– Feature Article – Liquid Lube Testing
– Shop Talk – The Best Pinewood Derby Rule
– Pinewood Derby Car Showcase
Liquid Lube Testing
On occasion, a package arrives in the mail from a lubricant manufacturer. Generally, the package contains a lubricant that the company would like for Maximum Velocity to offer on our web site. I then schedule the time to do a preliminary test to see if the lube is worth pursuing. Typically this preliminary test is either a spin test or a slide test (no need for track testing if the lubricant doesn’t perform well).
Late in 2008, I received one of these packages, which contained four liquid lubes. Since the season was getting ready to start I didn’t have time to pursue testing then, so I put the lubes on the shelf and scheduled the test for the summer of 2009.
When it came time to do the testing I read the specifications and found that one of the lubes could react with some plastics, so that one was scratched off the list. The other three were:
- Methyl Silicone 5 – 5.0 cSt1 – A colorless, transparent, nontoxic, non volatile liquid used in a variety of applications.
- Methyl Silicone 20 – 20 cSt – Same as above.
- XOil – 15.3 cSt – A transparent, colorless mineral oil, It is generally used for lubricating measuring tools and related instruments.
To screen these products for possible sale, they would need to be spin tested along with the existing liquid lubes that we offer: Krytox 100 and NyOil II.
The equipment used for spin testing was previously described in Volume 8, Issue 6 – “Grooved Axles”.
As a refresher, the apparatus consists of a machined steel ring which is sized to fit snugly over a machined BSA wheel. The ring weighs two ounces, which is essentially the load on a rear wheel of a pinewood derby car.
Figure 1 – Weighted Wheel Spin Jig
After sliding the ring over the lubricated wheel-axle assembly, the axle is mounted onto the apparatus. A length of fishing line with a weight on one end is wound around the ring (there is a small pin on the ring not seen in Figure 1, to which the non-weighted end of the string is attached). On each test, the string is wound until the weight touches the eye hook. The weight is then released and a stopwatch is used to measure the spin time. The string is sized such that it is released from the ring before the weight reaches the ground.
In order to avoid lubricant contamination, two wheels were used for each of the five lubes (ten wheels total), and one axle was used for each of the five lubes. The reason for two wheels for each lube was to ensure that the performance of a lube was not exaggerated or degraded due to a “fluke” wheel. The wheels were Ultralight Speed Wheels, which are machined inside and out. To further minimize variance, a single mold number was used for all of the wheels.
Each wheel/axle was lubricated in the same manner (lube applied, allowed to flow over the axle, and then blotted off). Then the assembly was placed onto the spin jig. To break-in the lube, five spins were given to each wheel.2 Then five timed spins were performed and recorded.
Somewhat to my surprise Methyl Silicon 20 and XOil performed quite well in the spin tests. In fact, they both tested slightly better than NyOil II.
Figure 2 – Spin Test Results
So, some track testing was called for. As the Methyl Silicone 20 is rather expensive, further testing was focused on XOil. That testing showed similar results to the spin tests.
As a result of this testing, Maximum Velocity is now offering XOil in lieu of NyOil II.
1cSt stands for “centistokes”, the standard for the viscosity of a liquid. As a comparison, Krytox 100 is 4.0 cSt.
2Except for the Methyl Silicone 5 – in this case the fastest spin was the first; each subsequent spin was slower.
The Best Pinewood Derby Rule
Although you can get away with using a cheap plastic ruler for an occasional pinewood derby car, having a nice, accurate rule (not ruler) is a must for any serious craftsman. But like any tool, there is a large variety of rules available on the market. Today, I want to share with you my favorite rule. In my opinion, this rule is a must have for pinewood derby enthusiasts.
The rule I am referring to is the Incra Six Inch Precision Bend Rule. Although this rule wasn’t specifically designed for pinewood derby use, I have to believe that the designer was a pinewood derby parent.
Photo 1 – Incra Six Inch Bend Rule
Photo 2 – Making a Measurement
Photo 3 – Marking a 1/8 inch Offset for Axle Holes
Photo 4 – Drawing a Horizontal Line
Photos 5 & 6 – Finding the Center of the Block
Pinewood Derby Car Showcase
(As an exception, I am dedicating the Car Showcase this week to a car built by Stephen Parks).
I was browsing your newsletter archives, and saw the article on the direct drive outlaw car that you built — Volume 8, Issue 3. It was interesting to me because, as an engineering student, I competed in the ASME student design competition, and designed a “string transmission” for a transport device.
For last year’s pinewood derby event at work, I wanted to make an electric car for the Outlaw class, and initially thought of using the same type of transmission. However, it has some issues. If the wheels spin, then you may not have enough string to power all the way to the end, and if the wheels don’t spin, then you probably should have used more power! Eventually I abandoned the idea of a string transmission, and decided to just use a gear drive. A co-worker races electric RC boats, and sourced a Lithium-Polymer battery. These batteries are expensive, but relatively light, and have almost no internal resistance. I found a few motors that looked to be a reasonable size, then built a dynamometer to test and compare them. This approach wasn’t very consistent, so in the end I simply picked the motor that sounded and felt the strongest.
So far, this wasn’t nearly complicated enough for me. I figured that this drag car ought to look like one, so I decided to hide the drive train, switches, etc. into a drag car model so that it would be a “sleeper”. The model I chose was the Stone, Woods, and Cook Willys.
Model Box Photo
Quite a bit of work was required to transform a model kit that was intended to be stationary into a rolling, self-powered, self-guided vehicle. Here are photos of the chassis, showing the motor and gear layout. The silver rectangle is the battery pack. The gears are out of a broken DVD player.
Top of Chassis
Bottom of Chassis
This year I’ll probably reuse the motor and battery, but forgo the fancy body in favor of a much more robust frame, and I’ll build a stopping device to fit onto the end of the track. I may also switch to front wheel drive to eliminate the possibility of wheelies, and I can then clean the graphite off of the tires after each run to maximize traction and maintain consistent times.
Could you give me the order in which to prepare wheels and axles? I have an Advanced Speed Kit, but I’m a bit overwhelmed and don’t know where to start.
I would do it this way:
- Wheels Preparation (assuming raw, out of the box wheels)
- Cone the Hubs using the Pro-Hub Tool
- Polish the wheel surface and inside edge using the Pro-Wheel Mandrel and the fine grit sandpaper (wet the sandpaper).
- Polish the wheel bores with the Bore Polish
- Axle Preparation (assuming raw, out of the box, BSA axles — if they are something else, this would change.
- Remove the burrs and crimp marks with the mini file (while nail- axle is spinning in a drill).
- Polish the axles with the axle polishing kit.
- Lubrication – Lubricate thoroughly with the graphite
- Mounting – Mount the wheels on the car. Use the gap gauge to set the gap between the car body and wheel hub.
While racing, the two men who were clearly in charge were talking about our cars and showing a disturbed look. I went over to see what the problem was and they told me that the cars only had three wheels touching and that it was a “grey area”. I explained that I was informed that as long as three wheels touched that the cars were in line with official derby rules. My question to you is this, “What is the true stand on the issue of the raised wheel by top officials in the Cub Scouts of America?
Unfortunately, “legislating from the bench” is very common in pinewood derby racing.
The only “official” rules for pinewood derby racing issued by BSA are the rules in the kit box. Those rules do not prohibit running on three wheels.
If a pack is going to use a more comprehensive rule set (which I encourage), then that rule set must be distributed to all participants when the car kit is distributed. Changing rules after kit distribution is a big no-no in my book, as it penalizes those that use their time wisely, instead of waiting until the last minute.
I was wondering if I could use rod type axles for a BSA car. If so, do you think they are faster than nail type axles?
Generally, in Cub Scout races you must use the nail axles supplied with the kit. But you would need to check your local rules for clarification on this. However, I have found that the nail axles are generally faster than the long rod axles.