Walkera Dragonfly 4
- main frame replacement
Replacement of the main frame on the Dragonfly 4 is the biggest job of all, simply because it means a complete strip-down and rebuild of the helicopter.
The main frame is Walkera part number HM-004-Z-27 and, from my experience, it has two inherent weak spots where cracks appear if your landings aren't quite as they could be. One is immediately in front of the tail boom securing screw, and the other at the joint directly above. Both are arrowed in the photo below:
While you can keep flying with a cracked main frame, a time will come when the crack in front of the screw will become bad enough to cause serious movement in the tail boom, leading to all kinds of stability problems in the air.
As yet, I've not found a glue that will adhere to the material of the frame for very long - so when the cracks get bad, it's time for a new main frame...
Prepare yourself and take your time!
The replacement of the Dragonfly 4 main frame is a fairly big job, and it's no good trying to get it done in 5 minutes!
With good preparation, a good clear working space and a relaxed, beer-free mind (ug!), you should be able to do it within an hour - although a lot does depend on your practical abilities too.
So, outlined below are main frame replacement guidelines, with photos where appropriate. Apologies for any errors in the order of doing things etc., but to the best of my knowledge this is what I did.
You might notice that sequentially some photos don't follow, but this is a minor issue. Also, the sequence that follows isn't the only option, with regard to order-of-doing-things.
Tools for the job...
My personal choice of tools to use is shown here, and include a set of watchmaker's screwdrivers, modeling pliers (thin-nosed), a standard Philips screwdriver, the allen key supplied with the Dragonfly 4, a soldering iron, solder and a bit of double sided tape to fix the rx.
Look at everything first...
Before you do anything, familiarize yourself with everything! Particularly the rotor head assembly. Take a photo of it before you strip it apart, or use this one for reference - click on this one for a larger view with labeled references.
This main frame replacement does double up as a bit of a memory test too, for when you have to put it all back together. If you have doubts, make notes as you go!
The receiver...
Unplug all connections to both motors and both servos. Unattach the rx antenna from anything that it might be attached to (tail boom, landing skids etc) and very carefully use a modeling knife to prise off the receiver. It's stuck well, so take you time!
Servos...
Remove the servos. Both servos are held in place by clips, one top and bottom (arrowed), which need to be released. A small flat-bladed screwdriver slid between servo and clip is good for the job, but be careful not to damage the servo casing.
Obviously you also need to unclip the servo connecting rods from the swashplate.
Main motor...
Remove the main motor by taking out both mounting screws, accessible from underneath the main frame.
Rotor head assembly...
Start by removing one of the flybar paddles - no need to completely remove the screw, just loosen it enough so that you can slide the paddle off the end of the flybar rod.
[Incidentally, removal of the flybar and main blade holder isn't necessary, but things are easier with them out the way.]
Next...
Loosen both flybar grub nuts with the allen key supplied with the heli, and gently slide the flybar out through the rotor head ring and head assembly.
Next...
Unclip the two short tie bars that connect the rotor head ring to the main blade holder. Using thin-nosed pliers is best but be careful not to chew up the plastic.
Next...
Once both short tie bars are disconnected, you can carefully prise off the main blade holder. Don't grip the top of the rotor head too tight with the pliers, just hold it gently. The holder will need a firm pull to release it from the bearings.
Next...
With the main blade holder out the way, unclip the two long tie bars that connect the rotor head ring to the swashplate, in the same way you unclipped the two short tie bars previously. Lift off the rotor head ring.
Next...
Here comes the tricky part! Pull out the metal pin that holds the rotor head assembly in place. It's very tight, so be patient. Twisting the pin should make things easier. Once the pin is out, lift off the rotor head, the guiding ring will come with it. Don't lose the pin!
Lift the swashplate off the main shaft.
Main gear...
With all rotor head gubbins off the shaft, remove the circlip that holds the main shaft in place. The easiest way is to start prising it off with a small flat-bladed watchmaker's screwdriver, then once it's a little way off the shaft pull it completely clear with pliers.
Next...
The main gear should now drop out of the main frame Incidentally, I haven't mentioned anything about removing the landing gear and battery holder yet - if you haven't done so already, now's a good time to do it!
Next...
Remove the main gear bearings, as new ones only come with new main gear and not a new main frame. A small screwdriver does the job, but it's not so easy to get them out if they're a tight fit.
Tail boom & motor...
Once the main frame is clear, next comes the back half of the helicopter. Unsolder (don't cut) both wires from the tail motor, making a note of which color belongs to which connection.
Next...
Loosen the securing screw and slide the whole tail rotor/motor assembly off the end of the tail boom. There's no need to break down the assembly into its separate components, unless you're replacing the motor too.
Next...
Undo the tail boom securing screw on the main frame, and slide the tail boom clear of the main frame. Remove the tail motor cables, but first have a look to see exactly where they enter the frame to run into the boom.
Halfway there!
If you've followed the steps above, you should have a bare main frame and a lot of bits...
And now all you have to do is get your new main frame and put it all back together. And as the good people of the Haynes workshop manuals put it... "Refitting is a reversal of the removal"
Related pages
Motor upgrade - fit a better quality brushed motor.
Battery upgrade - time to go Li-Po.
Landing gear & skids upgrade - add a touch of class to your helicopter.
The Dragonfly 4 - what you get and what to do with it all.
Spares & repairs - useful tips for the Dragonfly 4.
Rotor blade balancing - a crude but effective way if you don't have a balancing tool.
Rotor blade tracking - how to get the blades tracking correctly.
Flybar balance and paddle pitch - more ways to stop vibration.
Index - to all Walkera Dragonfly 4 related pages.
