Secret Oil Process
- Thread starter birddog
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Thinking is good, don't stop doing that!! There could very well be some speed in it just nothing I personally have tried. I know others have or still do wax axles, if they are, their not say much about it any more.
I have tried waxing axles and running with both the axle and bore surfaces coated or made of something like Teflon. It tends to shed the oil... like a waxed car. You need one surface to be able to grab the oil and hold it and the other surface to be slick. It's the whole hydrodynamic lubrication, boundary layer thing.... where is Stan or M when you need them.
taken from: http://www.phy.davidson.edu/fachome/dmb/PY430/Friction/lubrication.htm
my notes are in {}
Lubrication
The modern period of lubrication began with the work of Osborne Reynolds (1842-1912). Reynold's research was concerned with rotating shafts rotating in bearings and cases. When a lubricant was applied to the shaft, Reynolds found that a rotating shaft pulled a converging wedge of lubricant between the shaft and the bearing. He also noted that as the shaft gained velocity, the liquid flowed between the two surfaces at a greater rate. This, because the lubricant is viscous, produces a liquid pressure in the lubricant wedge that is sufficient to keep the two surfaces separated. Under ideal conditions, Reynolds showed that this liquid pressure was great enough to keep the two bodies from having any contact and that the only friction is the system was the viscous resistance of the lubricant.
There are four essential elements in hydrodynamic lubrication the first two are obvious, a liquid (hydro-) and relative motion (-dynamic). The other two are the viscous properties of the liquid, and the geometry of the surfaces between which the convergent wedge of fluid is produced. When considering hydrodynamic lubrication we must be very careful about how we treat the viscous properties of our lubricant. Since the only friction present in a hydrodynamic lubrication system is the friction of the lubricant itself, it would make since to have a less viscous fluid in order to minimize friction: the less viscous a liquid the lower the friction. Too low of a viscosity jeopardizes our system though. We have to be very careful that the distance between the two surfaces is greater than the largest surface defect {why polishing is so important}. The distance between the two surfaces decreases with higher loads on the bearing, less viscous fluids {part of the magic of DD4H's modification to Krytox}, and lower speeds.
The surface geometry is also very important. The surfaces have to be such that a converging wedge of fluid can develop between the surfaces, allowing the hydrodynamic pressure of the lubricant to support the load of the shaft or moving surface. This is obtained in a number of ways, a common design other than the shaft and bearing {perfectly round wheel bore and axle}configuration is the tilted pad bearing, where a tilted pad skims over a sheet of fluid.
Hydrodynamic lubrication is an excellent method of lubrication since it is possible to achieve coefficients of friction as low as 0.001 (m=0.001), and there is no wear between the moving parts. Special attention must be paid to the heating of the lubricant by the frictional force since viscosity is temperature dependent. One method of accomplishing this is to cycle the lubricant through a cooling reservoir in order to maintain the desired viscosity of the fluid. Another way of handling the heat dissipation is to use commercially available additives to decrease the viscosity's temperature dependence.
We also have to pay special attention to the extremes of motion, when using hydrodynamic lubrication: starting and stopping. When the surfaces are at rest with respect to each other, or at very low speeds, the distance of separation is theoretically zero."
my notes are in {}
Lubrication
The modern period of lubrication began with the work of Osborne Reynolds (1842-1912). Reynold's research was concerned with rotating shafts rotating in bearings and cases. When a lubricant was applied to the shaft, Reynolds found that a rotating shaft pulled a converging wedge of lubricant between the shaft and the bearing. He also noted that as the shaft gained velocity, the liquid flowed between the two surfaces at a greater rate. This, because the lubricant is viscous, produces a liquid pressure in the lubricant wedge that is sufficient to keep the two surfaces separated. Under ideal conditions, Reynolds showed that this liquid pressure was great enough to keep the two bodies from having any contact and that the only friction is the system was the viscous resistance of the lubricant.
There are four essential elements in hydrodynamic lubrication the first two are obvious, a liquid (hydro-) and relative motion (-dynamic). The other two are the viscous properties of the liquid, and the geometry of the surfaces between which the convergent wedge of fluid is produced. When considering hydrodynamic lubrication we must be very careful about how we treat the viscous properties of our lubricant. Since the only friction present in a hydrodynamic lubrication system is the friction of the lubricant itself, it would make since to have a less viscous fluid in order to minimize friction: the less viscous a liquid the lower the friction. Too low of a viscosity jeopardizes our system though. We have to be very careful that the distance between the two surfaces is greater than the largest surface defect {why polishing is so important}. The distance between the two surfaces decreases with higher loads on the bearing, less viscous fluids {part of the magic of DD4H's modification to Krytox}, and lower speeds.
The surface geometry is also very important. The surfaces have to be such that a converging wedge of fluid can develop between the surfaces, allowing the hydrodynamic pressure of the lubricant to support the load of the shaft or moving surface. This is obtained in a number of ways, a common design other than the shaft and bearing {perfectly round wheel bore and axle}configuration is the tilted pad bearing, where a tilted pad skims over a sheet of fluid.
Hydrodynamic lubrication is an excellent method of lubrication since it is possible to achieve coefficients of friction as low as 0.001 (m=0.001), and there is no wear between the moving parts. Special attention must be paid to the heating of the lubricant by the frictional force since viscosity is temperature dependent. One method of accomplishing this is to cycle the lubricant through a cooling reservoir in order to maintain the desired viscosity of the fluid. Another way of handling the heat dissipation is to use commercially available additives to decrease the viscosity's temperature dependence.
We also have to pay special attention to the extremes of motion, when using hydrodynamic lubrication: starting and stopping. When the surfaces are at rest with respect to each other, or at very low speeds, the distance of separation is theoretically zero."
G
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I am not a pro builder and have yet to compete outside of Royal Ranger (dowel rod) cars. My dabbling in the BSA style is due to teaching physics through the use of pinewood derby cars. I am only 3 years into this hobby and am in no way an expert on anything. That being said, I do have a general understanding of physics and the scientific method. Sorry if the previous post was overkill. To apply the previous post to what we know of derby cars from this forum:
- DD4H's oil is legit. I have tested nothing faster with my students (that does not mean there will never be a better fluid, but for now get the DD4H oil).
- The boundary layers are more likely where a person can find some improvement. Silicone and Teflon are both hydrophobic and partially oleo-phobic. They create the "slippery layer" that the fluid slides on. As nano scale products continue to advance, we may yet find the perfect (possibly permanent) silicone/PTFE product.
- Finding a better fluid gripping, yet slippery substance to hold the oil to the other surface is also entirely possible. As 5K mentioned, making both layers extremely slippery = shedding of oil and loss of the hydrodynamic fluid boundary effect. Thus, the testing of ski waxes and other waxes. With skis, they work by holding melted water to the ski creating a fluid barrier between the ski and snow. If a non shedding very smooth wax with ski wax properties could be applied at a sub-micron scale.......
txchemist said:So after that enlightening bit of info, anyone want to guess what the coefficient of friction is in the best non bearing car? Hint: eliminator class
8675309
Oh wait that's a different number.
Resophonic Racing said:8675309 Oh wait that's a different number.txchemist said:So after that enlightening bit of info, anyone want to guess what the coefficient of friction is in the best non bearing car? Hint: eliminator class
Really Reso? SOB now I can't get that song out of my head!
+1
5KidsRacing said:Resophonic Racing said:8675309 Oh wait that's a different number.txchemist said:So after that enlightening bit of info, anyone want to guess what the coefficient of friction is in the best non bearing car? Hint: eliminator class
Really Reso? SOB now I can't get that song out of my head!
This is for my PWD brothers ...
http://www.youtube.com/watch?v=6WTdTwcmxyo
http://www.youtube.com/watch?v=6WTdTwcmxyo
E.T.Racing said:+15KidsRacing said:Resophonic Racing said:8675309 Oh wait that's a different number.txchemist said:So after that enlightening bit of info, anyone want to guess what the coefficient of friction is in the best non bearing car? Hint: eliminator class
Really Reso? SOB now I can't get that song out of my head!
5KidsRacing said:Resophonic Racing said:8675309 Oh wait that's a different number.txchemist said:So after that enlightening bit of info, anyone want to guess what the coefficient of friction is in the best non bearing car? Hint: eliminator class
Really Reso? SOB now I can't get that song out of my head!
5k,
Whats not to like....solid riff....killer 80's chorus effect on the guitar intro. That video caused a little reduced friction in middle school for sure....LOL.
John needs to open the garage door once in a while and let the fumes out. His number is a tad high. So far Chief is closest. Kickaxe, Don't you have an estimate of the COF for the fastest non-bearing cars. If not, what do you estimate your students are getting with what they build?
Thanks Chief and everyone for the song....I can't get it out of my head now
Chief said:This is for my PWD brothers ...
http://www.youtube.com/watch?v=6WTdTwcmxyo
E.T.Racing said:+15KidsRacing said:Resophonic Racing said:8675309 Oh wait that's a different number.txchemist said:So after that enlightening bit of info, anyone want to guess what the coefficient of friction is in the best non bearing car? Hint: eliminator class
Really Reso? SOB now I can't get that song out of my head!
TX,
Dr. Jobe claimed to have achieved .04 with is oil/graphite combo, but that was on a test rig testing one wheel not at race conditions.
My students are 8th graders just entering Geometry or leaving Algebra 1, so trigonometry is outside their wheel house. We do not currently test COF. I have just started to gain interest in COF and hydrodynamics over the last 6 months. The trick is, how do you test it under race conditions instead of a spinning wheel with an aluminum rig? The mini lecture I quoted suggests COFs as low as .001 with perfect hydrodynamics.
I believe DD4H was quoting the viscosity of his oil instead of the COF, but since normal Krytox has a viscosity of 24.2 cP that would be a significant reduction of viscosity from the original product. At room temperature, water has a viscosity of approximately 1 cP (depends on temerature). The key to a great pinewood derby oil for low temperature and pressure is having enough viscosity to stick to a surface while shearing easily to reduce the energy needed to create and maintain the boundary layer. One would desire to get as close to 1 as possible while maintaing the boundary layer. His number of 5.86457321098 could be the magic cP number for a fluoro oil.
and +1 for Chief's music of the day
Dr. Jobe claimed to have achieved .04 with is oil/graphite combo, but that was on a test rig testing one wheel not at race conditions.
My students are 8th graders just entering Geometry or leaving Algebra 1, so trigonometry is outside their wheel house. We do not currently test COF. I have just started to gain interest in COF and hydrodynamics over the last 6 months. The trick is, how do you test it under race conditions instead of a spinning wheel with an aluminum rig? The mini lecture I quoted suggests COFs as low as .001 with perfect hydrodynamics.
I believe DD4H was quoting the viscosity of his oil instead of the COF, but since normal Krytox has a viscosity of 24.2 cP that would be a significant reduction of viscosity from the original product. At room temperature, water has a viscosity of approximately 1 cP (depends on temerature). The key to a great pinewood derby oil for low temperature and pressure is having enough viscosity to stick to a surface while shearing easily to reduce the energy needed to create and maintain the boundary layer. One would desire to get as close to 1 as possible while maintaing the boundary layer. His number of 5.86457321098 could be the magic cP number for a fluoro oil.
and +1 for Chief's music of the day
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