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Masten Gregory
Novice builder busy researching how to build from the many experts and gentlemen on this site.
Posts: 11
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Post by hm on Dec 23, 2013 17:13:17 GMT -5
I find this topic very interesting but surely if ball bearings were needed on axles they would have appeared on motors first due to their faster rotational speeds. I accept they are better balanced but they are faster and if you ever put one back together without all its spacers move axially a lot when revved when not engaged with a pinion?
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Post by f143 on Dec 24, 2013 2:47:18 GMT -5
These cars we play with are toys. ( so I am told. ) Ball bearings are expensive. Slot racers, use ball bearings because they are an engineering solution to reducing friction in the drive train. If you want a higher tech solution to reducing friction in the drive train, use ball bearings. If you want a low cost solution use oilites, perfectly acceptable or lower cost, plastic/nylon bushes. A lot depends on your personal budget, just like real Grand Prix racing. Just my 2p. Nigel
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Post by Peter Seager-Thomas on Jan 14, 2014 15:21:44 GMT -5
I would now disagree that ball bearings are better. I simple test has proven this.
A ball bearing mounted axle, with wheels acting as flywheels pretty well stops as soon as you stop spinning it, a similar axle, mounted in brass bushes spins for a while. The same test carried out on front wheels gave the same result.
I'd guess the main advantage with ball bearings is almost zero wear.
Spec charts (NTN) show that ball bearings only show their true worth running open (without shields or seals)with a generous oil mist for lubrication.
I'll still use them since most of my cars have a surplus of power, so any minor losses are of no great concern.
Peter.
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Post by munter on Jan 9, 2015 4:14:19 GMT -5
A combination I like for a couple of reasons is the slotit axle and the oilite that Champion produce. Cost and function are those reasons. They fit together with a snug but not tight interference. The axles are readily available and the Champion oilites can be bought for reasonable prices in a six pair pack. My supplier for the Champion bearings...is here. I doubt you will use him because he is so far away. Champion oilites 6 pair pack
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Post by bob on Jan 10, 2015 12:03:28 GMT -5
dmwproducts.com/products-ballbearings.htmlThis is an interesting discussion indeed. First off I get my bearings from here, link above, price is very good I find, and shipping is quite reasonable and quick. Second I also counter sink my brass bushings by hal to reduce the friction surface, and also use a home made lubricant. Third, on the oilites, I have been told, but not yet tried, placing them on Mrs Iron and letting them get quite hot to dry them out. Then upon install, apply a low viscosity lubricant. Im really not sure what the iron and heat does to the oilites, but a couple of the lads I race with do it and swear by it. Perhaps someone here may be able to explain it. With regard to the brass bushings, I use 3/32 reamer to ensure I have the correct inside diameter. It is my understanding that the sole purpose of the bushings is to provide axle seating and alignment, so I agree with the countersink, keeping the contact patch to the outside. The othe little thing I have tried is what I did on a Fly Williams gearbox. I drilled multiple small holes right through the gear box thereby removing plastic which lessened the contact patch where the plastic shaft runs. This decreased the friction area and allowed the usually slower Williams to perform much better, and added lube points. If one where to do this with a brass bushing, I don't see why it wouldn't give the same effect, as you are still removing friction area. I wish I knew the technical reason behind the heating of the oilites, but I'm afraid it is just a bit of info I picked up. Hope I am making sense here. Bob
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Post by munter on Jan 10, 2015 16:02:20 GMT -5
My understanding of heating oilites is....don't. The oilite is impregnated with oil and heat drives it out. I have soldered oilites into brass brackets with little effect though. I have since followed others advice and used loctite to fix them in place.
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Post by Phil Kalbfell on Jan 10, 2015 16:28:09 GMT -5
Heating oilites tend to remove the oil that is impregnated in the bearing material. To add the oil back into the bearings they should be heated in oild and then cooled so the oil is absorbed into the porus bush material.
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Post by slo on Jan 10, 2015 17:58:31 GMT -5
I'm finding this is an interesting topic, with some new and interesting ideas. The front oilites on our GP'd bt19 I immersed in the oil bottle, with the lid opened it was then put in a spray paint pressure pot and pressurized up to 60psi and left there for ten minutes. The idea was to force oil into any empty capillary voids in the sintered bronze I used to machined the oilites with. I too used loctite to fix the front oilites, this its the first time I've glued any oilites in place so I was a bit reluctant to glue the rear ones not knowing if gluing would be adequate, they were soldered. I cleaned the oilite outer by wiping them with circuit board cleaner before being glued and soldered, just seemed like a surer way for a stronger bond. Incidentally, the fronts on this car spin more freely on this car than any other I have had anything to with and the glue held them in place adequately. I have never used bearings before so cant really comment. I would think a lower viscosity oil might be beneficial. I think Taffy used bearings on his Matra, It would be interesting to hear what he thinks. Just putting in my 2bobs worth.... Phil, any idea on how much heat is needed to reheat the oilites?
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Post by Phil Kalbfell on Jan 11, 2015 6:29:37 GMT -5
Stu can't remember what temperature now, we were supplied with container with pressure control that we would put on a gas ring. All supplied my the machine manufacturer , I do remember that it was a job we did every 8 to 12 month depending on run time.I think the oil was a thin Tellus.
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Post by David Lawson on Jan 11, 2015 7:50:56 GMT -5
Phil and Stu
I have always soaked my oilites in oil for a day or two if they've been subjected to soldering heat but I've never warmed the oil or applied pressure. I haven't had any problems with these bearings so always assumed what I was doing was effective, are you saying that what I'm doing isn't having a beneficial effect?
David
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Post by Andrew Rowland on Jan 11, 2015 15:12:01 GMT -5
I would now disagree that ball bearings are better. I simple test has proven this. A ball bearing mounted axle, with wheels acting as flywheels pretty well stops as soon as you stop spinning it, a similar axle, mounted in brass bushes spins for a while. The same test carried out on front wheels gave the same result. I'd guess the main advantage with ball bearings is almost zero wear. Spec charts (NTN) show that ball bearings only show their true worth running open (without shields or seals)with a generous oil mist for lubrication. I'll still use them since most of my cars have a surplus of power, so any minor losses are of no great concern. Peter. Peter i'm quite surprised by the results you speak of. I have to suggest with all respect to your engineering excellence that something is not quite right with your test! The problem I have found is that setting up ball races accurately is very difficult. The motor mount / bearing holder needs to be very very accurately set up so that the bearings have no rotation otherwise they do indeed give the result you speak of. They have no play allowed so need to be perfectly set up on the centre of rotation. Oilites and simple bushings are far more forgiving in set up as there is always a lot more play between the axle and the bushing itself. This allows imprecision in alignment to be unnoticeable. I have found that even the tightening up of the motor screws can realign the bearing positions as any distortion of the motor and / or motor Mount is changed as the screws are tightened. Another thing is that when scratchbuilding it is very common for tiny bits of filing (steel, brass, plastic or resin) to get into the bearings even when they have side covers. This needs to be carefully blasted out using a WD40 spray or similar. If you do this on clean tissue you can usually see any filings sparkling in the puddle left over. All in all ball races, if set up properly WILL DEFINITELY reduce friction in the drive train. I saw this effect first hand once when racing someone elses car (with bearings) at Wolves Early Birds. The power was cut at the end of the race and my car just kept on rolling, past my competitor and past the finish line so I completed another lap!! OK only 6 feet or so but much more than anyone else. Of course this effect can play havoc with braking and may not actually be desirable for these low torque motors where braking effect is so important!!!! Just my tupnny Worth... Andi
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Post by slo on Jan 11, 2015 17:04:23 GMT -5
Hi David. I machine my oilites from sintered bronze rod which is already impregnated with oil, and in the turning down to size, the swarf gums up because of the oil. Swarf does not fall away from the machined part so I wipe the swarf off using a clothe wetted with either isopropyl alcohol or circuit board cleaner. In wiping the oilite I'm machining, measurements with the verniers can be done more accurately and minimizes any swarf interfering with the fitting of the oilite into its sleeve. Wiping it clean using these products dries out the oilite. Rather than relying on the oil to soak in, I used pressure to further ensure oil penetration into the material with minimal air retention trapped in the voids or capillaries of the sintered oilite. Oilites purchased off the shelf are not subjected to this drying as the ones I make are. It also allows me to have some control over the oil present in the oilite. I use an oil by Ultimate, which is red in color, probably an auto transmission type of oil if the truth be known. Not implying you or anyone else is doing the wrong thing at all, just merely sharing ways to replenish dried out oilites.
Cheers Stu
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Post by bob on Jan 11, 2015 21:44:04 GMT -5
Stu I did a little further research on the oilites and the iron technique Apparently it does a couple of things . With the regular brushes such as on an SCX rx motor, it hardens them. But on the oilites it heats the thicker oil impregnated in the oilites out. Then they are put into a lighter oil such as a tranny , or power steering fluid which it is soaked in to reimpregnate the oilite. Ideally if done in a pressure pot it gets a better result for impregnation. Some of our guys are just using a paint pot at 60psi. The advantage is small but is still an advantage apparently. I already stated I use a special mix for my oil which consists of 90% 0w 20weight synthetic motor oil, and 10% ZMax motor additive. it gives a finer oil base and is still a good lubricant. The Z Max is a bit pricey, but the quart or litre of oil is Castrol and normally priced. One time will last a long long time. it is also good on the other lube points too. Bob
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Post by Peter Seager-Thomas on Jan 12, 2015 5:10:46 GMT -5
Peter i'm quite surprised by the results you speak of. I have to suggest with all respect to your engineering excellence that something is not quite right with your test Actually the test was and is fine. The axle with the plain bearings did and does spin better. The bearings in question for the rear were shielded and as supplied, greased. The issue therefore was not friction, but drag. These bearings are exposed, so I prefer to keep the shields. The front wheel bearings were of an open type, so these were indeed flushed through with WD resulting in almost zero drag. These bearings are enclosed, so dust etc should not be an issue. Peter
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Post by Andrew Rowland on Jan 12, 2015 9:11:30 GMT -5
Peter, then accept my apologies. Just that i've done the same test and found the opposite. Maybe it was my test that was wrong then!
Best wishes Andi
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