Walkera 4#3 FAQ

Or: "FAQ in a wider sense" (no questions)
Note, the following text contains a lot of "I believe...", "in my opinion...", "in my experience". This is not the tone one would expect from a FAQ, but the reason is simply: I don't know. And I wonder if anybody else does, excluding those who have signed a NDA with Walkera.
Nonetheless, I hope the following text is useful.

In my opinion...

Please, don't do any modifications unless you are very sure that something is broken. “It wobbles around in crazy spirals and generally doesn't obey my commands very well” is an indication that something could be wrong. Still, most likely the heli is technically OK, and the pilot is the cause.
Trim the cyclic and rudder as carefully as possible. Repeat often during flight, because they drift slowly.
Find a big enough space. A small room makes for slow learning, because there is no time to recognize and then correct mistakes, and learn the correct moves.
Learn to fly... nobody said it's easy... be patient.

Risk of fire
The 4#3 uses a Lithium-Polymer battery that can burst into flames in case of electrical defect or mistreatment.
Unfortunately, there was at least one incident where a LiPo-powered children's toy set the children's room ablaze (link). The 4#3 has about four times the battery capacity of said toy.
The batteries should not be left unattended both while charging and when connected to the heli
It is recommended to charge and also to store them in a fireproof container (flower pot etc)
The same risk exists with any kind of LiPo-powered electric toy, so this is not specific to Walkera. But note, that a comparison with mobile phone batteries, cameras etc is not valid for several reasons.
What is interesting is that there are literally hundreds of threads regarding LiPo fires on rcgroups.com, where the poster states “I thought this could not happen to me.
LiPo batteries can burn with an intensity of fireworks of the same size. Take care.
That said, I haven't heard of any 4#3-related LiPo fire yet, and we all hope that this doesn't change.

“readme”:
I got a 2nd 4#3 two weeks ago and “started from scratch”.
Now there are dozens of known modifications for this heli.
IMO, only fixing the swashplate is essential, for example by tying some thread around the main shaft above the swashplate.
Unwrapping the antenna cable is another “mod” that may be necessary, if radio glitches are a problem (includes random tail kicking)
All the other mods can wait...

Introduction

The Walkera 4#3 is in my opinion a mixed bag. On one side, it is an incredibly small heli, and really cheap.
Alternatives like Micron V2 are much more expensive, bigger, and reportedly don't fly as nearly as good.
The RCgroups thread has at the time of writing 2400+ posts! I haven't seen that much enthusiasm for a technical product in a while.
On the other hand, it's not easy to make it fly - depending on the case. In my personal opinion, based on the one "sample" I know, quality is a disappointment. Still, it's not a lost case. It takes some work, but the result is well worth the effort.
Word has it that Walkera improved quality, compared to the first batch that went on sale (also that Hirobo rejected a batch of their spare rotorheads because of quality problems) - and in some components the design has changed (example: there is now a ventilation hole in the main motor).
The helicopter is a rather simple mechanism, and with a bit of patience there is no problem that one couldn't solve (by throwing enough spare parts at the problem...).
With this page I'm trying to provide information I hope will be useful for current and future 4#3 owners.

First time buyers, yes or no?

My answer is both. It may well be one of the most difficult helis to fly, but it is generally very robust, in the same sense that a mouse can survive a 1000 m drop into a mine shaft. Stepping on it is another story.
There are examples of complete beginners who successfully learned to fly with this heli, and others who say it's impossible.
I guess it will work out fine for people who are patient and comfortable with the idea of sliding around on the kitchen floor for two weeks without ever lifting off.
If one treats it as if it were the last heli in the world, then I think the chances for success are good. The most important rule is: Cut the throttle before impact.
A larger heli would be easier to handle, slower in hovering, more stable, and require less retrimming. But it won't fly in the living room, and that is one of the big advantages of the 4#3.

Tool or toy?

The big advantage of the 4#3 is that one can fly in small spaces, at home or in the garage. This gives a lot of practise opportunity, and learning to fly takes many flight hours of practise.This makes it attractive for many, who don't have the room to fly a bigger heli.
However, there is indication that the 4#3 is not made for this kind of heavy-duty use:
The motors seem to have a limited life time, and it appears that the enthusiasm for the heli on the forums has cooled down a bit, now that every third post is “another main motor gone” (BTW, my own is currently grounded for the same reason EDIT it flies again, little spinning bundle of joy).
The 4#3 is probably not the best choice for people (like me) who want to spend as much time as possible in the air, and consider repair / tuning work as a necessary evil:

It may take a lot of effort to make it fly well
It may require even more effort to keep it in flying condition
Spares usually come by mail order with some delay, and they are not that cheap

In comparison, a bigger heli can be kept in the air with very little running cost besides the occasional bearing replacement and comparatively little work.

Buying the heli/ spare parts

Given the prices of spare parts, it may be a good idea to buy a second complete heli as backup. Some shops (rc-fever) will increase their shipping costs with the number of helis ordered, making it more economic to buy at a more expensive shop.
The transmitter is listed at 40 dollars, and it looks like wasting a lot of money. But keep in mind, several people had Tx failure, or radio problems. Having a second independent setup to cross-check can save many hours of fruitless debugging work. Also, the battery pack alone has a list price of 20 bucks, although they can be found for a lower price (but beware of shipping cost rip-off on Ebay).

Training kit

A training kit prevents the heli from falling over, usually on its side.
For the 4#3 it is not as important as for bigger helis, because the rotor blades are next to impossible to break (the rotorhead is a different question, see below).
Nonetheless, one can easily improvise a training kit, either with stiff drinking straws, or a single carbon fiber rod.
However, it may be not a good idea to add too much extra weight: The heli has plenty of power to spare, but many people had problems with short motor life time.
A training kit needs to slide easily on the ground, friction is bad.

Shops

Below shops I have dealt with, there are many others.
If I were unhappy with any shop (which is not the case), I wouldn't list them here.

RC-fever Shipment is expensive. They shipped after a couple of days.
Flying Hobby Shipment within a couple of hours. Mr. Fung is one of the regulars in the GAUI EP 100 thread and I understand that his shop has a very good reputation.
EHiboro Shipped after a couple of days
DerSpielstein Germany / Europe. They offer same-day shipment for COD or PayPal orders, and they replied to my mails immediately.
Ebay sellers: Watch out, the shipping costs are usually excessive.

Recommended spares

If I were to buy a spare heli, I would possibly still buy most of the parts below.

One extra accu
Two rotorheads
One or two flybars. Alternatively, make a replacement from 1 mm carbon fibre rod or piano wire
Two main motors
Two tail motors
maybe spare servos
maybe the carbon fiber bar that holds the canopy, only because it can get lost so easily. Alternative: Reuse broken flybar or sacrifice one spare
maybe spare bearing pairs for main / tail rotor

A spare main rotor or tail rotor is in my opinion not that important
For those who are planning to fly with a group (in a club): A second set of crystals on a different frequency.

Mode

Newcomers, watch out: The "mode" is the order of controls, throttle left or throttle right. Check out, what "mode" is common in the geographic area you live in. For Europe, it's mode 2 - throttle on the left. In some regions (asia?) mode 1 is more common, throttle on the right.
As I understand, it is possible to resolder the transmitter and change the mode. But it will be very difficult to re-learn flying with a different control layout.

Frequency

The band depends on local legislation. If in doubt, ask someone from a local club for recommendation.
When buying two helis, ask for different frequencies. The crystals can be swapped easily.

Flying

Pre-flight checklist

The pre-flight check is required by aviation law :)

Is the tail rotor firmly attached to the wheel, and is the wheel at the correct position on the drive shaft?

Is the canopy centered, so that the left servo arm can move freely?

Connecting the battery

Zero rudder trim. The gyro will use it as center setting, when the power is connected
Put on a flat surface
Connect the battery
Wait a couple of seconds for the gyro to calibrate (and don't move)
When it starts to emit a quiet, high-pitched hum, it's ready to fly. Also, the Rx LED stops blinking, but it's inside the canopy.
The battery should be placed as far forward as possible, to move the center-of-gravity ideally into the plane of the rotor shaft. It can be turned with the cable facing backwards. Some people have attached a 2nd battery holder to be able to move it forwards.

Rudder trim

The gyro will zero to the rudder setting set on the transmitter, when the power is turned on.
With a heli that works as intended, one sets the rudder trim to center, powers up, and retrims a little bit. In reality, more often than not, see below, “problems” section.

Lifting off

The sideways push of the tail rotor is very strong because of the small size. Just lifting off with cyclic at center will blow the heli about two meters to the left within one second. This is just a matter of practise, compensate with a short cyclic right push.
And fast takeoffs are easier, it may be best to "jump" to 30 cm of height and then stabilize the heli.

When to stop

Lithium-Polymer accus may not be discharged below 3.0 V. Otherwise, they will suffer irreversible damage.
Unfortunately, the 3#4 does not include low-voltage cutoff circuitry, as is otherwise common. Therefore, it is possible to deep discharge the accu.
For example, I managed to reach 2.4 V before the heli suddenly dropped out of hover. The throttle stick did not “hit the ceiling”!
There are many reports of short overall battery life time, and accidental deep discharge is the most likely reason.
Using a kitchen timer may be not such a bad idea, at least for those who plan to spend a lot of time in the air with minimal cost (BTW, the list price of the Walkera battery pack buys a standard-size LiPo with four times the capacity).
The risk for deep discharge is highest when hovering very low in “ground effect” (and even more when sliding on the ground), because it requires much less motor power than free flight.
When the battery is almost empty, there is a risk to lose tail authority (the heli will refuse to rotate right, and finally start to spin left).

A good setup

The first time I tried an RC flight simulator, this was my first impression:
The cyclic stick sets the angle of the rotor plane (relative to the ground). I control the rotor plane, and if I take my hand off the stick, its angle remains as is.
When the heli is set up correctly, broken in and trimmed, it will behave almost in the same way. I had the same experience five weeks after receiving the heli, and two rounds of spare parts later. It feels good... Move the stick, the rotor moves. Hands off the stick, the orientation of the rotor remains unchanged.

A bad setup

When the setup is bad (cyclic trim is off, or there are technical issues like friction in the rotorhead or possibly the swashplate moves up and down), the plane of the rotor will not remain fixed, when I take my hand off the cyclic stick.
As a consequence, the heli "wobbles" from left to right. It flies, as if it were a marble inside a bath tub (or as someone put it: "Toilet bowl effect"). I think the term "Wobble of Death" is also being used, although the pilot is part of the oscillations.

Small rooms

Helis cause air motion, and the air in a room starts to get turbulent after a while.
Depending on the room, this can be a real headache: Suddenly the heli runs away in some direction, as if by its own will and without warning.
The turbulences make it more difficult to fly in a small room (and the presence of walls doesn't really help either).
Half of the solution is correct trimming of the cyclic stick (I know, this is easier said than done). The other half is

Eliminating friction from the rotor mechanics
Correct blade bolt tension
keeping the swashplate in place

This should be emphasized: An inexperienced pilot and bad trim will produce exactly the same “wobble”.

Fixing problems and modifications

Insufficient rudder trim range

The problem appears as follows: Even though I connect power while trim is full left, the trim range to the right is insufficient over the duration of one battery.
Resetting trim to the left and reconnecting the power to the heli helps temporarily.
What happened to me is that after a while, the tail motor lost too much power and couldn't hold the heli anymore, even with trim and rudder full right.
Replacing the tail motor fixed the problem. The original motor was just bad, it caused a lot of vibrations. The new one runs much quieter and is more efficient.
Another possible reason causing the same problem is friction in the tail mechanics. The tail rotor shaft should have some space (< 1 mm), in other words, the gearwheel should not be pushed all the way to the bearing. The gap prevents friction.

spacing on the tail shaft between gearwheel and bearings

Bad tail rotor bearings have also been reported as a problem, the symptoms are the same.
Friction will reduce the life time of the tail rotor. It is a good idea to check frequently, that it spins freely. When blowing at the right spot, the tail rotor should spin to speed, and (blowing a bit harder) it should keep turning for one second.

Servo glitches

The connectors between the receiver and servos are another weak point, many 4#3 owners reported problems.
A quick-and-dirty fix (avoiding the word "solution") is to push all 3+3+2+2 connector ends individually to the board, as far as they will go.
Possibly, the connector itself is not the main source of problems, but the crimp connection on the plug of the servo wire!

Pushing the individual contacts with a screwdriver

Radio glitches

The heli will fly with the receiver antenna wrapped to a tight bundle, and the transmitter antenna pushed in. Depending on the environment, radio glitches may be a problem, or not. Also, maximum distance will be limited. The receiver performance will deteriorate, when the battery is low.
The radio works best, when both antennas are fully extended and straight. For the receiver, some compromise needs to be made, since the antenna is too long.

Antenna loosely wrapped around the tail and back

Radio glitches are much less likely, when the transmit antenna is fully extended.
And if that wasn't obvious enough, here's one more:

Don't fly into the transmit antenna....

Swashplate mod

One reason of instability is the swashplate moving up and down. It is only suspended by pushrods.

For the modification, the main shaft is removed, and the swashplate taken off. The metal ball links can be pulled out with gentle force.
Add two pieces of shrinking tube are added, one over and one under the swashplate (In my heli it is the silicon insulator from a wire, kept in place with shrinking tube. It is a bit more flexible, but I guess the result is more or less the same).

Two sections of shrinking tube keep the swashplate vertically aligned

Suppressing tail wag

On my 4#3, the tail wag disappeared after I removed the receiver circuit boards from their cardboard enclosure, and attached them to the frame with gyro tape.
Note that gyro tape is not the same as ordinary foam tape!

Rotor head replacement / removing the main shaft

The pin holding the main wheel can be pushed out with a needle.
Note: It is cone-shaped, and needs to be pushed out in the right direction. On both 4#3 I own, I was able to push it out with very gentle force.
Some owners reported that it was very difficult to remove the pin.
I had no such problems, but this may vary from heli to heli. If the rotorhead is already broken, one option is to simply cut the mainshaft in half and pull it through.
Use pliers and a pin to push the bolt out, and keep the pin end very short. This way I can use as much force as it takes. When it yields, the bolt comes out a millimeter and is easy to pull out.

The bolt is pushed out easily using a pin (short end!) between pliers

By the way, if it ever "disappears", a spare bolt come with the rotorhead.

Rotor head

The plastic rotor head is arguably the weakest part in the 4#3. At the top there is a gap in the plastic that seems to serve no other purpose than to increase the demand for spare parts.
It is recommended to fill the gap with epoxy before the first flight.
I have used the following procedure on the two 4#3 I own. Both modified rotorheads haven't broken yet, despite rough treatment.

The contents of the rotorhead spare kit (rotorhead with main shaft, bearing x 2, bolt

Below the procedure I used twice, successfully. It includes all the “gory details”, but take it as a suggestion only - there will be many different ways to get the job done.

Remove the two plastic links between flybar and rotor (hold the rotor centerpiece with one hand, and pull back the link with a fingernail until it snaps off)
Pull off the rotor straight upwards. This is somewhat difficult, but should not require undue force. Try to tilt it slightly forwards and backwards while pulling.
Remove the two ball bearings from the rotor head
Scrape the inner surfaces with a sharp knife to remove the surface layer
Cut a piece of steel wire that fills the gap, for example from a pin board needle. In the gap, it should be flush with the top surface.
Mix good quality two-component epoxy. Stir very carefully, but without causing bubbles
fill the gap with epoxy
Insert the steel wire
wipe off any excess epoxy
Place under a halogen lamp and let the epoxy cure at elevated temperature

As an alternative, small.planes on rcgroups.com manufactures and sells an aluminium rotorhead. I haven't tried it myself (still plenty of spare rotorheads “on stock”, and the reinforced ones seem to last), but I saw one on a friend's heli and it is a beautiful piece of work. Definitely recommended.
There appear to be different versions of the main shaft / rotorhead part with slightly different lengths. Therefore, replacing it may require adjusting the length of the servo links.

Breaking in the heli

It may be a good idea to tape the heli to the bench, and run through a full battery pack while keeping the cyclic stick in a corner. This will work the ball joints, which should move as easily as possible.
However, with the newer 4#3 this wasn't necessary anymore.

Main blade balancing

The newcomers who have never balanced blades, skip this step. It flies straight out of the box in any case.
Otherwise, it is a good idea to balance the blades

Tail rotor balancing

This is easy and fast, no equipment required. The carbon fiber rod that holds the canopy is used as "blade balancer", between two glasses.
The patch of tape I had to add was rather small (~ $2\,mm^2$ ), but there were reports, where the tail rotor was badly out of balance.

Balancing the tail rotor

Blade tracking

Blade tracking means, that both blades generate the same amount of uplift, and therefore bend equally under load.
During operation, this can be checked from the side: If both blades spin in the same plane, blade tracking is OK.
If one blade runs higher, one can gently twist the lower blade to a higher pitch, so that it gives more lift.
Alternatively, one might consider changing the main blades entirely.

Tape on the canopy mount rod

While we're at it, it is a good idea to put some tape on one side of the carbon fiber rod that holds the canopy, so that it is on the left side.
It prevents the canopy from touching the aileron servo arm. Not important, though.

Tape to prevent the CFK rod from sliding to the right

Motor life time, cooling fins

To be written, I don't have sufficient own experience at this time.
Some users report very short motor life time (7..10 accu lengths). Others have installed cooling fins on the main motor, and it seems not even to get hot anymore.
One question is, whether the short lifespan is due to overheating, or caused by brushes wearing out.
Until then, order spare motors, but don't throw away the old ones. There may be replacement brushes soon.

Main motor heat sink

Here is a CNC main motor heat sink for a very reasonable price. Mine fits very well to the motor.
Use thermal paste from electronics / computer shop to achieve best cooling. It makes a big difference, because the unavoidable air gap conducts heat very badly.

CNC heatsink for main motor

Flybar length

A shorter flybar reduces cyclic response and makes the helicopter easier to control for a beginner.
Often, one end breaks close to the paddle. Properly re-centered this is not a problem. Some people intentionally shortened their flybar for a more “beginner-friendly” heli.
A simple way to make the heli easier to control is to wrap equal amounts of wire around the flybar ends (experiment).
Because of the weight, more stick input will be required for a given roll rate (both cyclic directions), and the impact of servo inaccuracy reduces.

Servo arm length

A common modification is to move the balls on the servo arms one hole to the inside. This makes the heli less sensitive. More important, the servos have a limited step size and “deadband”, and shorter servo arms result in more precise control (at the expense of control authority).

Blade screw tension

The two screws that tighten the main blades should be loose enough, so that the main blades can move almost freely.
There should be a small amount of friction,

Transmitter battery

For the transmitter, any rechargable NiCd / NiMH “AA” battery will do, and so will ordinary (non-rechargeable batteries).
Currently, the best I have seen is NiMH 2650 mAh.
Depending on the battery, it may be necessary to cut away some plastic ridges in the battery holder (picture) to make contact.

For some batteries, the contact is too short to reach past the plastic ridge (left: original; right: cut)

It is possible to LiPo batteries having the same connector instead, for example from a Lama.
3-cell packs (3s) are reported to work best (12.6 V). 2-cell packs (2s, 7.4 V) may work at reduced range.

A LiPo battery instead of the transmitter pack

Note: Accidentally charging a LiPo through the transmitter's charging jack with a standard NiCd/NiMH charger will cause a fire!

Credits

Everybody on the RC groups thread for reporting problems and solutions.

Links / further reading

Antenna tube_
Alternative heat sinks suitable for the main motor_
Walkera catalogue including the unreleased 4G3 with cyclic pitch_
Reading material while waiting for spare parts..._
More setup tips incl. narrower blades for higher headspeed and heat shielding to reduce gyro drift_
Cheap batteries and spares_
even cheaper batteries Possibly without connector?

© Markus Nentwig 2007-2008
The content of this page is provided without any warranty and may not be reproduced without permission.

Comments? Questions?

Please send me a mail! mnentwig@elisanet.fi