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Finding good arms


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#1 Upfront slot cars

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Posted 30 August 2016 - 06:26 AM

Is it true that if you meter several arms of the same type that the ones reading the least resistance will be the best ones ? Wondering if there is a way to sort out the duds from the good ones. I know the real answer is track testing but would like to narrow them down to known good ones before testing. Thanks
Andrew Ford




#2 Phil Hackett

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Posted 30 August 2016 - 02:40 PM

Is it true that if you meter several arms of the same type that the ones reading the least resistance will be the best ones ? Wondering if there is a way to sort out the duds from the good ones. I know the real answer is track testing but would like to narrow them down to known good ones before testing. Thanks

 

Yes... but (there's always that word) testing by running is the ultimate way to check arms. When we had the micro ohmmeter you could make good predictions but not all low-reading arms are good and quite a few high-reading arms ran very well.

 

Your track's power and other factors will determine whether the meter readings are relevant.


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#3 havlicek

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Posted 30 August 2016 - 03:22 PM

First off, if you're going to meter arms, you'll need a meter that can resolve to the thousandth of an ohm to get a good idea of what's going on.  Meters that can read a tenth are all-but-useless except for a few things.  Having said that, if I were looking at a group of spec arms (*all the "same" wind), I think I might look for more consistent arms...ones with as close to the same reading from pole-to-pole.  After that, I'd further separate them by the ones with the lower resistance readings.

 

-john


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#4 MSwiss

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Posted 30 August 2016 - 03:48 PM

Both good posts, above.

I'll repeat my real life situation, before mentioned, comment.

A I15 racer, after TQ'ing at the Nat's, commented me "When I metered the arm, before loading, it read real high, but I still put together for a practice motor".

IOW, the meter is OK, but unless you try them all, you might leave your best motor in the box.

Of course, this applies much more when on a track that that particular motor has never run on.

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#5 idare2bdul

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Posted 30 August 2016 - 07:54 PM

The other variables are the can, magnets, air gap,, gearing, brush type and brush length and the ever popular spring tension. Small changes in any of these areas can make a big difference. The guys that can run a harder tire may be blowing by you or they may have a better mounted body. Nobody said this was an easy hobby.


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#6 Samiam

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Posted 30 August 2016 - 08:13 PM

Hence the popularity of sealed cheap motors.


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#7 Phil Hackett

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Posted 30 August 2016 - 09:06 PM

Hence the popularity of sealed cheap motors.

 

Yup... only trading looking for the magic armature to looking for the magic motor. Nothing has changed.


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#8 Samiam

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Posted 31 August 2016 - 08:34 AM

1/24th Amendment:

 

A well regulated set of rules, being necessary to the security of a fair race, the right of the people to buy and test arms, shall not be infringed.


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#9 Uncle Fred

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Posted 31 August 2016 - 04:15 PM

Towards the end of my spectacular GR27 career I started having arms metered when I sent them out for reconditioning to not noticeable advantage.......


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#10 havlicek

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Posted 01 September 2016 - 06:57 AM

All good, but the subject here was *looking at arms only, and even then, just what "metering" might find*.  Certainly there are many many factors when looking at the whole motor, and other things to look for when only looking at the arms.  Andrew even said in his original question:

 

 

 

I know the real answer is track testing but would like to narrow them down to known good ones before testing. Thanks 

 

I'm a funny guy, I figure we should answer the questions people ask instead of the ones they don't ask (*sorry for the slight snarkiness ;)  ).  I don't have any way of knowing if any results from just metering arms would produce information significant enough that it might show up when considering an entire motor, much less an entire car and body.  I would guess the open and eurosports guys who routinely look at butterfly farts and the weight of one screw vs another might know.   :D


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#11 Samiam

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Posted 01 September 2016 - 07:36 AM

I think metering arms is more effective at finding bad arms. Either defective or way off spec. arms not worth loading up and track testing. I think that is what Mr. Ford is looking to accomplish.


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#12 Ramcatlarry

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Posted 01 September 2016 - 12:59 PM

Metering ONLY evaluates the resistance of the wind an commutator connections.  What it does NOT tell you is the timing of the arm, the shaft condition, balance or rotor web to magnet flux conditions.   Putting an arm in different setups will give different results on the track and on different tracks.


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#13 havlicek

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Posted 01 September 2016 - 05:10 PM

Metering ONLY evaluates the resistance of the wind an commutator connections.  What it does NOT tell you is the timing of the arm, the shaft condition, balance or rotor web to magnet flux conditions.   Putting an arm in different setups will give different results on the track and on different tracks.

 

Yes, and like I said, looking for consistency tells you more than that.  As for the other armature factors you mention...that a meter can't tell you, he didn't ask about any of that and for all I know, he's probably aware of those.  Timing and shaft condition can be determined with no fancy gear anyway.  So, metering alone CAN tell you some things...and those alone can be helpful.

 

-john


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#14 Bill from NH

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Posted 01 September 2016 - 06:06 PM

In the days of old, I used to keep a black on each arm. I kept a second record for springs & motor brushes used with each arm.


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#15 James Grandi

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Posted 01 September 2016 - 07:57 PM

To be honest, even when I had a meter set up to read armatures, I never based my decisions off that. I always looked first at the quality of the wind job, and then at the arm timing. How tightly wound each pole was, and if all 3 were well wrapped, was usually a real good indication that it had potential. Most of the time, it was accurate
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