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Converting a HK-5320 servo for use on a Walkera MiniCP Helicopter

By Chubbs

Why do it?

The stock MiniCP servos have a tendancy to strip out, especially during inverted crashes. Replacement servos are

avialable from many different websites, and prices range from about $13 + slow-boat-shipping from China, or

upwards of $20 if you want to buy some here in the US and get them within a week. $20 for a servo that can strip

in one crash? Unacceptable.

Solutions?

The easiest “solution” is to do the “servo saver mod”, also known as “ruining your servo arms”, in my opinion. The

process is detailed elsewhere, but basically you put a cut in the splined part of the servo horn, so that rather than

gripping the servo tightly, it is allowed to slip during a crash. The problem I found is that it doesn’t just slip during

a crash, it slips all the time! Using heat shrink wrap around the servo horn to “tighten it up”, didn’t work in my

case. Many have claimed success with this mod, but all I did is ruin my servo horns. Good luck if you go this route.

There are a couple of options to retrofit cheaper servos into the MiniCP. One option is the HK-282A servo, though

I did not successfully get this one to work. There are a couple of issues. First off, it is physically too large to fit.

You must dremel/sand/otherwise remove nearly all of the plastic case to get the dimensions small enough to fit

within the tight servo arrangement of the MiniCP. You must also swap the two outside wires on the connector

(easy to do). Once I finally got it in place, it made a horrible buzzing noise and got tremendously hot. Not a good

servo for the MiniCP in my opinion, but some claim success. It is also not available in the US warehouse, so

shipping will take a while.

Hobbyking sells a great little servo called the HK-5320 Ultra Micro Digital Servo, which is available from the US

warehouse for $3.66 at the time of this writing. This is definitely my pick for a servo replacement. It’s actually

smaller than the stock walkera servos, but filling a gap is easier than making one. The other issue: These servos

move the wrong way once hooked up! How to fix that? Get out your soldering iron!

This process will take you about 20 minutes your first time, especially if you aren’t familiar with soldering on a

curcuit board. After I did 2 though, I now find that I can knock one of these out in 3-5 minutes…easily worth the

$15 cost savings over a walkera servo.

Summary of content (8 pages)

PAGE 1
Converting a HK-5320 servo for use on a Walkera MiniCP Helicopter By Chubbs Why do it? The stock MiniCP servos have a tendancy to strip out, especially during inverted crashes. Replacement servos are avialable from many different websites, and prices range from about $13 + slow-boat-shipping from China, or upwards of $20 if you want to buy some here in the US and get them within a week. $20 for a servo that can strip in one crash? Unacceptable.
PAGE 2
Fig 1: Size comparison between the HK-5320 (white), and the stock walkera servo. Step 1: get your stuff You’ll want to have all your parts ready first, but don’t worry, there aren’t many. 1. 2. 3. 4. 5. HK-5320 servo “Microheli balls” like these from an MCPX. Just search “Microheli balls” on ebay and they should come up. http://www.ebay.
PAGE 3
Step 2: Swap the servo wires Figure 2 shows the problem…the signal and ground wires are backwards when comparing the HK-5320 to the walkera servo. This is an easy fix. Just gently pry up on the little white tab holding the servo wire in place, and give the wire a little tug. It should slip out. Remove both the Yellow and brown wires, swap them, and reinsert. If you have trouble with this, please stop now…it gets worse. Fig 2: Walkera connector is on the right, HK-5320 connector is on the left.
PAGE 4
THIS THING IS TINY!!! I used this soldering station, available from the Hobbyking USA warehouse http://www.hobbyking.com/hobbyking/store/__19240__Soldering_Station_with_Adjustable_Heat_Range_USA_W arehouse_.html It has a very precise tip, and works excellent for small circuit board jobs like this. Get one when you order your servos, you will find lots of uses for it. While soldering, be very careful not to “smear” solder across all the contacts and short them out.
PAGE 5
Fig 4: The middle wire is now swapped with the left wire
PAGE 6
Step 4: Swap the motor wires Flip the circuit board over, and you will see two wires running from the board to the servo motor. These wires now need to be switched. See Figure 5 Below. Figure 5: Motor to circuit board connection. Swap these 2 wires.
PAGE 7
Step 6: Servo arms and balls Here, you’ll need to take one of your MCPx balls you got from ebay (or your preferred source), and attach them to the innermost hole on the servo arm, on the back side. See Figure 6. It’s hard to overstate how tiny these things are, so don’t drop them. You’ll need a VERY tiny standard screwdriver for them. Figure 6: The mini heli ball goes on the backside of the servo horn (which will be closest to the servo) on the innermost hole.
PAGE 8
Step 7: fitment to MiniCP The final step! Here we will deal with the size issue of the smaller HK-5320 servo. If you just put them on the MiniCP as is, they will simply fall out; there is just too much play in the mounts. You can fix this however you like, but I decided to simply run a bead of hot glue down each end of the servo (by the mounting tabs). Run a 1mm or so thick bead down each side, and let it cool/dry. Put it back into the heli, and see how it fits. Use more glue if necessary.