Flyzone Micro Dr.1: Long 7mm Motor/Gearbox Upgrade - RC Groups
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Dec 15, 2011, 11:21 PM
in persuit of low wing loading
Gordon Johnson's Avatar

Flyzone Micro Dr.1: Long 7mm Motor/Gearbox Upgrade

First, I have flown the new Hobbico Dr1 at NEAT, and now that mine arrived on Monday in my front yard. It's a great flier and will loop. That said, can more thrust be obtained without going to brushless or substantially heavier gearboxes such as the one from the Parkzone Mustang (substantially heavier). The answer is yes.

Bob Selman of BSDmicroRC has sold a fantastic 7mm ball bearing gearbox for years. It has a hardened 1.5mm drill bit shaft, dual ball bearings, a nice molded housing, and Didel gears that run quietly. This gearbox has always had holes for mounting on two carbon fiber rods. The Hobbico 7mm gearbox has horizontal mounting tabs that stick out to the sides. BSDmicroRC has a new variation of their gearbox that has a piece that is screwed onto the two existing holes for rod mounting that adds a horizontal mount that makes it easy to mount in a Hobbico plane.

The other piece of this puzzle is a longer 7mm motor with a good wind for this application. All the Didel/SuperSlicks 7mm motors as well as the Hobbico Playmate/Albatros/Fokker Dr1 motors are 16.5mm long. BSD now has a longer can 7mm motor that is 20mm long. At the present they are selling this motor only in the new variation of the gearbox. The gearbox can be found on their site here. At the time this unit was added to BSD's web site we did not know how long the shaft needed to be to extend out through the dummy radial motor and cowl. Now we do. It may take him a few days to get the gearboxes with the longer shaft on his site. Call him on the phone till that happens to make sure you get the longer shaft version of this gearbox. The BSD gearbox has a lower ratio at 4:1 than the Hobbico gearbox. But, with the longer can motor it can swing a larger GWS 5x3 prop compared to the 4.5 inch prop that comes standard on the Dr1 and the other Hobbico micro planes.

So, bottom line, what are the results of this gearbox transplant?
* 18% more thrust. The stock system develops 26.6g of thrust at 3.5V. The long motor with a GWS 5x3 prop and 4:1 gearing in the BSD gearbox develops 31.5g of thrust, 18% more.
* Amp draw increases marginally by 0.10 amps. You can still use the battery that came with the Dr1.
* weight for the new gearbox with longer motor and the GWS prop increases the overall weight of the plane by 1.5g.

There you go. The next few posts show how I performed the surgery to do this gearbox swap.
Last edited by Gordon Johnson; Dec 16, 2011 at 11:25 AM. Reason: corrected typo: weight gain is 1.5g not 1.8g as originally typed
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Dec 15, 2011, 11:24 PM
in persuit of low wing loading
Gordon Johnson's Avatar
First, you have to take the Dr1 apart. The fuselage halves are held together with a thin strip of double sided tape. This can be disolved with Naptha, available at most hardware stores. I got a glass eyedropper at the drug store. I discovered that it's impossible to remove the cowl first. Once I finally got the plane apart I was able to see why. There is a foam "tongue" that sticks out from the firewall and the cowl is glued to this as well as the seam where it mates with the fuselage. Here is how I finally got it apart:

(1) Using a hobby knife carefully cut through the glue around where the bottom wing struts are glued to the bottom wing. Then, pry the strut out of the foam, which will leave a small area with foam that came out. This will all be fixed when you reassemble the plane with a dab of Uhu Por glue.
(2) Repeatedly apply Naptha to the seam where the cowl mates with the lower fuselage half, and the seam that runs lengthwise down the fuselage between the two halves. Keep doing this till you can wiggle the fuselage halves apart, start at the back, and the seam with the cow for the lower half.
(3) Remove the lower fuselage half by sliding it backwards and down. Otherwise if you pull it straight down, the dummy radial engine will break off the lower pieces of the cowl (I did this and broke mine, but glued them back in place).
(4) Unplug the motor plug from the pigtail going to the brick.

There, you've taken it apart and can now see the guts.
Last edited by Gordon Johnson; Dec 18, 2011 at 10:43 AM.
Dec 15, 2011, 11:24 PM
in persuit of low wing loading
Gordon Johnson's Avatar
In the pictures below I show the standard motor, and the new longer can 20mm long motor, as well as the BSD gearbox with the longer motor and the horizontal adapter installed. Now some foam surgery is reqired:

(1) Remove the dummy radial engine by cutting through the glue that mounts it to the fuselage, including the foam tabs that stick into it. The radial engine will need to be hogged out with a Dremmel to accept the larger spur gear of the BSD gearbox. So, remove it now since this will allow cutting out the foam for the new gearbox.
(2) Remove the Hobbico gearbox by cutting through the glue around the edges of the mount. Then, cut underneath the mount by sliding a hobby knife in from the front underneath the horizontal mounts.
(3) Place the BSD gearbox on the motor mount area, and trace around it with a hobby knife to score the foam where you want to cut. Cut downwards around this perimeter from the top. Then, cut back from the front on the sides and bottom. You want the new floor where the horizontal mounts to go to be about 5mm below the top of the gearbox mounting area. The reason the foam needs to be cut down is the BSD gearbox horizontal mounts come out about midway down the gearbox sides, while the Hobbico gearbox has them near the top. You want the prop shaft to be on the same level as the top of the motor mount foam on the bottom fuselage half. You also have to cut down in the middle for the motor, which results in a small hole down into the battery area, but this won't pose a problem for the battery.
Last edited by Gordon Johnson; Dec 16, 2011 at 12:55 AM.
Dec 15, 2011, 11:25 PM
in persuit of low wing loading
Gordon Johnson's Avatar
(1) Dry fit the BSD gearbox into the foam you've cut away. It should have the same right thrust as the original gearbox. Keep shaving away foam from the front of the area you cut out till the propshaft has about 2 to 2.5 degrees of down thrust. The prop shaft should be about level with the top of the lower fuselage half.
(2) Cut off the female plug from the stock motor and solder it to the leads for the new motor.
(2) With the gearbox dry fit in the foam, hold the dummy radial in place and see where it needs to be hogged out to allow room for the spur gear. Use a Dremel tool to do the hogging. I used the abrasive bit and worked slowly.
(3) After the dummy radial engine has been hogged out, glue the gearbox into the foam with Uhu Por glue. Then, glue the dummy radial engine back in place on the nose with Uhu Por glue.

All I have left to do is use Uhu Por glue to glue the fuselage halves together.

I probably won't get a chance to fly this modified Dr1 till the end of next week. But, I fully expect it to have more spirited performance, as well as being quieter.

Last edited by Gordon Johnson; Dec 16, 2011 at 11:23 AM.
Dec 15, 2011, 11:26 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Dec 16, 2011, 06:34 AM
Registered User
Bwattie 2's Avatar
zzzzzzz Agree! Original flys fine....
Dec 16, 2011, 09:14 AM
Just some guy
D Johnson's Avatar
Look forward to the flight reports! How much down and right do you have on the thrust lie? It is hard to see in the pix.
Dec 16, 2011, 11:20 AM
in persuit of low wing loading
Gordon Johnson's Avatar

Right thrust is the same as stock. Down thrust is about 2.5 degrees.

Dec 16, 2011, 01:16 PM
Just some guy
D Johnson's Avatar
Gordon, I would highly recomend increasing that to 5~6.

Dec 16, 2011, 01:55 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Too late now. It's very well glued in. I'll trim down elevator and live with it.

Dec 16, 2011, 03:35 PM
Power Wheels Guru
UNGN's Avatar
Thanks for this write up, Gordon, this is excellent info.
Dec 16, 2011, 05:44 PM
Ego varius quis.
Cheesehead's Avatar
Any chance you can persuade the construction of an HP03S gearbox? Same weight, twice the thrust.
Dec 17, 2011, 12:04 AM
in persuit of low wing loading
Gordon Johnson's Avatar
You could contact BSD to see if they have any plans to do such a gearbox. I think they may have done some work in that area, but I'm not sure if it was for an AP03 or an AP02 motor. Let Bob know you are interested.

Dec 17, 2011, 02:19 AM
semper mitis
gentle ben's Avatar
Dec 17, 2011, 08:42 AM
in persuit of low wing loading
Gordon Johnson's Avatar
After letting the glue for the gearbox and cowl dry for 24 hours I've now glued the entire plane back together. There has been a slight weight gain from the glue. The final weight with battery of the gearbox upgrade DR1 is 36.57g, compared to the stock DR1 with battery at 34.94. So, the final weight gain was 1.6g.

The thrust to weight ratio has improved from 0.76 to 0.86. I hope to fly both of them indoors next Friday.


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