MJX F45 brushless tail conversion - RC Groups
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This thread is privately moderated by tiggertoo1962, who may elect to delete unwanted replies.
Jul 14, 2013, 01:39 AM
Scotsman in Germany
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MJX F45 brushless tail conversion

Hi Folks

Finally got round to collecting the info and parts to enable me to get rid of the stock tail motor and PCB on my F45. The main reasons for doing this mod were:

1. Sick of replacing tail motors.
2. To let me do banked turns on my F45. For anyone who isn't aware, the way the stock PCB is set up means that the cyclic response is proportionally diminished when you apply rudder (thanks to fauconnier for discovering that one).
3. One less TX to cart around if I want to fly both my F45 and my V912.
4. To see if I could.

The parts I used are listed below. I already had the RX as it came delivered with my FS TH9X, but since I wanted to have the parts listed together and only know how to include photos at the end of the post I decided to look for a link to it .


I would actually recommend a smaller RX if you're not just using stuff which is lying around, since the canopy is pretty crowded with that one under it.

The tail mount was made out of a 2mm CF sheet. To fix it onto the tail boom I used a spare vertical tail fin mount with a couple of M2.5 x 10mm screws, as the original screws are too short. Don't know how long it'll hold, but it seems solid enough at the moment.

Many thanks go out to BThirsk and zdawg for their tireless help and patience regarding parts, technical knowhow, and setup. To date I have only had one short flight with the bird and still need to do a lot of tweaking to get it to fly just the way I want it to, so there's no sense in posting the precise settings I've been using so far. Below is a list of some of the basic menu settings where I've been messing around to save you all from having to find them for yourselves - just in case you're as lazy and impatient as myself .

Firstly, to get your gyro to go into set up mode, you need to set your FS TH9X (stock firmware) as follows:
Default setting is INH (off). Has to be changed to ACT (activated)

Once I had it up and running, this is where I went to mess about with the tail settings:
So far I've tried 2 methods. In the 9X menu I set it to:
GYRO SENS: ACT (activated)

GYRO SENS: ACT (activated)

When I did the test flight, MODEL STD was chosen as it gave me a relatively stable tail once I adjusted the rudder sub trim in the menu. When I had MODEL GY chosen, no matter what XXX values I had the tail was wagging like a happy dog and I had absolutely no stability. Guess I'll just have to get out there and mess about with it til I'm happy, but at least now I know where I have to go to play with the settings, however...

SHOULD anyone who knows the 9X better than I do (just about everybody who has one ) know of other ways of playing with the rudder settings, please don't hesitate to further my education. Meantime...

Successful modding and happy flying guys.



Got a couple of questions on the menu setting if somebody could help me get my head round them please.

1. What do uprate and downrate mean in practical terms?
2. When MODEL GY is selected the default setting was NOR 100 for both uprate and downrate. Hitting the minus key takes you from 100 to 001 with the NOR prefix. You then have 000 with no prefix and pressing the minus key further takes you to AVC 001, increasing to AVC 100 which is obviously at the opposite end of the scale from NOR 100. What on earth is this all about?

full BL F45 1st test flight (3 min 34 sec)

Update 09.08.13:

I finally got around to taking a couple more pics to show the mod in more detail. The wiring needs tidying up a bit, but at least it gives anyone looking for more info an idea of one way which it CAN be done

As you can see I made the RX mount out of the same 2mm CF sheet as the tail mount. To fit it I just drilled holes to match the original PCB mounting pegs, chopped off the tops of the pegs to lower the RX a little (it's crowded under the canopy, which is why the mount is angled downwards) and put some velcro on the mount and the RX.

The GA250 gyro fits nicely on top of the tail mount and is mounted using the metal plate with thick double-sided mounting tape above and below it. I may try putting another layer on to see if it reduces the vibration any, but only time will tell

Both ESCs have just been stuffed below the back of the RX mount. Reason being I wanted to keep them together since they both go into one deans plug and couldn't think of anywhere better for them but, as always, I'm open to suggestions

Since I wanted to try it out with my 2000 mAh nano-techs I made up a deans to JST lead. Actually works pretty well as I managed to keep the weight down a bit, and once I decide to buy some 3S batteries instead of more helis I'll have a spare lead for my B6 charger

The brown wires in the last pic are extensions between the tail motor and ESC which I just ran through the tail boom and colour coded with heat shrink so I don't end up with the tail prop going in the wrong direction when I do any maintenance or adjustments. I made sure they weren't going to be too short, so now need to clip and reroute them through the chassis - once again, whenever I get round to it .

End of update. Get modding guys, and happy flying.
Last edited by tiggertoo1962; Aug 09, 2013 at 02:58 PM.
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Jul 14, 2013, 01:05 PM
Scotsman in Germany
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Got out to the park and tweaked my settings a bit more today. Not much room where I was, but it's still bigger than my living room . Still have a slight twitch in the tail, but I think it's something I can live with. I'll know better once I get out to a bigger flying field where I can let rip.

The settings I'm using at the moment are:

GYRO SENS: ACT (activated)

The sub trim on the rudder is set to -85 at the moment, but I change that usually between -80 and -90, as it seems to be different each time I bind. Before I fly I just go into the sub trim menu and leave it there for quick access while I'm flying.

I'm using MODEL STD cos I didn't even come close to losing the twitch when I had it set as MODEL GY.

The UPRATE and DOWNRATE are really just arbritrary values, since I still don't know what they do and I fixed most of it with the sub trim. Thing is, I need to give constant left rudder once the tail is bound to stop it spinning while the heli is sitting still. Anyone know if this is normal, or if there's a way to get rid of it?

Anyway, here's how it's flying just now...

full BL F45 park test (4 min 6 sec)
Jul 16, 2013, 04:43 PM
Scotsman in Germany
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Got back out this morning and did some more testing/tweaking. Found out that - at least with the setup I'm using - what the UPRATE and DNRATE settings do is adjust how much the tail kicks out when you apply or remove throttle. The further the setting is from 100 the more the tail kicks, so I've just left both set at 100. Pity you can't go to 120 .

I had pretty similar results with the MODEL set to GY, where NOR 100 was fairly stable and AVC -100 just made me dizzy .

I really don't think there's a way to completely remove the twitchy tail using this setup, but if anybody wants to prove me wrong I'll be only too happy . Meantime it's MUCH more fun to fly it this way than using the stock RX. You just have to take account of the fact that it'll kick slightly to the left if you up the gas and slightly to the right if you come off it. No big deal really... I mean we all want to fly, not just hover in one place. Otherwise we'd all still be flying coaxes .

full BL meadow test (8 min 11 sec)
Aug 11, 2013, 01:58 PM
Scotsman in Germany
tiggertoo1962's Avatar

Full BL F45 in the wind

Wanted to test the tail holding on my full BL bird, but it was a bit too windy to test properly... so I ended up just having fun flying it instead .

What I did discover was that the twitch was somewhat worse than I remembered it being, but maybe it was just exacerbated by the wind. Anyway, it was enough to make me real careful on right hand turns, as the river which claimed my other BL F45 is on that side. I did manage to get some nice left hand banked turns in though.

Oh well, back to the drawing board to see if there's anything I can do to iron out the tail twitch. If not, it's still much more fun than flying it stock, AND I'm finished with changing motors on the thing

Full BL MJX F45 in the wind (6 min 55 sec)
Feb 24, 2015, 08:39 PM
Registered User
There is a new carbon vertical stabilizer for brushless tail motor.


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