Author Topic: Full Ceramic shaft bearings (Read 1435 times)

Dennis Toth · « **on:** October 04, 2012, 02:05:49 PM »

Guys,
Boca Bearing (and I'm sure others) have a line of full ceramic ball bearings that would replace the normal steel set that comes in most engines. The ceramic's are about 1/3 the weight (and at least 3 times the price) of the full steel. They are used in gas turbines and other high stress applications.

My question is has anyone used full ceramics ball bearings to replace the shaft steel ball bearing and do they hold up to our type of stress?

Best, DennisT

phil c · « **Reply #1 on:** October 04, 2012, 02:44:27 PM »

If by full ceramic you mean ceramic balls and ceramic races that is kind of overkill. The main reason to put in ceramic bearings is to pretty much eliminate the effects of corrosion. Just ceramic balls do that. The balls take a big beating compared to the races, so a tiny amount of corrosion can quickly cause the ball to start shedding bits.

If you take the time to run the engine dry after every flying session and put some airtool oil in and work it around with a dozen or so prop flips standard bearings should last at least 500 flights. Ceramic balls give you and added degree of protection in case you forget the engine cleanup and will probably last 3 times as long.

RandySmith · « **Reply #2 on:** October 04, 2012, 02:56:32 PM »

Quote from: Dennis Toth on October 04, 2012, 02:05:49 PM

Guys,
Boca Bearing (and I'm sure others) have a line of full ceramic ball bearings that would replace the normal steel set that comes in most engines. The ceramic's are about 1/3 the weight (and at least 3 times the price) of the full steel. They are used in gas turbines and other high stress applications.

My question is has anyone used full ceramics ball bearings to replace the shaft steel ball bearing and do they hold up to our type of stress?

Best, DennisT

HI Dennis

Yes I have tried this many times over the years, The ceramic bearings give about 20% more wear time...ie bearing sets last about 20% longer, in properly taken care of engines. Myself ,the 2 Billy's , and the Bear were the test mules
They Give no increase in performance in a stunt application, They do in racing combat motors, and are more expensive. The rust issue could be a big one with people running all synthetics or ones living on the coast, or those who don't take proper care with the motors.
Also don't forget they are available with just ceramic balls with steel races, and phenolic cages

Randy

steven yampolsky · « **Reply #3 on:** October 04, 2012, 03:06:36 PM »

Quote from: RandySmith on October 04, 2012, 02:56:32 PM

Also don't forget they are available with just ceramic balls with steel races, and phenolic cages

Speaking of bearings,

I had to replace bearings on a 40VF and ordered ceramics with phenolic cages. The motor performance worsened(consistency wise, not power)! Is there a rule on how to install them? Should the cages face the front of the back of the motor? Should I have ordered steel races?

Randy Cuberly · « **Reply #4 on:** October 06, 2012, 01:40:55 AM »

Not of particular importance for the application in a stunt engine, but one of the primary reasons for engineering ceramic bearings other than the obvious increase in corrosion resistance is the fact that the lower mass of the ceramic balls makes it easier for them to move and roll in high speed applications than the heavier steel balls. This can be a significant improvement in bearing life and friction losses in very high speed applications.
The bearing race and ball speeds at the RPM range we run stunt engines is not really high enough to make the extra expense cost effective.
I've used them in a couple of ST60's and except for the "cool" factor couldn't see any improvement in performance. Incidentally the cost of those particular bearings were a lot more than the metioned 3X. more like 6X the cost of conventional bearings.

Randy Cuberly

Randy Cuberly · « **Reply #5 on:** October 06, 2012, 01:55:47 AM »

Quote from: Steven Yampolsky on October 04, 2012, 03:06:36 PM

Speaking of bearings,

I had to replace bearings on a 40VF and ordered ceramics with phenolic cages. The motor performance worsened(consistency wise, not power)! Is there a rule on how to install them? Should the cages face the front of the back of the motor? Should I have ordered steel races?

Hi Steve,
For small bearings like we use, phenolic cages can give higher friction coefficients. I'm not sure of course that this factor is why you had problems.
The cages (closed end) should face toward the direction of thrust load. It is significantly easier to damage phenolic cages than conventional steel ones if installation loads are misplaced. Normally special tools are used to place equal and even loads on the inner and outer races during installation to insure that the balls are not driven into the cage which can be broken or damaged if uneven loads are placed on the bearing during installation.

Randy Cuberly

Lauri Malila · « **Reply #6 on:** October 06, 2012, 03:01:57 AM »

Hi.

In speed classes, especially in RC pylon racing, they use ceramic balls mainly because steel ones don't stay in one piece in such high rpm. It's quite common that the inner "ring", or the groove is machined directly to crankshaft.
But another interesting thing is that you get allmost the same wear time if you replace even one steel ball in the bearing with a ceramic one. (for balance reasons it's good to replace two in our engines). It somehow keeps the ball grooves smooth.
Also, I've seen some F2A (speed) engines with 1/2 or 1/3 of balls ceramic. I think the reason for that is to get rid of unwanted resonances.
Steven, there is quite a few things that go wrong when you replace bearings. To make it short, "standard" bearings tend to have too little clearance for our engines, and when you compress the bearings into case/shaft, you may end up with too little axial play. Normally C3 or C4 clearance is used.
I think that with the rpm we use in stunt, and the amount of lubrication, all kind of bearing and cage materials will work succesfully if they are well set.

Lauri

Dennis Toth · « **Reply #7 on:** October 09, 2012, 10:21:13 AM »

Randy,
I understand the corrosion benefits of using the ceramics. Since you have done actual testing and they did hold up to our application now the question is what is the weight savings (if any) of the full ceramic bearing vs the steel ones? Seems regular steel bearing for a 40 - 60 are about 1 oz ish. I thought the ceramics are about 1/3 to 1/2 the weight of the steel so you could save 1/4 - 1/2 oz depending on the engine bearings size?

In the nose of the ship this could be significant if one has to add tail weight to balance, the total weight savings could be 30% more?

Best, DennisT

RandySmith · « **Reply #8 on:** October 09, 2012, 12:19:54 PM »

Quote from: Dennis Toth on October 09, 2012, 10:21:13 AM

Randy,
I understand the corrosion benefits of using the ceramics. Since you have done actual testing and they did hold up to our application now the question is what is the weight savings (if any) of the full ceramic bearing vs the steel ones? Seems regular steel bearing for a 40 - 60 are about 1 oz ish. I thought the ceramics are about 1/3 to 1/2 the weight of the steel so you could save 1/4 - 1/2 oz depending on the engine bearings size?

In the nose of the ship this could be significant if one has to add tail weight to balance, the total weight savings could be 30% more?

Best, DennisT

HI Dennis

The cost is a deal killer to some, others, not so much, I guess that is the reason I have sold so many magnesium parts, For many it is worth the cost,
If you want the weight savings , you will have to buy Full Ceramic with both the inner and outer ceramic along with the balls.Now if it is just corrosion, you can install stainless bearings.

Randy

Randy Cuberly · « **Reply #9 on:** October 09, 2012, 01:36:47 PM »

Quote from: Dennis Toth on October 09, 2012, 10:21:13 AM

Randy,
I understand the corrosion benefits of using the ceramics. Since you have done actual testing and they did hold up to our application now the question is what is the weight savings (if any) of the full ceramic bearing vs the steel ones? Seems regular steel bearing for a 40 - 60 are about 1 oz ish. I thought the ceramics are about 1/3 to 1/2 the weight of the steel so you could save 1/4 - 1/2 oz depending on the engine bearings size?

In the nose of the ship this could be significant if one has to add tail weight to balance, the total weight savings could be 30% more?

Best, DennisT

Not sure which Randy you were addressing but I'll answer also.
The ST60 bearings I used weigh only .2 oz less than the original steel bearings (that's the combined weight of both bearings). Obviously most of the weight is in the races!
Cost was $62 for the rear bearing and $51 for the front for a combined cost of $113...lot of green for .2 oz.
And...that was several years ago..maybe more now.

Randy Cuberly
PS: That was ordered through Raytheon with a discount!!!

Mike Greb · « **Reply #10 on:** October 09, 2012, 05:59:13 PM »

When I WAS racing nelson 36 motors in slow rat, i put a set of boca ceramic bearings in, could not tell any difference between them and the "High Speed" boca bearings I had in other motors.

phil c · « **Reply #11 on:** October 12, 2012, 11:53:01 AM »

If you're interested mainly longer bearing life give a full complement bearing some thought. You almost have to make them yourself. It involves grinding access notches in the inner and outer race so you can remove all the balls and the cage and stuff in a "full complement" of balls with no retainer.

The durability can be substantial. Combat buddy Bob Burch did some bearing calculations(he's more of an engineer than I am). The standard bearing is 17mm i.d. by 25 mm o.d. with 16 very small balls, a very small, light bearing. A standard bearing in a similar size engine case usually is about 12-15mm i.d. by 28mm o.d. and probably weighs twice as much. According to the numbers by Bob(side force on the bearing, # of balls, size of the balls, material, rpm, and vibration forces) gave the lightweight bearing an estimated 6 hrs of run time(at around 25,000 rpm). Going to full complement, 22 balls, upped the estimated life to 30 hours.

Per Randy and Lauri's suggestions, if you must replace the bearings get stainless steel bearings with the same class of clearances and a plastic cage. The plastic is light, low friction, doesn't fatigue, and if somehow bits do come off they are very unlikely to damage the engine(unlike a steel cage).

Chris Wilson · « **Reply #12 on:** October 14, 2012, 04:24:25 PM »

Quote from: phil c on October 12, 2012, 11:53:01 AM

Per Randy and Lauri's suggestions, if you must replace the bearings get stainless steel bearings with the same class of clearances and a plastic cage. The plastic is light, low friction, doesn't fatigue, and if somehow bits do come off they are very unlikely to damage the engine(unlike a steel cage).

Do plastic cages stand up to model diesel use?

phil c · « **Reply #13 on:** November 24, 2012, 06:26:36 PM »

I never asked about kerosene, but they stand up to after run oils just fine, even with a year in storage. Even if the plastic cage is affected I'd expect it to get brittle, not melt away. If it saves one steel-caged bearing breaking in your engine it would still be worth it.

Author Topic: Full Ceramic shaft bearings (Read 1435 times)

Dennis Toth

Full Ceramic shaft bearings

phil c

Re: Full Ceramic shaft bearings

RandySmith

Re: Full Ceramic shaft bearings

steven yampolsky

Re: Full Ceramic shaft bearings

Randy Cuberly

Re: Full Ceramic shaft bearings

Randy Cuberly

Re: Full Ceramic shaft bearings

Lauri Malila

Re: Full Ceramic shaft bearings

Dennis Toth

Re: Full Ceramic shaft bearings

RandySmith

Re: Full Ceramic shaft bearings

Randy Cuberly

Re: Full Ceramic shaft bearings

Mike Greb

Re: Full Ceramic shaft bearings

phil c

Re: Full Ceramic shaft bearings

Chris Wilson

Re: Full Ceramic shaft bearings

phil c

Re: Full Ceramic shaft bearings