best method/meter for determining motor wind
 

What is the current and best method for determining brushless motor winds?

My volt meter’s ohm setting may not be up to par/accuracy.

I have heard Fluke or Istek or BK meters will do the trick , measuring from pole A to the timing ring.

I ask in this forum, as onroad seems to be more it tune with this sort of thing.

There have been some suspicious comments about a few local cars being fast , and I wish to put an end to that asap.

There's no real method to test for that as it depends on how much wire is used. Not all stators are wound the same. Now if you were able to convince roar to give you the IR that was tested at the time of approval, you'd be able to do that. Unfortunately, it's not listed publicly.

Here is a link to an older thread on how to check it without expensive equipment - http://www.rctech.net/forum/radio-el...esistance.html

*The resistance numbers at the bottom are from 2013. I'm sure the newer motors are better but still gives you an idea.

For example a standard stator will have a higher IR than a short stack as the length of the stator is shorter. The new motor from Team Scream would lead you to believe they are cheating immediately, but those stators have a really small wind without a stator guard. It's tough to do without having another motor of the same brand sitting next to it as a reference. Also, temperature matters....BIG TIME.

Not sure how good those values are now

I use a Racing Measurement Systems MM2 Motor checker, and the latest 21.5's are in the low 30 milliohm area, the older ones around 35-40

Measure inductance to determine the number of wire turns on the stator. The 13.5 and 17.5 ROAR approved motors should have a minimum inductance number associated with the approval of the specific motor. Those meters are around $275.

Can you recommend brand or source ?

R= rho * L / S

depends on the material, the length, the wire gauge...

Net, you can read an R on whatever meter you use, but figuring out the wind straight from this could be a challenge ;)

These numbers aren't listed publicly. I think that is the true problem with using any kind of meter to detect the number of winds a motor has.

Here's the description Roar gives for a 17.5:

8.5.4.3.1

ROAR Stock motor: Only three slot “Y” wound stators are permitted. No delta wound
or slot less stators are allowed. Only circular (round) pure copper magnet wire
permitted. The three slotted stator must be wound with 17.5 turns of 2 strands of a
maximum diameter of .813 mm per slot. The resistance for each slot of
the stator shall be tested and a minimum resistance figure will be determined upon
submittal.

The real problem for tracks inspecting motors is that the minimum resistance figure they determine upon submittal, isn't a public number.

Hi,

You, yourself, can establish a baseline tied to your specific device and the specific motors and their specific testing voltages at a particular frequency/temp/run-time-to-sample-interval using an inexpensive ($100 or less) DMM with inductance/LCR capability:

https://www.amazon.com/Multimeter-Re.../dp/B00Q2CF5QO

https://www.walmart.com/ip/DMM-Digit...&wl13=&veh=sem

If those units seem stable on milli-ohm measurements, as well, you can factor in the static resistance to your impedance points gleaned from the above processes.

You'd also have to decide if you're going to bring rotors into the equation, because their presence in the stator's magnetic field will change readings substantially.

In other words, from careful and repeated testing of many motors of several different "winds" you can provide a picture of what an "average" 21.5T (or any other motor) would look like when tested on your equipment with the same criteria. This is actually very precise for your sample sets, although probably not accurate against the aforementioned secret measurements.

So, the largest investment would be your time in reading up, testing (if everybody will agree to it) and plotting your results.

Even if you shell out several hundred dollars for dynamic inductance unit, you'll still need to test against the above criteria and equate that to: turns of wire of a certain gauge? rotor composition? wind pattern? presumed length of the wire? ...

The end result will be simply testing the racers' motors before events and having a cap on an overall inductance:resistance quotient and/or rotor size/composition - which is really the historic issue all over again, except not focused on wire diameter/length as actionable points.

I'm not bashing your idea AT ALL, I find it very interesting, you'll just need to get an easily repeatable process going and sell it to your club.

I would offer this: get a used dynamometer and a cheap oscilloscope and simply measure the motors at a certain voltage and phasing frequency. Don't worry about amps drawn or any of that, just use the same setup all the time for all measurements.

The only important criteria are the voltage and switching frequency against a particular load. About the temps, bring them up to 5-10F above ambient with a hair dryer prior to testing and then forget about it.

You won't have to spend much, study much or argue much if you simply present this as a leveling opportunity. If they grab their lexan scissors and Xacto knives...drop the subject ;)

Gene

Here's the problem in a real world scenario.

(no preference, just motors I had on-hand at the time)

Trinity D4 with HT rotor: 21 IR 35 Inductance
Maclan Team Edition with HT rotor: 20 IR 33 Inductance
Team Scream "The One": 18 IR 24 Inductance

All 3 are Roar legal. The TSR is really a 1/12th motor as it loses it's true benefit in a TC. But how exactly do you set a "tech limit" in this day and age? Answer....you can't. Roar took away most of the limiting factors in their rules, so sky's the limit now...or should I say "basement"?

Yep, if you get down to it, controlling dimensions and materials to a certain spec...yields a spec motor - so just hand'em out...

Roar did pretty good with the 25.5 spec. Really limits what can be done.