12 replies to this topic

[Big Booty]

How do people go about choosing the right magnet/arm air gap?  Do you simply set the gap because "Joe Blow" said it was the right gap to run or is there some science/engineering basis for selecting a particular gap?  Is it simply a trial and error process that you do for each magnet/arm combo?  Read lots of posts about people rezapping their magnets, surely this then changes things and how can you assume that your air gap is still optimum?  Any thoughts are most welcome.

 

 

[gotboostedvr6]

Ask first, then research online, then test and adjust accordingly.

We would need to know what kind of track and length, voltage, class of motor, weight of car and type of rubber typically used at the track in question.

[Big Booty]

Wow thats a lot of variables there.  Are you saying you take all of those into account when selecting the air gap?  Man how do you do that?  Trial and error and then test at the track or do you do some sort of measurements prior to hitting th etrack?   My take on it is a lot simpler.  For a given arm/magnet combo Ive found there is usually an optimum gap.  I change the gap and measure no load rpm and stall speed torque.  Multiplying these two gives me a number. I then play with the gap until the number is a maximum.  I then gear the car accordingly.  Seems to work on lower powered motors, not sure if it holds true for G7, 27 etc type of motors. 

[Matt Sheldon]

My limited experience says that you have to be willing to endure the thrill of the hunt in finding the best combination. Then just when you have the right one you will throw a winding and have to replace the arm only to find out the new arm is not quite as happy in its new surroundings as the old one. There are many, many people with tackle boxes full of experiments trying to find the "perfect" setup. Big reason why sealed motor racing has become so popular.

 

So my answer is if you want a "simple" setup then you go with "Joe Blow" and you will have a decent set up. If you are looking for optimal and documented findings then you start with a wide spectrum of arms and setups and you start tight and work your way up honing every .002. Almost everybody will tell you that bench testing just shows you which one spins the fastest on the bench, you need to put it on the track for the real answer. Not uncommon (sometimes the norm) for a motor that is 500 - 1,000 rpm's slower on the bench to be much faster than higher revving bench monsters on the track. Just like a chainsaw these little motors need to be under load to do work.

 

Just my .02 cents.

[gotboostedvr6]

Rick,

 

What classes do you run?

[Marty N]

 For a given arm/magnet combo Ive found there is usually an optimum gap.  I change the gap and measure no load rpm and stall speed torque.  Multiplying these two gives me a number. I then play with the gap until the number is a maximum. 

 

Not a bad guide and quite useful for drag motors. I think the guys are trying to say that in road use drivability is just as or...maybe more important than  raw horsepower?  Air gap effects braking and smoothness of throttle I'm told. My races are over in fractions of a second. Never could turn left. Just a thought Rick.

[Big Booty]

Rick,

 

What classes do you run?

 

 

I dont run on commercial tracks (anymore) although I do run on a private commercial sized track.  Most of the classes used sealed motors and the classes are hard body true scale.  No womp or winged stuff.  They are not National or International classes as such.  Plafit Fox and Cheetha and NSR. The Parma S16D and Deathstars are not sealed so thats where I can tinker and experiment.  Just not allowed to tinker with the arms.  I like to tinker. 

[gotboostedvr6]

Can you hone magnets in dead star or s16?

[Steve Boggs]

If you have the equipment to find "no load rpm and stall speed torque", then finding the optimum airgap should be within your reach given enough time on the track.

[Danny Zona]

Another factor in choosing an air gap is the weight of the car. Also a factor is what controller you are using. Some have way better brakes then others.

I'm sure I'll be told I'm crazy but they are big factors, IMO.

[Fast Freddie]

Just for a starting point .007 for high speed tracks and .010 for flat tracks. When you get into the sticky goo of all that should be considered it can be mind bogging. For instance, type of arm, arm diameter, magnet size, magnet type, magnet strength, can configuration, car weight and type of track. One thing you can hardly ever go wrong with is to try different arms in the same setups using different air gaps. Some people, and I'm one, try different arms in several different setups with different air gaps. Sometimes you see big changes sometimes little changes and the maybe no change at all. Your going to have to resolve yourself to a lot of testing on the track because while a motor sounds good on the box it can end up being an entirely different animal on the track.


Just for your info and don't tell anyone it's TOP SECRET here is how I've set up some of my motors.

PS 16D... PS magnets, PS 45 degree .560 arm, .575 air gap. Ran very good on both flat and high bank tracks.
PS 16D... PS magnets, PS 45 degree .560 arm, .585 air gap. Ran very good on flat track.

Contender...Red Fox can, Camen magnets, PS 45 degree .540 arm, .560 air gap. Ran very good on flat track.
Contender...Koford UL can, Cahozza T-5 magnets, BOW 45 degree .540 arm, .560 air gap. Ran very good on flat track.

Super Wasp*...Red Fox can, SMQ magnets, Koford 42 degree .518 arm, .540 air gap. Sounded good but was a dog on a flat track.
Super Wasp*...Koford Feather can, Cahozza Type 1 magnets, Koford 42 degree .518 arm, .535 air gap. Ran very good on Gerding King.
* Same arm in both motors used on two different tracks in different setups.

Gp12...Red Fox can, Mega II magnets, PS 38 degree .518 arm, .535 air gap. Ran good on most tracks I used it on.
Gp12...Koford Feather can, Cahozza Type 1 magnets, Koford 38 degree .518 arm, .533 air gap. Ran very good on Gerding King.
Gp12...Koford UL can, Cahozza T-5 magnets, Koford 40 degree .518 arm, .535 air gap. Ran this motor in the 2011 Nats at Chick's. In the final heat it turned a best time of 2.509 with a full field. This same motor turned a practice lap of 2.367 at Mimi's. It's the fastest AM12 I ever had.

If your wondering how I can remember all this, I can't. I keep stats on all my motors until a track closes and the stats no longer apply. I still have most all of my motor stats. Especially the ones from the Nats I attended.

[Guy Spaulding]

Dealing with 16d or S16d motors is unique, because the magnets are vastly oversize.  So, much greater air gap is common.  I've heard of winners using .540 arms in .600 setups

[havlicek]

 

 

How do people go about choosing the right magnet/arm air gap?  Do you simply set the gap because "Joe Blow" said it was the right gap to run or is there some science/engineering basis for selecting a particular gap?  Is it simply a trial and error process that you do for each magnet/arm combo?

 

 

The simple answer is.............."yes!"  The actual physics involved is beyond what mere mortal slot racers could figure with way too many variables in play to even start to be able to simply plug numbers into a calculation and get an answer.  The time-tested trial-and-error method (as well as "intuition" in the case of really talented and experienced builders whose names are the stuff of legend now) slotters have used since the paleolithic era has resulted in motors that defy the expectations of even the actual physicists.

 

-john