TOPIC:

I have some doubt that you use wrong gear ratios.
Never had these problems, with ball bearings and with timing.

Max

Thanks guys,
Eddrick I am not sure that the bronze bushes are better than ball baerings. I am ok for the turbo because the axle is just put with a lot of play. It is the oil pressure wich center and cool the turbo. BBut a turbo run between 100000 and 150000rpm. On a motor the rotor is maintained by the bushes and the contact surface is largely bigger than the 10"points of the balls. Ball bearings accept more charges than bronze brushes. The bronze is used because it is a very fat alliage. there is lead and pewter in. The interest is that is a auto lubricated alliage without care. Bushes become hotter with the risk to tight. Ball bearings make less frictions. Personnaly I never modified myself any motor but these I use with BB are better than bushes.
TThanks a lot for the infos guys
FLO

This is a false problem. You can easy avoid the problem of very high rotation speeds also with ball bearings. The solution is simple.
You can just put one ball bearing inside another one so each of them made the half rpm.
Anyway there's no doubt about friction performances between bushing and bearings.

Max

stingray-63 wrote:

Thanks guys,
Eddrick I am not sure that the bronze bushes are better than ball baerings. I am ok for the turbo because the axle is just put with a lot of play. It is the oil pressure wich center and cool the turbo. BBut a turbo run between 100000 and 150000rpm. On a motor the rotor is maintained by the bushes and the contact surface is largely bigger than the 10"points of the balls. Ball bearings accept more charges than bronze brushes. The bronze is used because it is a very fat alliage. there is lead and pewter in. The interest is that is a auto lubricated alliage without care. Bushes become hotter with the risk to tight. Ball bearings make less frictions. Personnaly I never modified myself any motor but these I use with BB are better than bushes.
TThanks a lot for the infos guys
FLO

I spoke for the turbos on real cars. This type of bushes is not the same than our wheeles or motor bronze bushes. On turbochargers the rotor has no maintaining. It is the oil pressure wich center it. The oil is lubricanting and cooling the turbo. Other very important thing, one side temperature of the turbo is more than 300

This is the only real reason for the bushing in the turbocharger and not the ball bearings.
300

Has this become a contest to see who can say the most innacurate thing?

I'd like to join in myself You'll have to give me some time though, the competition seems quite fierce

I'll have to read back but luckily my own statements are completely accurate at all times.

Absolutely!!!
Maybe have I not all understand.
It is not important. I had my response by Kontemax. It's cooooolllll. Now I know to upgrade a motor or receive it in the mouth

As I said, RC car motor ballraces just raises an eyebrow with me, for theoretical reasons. I've never actually raced with a ballraced motor. As for the racket my retro-ballraced motors make, perhaps it's to do with the crappy fit of the bearings on a slightly worn spindle - again, the observation was made during bench-testing, not actually running it loaded up.
The other thing to consider is there's uneven radial forces on the bearings too, due to the "lumpy" magnetic attractions as the rotor spins.
I agree, 10 points of contact will mean less friction, but it is still metal-to-metal contact which will cause heat build-up & wear....theoretically.
It's one of those things that works better, for just long enough, that it doesn't matter that it's the wrong thing to do

Back to turbo bearings - the ones I've replaced have all been 2-piece, ie there's one sleeve inside another, which in turn bears on the shaft, the outer sleeve can also rotate within the housing, like Kontemax said, to get the effective rotational speed of the bearings down. & yes the spindle "floats" on a cushion of pressurised oil when running, it doesn't (Or shouldn't) touch the bearing metal.
Yes, turbo bearings are relatively "sloppy" feeling, but this isn't inaccuracy - they HAVE to be VERY accurately made, as the clearance is related to how fast oil of a certain viscosity at a certain temperature can flow through them (To keep them clean & cool), whilst still maintaining enough pressure to keep the metal bits apart. If you grab one of the turbines & give it a wiggle, you'll probably see 2-3mm, but the actual clearance between the bearing surfaces can be less than 0.02mm, depending on how well polished the surfaces are. & yes, this clearance will also take into account the different temperatures inside & out of the unit, & differing expansion rates of the dissimilar metals used for bearings, shaft & housing.

The same thing applies to big end bearings, which is the reason stuffing cheap 20/50 in an engine designed to use 10/40, will wreck it - the thicker oil won't flow through the clearance to keep the bearings cool & clean, the bearings end up getting increasingly contaminated & wear out quickly

Speaking about r/c brushed and brushless motors.

The r/c bronze bushings don't have the same accuracy then a big turbofan.
The r/c motor bushing is self lubricating or lubricated with some sort of grease or oil. Oil is not in pressure and doesn't flow.
In an r/c motor dirt and debris arrive to the end bell bushing.
In an r/c motor the rotor shaft has another side force that pushes it always in the same side of the bushings making the holes elliptic.
In an r/c motor the rotor shaft will wear where is in contact with bushing, so the tolerance will go away.
In an r/c motors the bushing warms up. It will grow up for heat and resistance will increase. Increasing the resistance the bushing will heat up more again.

Other arguments?

The best thing to do is make some experiment by yourself.
Buy a couple of motor ball bearings. Take one of you well known motor and replace the bushing with BB. Use it. Same car, same battery, same motor, just only the bushing replaced with bearings.
Try the car, not the motor, or try the motor and then the car. You will hear a different sound and you will see increased performances and discharge time.

Max R/