CONVERTING HOBBY KING’S JUNKERS JU-52 TO A TRUE 3 …CONVERTING HOBBY KING’S JUNKERS JU-52 TO A...

CONVERTING HOBBY KING’S JUNKERS JU-52 TO A TRUE 3-MOTOR VERSION

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The Junkers JU-52 sold by Hobbyking is a very nice looking plane with a lot of scale details and it would be perfect only for one thing – it has only one motor up front with a huge propeller and the other two wing motors are non existing and only made to look like they have motors, using smaller – probably more scale – propellers which are only free rotating. So I have converted this plane to a true 3-motor version and you can see the result in above picture. For the conversion I used:

1. 2 units Donkey Motors from Hobbyking, type ST 2004- 1500KV 2. 2 units Mystery ESC, type MY12A for 12A, also from Hobbyking 3. 3 units 3-blade Master Airscrew 6 x 4 inch propellers, one of them is a pusher 4. 3 mm Prop Adaptors, collet type 5. A few meter of silicon cable size AWG 16 (size AWG 18 is sufficient) 6. 3 mm plywood

The installation of the motors was done as following: Cut away the cowlings for the wing motor as shown here. Be sure to cut exactly as shown. Inside you have two plywood disks glued together and it is important that you cut in the middle of them so that they are split up.

BEFORE

AFTER


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Here you see the two plywood disks which are now split in half. In the centre of the disk to the left, there is a screw which you should remove. This will loosen up the front plywood and this screw is also holding the idling propeller.

Now split the motor cowling in half as shown here to the right

When you open up the cowling, the front plywood (the one holding the screw for the idling propeller) and you will not need this plywood disk

Now pry away the plywood disk which is glued to the wing motor bay

You will now see in the bottom of the motor bay that there is a “tunnel” which leads all the way to the wing centre and this will be used for the motor cables.


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Make 4 units 3 mm plywood disks with outer diameter 44 mm and a centre hole of 10 mm. The U-shaped slot in the disk has around same size as the one on the disks you pried out from the motor bay. This U-slot is for the motor cables

Drill 4 holes on the plywood disks you just made. The holes should fit to the leg of the Donkey motor. Then glue together 2 disks of the ones you made so that you have a total disk thickness of 6 mm

Mount the Donkey motor on the double plywood disks with wood screws

On the cowling halves, you will need to file away a larger opening which should fit to the disks you just made


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When you test fit the motor, you will see that you need to file out more space in the foam to fit the legs to the motor as shown here

Test fit the motor and make sure the plywood base fits snugly and that the plywood base is in an even line with the motor cowling as shown below

Now add glue to the plywood disk and fit it with the plywood disk you pried out from the motor cowling as shown on page 2.

Then drill holes and glue as well as screw together the disks as shown here.


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Thread 3 cables for the motors through the wing “tunnel” as shown above

I reinforced the inner part of the motor bay with thin glass fibre + epoxy (sorry no pictures on this) This to give extra strength to the motor mount. After this, solder the motor cables and insulate them with shrink tubing. After this glue the plywood motor base into the motor bay as shown in the upper right picture. But before gluing the motor base, make sure the motor is working (that the cables are properly soldered).

I also reinforced the inner part of the motor cowling.


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After this the cowling is mounted with screws to the inner plywood disks. I used ony 2 screws, one on each side which is enough. Above right is the final result with the propeller mounted on the adaptor. I left the centre motor as is. It is bigger than the two wing motors but it doesn’t matter. This motor was also equipped with same propeller size as the wing motor. It could of course hold a bigger prop but would not look good. And there is enough power with all 3 motors working together.

I also kept the original ESC for the centre motor and I let the BEC from this 20A ESC drive the servos. The two Mystery 12A ESC were mounted on both sides of the cabin, behind the blue original ESC as you may be able to see on the picture to the left. And make sure you cut the BEC current cables from the two Mystery units (cut the middle red cable) so that they does not interfere with the BEC from the original 20A ESC unit.

For the props, I used one pusher on the left wing, the other centre and right wing wer with normal puller props. And make sure the motor for the pusher prop is rotating in the opposite direction of the two other motors


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The plane flew great with a lot more power than I have seen from the video shown on the Hobbyking web site. My friend took a video of this plane when it was maidened and I will try adding a link to this. I had a poor landing after a few flights and the landing gear collapsed and one wing motor was damaged. The gear was easily repaired and it was also easy to change to a new motor since the cowling is only attached with screws. And motor can be removed by loosening the 4 leg wood screws and then pull out the cable from the U-slot in the motor mount and solder the new ones. So my advice, spend 10 bucks and buy a spare Donkey motor. Bangkok March 2012 Peter [email protected]

CONVERTING HOBBY KING’S JUNKERS JU-52 TO A TRUE 3 …CONVERTING HOBBY KING’S JUNKERS JU-52 TO A...

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