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Old 08-01-2013, 09:18 AM   #16
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Kv means nothing in respect to a motor's performance. Kv is RPM/Volt. A 2000Kv motor will theoretically turn 2000 rpm at 1V. It does not mean it will turn 16800 rpm at 8.4V as other factors will become involved at higher rpms (rotational mass, electrical resistance, friction, etc...) Kv will not tell you the potential power range, or curve, a motor will perform at. A loaded dyno, using a slave motor, can show you what the power potential of a motor is. However, this only gives you the data of the motor itself. The best bench motor in the world will still suck balls when paired with an inefficient drive-train or geared incorrectly.

Rotors: (measured in Gauss (G) )
Size: smaller(12.3) more rpm vs larger(12.5) more torque.
Strength: Higher Gauss more torque vs lower Gauss more rpm.
Magnetic balance: having a balanced +/- pole gives a smoother powerband. Having a higher G+ vs G- rotor can cause a motor to appear "jumpy" through its powerband. This isn't as critical on higher turn motors, but can be noticeable on low turn motors, especially on the bottom end.
Realistically, you could get a 12.3 high G rotor to perform nearly identical to a 12.5 low G rotor. It's all about the torque/RPM trade-off and tuning the motor to the current track conditions (grip, temp, layout, driving style).

The basic brushless motor checkers are not realistically useful. I have one of the Extreme BMC-01 versions, but only use it to free-spin motors to set/check float, break-in bearings, and test sensor boards. That is pretty much all they are good for in the realm of modern sport/racing motors.

As far as rotor numbers, there really isn't a static best or target number. Fantom, RMS/MMS are decent consumer/hobby grade meters to check rotors (Epic i-Gauss = meh...). No two meters are going to read the same and the same meter will likely read the same rotor differently over time. Unless you have access to a calibrated gauss meter inside a vacuum Faraday cage at the NIST, it's best to just use the meter readings as a reference to compare two or more rotors.

Quick example: (gearing, timing, track conditions identical)
Two 12.3mm rotors with balanced +/- poles, one 1400G the other 1300G.
1400G = Lower powerband vs 1300G, resulting in more low->mid-range power, but less top speed. (power curve begins and drops off sooner)
1300G = Higher powerband vs 1400G, resulting in more mid-> top-range power, but less low end torque. (power curve begins and drops off later)
"Shut up and Drive!"

Last edited by Jethroz; 08-01-2013 at 01:29 PM. Reason: Math fail
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Old 08-02-2013, 03:10 AM   #17
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Originally Posted by Josh-n-ya View Post
The Higher the KV value the higher the RPM is what I have been seeing on a motor tester! When you adjust timing + those numbers increase. What is a good range for KV and RPM to be at to have a fast but torqy motor? How would you test for torque? Would using a High Torque rotor be the only way to increase torque? Also have been testing some rotors. Are the best rotors pretty evenly matched as far as + and - or do you want + value to be higher or lower? What are some good 12.3 rotor + and - numbers in HT, Broadband, RPM and the same question for 12.5 rotors.
To answer these questions you would need to build yourself a flywheel dyno, which would give you complete curves of power/torque/current vs RPM (like the one attached). Myself and a few other similar geeks have done this, as it's a very useful tool and elliminates all the variables/costs of track testing.

Or just find the guy with the fastest car and copy his setup, which is much easier and a popular approach
Attached Thumbnails
Rotor shimming-dynamite-max-vs-powers-max.png  
Team Xray
RC-Timing Software - http://www.rc-timing.com
Mercedes AMG F1 - http://www.mercedes-amg-f1.com/
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