Saturday, August 13, 2011

Helicopters: Where to fit your ESC

Where to fit your ESC.

By Lood Birk

Ermelo Radio Flyers

Ok, so the title is slightly a bit misleading. This article is going to be about where to fit your ESC in relation to your receiver. This is kind of a strange subject to talk about. Not really. Let me try to explain.

To understand why we are talking about the position relationship between your ESC and your receiver, you need to know a little bit as to how an ESC operates. The ESC does not provide a constant current to the motor. That would make the electronics of your ESC big and heavy. Instead, it pulses the motor at a very high frequency. This electronic technique is called pulse width modulation or PWM in short. The frequency in which you pulse the motor is so high that you can even hear it as that high pitch electric whine you hear from the engine. In high current ESC modules, you can even hear it on the ESC’s PC board. Now the thing is this. In any conductor that carries current, a magnetic field develops around it. That is fine, but should the current pulse, or change polarity frequently it starts do develop the ability to induce a current into a conductor close by. The more current is drawn in the conductor that is pulsing, the more voltage is induced in the conductor close by. A transformer operates in that way.

Now comes the part I generally have trouble to explain to guys in general.

Your ESC has got a lot of conductors on the PC board. The same goes for your receiver. It has got a lot of conductors on the PC Board. No imagine that most of those conductors on the PC board of the ESC is pulsing. Some of them are high current conductors like the output wires to the engine. Now imagine if you put your receiver close to that ESC what voltages are induced into the circuit of your receiver. To ram the nail home, I want to bring to your attention that on the receiving end of your receiver we are talking about voltages as low as 30uV (0.000 030V) and it is not uncommon that a voltage of 50mV (0.050V) can be induced into a conductor in our case study. Let us put it another way. It will be like trying to see when looking directly into the sun. The effects of the induced voltages are especially noticeable wit the 35MHz system as twitches and even the receiver going into failsafe. On the 2.4G systems, the effects are not as noticeable as the signal is of a digital nature with error checking and correcting protocols as part of your signal, BUT the 2.4G radio systems are NOT immune to the induced voltage effects.

I must say, though, that designers of the ESCs and receivers try their best to shield the electronics and conductors and also employ clever design techniques to counter effects of induced voltages. Yet, no electronic device is fail safe from induced interference.

So, how do we try and prevent the two devices from interfering with each other? Well, you could put the ESC in a lead box but I assure you that your plane or heli won’t go anywhere, so it’s probably not advised. The other way is to space your ESC and you receiver as far apart as possible. I know this is difficult, especially in smaller planes and choppers.

I normally space my ESC and receiver apart about 7 to 10cm. In the case of high powered ESC, I tend to make that distance a bit longer. Another little trick is to ad a ferrite ring on the lead going from your ESC to your receiver. The ring dampen any induced voltages, in the lead at least. Below is a picture of a typical ferrite ring and a ESC lead wrapped around it.

For those that are not sure where to place your ESC and receiver, below is a picture taken from a typical heli manual to help you along. Mostly on the instructions of your receiver as well as the ESC it has ideas and tips on how to space your ESC or receiver. So it’s always a good idea to check the instructions.

As you can see, they try and space the ESC and receiver far apart in any of the setup configurations. Personally, I prefer the receiver at the back away from the motor in this particular Chopper.

I hope that this article helps you to understand the interaction between the ESC and receiver and in future you know to space the two for better reliability.

Happy Landings

No comments: