# Life like ?'s



## copperhead71 (Aug 2, 2007)

Got two LL chassis with four bodies.....I D help how do you know chassis type...2 one has red arm with blue n wht goodyear racing body ,The other has twisted /slanted green arm ,silform and 88 ford credit possible modify?(and they came with duplicate bodies)for $15.wht /blue goodyear body was other duplicate.


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## smokinHOs (May 30, 2006)

*LLs...*

The Goodyear cars (two different paint schemes) came in a set. Based on the age of the set I would guess they are the standard "M" chassis. The M chassis and T chassis are very easy to tell apart. The M chassis has thick motor mags, no traction mags, and a large metal "retainer" for lack of a better word on the top of the motor mags that covers both motor mags and armature.

The twisted armature came standard a few years ago toward the end of the M chassis run. I have half a dozen or so like that and have a few cars in the package with them, so I know they came as stock arms. They were not allowed in a LL race I attended, but not sure why. I have never ohmed them so I am not sure what the performance difference is if any. And judging by the fact that most of my LL "race" cars have the standard arm, I must not have found them to be better. LL also released green arms that were nt twisted. Maybe someone else on the board can tell you if there is any difference...

-Marc and Marcus


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## AfxToo (Aug 29, 2003)

Those arms are from the "Power Tracker" series. I have a couple of them and they seem to have very good torque characteristics but no better top speed than the stock configuration. The technical term for these arms is "skewed winding" and you will see this configuration on larger power tools and industrial motors that are designed to operate at very low speeds. 

The reason for the skewed winding is to reduce the natural cogging effect that happens when the motor is operated at low speeds. Cogging occurs because each pole is sequentially energized, one at a time, which generates a discrete force impulse as each pole is energized. Consider a freewheeling bicycle wheel that has bad bearings or the brake partially applied. If you were spinning the bicycle wheel by hand, each time you push the wheel would represent a force impulse. If the wheel did not have a lot of rotational inertia it would alternately speed up and slow down every time you whacked the wheel with your hand. This speed-up/slow-down pattern is called cogging and it is more pronounced at lower rpms. If the wheel was spinning at a faster rate the force impulses would have less of a noticeable effect because the inertia is keeping the wheel going. The same exact behavior applies to DC motors. 

So how does skewing the armature help? It changes the characteristics of the force impulses. By definition an impulse is a discrete force (mechanical, electrical, magnetic, etc.) that is applied over a very short period of time. A discrete force means it goes from one value to another value. An impulse means it starts at one value, changes very briefly to another, then returns to the original value. Tapping a nail with a hammer is a force impulse. In a DC motor, energizing a pole in the armature is the equivalent to the hammer tap and conventional armatures are designed to provide the largest possible "tap" by maximizing the relationship between the armature magnetic field and the magnetic field of the field windings or permanent magnets. By skewing the armature windings you are actually making the magnetic relationship less optimal at the beginning and end of the period of time the armature is under the influence of the field windings/magnets. This changes what is normally an impulsive force (OFF->ON->OFF) to something more like a ramp (OFF->HALF ON->ON->HALF-OFF->OFF) with a more gradual build-up and taper off. This makes the motor run more smoothly in low rpm situations, less cogging effect, but as you can see by itself it doesn't improve the maximum "ON" force, it just brings it on more gradually, so it is not going to give you better speed. However, if you both skew the arm windings AND go with a hotter wind then you can pick up some of the lost top end that you lost. I suspect Life-Like did a little experimentation to try and get both smoother low end while not giving up too much on the top end. Based on my use of the LL skewed arms I think they succeeded more on the low end but still give up a little on the higher end. It's a bit of a mystery to me why they would bother on a slot car because we tend to run at high speeds. I would guess maybe they had someone from their model train group bringing some ideas across to the slot car part of the business. As you might imagine skew wound armatures are very popular in model train motors, probably more prevalent than straight wound motors.


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