used a big hammer like this to bend it back to shape.   

Even with the sharp end directly hitting it 2 dozen times, it won't go back to the original shape.  If a crash impact could do this to a steel shaft, I'd imagine the hub, arms, and the shaft could be twisted or misaligned in some other way.  

So... here is what I would do. 

[1] look for vibration.  If it's obvious, like the wheel, replace that.  

[2] If it's not obvious and vibration persists, I'd replace the hub. 

[3] If that doesn't work, arms too. 

[4] Then universal.  

[5] If necessary, I'd hot glue some nuts on the lighter end of the wheel to balance the tire too.  

Hopefully, the gearbox or the chassis are fine.  But sometimes they can be deformed from an impact as arms twist the attached points... (next to impossible to do that to a carbon fiber chassis, though) 

How much vibration is bad?  For high-end buggies, only as much vibration as circular tools.  

These circular tools still vibrate, but not too badly. (If it did, it'll break and send shards all over user's face)  Wheels of a good buggy shouldn't vibrate any more than that. 

Which is why I don't like using super glue to glue tires.  Tires can be unbalanced in 100 different ways, and super glue doesn't give you enough time to re-adjust it.  Slow setting shoe glue or silicone caulks gives you time to adjust tires, also easier to remove and re-do. 

If the tire can fit, a prop balancer can be a useful tool.  Even though I have one of these things, for most RC cars, I just rotate it without the dog bone attached and see where it stops.  Do it several times.  Mark the top, and that's where the weight should go.  Repeat until the tire turns smoothly.  

I hope some of our collective ideas would be helpful.  

[Jonathon Gillham 4605]

Thanks everyone for the input.

The front universals were bent. One broke 2 meets ago and they come in pairs so I had a spare. The new one was fine but the old one was obviously worse than the other 3, so replaced that and all are even now.

There was an issue with the centre diff as well. No idea when this became an issue, but it was more spool than diff. I don't think it was adding vibration but I definitely think it wasn't helping with nothing in the centre to absorb the shocks.

I think (hope) the vast majority of the problem was the wheels and tyres. They were an old worn set which came with the car and I never worried too much as Jamie was 5 when he got it and traction wasnt much of an issue. I bought new wheels and tyres and with them on the car it all seems fine now. That'll teach me for cheaping out - if I had bought him new wheels and tyres when he got the car it probably would have saved me a lot of hassle and 20 odd bearings. 

As an aside, I knew i had to replace a shock shaft on the front as one was bent. The replacements i got were shorter than the kit ones. It turns out the other was bent too, just less so, and the D413 shafts were too long and it was a common problem.

Also found a broken shock tower. Grrrr

$200 secondhand roller. Now at $50 worth of replacements, still $400 cheaper than a new kit but I suspect I will be regretting not buying new this time next year 

[nowinaminute 2815]

14 hours ago, Juggular said:

Oh, yes, I was leisurely watching "NASA's Dragonfly mission to Titan" on youtube.

A man after my own heart!

[DK308 219]

Make sure you shim the hubs. The less play there is, the better. Shimming will add stability between the shaft and inner bearing race.

Make sure your wheels are balanced. Unballanced wheels are just as hard on bearings as bent shafts. Use a good lube. I know many like a thin oil that makes the bearing spin really freely, but it does not protect the bearing from neither dirt, heat or impact. Use a thin teflon grease inside. Initially they may seem a bit stiff, but excess grease will be pushed out, and the bearing will spin much more freely once it gets a bit of heat into it.