# Tech brushless motors



## big twins (Oct 18, 2008)

Need Help understanding and how to tech a brushless motor at races. I have heard of the Zubak meter and heard of taking the diffence of the two numbers and what? What does all the numbers mean, and how do you tell if you have a legal or illegal rotor or motor. 

Also where can I aquire a zubak meter or something of the same nature to spec motors? 

Please help me under stand new to brushless and trying to open a track and make everything work when doors open in Sept.


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## hankster (Jan 1, 1998)

Best bet would be to ask in the Oval Brushless Racing forum located at http://www.hobbytalk.com/bbs1/forumdisplay.php?f=244 It's been discussed a number of times there.


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## swtour (Oct 8, 2001)

Before you can TECH them, you have to have your MOTOR Rules.

What MOTORS are you going to allow?

ie: Wind, Brand, etc.

For instance, if you were running a 13.5 NOVAK ONLY type class.

You could specify "Only the STOCK 12.3mm Sintered Rotor" is allowed.

Then you could check the diameter of the rotor w/ a set of digital calipers, and is should be 12.3 mm with a slight +/- factor. 

The Meters like the ZUBAK and RMS-1 won't decide a "Legal" rotor, they just show you the magnetic strength of the rotor (Larger and Smaller rotors will read slightly different due to how close the rotor is to the p/u sensor measuring the strength I believe) 

If you are going to allow OPEN BRAND motor rules, you need to LEARN each motor you are going to allow. Learn the +/- range on the windings, and all the other quirks. 

Some motors (Like TRINITY) color code their motor cans, where the latest batches of NOVAK's SPEC motors use a colored ring near the solder tabs to identify the winds (You need a chart or something to keep track of what color is what wind) ie: Green = 21.5


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## kevinm (Jan 16, 2002)

There's an even simpler, cheaper method of checking motor windings (brushed or brushless). The attached diagram shows how to measure resistance of the windings (instead of inductance) which is not affected by rotor strength, position, etc. The only thing that changes the resistance of a motor is temperature, so as long as the motor is near room temperature, it will produce very consistant numbers.


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## swtour (Oct 8, 2001)

kevinm,

Have you ever priced a decent MILLI OHM meter? 

You can't do that with your regular DVM!


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## kevinm (Jan 16, 2002)

This circuit essentially turns a standard DVM into a milliohm meter. The voltage regulator & resistor creates a 1/2 amp constant current source thru the windings. The DVM then measures the voltage drop with separate alligator clips (very important) so that the "contact resistance" of the clips on the motor tab is not an issue. It's the same principle used to test small DC motors when they build them.


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## mr_meat68 (Jan 30, 2005)

imo, no track needs to have a rotor checker. just a caliper, temp gun, and inductance meter... all can be bought pretty cheap if you look around.

the racers use the rotor checkers to pick through their rotors or check to see if they have a good/bad one.


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## samgkd (Dec 30, 2003)

Kevinm,

In theory your circuit will do what you say. But in practice, if you built ten of them, you would get ten different readings due to tolerances of the parts and accuracy of the different DVM's. That's the problem with any less than lab quality piece of equipment.

Sam


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## kevinm (Jan 16, 2002)

samgkd said:


> Kevinm,
> 
> In theory your circuit will do what you say. But in practice, if you built ten of them, you would get ten different readings due to tolerances of the parts and accuracy of the different DVM's. That's the problem with any less than lab quality piece of equipment.
> 
> Sam


All true, but pretty much irrelevant. It's purpose it to check for illegal/tampered with motors at your local track, not create a national standard with 1% tolerances. One track doesn't need 10 of them.

The difference in readings between a 13.5, 17.5 and 21.5 is large, and it appears to be much more consistant than an inductance meter for less than $10 of parts from Radio Shack.


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## CustomWire (Jan 12, 2009)

if this is the thing i was sent the drawings on .. it has 4 clips but yet nothing to say how when where what on it .. i see only 3 tabs on a motor .. 

any ideas ??


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## badoty (Aug 29, 2007)

looks like you hook two clips to one tab and check between phase A&B and for the same between B&C then back to C&A I would assume......


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## kevinm (Jan 16, 2002)

badoty said:


> looks like you hook two clips to one tab and check between phase A&B and for the same between B&C then back to C&A I would assume......


Put the 2 clips on the left side of the drawing on one tab and the 2 on the right side on another tab. You can use just 2 clips, with 2 wires on each clip, but this method isn't as accurate. You need to wiggle and/or squeeze the single clips a bit to get a good contact on the tabs. I've also built some special "probes" that work similar to meter leads, you just press them against the tab. They're a bit tricky to make, so I stuck with the simplest method for the basic drawing.


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## Lazer Guy (Sep 12, 2005)

I've been using the circuit Kevin posted for about a year with 2 alligator clips with 2 wires on each clip. 
I do have to wiggle the clips to get a good contact but it has worked great.
The great thing about this circuit is I can tech BL motors in the cars ready to go on the track :thumbsup:


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