funflier

Installation of a Esky 3900 motor with a 10 tooth pinion.
Pic shows the alumn spacer (adaptor for a 370 motor aprox 2mm thick) I picked up at local hobby shop. Redrilled the narrow mount holes larger for the 3x10 button head allen screws backed with 3 mm washers. This was so I wouldnt crush or mangle the mount holes with their small flanges as this would weaken the mounting.
Note that the alumn adaptor mounts the motor high enough that it will not interfere with the flanges around the motor mount. If you grind off that "ledge it weakens the frame considerably leading to a cracked frame.
Also if you opt to run a 3800 motor, which is 28 mm, it will NOT be necessary to remove the ledge.
I chose the button head allens so they wouldn't interfere with the frame (frame is made with a slight notch in it and I got better access to them with my Allen driver (shown installing the screws) then either cap screws or phillips.
The picture of the two metal scales is to show that there is nearly 1 mm behind the 26 mm in diameter motor (scales are each nearly 1/2 mm thick). this can also be seen in another picture. Actually the frame is curved at this point so it's a little hard to show clearly I have a non functional 400DH which is 28 mm in diameter and when I tried fitting it with the 10 tooth that on it, motor was a little to tight to sit perfectly square against the frame or the alumn mount (the outrunner part Does clear the back part of the frame) a touch with a Xacto or Dremel would take care of that.
As it is my gear mesh is perfect with the 3900 and 10 tooth and I have plenty of room mount/screw hole wise for adjustments. My ESC is a 35 amp (overkill but it will never overheat) Exceed-RC (26$) set for a super soft start and medium timing (keeps it from stuttering on beginning throttle stick movement. I moved my battery/ESC onto a hardwood extension and forward to get my weight/balance closer to what I wanted to see. After 3 batteries one after the other at hover the motor is barely warm to the touch and the ESC is not even warm.

caylorray

Good post, but I'm a bit confused now. Everything I've read in this forum says the 3800 requires either frame mod or an adapter, and the 3900 fits without any mod or adapter. I just ordered a 3900 based on that. Is it possible you got the two switched around?

fourstarforty

I installed the 3900 with a 10t pinion on my honeybee king 2 no problems. All you have to do is remove a small ridge with your hobby knife on the heli frame, takes 1 minute and install your motor.I have over a hundred flights and no frame cracks etc.

4*

funflier

That's a 3900 installed with a 10 tooth pinion (10 tooth is larger in dia that the 9 tooth with same tooth pitch) and the adaptor is 26 mm in dia and about 2mm thick. It raises the motor above the ledge so it does not have to be cut. That ledge strengthens the mount same as a vertical slate in a spar strengthens a wing. The adaptor also works as a larger load bearing surface for the motor to distribute its load on, could also work somewhat of a heat sink (I have thermal compound under mine) but that is debatable. I don’t know about a 9 tooth on a 3900 but I think the motor would hit the vertical part of the frame behind it and frame would need to be trimmed.
The 3900 is 26mm in dia the 3800 is 28mm and the 400DH is also 28mm (27.5 by my measurement).
The original motor probably used the 9 tooth for the "tractor" effect to get it off the ground (rpm converted to low gearing) both my original motors lived short hot lives with 3-4 deg pitch at mid stick

Assuming you are using the adaptor...
With any installation of one of the 3 motors no cutting of the ledge is needed. It's the interference of the vertical part of the frame behind the body of the motor prevents good gear mesh that seems to be the culprit
Installing a 9 tooth on a 400DH would put the motor against the vertical of the frame and need considerable trimming from what I can see. The 10 tooth on the 400DH puts it against the frame and would need just a touch of trimming to get a good gear mesh. I don’t know why a 9 tooth would be installed on a 3800 400DH or a 3900, as these are pretty strong motors compared to a stocker.
Idea is to get the headspeed up with power to use the given pitch. I run 3 deg at mid stick with the 3900 and 10 tooth and that’s far more then enough power for a hover out of ground effect. (still working on headin landings soo..) No idea whets required for 3D pinion wise but my headspeed is calculated at about 2470 full stick (never had it there in flight though).
http://www.runryder.com/helicopter/g...5/hdspeed.html
I doubt the number of flights is what causes the frames to fail its the number and severity of the hard landings (controlled crashs).
I seem to make a lot of landings where I didn't reset the "altimeter" for the correct field elevation...[]

funflier

Sorry forgot to add this...The adaptor was used cause I was orginally going to use the 400DH till I found it was dead. As I had the adaptor I used it just to experiment with. It is NOT needed for the 3900 but be sure to use much shorter mounting screws or you will hit the motor windings.

DumbDawg

My Feedback: (3)

I just finished putting in a 3900 motor and 43t pulley as well. The 3900 I have an 11t pinion on it. I made a gasket of cardbord, the type used as backing on display products. NOT corregated but flat thick cardboard. Cut out corresponding holes to the frame and mounted the motor. Worked VERY well in raising the motor to the right hieght. Now all thats left is to adjust my tail belt tension and gyro and I'm away.

tbaus

I am no great expert or anything, but I just widened up the slot enough to fit my 10 tooth pinion through ( very little widening was done ... an exacto knife was used) I used some short screws I had and just bolted my Esky 3900 motor on, wire tied my brushless ESC on and went flying.. If I did something wrong, don't tell my heli! It's been flying this way for over a year and since it doesn't know any better, it has been working just great!

DumbDawg

My Feedback: (3)

A little red green goes a long way sometimes... lol its whatever works imo

funflier

I didnt have to widen my frame for the pinion as its a pretty big hole it drops through. I velcord my esc on as I finally decided where I was going to leave it at...
Did you take the cover off your esc for cooling, I have seen a few where this was done not sure if its a good idea or not having a open circuit board exposed. Orrr if it really matters at all

DumbDawg

My Feedback: (3)

Well I have a 30A esc that I put on with the 3900 and so far I haven't noticed that this is a problem.

tbaus

I too use a 30A ESC and left the cover on. I have a few helis and haven't ever removed the plastic wrap on any ESC. I think it provides a bit of protection to the ESC, certainly against shorts.

DumbDawg

My Feedback: (3)

It'll protect against dust and dirt which can cause shorts on boards. I would think it would be much better to leave the plastic on. If its over heating I'd think its because of the esc being to small for the motor or you have another problem somewhere, ie loose connectors, bad soldering or something like that.

funflier

yes probably would, I did leave mine on just curious if anyone runs theres without the cover.
I have a 30 Amp on mine and mounted it above the battery up front. Not very good air circulation up there, however, it it barely gets warm after running 2 batteries out at hover. My 3900 motor doesnt even get warm.

DumbDawg

My Feedback: (3)

Yup... the outrunner motors are a definate plus over the stock junk motors. Same with mine... just doesn't get hot. As for my esc I mounted mine on the outside of the lefthand side (port) of the frame. It stays nice and cool there.