Should Gears be Lubed?

[HO RacePro]

Is it a good idea to lubricate gears? There are several factors to consider here...

First, what are the gears made of? I have been using unlubricated sidewinder aluminum gears designed for drag racing in my scratch-built 1/32nd scale cars. That choice is based on trying to get maximum performance, accepting high cost and short wear life. If I were more interested in low cost and long wear life I would be using a plastic spur gear, and maybe a steel pinion gear.

There are different kinds of plastic gears. The best is probably what is known as a Nylatron gear. That is a gear made of Nylon plastic that is impregnated with a solid lubricant. Nylatron gears are often used in industry where applying a lubricant is not possible. And, depending on the application, Nylatron gears can often outperform and outlast metal gears. But there are few Nylatron gears designed for slotcar use, and fewer still that have a fine tooth pitch and accurate tooth form. -- both qualities I seek for high performance.

The problem with lubricating slotcar gears is keeping the lubricant on the gear teeth. The impacts of gear operation plus the centrifugal forces of rotation can quickly squeeze and sling lubricant away from where it is needed most. And a lubricant that is sticky enough to stay put will absorb mechanical energy, turning horsepower into heat. The gears may last longer, but performance will take a hit.

My theory is that running gears unlubricated maximizes performance, with the understanding that gear life will be short. I accept that I'll need to replace gears frequently and it'll cost me. But theories sometimes fail to reflect reality. I'm interested in hearing some discussion on this topic.

[4424ever]

Yes PTFE

[Mikeinclover]

Why do you think that would be a performance advantage? If it is wearing out quickly it has resistance and that will slow you down. Lube makes it move easier.

[Bal r 14]

My thoughts as well. Friction will impact performance. The lube I use doesn't accumulate or get thrown all over the place.

[Silberpfeil]

Shamelessly "time-shared" from your friends at "Scientific Magazine".
For your dining and dancing pleasure...






Calculation of Tooth Face Friction Factor of Spur Gear under Different Lubrication Conditions


Gear transmission system mainly has 4 different lubrication states, including elastohydrodynamic lubrication, mixed lubrication, boundary lubrication and dry friction. The friction coefficient of tooth surface is different under different lubrication conditions.


1. Calculation of Friction Factor under Elastohydrodynamic Lubrication
In actual operating conditions, relative sliding speed, lubricant viscosity and other factors will affect the friction coefficient, which also becomes a function of time t.It is known from literature [15] 846-846 that the friction coefficient of tooth surface at any engagement point of main and driven wheels under ejection-hydrodynamic lubrication is.

F (s (t), Fhzi (t), Fhzi (t), 950, Sav) =b1+b4|s (t) |s (t) |Fhzi (t) |Fhzi (t) |Fhzi (t) lg0+b5e-|s (t) |Fhzi (t) lg0+b9eSav, b1-b9 are empirical regression coefficients; Fhzi (t) lg0+b9eSav, b1-b9 are empirical regression coefficients; 0 is dynamic viscosity coefficient of lubricating oil; Sav average surface roughness, mm; s (t) is average surface roughness, mm; s (mm; s (Hertz contact stress of driven wheel with Fhzi(t) dominant

In this formula, the normal load per unit tooth width of driven wheels with pei(t) dominant is calculated as N/m.

In the formula, T is torque, N_m; Bi is main and driven gear tooth width is m M.

Average tooth surface roughness Sav is

In the equation, S1 and S2 are respectively the roughness of the tooth surface of the primary and secondary gears.

The radius of curvature R(t) is

Relative sliding speed vs(t) and entrainment speed ve(t) are respectively

The roll-slip ratio s(t) is

The empirical regression coefficient is b1=-8.916 465, b2=1.033 030, b3=1.036 077, b4=-354 068, b5=2.812 084, b6=-0.100 601, b7=0.752 755, b8=-0.390 958, b9=0.620 305.



2. Calculation of friction coefficient under mixed lubrication:
The expression of the friction coefficient umi(t) of the tooth surface at any engagement point of the main and driven wheels under mixed lubrication is as follows:



3. Calculation of friction coefficient under boundary lubrication
The expression of the friction coefficient of the tooth surface at any engagement point of the main and driven wheels under the boundary lubrication state is as follows:

In the formula, MUAV is the average friction coefficient; _is the adjustment factor, and 50 is usually taken to satisfy the smoothness of the curve; _is the gear ratio; Xi (t) is the periodic displacement of the meshing gear secondary and driven wheels, and its calculation formula is as follows:

In the formula, the indexing circle radius of ri-dominated and driven wheels is mm.


4. Calculation of friction coefficient under dry friction condition
The dry friction coefficient of the contact surface of the gear can be measured by measurement. Generally, the dry friction coefficient of the tooth surface in the gear drive is in the range of 0.1-0.5, where the friction coefficient of the tooth surface is mud=0.4.

[slothead]

These days many people distrust 'experts' because lacking an understand the topic allows people to imagine those in the know are just making it up. I think this shows that with a sound basis in math and engineering complex topics can be quantified and solutions found. My simplified interpretation of the above as it regards this topic is - contact a quality hobby shop (SCC or Clover Leaf) or racer (Dennis Samson or Chris Walker) and ask what they recommend or use.

[Brumos RSR]

My head hurts now….

[mattb]

We run Cox, Parma, or Weldon nylon gears, brass or steel pinions. After a car is assembled, run and timed, I oil gears and see a lower lap time. It's hard to argue with the clock.

[4424ever]

Very good point Kevan

[6666hotrod]

THERE ya' go : I recently assembled a brand new Chassis, and it's required parts, prior to getting the body on. It was noisy, from the gears maybe slightly binding, but it was still quick. A LITTLE, lubrication on the pinion and crown gears, and chassis transformed, into a relatively quiet, Smooth little Rocket, with the quickest lap times of any non-traction-magnet slot car, I have !!

[4424ever]

I’d say it’s more common sense

[Kevan]

Everybody's 'common sense' is different, a person who chooses different to you is using their 'common sense' whether you think it's generally right or wrong.

[HO RacePro]

Here's the thing...

Ideally gears do not rub, they roll. Gears with involute teeth are supposed to transmit power without any rubbing. So in theory friction does not come into it. Look at the animation in the Wikipedia link below. You should be able to see how involute gears roll.

https://en.wikipedia.org/wiki/Involute_gear

In actual practice there is such a thing as 'rolling friction', but that requires some distortion at the interface between the gear teeth. A great example of unlubricated rolling is railroad wheels. They have to be very, very efficient given the immense tonnage that a modern railroad train represents. The contact patch between a railroad wheel and a rail is very small, because both are made of steel, and the amount they deflect is tiny despite the heavy load. It is that slight distortion that makes for what little inefficiency exists in rolling down a level track. That, and the 'give' in the roadbed which also wastes some power.

Now it should be mentioned that most slotcar gears -- especially crown gears -- do not have involute tooth forms. They tend to have much more angular sawtooth shapes. So there is much more rubbing power loss than would exist if they had true involute tooth forms. So it is not surprising that those gears benefit from lubrication.

The drag race gears I use -- made by Sonic -- have what appears to be pretty accurate involute tooth forms. So in theory they roll. It would be very interesting to hear from drag racers who use Sonic gears, and whether they lube their gears or not.

[4424ever]

Yup

[mattb]

Heating gears helps smooth out the mesh, add a drop of oil, there isn't much more you can do. You could try to read those formulas above, but that would give you a headache and ruin the whole idea of a relaxing and fun hobby.
Here's the trick we have. No car is allowed to lap at faster than 4 seconds. You gear more or less to get the lowest legal lap time you can. It don't matter if your gears have been to space or gold plated, you can't have a car faster than 4 seconds.

[War Eagle River]

I never oil or lube anything. That way I can buy more gears, axles, bushings, wheels, guides, motors. You know, to keep the Hobby shops in business!

[Mikeinclover]

And as a dealer of such parts I do appreciate it.

[Aptosc6]

Way back people used to use Graphite for slot car gears. No parasitic drag like oil. For drag racing, this should be adequate for short time gearing as long as the gears are made of unlike materials (I.e., pinion of one material and spur of a different material).

[Loan Shark]

I use graphite mixed with a tiny bit of grease.

[dungeonracer]

Dunno if it's worth mentioning, but I have a car that uses the stock Slot.It 32t plastic gear that they provide with their sidewinder cars and a NSR 12t pinion.

The car has been through two 24 hour enduros (48 hours), with probably 2-3 hours practice time (now 50-51 hours).
I still use the car in club racing, and would guess it's probably got another 4-5 hours on it. (now 54-56 hours)

Still runs like a champ.

Lubrication? None, zip, na-da.

So should gears be lubed? IMHO, it doesn't matter. Lube 'em if you want, or don't....

[6666hotrod]

Now, THAT's good !

[Mickey thumbs]

Lubricants can actually lead to increased gear wear over time if not regularly cleaned off and reapplied because they attract and hold dirt and grit forming an abrasive paste.
4424ever’s recommendation of ptfe lube, especially for plastic gears, is interesting. Even after ptfe lube is wiped off plastic it seems to leave behind some slippery residue. I’ll test this out the next time I break in a plastic geared car. I break in new cars(not just motors) by running them on my track at 4v with Trackmate on. I usually run the gears dry for several minutes to break in, then lube them with slot.it grease - the lap times drop after lube. But they do get cruddy over time. Maybe the ptfe applied and wiped dry will stay cleaner, Worth a test!

[HO RacePro]

The Sonic brand drag gears I use are machined aluminum. At least I think they are machined. If so, they probably have a certain amount of surface roughness that might retain a lubricant.

Googling about greases recommended for aluminum, I find references to lithium, moly and 'aluminum complex' greases. Molybdenum (Moly) grease is supposed to chemically deposit a lubricating layer on metal parts. Dunno what the deal is with 'aluminum complex' greases. And then there is 'Super Lube' synthetic grease -- a grease I have used in slotcar applications.

I haven't seen much information about how these different greases might perform on aluminum gears. Or even if they are suitable for such service. I suppose the intelligent thing to do would be to try them and see if they have any effect on lap times. I already have a bunch of different greases in inventory used for motorcycle maintenance. A good place to start.

Could turn into a pretty big project...

And now that I think about it, might make sense to contact the folks at Sonic and see if they have any recommendations for lubing their gears. Seems logical they might have an informed opinion on the subject, yes?

[chrisguyw]

Hi Ed, Phil Hackett (Sonic) has been making high end precision slot gears for both drag and circuit racing for many years, and his products are very well regarded. He also has made some 1/32 .5 module pinions and Spur gears (MRSlotcar). I think you will find (should you contact him) that he will suggest that proper gear set-up is is far more important than any type of lubrication.
That said, for the 1 second or so that Drag cars take to make a pass, lube may be of some benefit in this form of racing, but not so much for any type of circuit racing,......most of the serious commercial track racing guts do not bother with gear lube,......gear set-up is much more important.

[Kevan]

Whilst searching for nano lubricants I found Cylion chain lube with:

Nanometer additives design brings excellent lubricating, anti-rust and anti-wear effects.

...I've used it since on gears and bearings.

[mattb]

I believe the only answer is for somebody to set up about 10 break in stands. Buy 10 similar chassis and change to every gear combination there is. Lubricate or not lubricate with all the above mentioned chemicals. Run the cars till the gears burn out. Make a big graph showing the comparisons of lube and run time. By sometime next year it should be done and we can know for certain what is the best gear treatment.

Or,,,,, just run your car and put a little fine gear oil on it and see if it is faster. Maybe that is too easy.

[HO RacePro]

While gear oil may sound like a logical choice, it is designed for applications where the gears are totally enclosed and in a bath of the stuff. It is typically a very thick lubricant -- much thicker than motor oil. It is primarily designed to prevent wear. Minimal power loss is an important, but secondary consideration.

[Kevan]

Setting the gearmesh correctly is much more important than 'to lube or not to lube'.