RC Helicopter Tail and Gyro Setup

Introduction

When i was first starting out in the heli world, one thing that i found very difficult was a good tail setup on my RC helicopter. How much of this was caused by my choice of a "cheap" gyro is unclear. But a good tutorial is definitely a must when setting up your first tail. Especially considering how many different radio/gyro combinations there are in the current market place. One thing is for sure, you will definitely spend less time on setup if you spend a few more pounds (or dollars) on a good, well known tail gyro, such as a Futaba 401 or Align GP 750.

First things first before touching the RC helicopter gyro, lets get the mechanics set up and the servo in place. Find the best servo horn to achieve 90 degrees to the servo casing at centre stick. Attempt this when the tail servo is plugged directly into the rudder channel. You will want to make sure no trims/sub-trims are set and 100% travel is configured. Now have a look through your box of bits (i know you have one) to find the best fitting horn or wheel.

The position of the ball link on the servo horn depends on the heli/servo configuration, but you want to find a suitable medium between having too much servo travel, and enough control of the tail (resoloution). Refer to the manufacturers guide if in doubt, or try trial and error (my best friend). Align the servo so the pushrod is straight down the tail (only really relevant if you have a boom mounted servo on your helicopter). Now position the servo on the boom so when it is at 90,the tail pitch slider is at the centre of travel between helicopter hub and tail casing. This can be adjusted later with the range and limits, but for now we want full deflection of the tail rotor.

A quick note, when powering up a gyro, do not move it, or apply any stick movements until any blinking lights have become constant. As when the system is initiating it needs this time to calibrate. Any movements can affect this. So especially once you plug in your Li-Po. Also if using a digital servo, make sure you have it selected according to servo type being used. Otherwise you can burn out an analog servo if it is set to digital mode.

Your RC helicopter gyro will have two leads, one for the signal for the rudder, made up of a cable with 3 wires. Plus one with single cable, this is the gain lead. It will depend on your transmitter brand and set which channel to place it on, Spektrum is "gear" others use "Aux" and it can vary from those, so double check the manual.

How to setup the channel for the gain switch is strongly dependent on the radio/gyro. Some radios will give 100% travel on that channel in both directions, so 0-100% standard mode, and 0-100% Heading Hold (HH)/AVCS when the switch is flipped (basically they are just treating it as another channel on the radio). In this case, travel limits are set on each of these end points that correspond to the required amount of travel. Other radios will have specialist gyro menus which make this much easier, allowing you to set the required gain in each mode then linking this to the switch.

The last type, from which i have experience is the Spektrum/Align way, where the "gear" channel is on a scale between 0-100%. Two points can be set on this corresponding to the two switch positions. One is set between 0-50%, representing the standard mode 0-100%, and the other point is set between 50-100% which represents 0-100% Heading Hold gain. So a setting of 75% on the radio menu would mean 50% heading hold gain. For a new pilot and also for the experienced pilot, 90% of the time it is best to be in Heading Hold mode, standard mode requires a whole lot more patience, and radio settings. We will encounter the standard mode briefly whilst setting up the limits on the gyro however.

Start with about 30-35% gain in each switch position for this task, it can and will be adjusted later when trying for the first hover. We also now need to check the reversing channel orientation is correct for your gyro/radio combination. As mentioned before on the Spektrum we have a scale of 0-100% which is split in two, with the heading hold mode in the top 50%, but this might not always be the case dependent on radio/gyro. Refer to the manufacturers manual for status LEDS on your gyro to tell if it is in heading hold or standard modes. For instance on the Futaba 401 gyro it will be constant for heading hold or blinking for standard. Reverse the channel as appropriate to get this in the correct order.

Most gyros will have a limit setting . Futaba 401 gyros have a "pot" that is adjustable via a screwdriver on the gyro, where as Align GP750's have it as part of the setup routine, where you physically move the transmitter stick to the required position to set the limits. The idea is to set it so that when moving in one direction it does not hit and bind at either the hub or the tail casing, this gives us our non-binding full deflection of the tail rotor.

Rudder Channel Direction

Normal rudder control means that when doing a right turn you are turning the rudder stick to the right. This means the nose of the helicopter will turn to the right. Check this by taking a look at the tail blades. Assuming a correct setup, and a normal direction of blade travel for a RC helicopter, the blades of the tail will rotate up towards the tail boom. That is there leading edge rotating towards the boom up from the ground, and into the helicopters down wash. Assuming this is the case on your helicopter, view the tail pitch slider, a right turn means the slider going towards the case, which gives a tail moving to the left and the nose moving to the right. This can be corrected on the rudder channel on the radio if it is happening in the opposite direction.

This also needs to be checked on the gyro, as there will be a setting for direction here to. This corrects for how the gyro and not the rudder stick changes the direction of the helicopter. Move the rudder stick a little to get the pitch slider in the centre of travel. Have the helicopter in front of you, with the nose to your left and tail to your right, bring the tail towards you and watch for the direction of correction in the tail slider. It should move away from you, if this is opposite, then you need to use the appropriate technique (menu, dip switch or setup procedure) to reverse the correction direction of the helicopters gyro. Double check with the above technique to confirm correct movement direction. Pull the tail towards you and the slider should move away, not with you and towards you.

Finalizing the Gyro Setup

This completes the general setup of your gyro. Now you will want to set the gain of the gyro to around 60-70%. Hover and then adjust to the "sweet spot" where there is crisp control and no "wagging" of the tail. This is an indication that the tail gain is set to high and the gyro is over compensating. A sloppy tail, or one that doesn't stop as quickly as expected indicates the opposite, that the gain is to low.