Summary
The Problem: it is exceedingly difficult, expensive and time consuming to obtain a highly competitive “stock” armature. The solution: Unrestrict the arm. This would change the objective from finding the fastest arm to optimizing an arm that is fast enough. If the arm were unrestricted, it would be much easier and less expensive to obtain an arm that is fast enough for a stock car. Speed costs money There is an old adage: “Speed cost money, how fast do you want to go?” This question epitomizes the economics of speed. Is it true that speed cost money? The stock HO car class is slowest… does it cost the least? A stock armature cost only $3.00… is it the most economical? These are the questions that are continuously debated within MHOSA and nationally; especially during this time when so called “stock” arms are evolving. We are all trying to achieve speed, yet many of us are restricted by cost. Do rules, which restrict armatures to stock, make it more affordable to compete? I don’t believe so. In this dissertation, I intend to demonstrate why I believe unrestricting the arm in stock class is best for the MHOSA. Definitions An “arm” is short for armature, which is interchangeable with motor. Historically, a stock arm is a mass produced arm that is manufactured with similar materials, design and specifications across multiple suppliers. Although “stock arms” do not have a published specification, they are widely regarded comparable if readily available and supplied with the ‘stock’ version of a car, regardless of supplier. Table
1 – available arms from top manufactures as of
December 2004
Stock
arms are inexpensive, however, quality is
inconsistent. These mass produced arms
vary greatly (10 percent or more) in key specifications which effect
performance: resistance, trueness of commature, and balance.
A hot stock arm is an arm that is reworked to address quality inconsistencies in stock arms. Three main variables in an arm that effect performance are: 1) balance, 2) trueness of commature, and 3) amount of resistance. A hot stock arm is an arm that is re-worked to improve the consistency of two of these three variables. A hot stock arm has generally become known to be a stock arm that is balanced, trued, and epoxied. Epoxy helps stabilize the reworked condition of the arm. The additional work done to a hot stock arm commands a higher price. The Hot Stock Myth Theoretically, a hot stock arm is guaranteed to be a better performing arm. From practice, we know this is not true… why? One reason is resistance. A hot stock arm does not address variance in resistance. Inconsistencies in wire diameter and wind can increase resistance which leads to poor performance. The use of a hot stock arm may increase the chances of good performance. Even if a hot stock arm triples the chances of good performance, it is not cost effective at three times the price. Wide gap arms use a slightly different armature lamination design to produce more torque. More torque means different power band, but not necessarily more speed. Again, there are too many other variables that are needed to produce speed. Timing is another arm specification that affects performance. In the past, timing was widely considered constant and therefore not much of an issue. Today, suppliers are producing advanced timing stock arms. How could they be stock if their timing is more advanced than a regular stock arm? And what is the timing set to? Is it the same accross manufacturers? Rework an advanced timing stock arm and you have a hot stock advanced timing arm. Does that seem fair? Ironically, it is not necessarily an advantage because the best naturally trued and balanced stock arms are just as good – just more difficult to obtain. The Problem with Stock arms The problem with stock arms, hot stock or not, is that variance in quality simply does not guarantee a competitive arm. Resistance alone varies by 10% or more. If you stack the tolerances of other characteristics you have a wide range of performance from stock arms. In order to have a highly competitive stock arm, you may buy and test 10, 20, 30 arms. Although hot stock arms will increase the probability of good performance, experience has shown that only one in several hot stock arms are top contenders. Which arm is fastest? In the stock class, we can say there are no stock arms that are “too fast.” Therefore it is important to know which are fastest. Any one of the arms mentioned above could have the right combination of trueness, balance and resistance (naturally or not) to be fastest. However, given the variance in quality, it is unlikely that a random arm of any stock variety will have enough speed to be highly competitive. The question is more difficult than meets the eye. Since no arm is too fast, the investment in time and money required to ‘discover’ the fastest arm is virtually unlimited. Conservatively, it will take 10, 20, even 30 or more arms to identify a highly competitive arm.
*
HC = Highly competitive
A
person might be lucky to find one highly competitive
stock arm in 30. At $3.00 per arm,
that’s $90.00. If a hot stock arm
triples the chances, it will cost approximately $100.00 (10 arms x
$10.00).
With this logic, a $30.00 arm that
guarantees you enough speed to be highly competitive would be a
bargain.
Perhaps the question shouldn’t be, “which is fastest?” but should be “which is fast enough?” As previously assumed, there is no such thing as a stock arm that is too fast. As long as this is true, there will only be one fastest arm and there will only be a few highly competitive arms out of 100. Other Problems with stock arms Gearing – stock arms simply do not provide enough speed to push the limits of stock traction magnets. Today’s improved traction magnets coupled with high down force tracks means that stock cars are underpowered. Simply put; cars have more hook than speed. To overcome this, higher gear ratios are used. Higher gear ratios sometimes give cars awkward handing characteristics, and put more stress (resulting in more heat) on the arm. Some car chassis and/or track down force combinations over-stress the stock arm and cause them to burn up. Brush spring tension – to get the most speed possible from a motor, higher tension springs are being used. This also causes additional friction and heat in the arm that reduces an arm's life, or ruins it altogether. Pick-up shoe tension – It has also become necessary to increase pick-up shoe tension to ensure maximum electrical flow resulting in better speed. Increased shoe tension leads to handling problems and accelerated shoe wear. Magnets define the class Magnets define the car class in magnet racing. The ultimate limit of how fast a car can circumnavigate a track is fundamentally based on how much traction (hook) the magnets provide. The countering force is speed. Speed (arm) and hook (magnets) must be optimized to achieve the fastest lap time. How does this resonate with the car classes we know today?
Stock is the only class that is limited by speed. It is imperative to focus on finding the fastest possible arm within the restrictions of the rules. Although stock class is limited by speed, it appears that gearing, tensioning, and the very fastest stock arms have closed in on what might be the theoretical optimized speed. However, only the fastest arms with over-gearing and heavy tension are achieving it. The solution is Unlimited arms If speed were not restricted, then we would not only have the case where an arm is too slow, but also the case where an arm is too fast. Unrestricting the arm would change the objective from finding the fastest arm to optimizing an arm that is fast enough. It is much easier and less expensive to obtain an arm that is fast enough for a stock car. Unlimited arms are too expensive Or are they? Even at $30, if you only had to purchase one arm to get enough speed and durability for a season, it would cost less than purchasing several stock arms to find a gem only to have it burn up on a high down force track. What are the options?: 1. Continue to use a stock arm – some MHOSA racers will continue to use and be competitive with a stock arm even if the rule were changed. 2. Green wire arm – at $12.00 and half the resistance of a stock arm, it’s sure to be much faster at only $3.00 more than a hot stock arm. 3. Tired RO arm – got any retired 35g arms in your box? This recycle option might be the answer to speed at no cost. 4. Custom winds – this is a more expensive option, but certainly, there is NO SPEED ADVANTAGE what so ever to a custom wind arm. Unlimited arms are too fast
There
is a point of diminishing return. ONe club are experiencing a
difference of
only about 4 laps per 8 minute race between stock class and modified
class
(stock class with unlimited arm). The
objective of an unlimited arm is not to go faster, but to ensure
that
everyone can go fast enough without excessive cost or testing.
Other advantages of a Modified class
Imagine
if speed were not the
issue. Imagine if you could choose the gear that best suited your
driving style, not just the gear that produced the needed speed.
Imagine if you could lighten spring tension to improve handling or
loosen brush tension to reduce heat and preserve arm wear.
Imagine buying just one arm that had all the speed you needed and would
last an entire season and not burn up on high down force tracks.
Stop the search for the killer arm and
focus on
set-up and driving!
Excepts from responses to this paper One MHOSA racer's experience is that approximately one in seven combination of stock and hot stock arms is highly competitive. Under this assumption the cost of identifying such an arm is $21.00 for stock arms (somewhat more if hot stock or advanced arms are used). He also points out this arm could be balanced and reconditioned to prolong life, but the same is true for any arm stock or open. Other observations are that the desparity between drivers will grow if open arms are introduced. An expert HO car/arm designer and manufaturer believes it takes methodical testing of 50 to 100 arms to identify a single "killer" arm. Another MHOSA racer is conderned that open arms might prove difficult for less experienced racers to handle. Yet another MHOSA is in basic agreement with the paper but cautions that open arms will not likely solve the problem of burned up arms on high down force tracks. Two MHOSA racers have responded that it is worth a try. One MHOSA racer reports that another group that changed from Super Stock class to Modified class found a growing desparity between the fast guys and the slow guys. And that the slow guys became even slower when using open arms. However, the group felt it would have been better to allow the slower guys to have open arms and restrict the fast guys to stock arms. Last updated December 29th, 2004 Feedback: webmaster |