קצת מידע על מנועי בארשלס

[matan 144]

אני (יותר נכון כולנו) מתעסקים הרבה עם מנועי בראשלס
ייצא לי גם ללפף כמה... להוסיף חיישנים ועוד שטויות.
אבל אני לא לגמרי מבין איך המנוע והבקר "מתקשרים" ביניהם.
1) לפי מה נקבעת מהירות המנוע? אם הבקר מזרים זרם כל פעם לפאזה אחרת, אז המהירות נקבעת לפי קצב ההזרמה מפאזה לפאזה? או לפי המתח שהבקר מוציא?
2) המתח שיוצא מהבקר למנוע הוא AC או DC? או אפילו שילוב שלהם?
3) איך הבקר "יודע" (במנועי סנסורלס) איזה קוטב של המגנטים נמצא מול הסלילים? הרי הבקר צריך להפעיל את כל אחד מצמדי האלקטרומגנטים לפי מיקום הרוטור (שעליו המגנטים)

[Ronny Cohen]

The brushless motors we run in our modern r/c's are true three phase AC motors. thus the three wires on the motor, one for each phase

ESC =electronic speed control
The ESC is a trapezoidal wave generator. It produces 3 separate waves, one for each wire on the motor (i.e. it converts DC to 3 phase AC). Controlling the speed of the motor has nothing to do with voltage or amps, but instead the timing of the current fed into it. By increasing and decreasing the wave length (frequency) of the trapezoidal wave on the three phases, the ESC causes the motor to spin faster or slower.

Since the ESC controls the motor with frequency, not voltage, when you plug 22.2 volts of battery into your power system, you have 22.2 volts going to the motor with the full amperage potential of the batteries backing that voltage.

The ESC switches polarity of the phases to create the waves. This means the voltage through any given winding flows "alternately" one direction, then the other.
This creates a push/pull effect in the magnetic field of each winding making these motors very powerful for their size and weight

The motor, and load placed on it determines the amp draw from the ESC and batteries.
So, it is the primarily the conversion of DC current to AC current that creates the "ripple" in the current from the batteries that the capacitors need to smooth out to protect the ESC. There are other factors involved, but in the interest of keeping it as simple as possible I'm not going there. (read: I couldn't explain it if my life depended on it)
1. The length of the wires from the batteries to the ESC is crucial to how hard the capacitors have to work to smooth the current flow to the ESC. The shorter the better, and the closer you are to maxing out the capacity of the ESC the more critical shorter wires become. (information varied system to system, but it seemed like 6-7 inches max length was a general rule of thumb)

I wasn't able to find an explanation on the actual cause and effect of wire length relative to capacitor performance, but it came up time and time again in my searches. Including a confirmation by Steven Nue that this is a critical component of capacitor health.

2. Capacitors are wear items. The reading I did pretty much confirmed something I had begun to suspect. The constant charging and discharging of capacitors, and the heat created, wears them out.

So our capacitors are going to fail eventually, but the harder you work them, the shorter their lifespan, and if you seriously overwork them, the will fail prematurely.

CONCLUSIONS, mine anyway, feel free to draw your own
Check the wiring length between the batteries and ESC and keep them as short as practical. I think keeping all wiring runs as short as reasonable is generally good practice.
Don't overload your system. Keep prop sizing conservative, and consider running 4s or 5s on stock components. If you are wanting to push the envelope, consider component upgrades sized to handle the extra load.
The capacitors aren't going to last forever. If you are confident replacing the caps, consider it a maintenance item. If not, be prepared to replace your ESC from time to time. I have no idea what the normal life cycle of a capacitor might be