Protech ZOOM 425 ccpm Specifications download pdf (Page 192)

So increasing the gain on a yaw-rate gyro has two effects:

• It dampens random movement more, so the tail is more stable. This is good.

• It also dampens intentional tail movement, so this decreases the maximum pirouette rate.

This is bad.

A standard single-rate yaw-rate gyro exhibits these bad behaviors. There are more sophistic-

ated yaw-rate gyros which partially fix some of these problems:

Dual-gain gyros allow you to set two gain settings on the gyro and switch between these two

gain settings from the transmitter, so you can decrease the gain when you need high pirouette

rates.

Remote-gain gyros allow you to set the gain from the transmitter by a knob or switch, so you

can decrease the gain when you need high pirouette rates.

30.1.10. How ESCs work

30.1.10.1. Pulse-width modulation

To fully understand how brushed and brushless ESCs work, it is necessary to understand the

concept of pulse-width modulation.

First, imagine that you have a water pipe with a valve which can only be fully opened or fully

closed. If you open this valve, the water flows through the pipe at 10 gallons per minute. If you

close this valve, it stops the water flow.

Now, if you want a water flow of 5 gallons per minute, you can open the valve for 5 seconds,

then close it for 5 seconds, and repeat. Since the valve is open for 50% of the time, the aver-

age water flow will be half of the max flow rate, or 5 gallons per minute.

If you want a water flow of 2 gallons per minute, you can open the valve for 2 seconds, then

close the valve for 8 seconds. The burst (peak) water flow will be 10 gallons per minute, but

the average water flow will be 2 gallons per minute.

An ESC works in the exactly the same way. If the throttle signal is 50%, then the ESC will ap-

ply full power to the motor for 50% of the time. If the throttle input is 20%, then the ESC will ap-

ply full power to the motor for 20% of the time.

This pulse-width modulation technique has several important limitations. If you ignore these

limitations, you will overload your power systems, and your heli will likely crash and/or the mo-

tor, ESC, or battery may be damaged.

30.1.10.2. Motor startup

An R/C brushless motor controller turns on/off three sets of windings in sequence to rotate the

motor. This turning off the windings on/off in sequence is called "commutation".

The brushless motor controller measures the "back EMF" from each set of windings to determ-

ine how fast to commutate. Basically, the current draw of the winding drops as the magnet

passes by the winding. The problem is this only works properly when the motor is running at a

reasonable speed. When the motor is starting from a dead stop, the motor controller must

pulse the windings in sequence without back EMF feedback to start the motor spinning to

about 100 rpm.

Technical Appendix

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Protech ZOOM 425 ccpm Specifications Page 192