F1technical.net

Smokes wrote:Right let get back to some basic geometry

I rpm of the inner race has a shorter circumerance than 1 rpm of the outer race. Thus the ball will travel less distance

A little bit about bearing friction

Bearing friction is dependant on the pressure created by the tolerance fit bettween the bore and the shaft the bearing is used to support. These tolerances are use to gurauntee that the races don't slip on the bore or the shaft when the parts expand and contract.They are also there to stop premature bearing failure due to axial radial movement and vibration.

For F1 i schools you need to use a finger press fit which very gently holds the bearing in place. please look at 1/12th RC race car front wheel.

An live axle supported by a bearing will require some method of controlling the axial movement of the shaft in bearing a nut or circlips. Which is stronger but longer. Than using a a dead axle with the bearings in the wheels. which shorter and slightly lighter.

To Prepare bearings for RC competions use. First make sure everthing is clean any dust of drit will ruin the prep work
Remove the bearing seals and a soak the bearings in brake cleaner to remove the OEM lubricant.

Then let the bearings dry out as brake cleaner is a solvent. Then use a lubricant I found, finish line dry chain lube the best. Then place the bearing on the axle and spin the excess lube out, by spinning the outer race. Wipe the bearing dry and put them in the parts. Do not refit the seals as they are a source of friction

You will find some bearing are better than others due transportating damage manufacturing tolerances etc. So i would advise you to buy say 20 bearings and pick the best of the bunch i.e the ones that spin the longest.

For sizing bearing it is usally based on the radial load. Using the smallest size possible will reduce the rotating mass and hence reduce the amount of energy used to turn the wheels though this is still dependant on load. idealy you should use two bearings per an axle to minimise radial movement

dan217 wrote:I sort of had an idea when all the others explained abou the inner ring and the outer ring. I had seen it happen in real life through experiments and thought the inner ring was suppossed to provide resistance to hold the axle in place and thus provide stability. Your explanation was very helpful and cleared all the misconceptions I had. The problem we are facing is that we cant find angular contact bearings with an inner diameter of 2m.m. I contacted Boca bearings if they could custom make them for us but they said the smallest they can go is 6m.m We are trying very hard to get a hold of angular contact bearings preferrably made out of ceramic. With the inner ring sized at anywhere between 2 and 3m.m. Ordering 20 of anytype of ceramic bearings means a lot of cost as they cost atleast $30 that is after the discount we get because we are a sponsored team.

thisisatest wrote:ive been trying to get my head around this bearing rotation thing, i took apart a bearing and marked it like tok-tokkie did. he's totally right.

When a ball bearing operates at high speeds, the centrifugal force acting on the ball creates a divergency of
the inner- and outer-race contact angles, as shown in figure 15, in order to maintain force equilibrium on the
ball.

...

Race control assumes that pure rolling occurs at the controlling race, with all of the ball spin occurring at the
other race contact. The orientation of the ball rotational axis is then easily determinable from bearing geometry.
Race control probably occurs only in dry bearings or dryfilm- lubricated bearings where Coulomb friction
conditions exist in the ball-race contact ellipses, the moment-resisting spin will always be greater at one of the
race contacts. Pure rolling will occur at the race contact with the higher magnitude moment-resisting spin. This is
usually the inner race at low speeds and the outer race at high speeds.

richard_leeds wrote:

thisisatest wrote:... http://ntrs.nasa.gov/archive/nasa/casi. ... 018943.pdf
...

...
The paper then goes onto define different equations for inner and outer race contact.

rjsa wrote:It's funny how now that the math has hit hone I'm guessing how in hell I didn't get it right earlier. The two rulers/pencil example was enough to get it right. The inner 'ruler' is shorter than the outer one in one rev. And I was converting linear distance into angular distance disregarding the difference in radius.

Sorry and thank you to those who where trying to push the truth into my thick skull.

richard_leeds wrote:

rjsa wrote:It's funny how now that the math has hit hone I'm guessing how in hell I didn't get it right earlier. The two rulers/pencil example was enough to get it right. The inner 'ruler' is shorter than the outer one in one rev. And I was converting linear distance into angular distance disregarding the difference in radius.

Sorry and thank you to those who where trying to push the truth into my thick skull.

That alone doesn't explain the difference between applying the drive to different races. I think your assumption (and mine too) was that slip and friction were proportionately distributed on each side. If that had been the case then the balls would move the same regardless of which race was driven.

However if the drive occurs on one side of the ball and the slip on the other (the NASA assumption), then the direction of drive does become a factor. That means the slip occurs either on the inside race or outside race (but not pro rata), and that leads to different friction depending on direction, and that results in different movement of the balls.

Smokes wrote:

dan217 wrote:I sort of had an idea when all the others explained abou the inner ring and the outer ring. I had seen it happen in real life through experiments and thought the inner ring was suppossed to provide resistance to hold the axle in place and thus provide stability. Your explanation was very helpful and cleared all the misconceptions I had. The problem we are facing is that we cant find angular contact bearings with an inner diameter of 2m.m. I contacted Boca bearings if they could custom make them for us but they said the smallest they can go is 6m.m We are trying very hard to get a hold of angular contact bearings preferrably made out of ceramic. With the inner ring sized at anywhere between 2 and 3m.m. Ordering 20 of anytype of ceramic bearings means a lot of cost as they cost atleast $30 that is after the discount we get because we are a sponsored team.

You don't have the mass or the load to justify angular contacts

Buy these
http://www.rc4less.com/product_info.php ... 266b769698
abec 7

ABEC standard

http://en.wikipedia.org/wiki/ABEC_scale

Look at this RC car manual

http://teamassociated.com/pdf/cars_and_ ... manual.pdf

Page 12 these cars go a lot faster and are heavier and pull more load 4g + and do not use angular contacts

flynfrog wrote:what are your theories are they based on existing aero science? How did you come up with your design and what do you hope to accomplish with it.

dan217 wrote:
The reason why im leaning towards these is because my radial ceramic bearings broke before the race. The balls had fallen out and i did a bit of research and apparently it was because of axial loads even though most of the loads are radial but the bearing couldnt take that load. Quite a few teams are using roller bearings and have reduced their times but we think the coefficient is to high. The only reason they reduced their time was because roller bearings are a bit more stable and less energy is wasted in the vibrations.The bearings which got broken were made completely out of ceramic if that helps in any way.

dan217 wrote:

flynfrog wrote:what are your theories are they based on existing aero science? How did you come up with your design and what do you hope to accomplish with it.

If you read the description the facebook page with the extrusion im trying to get the air to meet at the point where the gas canister releases a burst of CO2 so the gas has something to push againt while the other not to have any extrusions is basical to control the direction of the burst of gas from the gas canister; so it helps it to go in a straight line rather than wasting energy producing life or downforce.