[Previous entry: "Vive le CX, or Maybe the C6, or Maybe the DS9 or..."]
[Next entry: "Carcynic.com Barcode Landing Page"]

In addition to Cars, one thing we like to play around with here at CarCynic.com is Quadcopters. For one, they are cheaper and take up less room than cars, so we can play with lots of them.



We like building them, modding them, and on occasion -- flying them.

We previously reviewed the Air Hogs X4 "Stunt" Quadcopter in this article.



Frankly, we were pretty harsh on it. We were especially disappointed with the fake (non-functional) trim controls, and it's overall flying characteristics. But we are not ones to leave well enough alone. Whether or not it's broken, we'll "fix" it. So I whipped out my trusty Swiss Army Knife and dissected my X4. Read on to see my modifications, and the results....

Disclaimer: What follows describes what I did to my own Air Hogs X4. I am not suggesting that you do this, or do any such modification to this or any similar product.

The X4 is completely encased in foam. In fact, as we will see, it has no actual airframe. Even the battery is inaccessible, and this is yet another feature we do not like about this product. To get at it's internals, we had to use a knife. An X-acto knife works, but I found that the gently serrated blade of my Swiss Army knife made quicker cutting. The gooey glue that holds the top and bottom halves together is better handled by the X-acto Knife.

I cut close to the fans as shown by the green lines in the following picture. I did not want to damage the Fans; as mentioned in the review, they are part of the functional ducted fan system.

Warning: Do not try this at home. Really bad things happen if you cut into a LiPo Battery. Fire and serious injury can occur.



I cut carefully because I intended to be able to close it back up again. To do so, I re-attached it at the front with some Gorilla tape (orange oval), and I added 2 small pieces of high-performance Velcro at the locations marked with the orange squares (internally, of course). It now opens for access to the battery, and closes securely enough for flight.

After removing what seemed to be several pounds (not literally, of course) of the Goo-glue, I could access the motor wires, and the flight control board. There was plenty of extra motor wire pushed into the "body cavity" (OK, I know how that sounds - sorry). There is nothing but glue and foam holding the flight control board frame. The foam is the airframe.

Since the object of this Mod is to replace the Flight Control (FC) board, the motor leads were carefully de-soldered from the board. There are no connectors like on the competing Quads.

I then removed the FC board from the frame. This meant also destroying the switch and charger port.

Using hot glue in each corner, I attached the new FC board to the frame. The new Flight Controller is from a WLToys V202 micro quad. This board can be seen/purchased here (banggood.com.) This was chosen since the V202, like the X4, is direct-drive, and the motors are similar. The V202 board is half the size of the X4 control board. Installing the V202 board in the correct orientation is important, as is keeping it level and centered.

As of this writing, the LED "eyes" of the X4 were not connected, but the V202 board has connectors for 2 sets of LED's, or the "eyes" could be connected to the V202 boards' status LED.

Doing such a board swap is made more difficult by a significant problem. Each motor of the X4 rotates in the opposite direction as the V202. The V202 uses the "standard" configuration as shown here (for MultiWii). This required moving all 4 motors on the X4. Fortunately, this is not too difficult. The motors can be removed from each ducted fan housing.

I carefully removed each prop. The motor shafts are needle thin, so pulling carefully and straight was essential. I pulled on the propeller "skirt", not the blades. If you pull on the blades, you will get just the blades, and new props are not available.

The streamline motor bottoms appear to be held on by 3 each clips, but these are in fact glued, not just clipped. I got all of them off with no breakage by simultaneously and carefully cutting and prying with the X-acto knife (Never pry with an X-acto knife. If they break, they can cause damage to anything they hit, especially eye-balls. Do as I say, not as I do -- or at least wear eye protection.)

The motors can then be simply pushed out. The wires are held with a bit of clear tape. Inside the body they can be carefully pulled from the seam between the top and bottom.

The motors were then swapped left to right, and re-assembled. It was impossible to get the wires back into the body as they were. Small holes were made in the frame with a jeweller’s screwdriver and the wires were carefully pushed through from each fan back into the body following a path pretty close to the original.

The streamline end caps must be reinstalled as they are part of the aerodynamics of the ducted fan. I clipped them in position, and then, using a pin, applied one tiny drop of CA glue (Superglue) to each clip.

I then reinstalled the props. Each motor/prop now turns the same way it did before, it is just is in a different location. This is important since there are different CW and CCW motors (and obviously, props).

Next, i soldered the motor wires to the V202 FC board. M1=Right Front, M2=RR, M3=LR, M4=LF. I soldered to the bottom of the board, leaving the connectors un-touched. Of course a more sanitary solution would be to attach a connector to each of the X4's motor wires.

The FC board frame was then re-installed using some tiny strips of high-performance 3M clear double stick tape. When installed, this "tape" is very similar to the "goo-glue" that was originally used. Note that the white strips seen below are foam tape pads for the battery to rest on, not the aforementioned clear tape.



The battery of the X4 also lacks a connector. It was cut (Never short a LiPo - I cut one wire at a time) from the original board, and appropriate power connectors were attached. Note that just this part of the mod can be done to allow swapping of batteries.

Here's the completed Mod, with the "battery hatch" open:



From the top, it's hard to tell the "Franken Hog" is not a regular Air Hogs X4. The switch/charger port is missing, and there is a small hole for the V202 board antenna. The Original Air Hogs Transmitter is not WLToys compatible, and will no-longer work. Any transmitter that supports the WLToys protocol, or has a WLToys module in, it will work.



Most importantly, we now have real, functional trim controls !
So does it fly? Well... Yes and No.

It initially flies very well, with way more stability and control than it originally had. With the WLToys system, there are now 5 levels (20%, 40%, 60%, 80%, and 100%) of control sensitivity. At 20% it is still docile enough for beginners. 40% Seems to give slightly more control/sensitivity than the original "Expert Mode". 60% is great for an experienced pilot flying indoors, with way more control authority and responsiveness. It essentially flies like it should have from the factory. At 80%, there is plenty of control to deal with minor outdoor winds, and at 100% real (not pre-programmed) flips and rolls are possible.


Video of my Moddified Air Hogs X4. You'll never get slew rates like that (especially outside) from a stock X4.

It is almost perfect -- except -- it doesn't last. The Ducted fan arrangement, and the foam body of the X4 makes it aerodynamically different enough to cause problems for the V202 Flight Control System. After a short period of flying, some sort of "Wind up" happens in the WLToys FC software, and it becomes unstable.

With a well charged battery, several minutes of excellent, stable flight is possible. If you land, and take off again, it is stable again for a while. It seems that when the battery voltage decreases, the time of stable flight decreases.

Technically, it seems that the FC software expects the Franken Hog to be more responsive to yaw than it actually is. When the X4 does not yaw as it expects, it simply keeps adding yaw input until only 2 diagonally opposite motors are lifting the quad. When there is nothing left, it falls out of the sky, with 2 motors running at 100%, and the other 2 idling.

Left Yaw inputs seem to delay, or in some cases, arrest the instability. Right yaw causes immediate instability.

This yaw instability is likely due to the fact that the small ducted fan props on the X4 do not have the "bite" that the V202's props have. This means less effective torque.

There is no way to change the Flight Software or the Settings on the V202 board.

I tried adding more mass to the props, in the hopes of increasing the torque, but this would only increase the instantaneous torque, not the steady state torque, so it did not help.

Other ideas would be to remove some foam in an attempt to decrease the yaw (Z-axis) moment, as well as decease lateral aerodynamic resistance (for example removing the small "rudder").

It is also possible that the instability is caused by vibration.

Originally, the flying characteristics of the X4 were poor for an experienced flyer. Now they excellent for a short time, followed by un-flyable.

While the mod was not 100% successful, it does demonstrate how the X4 would fly with a proper Controller (Transmitter) and Flight Software. It shows what the X4 could have been if Air Hogs had done their homework.

It should also be noted, that I can easily re-install the original FC board, and still have the advantages of some weight-savings, and a replaceable battery.