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Discussion Starter #1
This is a quick suggestion for all tracks to consider.

Pick up an Inductance Meter to measure the winds of an armature without having to unwind it.

You can find them on-line for $60.00 and a very worthy investment.

Its a pain but occassionally checking the top 3 wouldn't hurt in any division.

If its an adjustible with a stub shaft then keep an eye on them.

You'll have alot happier racers if you do.
 

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Discussion Starter #2
Someone on here had a great inductance chart he had put into a spread sheet , If you could repost it that would be great.
Also used to check brushless motors , check Novak's site.
 

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Quick question, how do you check an arm with the meter? I assume you have to remove the arm from the can?? Just wondering how much time it would take to tech the top 3. I noticed on the novak site they tested brushless motors by leaving the arm in the can, is this possible with a brushed motor?? Sorry for the stupid questions but like you said this seems like a must have at the track and I would like to be as informed as possible. Thanks,
AC
 

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Discussion Starter #4
Hi Tony

NO question is a stupid question !

Yes , a brushless motor is easier to tech as all you have to do is unsolder the wires and spin the motor slowly to measure each pole.Check Novak site.

A brushed motor does require removing the arm and measuring each pole winding separately, but the meter tells the truth as a stk C-2 measures 50 something and a 10-12 turn I believe is in the teens.

I'm hoping the gentlemen with the spreadsheet chart will repost it.

A little track threatening never hurt or just check the winner, whatever works.
 

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Thanks a lot, thats what I figured. I think having the meter there and knowing it can be used if something does not seem right will be helpfull when it comes to fair spec racing. Tech on the TQ and top three probably is not a bad idea. Thanks again
AC
 

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I'm the guy with the spreadsheet. I'm going to ask Hank if he will put it in the downloads section so it won't get lost when the thread falls to the bottom.

As far as I know you don't have to unsolder the wires from the Novak Brushless motors to test them. However, they point out that the position of the rotor makes a difference and you have to turn the shaft to get the lowest reading on the brushless motor.

When I measured my arms, I held them in an aluminum clamp to keep the stacks away from anything magnetic that may have affected the reading. I would suggest at least removing the arm from the can so you know what you are measuring. The magnetic field may affect the reading and different cans and have different effects.
 

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Discussion Starter #7
That would be great if Hank could do that for this thread as it should be very helpfull to alot of tracks out there. :thumbsup:
So the speedcontroll does'nt throw off the reedings on a brushless ??
I've never measured one myself, just assumed you'd have to unsolder.
 

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Discussion Starter #10
Tracks , buy one to at least let the drivers know you can check their arm if neccesary, a small investment .
 

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Rodney,

Has the one you ordered come in yet? Do you have any sample readings to compare to the data in my spreadsheet?
 

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Discussion Starter #12
No , I'm surprised it hasn't , but I will let you know how close the reading are.

If I don't see it in a few days I've got to call the shipper.
 

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Someone sent me a PM asking how to use an inductance meter. Rather than replying to each individual, I will post my technique here.

a) Take the arm out of the can and come up with some way to hold it in a non-magnetic clamp (in other words NOT in a steel vise). I used an aluminum armature winding clamp. An alternative is to use a pin vise on the shaft and clamp the pin vise in a regular vise.

b) Clean off the com. I don't feel it is necessary to true the coms, but cleaning with a com stick or a rubber eraser would help to get good contact. If I was about to test an arm with a really dirty com, I would spin it in a drill and clean the com with a cratex rubberized abrasive point (and yes the com would need truing then).

c) Set your meter on the lowest range it has. My lowest range is 2mH (2 Milli-Henrys). Turn the meter on.

d) Holding the arm tightly in your clamp or pin vise, touch the meter probes to any two com segments. Press hard to get good contact (that's why I clamp the arm). Note the reading. If you are anal like me, you could do this a couple of times and take an average or just to make sure you are getting consistent readings. If you are even more anal, rotate the arm and do two different com segments. And then again for two more. The readings should be the same.

That is pretty much it. If you have some unknown arms, look at my table of readings in the downloads thread and see what you've got.


I don't know if the meter could tell you if one pole has less winds on then another since all the poles are electrically connected but I might wind an arm that deliberately has one less turn on one stack than the other two and see if my meter can tell which it is.
 

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Discussion Starter #14
I called today and its on back-order from the co. I ordered it from.
I love when they don't tell you that , easy to be the cheapest when its not in stock.
 

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I took the data generated by ta_man (nice work!), along with a bunch of my own data from about 25 arms I have here, and generated a mathematical curve fit approximation. I came up with a relatively simple formula to calculate the nominal inductance of any armature pole, and plugged it into a spreadsheet. I also added a tolerance input to allow you specify an allowable range. +/- 2 to 3 micro Henries is reasonable.

In addition, I have seen posts describing how to measure inductance by contacting the commutator brush surfaces. There is no need to make it that difficult. You can simply hold the armature in your hand (no ferritic or iron based clamps as that can change the magnetic circuit, affecting the readings slightly) and using alligator clip style leads, connect them them to the commutator tang that the wires are terminated on. (That's the copper hook that the wire is welded or soldered into, just below the brush contact surface.) It's pure copper, and generally makes a suitable contact surface. If the motor winder has done a particularly horrid job of soldering, it might be a little difficult to keep the aligator clips on. If so, feel free to throw a dead wombat and some rotten cabbage at the offending motor winder, at your earliest convienience. :tongue:

Hank, feel free to post this as well. Many track operators, or people wanting to tech motors, may find this a little easier to work with. I didn't actually check it with a stock motor armature, but mathematically, it should work for that too. It might predict just a little high. I'm leaving for a business trip tomorrow. Once I return, I will measure some 27 turn armatures and see if it needs a little tweaking. It's certainly good for 9-21 turns now.

-Tony Staples
 

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I did not get consistent readings with most of the arms I tried to test when trying to connect to the com tabs because of epoxy/flux/whatever on the tabs.

Thanks for the calculator!
 

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This is the inductance meter I have: http://www.amazon.com/Digital-Inductance-Capacitance-Multimeter-VC6243/dp/B00063SAQW/sr=8-2/qid=1170768212/ref=sr_1_2/102-1096605-5321754?ie=UTF8&s=electronicsThe price is right and it works great! $49.95 plus ship.

You should also note that all meters do not read the same. If a track is using one to tech, then the track should establish a reading based on his meter. That would be the inductance to go by, not by some friends in the pits. Like a scale to weigh cars, each of those can read different. We use one scale at any given time and we should use only one meter at any given time.

At ARCOR races I will be establishing a reading at that race, based on testing 3 motors in each class, to determine a low reading for each motor/class. The average low readings will be the ones used for tech at that given race.
 
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