Mikado warns Logo 700 owners - but why?

About a week ago Mikado published a warning notice to all Logo 700 owners due to an unwanted static charging issue occurring on the model’s tail. It sounds serious but what’s the real cause of this issue and why is this so important? I will try to explain as clearly as possible…

First of all, what’s happening? The source of the problem is the tail belt. During operation the belt can touch the inner wall of tail boom tube or the mounting block, this friction generates an electrostatic charge on these components. When the build-up of charge reaches a certain level it is then discharged by generating a spark somewhere – which itself then generates an electromagnetic field. The bigger the discharge, the stronger that field is.

The problem comes from here.

The helicopter has many sensitive electronic devices on board, like the servos, ESC, BEC (or BEC-ESC combo), FBL or gyro and the most important – the receiver. These devices are able to interact with this unwanted electromagnetic field causing undesirable effects. The most likely to interact with the unwanted electromagnetic field is the receiver antenna as this is what it is designed to do – just that it’s supposed to receive a field from your transmitter, not from this discharge – and it tries to interpret this as a kind of message, but obviously it can’t.

By now we have smarter and smarter receivers, most modern systems can notice the difference between a message from your transmitter and an erroneous one caused by this type of discharge and ignore the faulty ones – mostly… If the frequency of these sparks is higher than the limit of the fault tolerance, then there’s a crash. Fortunately the chance of this happening is unlikely, but it’s definitely not 0 percent.

Back to the past, and in the early years of helicopter modelling (before modern receivers) there were many issues like this to be handled. One of these was the electromotor. These motors were brushed motors, where the carbon brush contacting with the commutators timed the motor itself, generating a tiny spark with each rotation. The receivers were not prepared to distinguish between real and error messages causing many, many crashes as the motors wore from usage and generated bigger and bigger sparks.

This is one of the reasons why the brushless motor was a monumental change in helicopter modelling. Brushless motors don’t generate sparks or the associated unnecessary electromagnetic fields. Modern receivers then brought the next big change with error correction making RC helicopter flying much safer.

Although these innovations reduce the possibility of a spark causing an issue the chance is, again, still not zero. To be honest I have never flown Logo 700 but the symptom is not unknown even to me. As a beginner or semi-advanced pilot I had to endure this problem on a belt-driven T-Rex 500. I was flying the helicopter when I noticed a hiccup on the cyclic control periodically causing me a small heart-attack followed by stream of colourful language and then a landing by autorotation. Every 1-2 second the helicopter would jerk forward, forcing me to pull it back. It was a real fight for control.

This was a known issue even on T-Rex 500 CF

By that afternoon (ok, night…) I had found the problem. With its blades removed and on the kitchen table next to a desk lamp, with the noise of the 500 making my family very happy, I noticed the little sparks between the tail tube and the carbon fibre sheet, then the tell-tale shaking servos. I had heard that WD40 is a good solution on the belt, so I sprayed half a bottle on it. It did solve the problem, but only for a few days.

So I was ready to throw the entire helicopter in the bin, then one of my mates told me the ultimate solution (thank you Gabi Füge): a wire underneath the servo arm in contact with a screw on the carbon sheet, and voilà, job done. This wire discharges the potential continuously, preventing the build-up of charge and therefore avoiding all the sparks. No more hiccups, no more problems.

Now Mikado offers the same solution, but I hope it’s clear for you why this is so important