Tips And Tricks

12/28/08

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Useful Tips and Tricks for remotely controlled helicopter models. If you want to help me and provide tips, please Mail them to me.

bulletThrottle Jockey ATV to RPM conversion sheet.

Some people like to have a sheet with all the RMP's of the Throttle Jockey of Model Avionics given a specific ATV value. For that I have made an XLS conversion sheet for the Throttle Jockey that provides just that for the different transmitters. You can give in your gear ratio and print the sheet and take it with you to the field. 
Much better, you can also enter the head speed and find the required ATV values for the different transmitters. Thanks to Bas Delfos for the good Idea.
 

bulletSetting up the 401 gyro.

Setting up the 401 is fairly simple. First you select a control horn position on the servo such that the arm length on the servo is about 17 to 20 mm. Next set the tail control rod length such that when the servo horn is orthogonal to the control rod, the heck rotor blades have an angle about 10 degrees (pushing to counter the torque when hovering). Next select the proper gyro mode for you servo (e.g. DS on for the 9253 servo). Next put the delay on the gyro to zero (in case you have a fast servo like the 9253). 

Put the trim of your rudder channel in the zero position including sub trim etc. Make sure that there is no revo or any other mixing to your rudder channel!. Program you Tx such that you can control the heading hold and rate modes of your gyro (connect a channel that you can switch to the gain channel).  Now put your tx in heading hold mode, and turn on your receiver and wait for the gyro to initialize (the led should go on continuously). Now switch your gyro gain channel such that the gyro goes into rate mode (led goes off). Now turn down the limit pot on your gyro. Next put the rudder stick in one of the extremes, and rotate the limit pot until there is a maximum control throw on the blades without binding (check both directions). Choose the limit such that there is no binding on either sides.

Next put the ATV or EPA values of your TX rudder channel on 100% (reasonable piro rate for now). If you ever want a faster piro, you can turn up the ATV or EPA of your rudder channel. Now control your ATV or EPA values of the gain channel in both directions to 50%. Your basic setup of the gyro is done.

Go and fly and check how she feels. You can now turn up the ATV values of the gain channel in both gyro modes for all your idle ups such there is no oscillation in your tail (wagging). You can test this best by diving the helicopter from some height. If it does not oscillate there, then it is ok. Make sure that your gain is e.g. 5% below your maximum setting for the different idle ups (less strain on your servo). After this you can adjust the piro rate to your liking by adjusting the ATV of the rudder channel.

Thatís it, youíre done.
 

bullet

Throttle mixing on a TX that does not have a limit function on the ATV or EPA values (e.g. FF8 or FF9 etc.).

It is not essential to use throttle mixing, but indeed, for aggressive 3D it is very useful to keep the revs up. However, the 9C does not have a limit function for the ATV or EPA. This means that once you have set up the ATV values of your throttle, that engaging some mix with throttle as slave may result in overdriving the throttle servo (past the mechanical end point). There are two options. The first is to move your sub trim and mechanical setup such that the ATV for full throttle is at 140%. The servo will never be driven past that point. Then it is safe to do e.g. a roll to throttle mix. The second option is to make sure that the throttle only goes to e.g. 85% at full pitch.. You can then add a mix such that at full pitch and full mixing in (e.g. roll and pitch) the throttle will go exactly to 100% of the mechanical travel of the carb. Of course there are mechanical options (special control horns) that allow you to overdrive the throttle without mechanical problems. That way you can just engage a ... to throttle mix.
 

bullet

Maximum differential pitch on your swash plate

Typically the blade will not stall below e.g. 16 to 17 degrees or so. Since your heli will probably have a maximum pitch of 9 to 10 degrees, it is acceptable to put the maximum swash plate tilt such that there is a differential blade pitch of + and - 7 degrees. However, be careful that there is no binding at extremes (e.g. maximum pitch, and the pitch and roll at maximum TOGETHER).
 

bullet

Loosen up the split gear on a Raptor 50

The Raptor 50 V2 uses a split gear to have a driven tail during autorotations. However, the gear needs to be loosened up before installation. If you do that, you loose less energy when going to throttle hold to enter the autorotation.

The original white gear moves very difficult over the aluminum autorotation hub. It is designed this way to give the white tail gear some support since it is pulled towards the back of the heli by the tail belt. It is supposed to wear in over time, but this takes way too long. The method described below, will wear in the tail gear so that it rotates freely, and is still properly supported by the aluminium autorotation hub.
 
Just put the main shaft in a drilling machine, and attach the autorotation hub with the grey gear and the white tail gear to the main shaft as shown in the picture below.



Now hold the grey gear as shown, and slowly start the drilling machine. Now increase the speed of the drilling machine, and keep it rotating until the white gear starts to spin freely. Let it cool down for a couple of seconds, and feel if it rotates freely. If not, repeat this a couple of times. This will perfectly match the new white gear to your aluminum autorotation hub so that it rotates as it should, and that it is still properly supported by the autorotation hub.

This fix will only take a couple of minutes and is much easier than grinding or sanding the white gear! Furthermore, this way guarantees a perfect round fit with good support.
 

bullet

Saving your Futaba Campac data or any model data in your TX on to your PC

If you want to make a backup of your Model data inside your TX, then just copy it to the Campac. Next you can get the hardware from Model-Gadgets to read the Campac data from your PC. You can use the Software from Wallace Louie: CMS to read and write the Campac from your PC.

This list of tips will include tips about the following elements in the future:

bulletTemperature of different glow plugs
bulletChecking a glow plug.
bulletUniflow setup
bulletExtra ring between head and cylinder if the engine has problems with pre-ignition.
bulletRaptor 30 & 50 tips.
bullete.g. piece of tape before the most forward rudder control rod support to prevent it from moving forward and blocking the tail control rod.
bulletGeneral Heli setup tips.
bulletCorrecting the phase error in the head.
bulletEngine setup tips.

This Raptor with an OS 50 engine is running nice and rich, the way it should be.

 
bulletTrimming tips.  For now I have just listed a response I gave to a question at RunRyder why an inverted heli is completely out of trim on the roll axis.
bullet

Remember that the tail thrust is there to counter the torque (which it does). However, it does a bit more then counter the torque, it also generates a side thrust. As a result of that your helicopter is always tilting to the right a bit while hovering stable (right hand rotation heli that is). If the heli would be hovering perfectly level, it would drift to the left (again right hand rotation heli). You probably have trimmed the heli to stay put in a stable hover. This effectively means that you put in a bit of right cyclic by means of the trim.

Now, think about the forces acting upon the heli while inverted. You will see that the heli should now be trimmed exactly in the opposite direction for a stable hover. Obviously you don't do this. As a result of this, the heli drifts to the left while inverted and you are looking at the nose twice as hard as you had to correct for in the initial trimming in normal hover (again for a right hand rotation). You understand that for a left hand rotation the directions mentioned above are mirrored.

This effect can be reduced by introducing a mix: pitch -> roll.
 

bullet

But there is another thing.
Depending on the vertical position of the tail rotor with reference to the vertical center of gravity and the main blades of the heli it will start to roll to the right or left because of the increased thrust of the tail rotor, and that thrust being above or below the center of gravity and above or below the average point of sideways drag of the heli.

This effect can be reduced by introducing a mix: pitch -> roll.

 

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