Espritmodel.com Telemetry Radio
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Old Feb 21, 2012, 01:16 PM
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Originally Posted by hanginkanluran View Post
that battery is too heavy as well way too much current, this thing is not very well cooled & the motors get way too hot with a 1150mAh bat running continuous before it runs down, anything larger & your motors would be cooked in no time

the closest generic battery Ive found is here, but you will also need some male JST connectors & some 18 guage wire not the 22 guage crap they sell made up

http://www.hobbyking.com/hobbyking/s...gle_Cell_.html

or you could try your luck on some off brand stuff like this
http://www.ebay.ca/itm/260776993970?...84.m1497.l2649

I bought some of these but they have not arrived yet so I don't know if they are just crap, I will lwt yous know if they are any good, I seen some cheaper ones like this just re badged as 1200mAh with a sticker, lol
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Old Feb 21, 2012, 01:55 PM
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Originally Posted by bkraptor View Post
Thank you for those indications.

I disassembled the whole aileron servo and there does not seem to be anything broken, but everything does have a lot more play than the other servo. Another thing I noticed is that it has some kind of compensation circuit inside where if you forefully move it in one direction it will try to oppose that movement with a movement in the opposite direction. The observation is that the aileron servo fails to respond maybe 25-33% of the times, whereas the elevator servo does not fail to respond at all. This might be related to the metal skid behind the screw joint where it moves up and down over a coated surface that I suspect behaves like some kind of variable resistor, which I believe is the method by which the servo knows its position. I am going to disassemble it once more and see if there is anything wrong with that variable resistor.

Before I put it back together I took the time to tighten up the main screw (the one over which the servo goes up and down), which had more than 1 mm of play, and left maybe 0.25 mm of play. I did a short test run and I think this might have attenuated the wobbles a bit, but not by much.

<edit>
I opened up the aileron servo again and extended the metal skid in order to ensure proper contact is being made with the variable resistor. After assembly it responds to taps every time, but sadly in flight this makes no difference as it still wobbles a lot. Is there any other servo that is compatible with this format (6 wires, 2 screws)?

<edit #2>
I took the time to add some rubber rings that pull on the servo arms, eliminating a lot of the wobble. Still not 100% perfect, but a lot better. This confirms your diagnosis about a faulty servo. I will try to order one, but seeing as they are not quite cheap I might be better off buying a whole new F-28 helicopter with almost the same money. Is there any way these cheap helis might be counterfeit?


the servo is an mjx design as far as I know, way too much slop, it worked pretty good with the F27 but the F28 is just a real let down compared to its little brother, so far the only solution I have found is to move the servos when it starts bobbling that seems to help get over it faster, it also seems to bobble more when taking off or coming down too quick or close to the floor, the poor servo design also causes it to lift off it different directions depending on the servo position at lift off, with some experience you will get good at counteracting this effect, it seems to have a lot of lift @ low rpm which tells me the size or pitch of the blades are wrong for this heli, when flying out side you have poor forward motion until you throttle up past 70% range then you fly too high and that's with the elevator set to 100% from the factory 80%

It would be nice to get good forward motion @ 10 to 20 ft out side but to do that we need to get the rpm's up without raising the heli, this would mean trying smaller blades but before I go that route I want to heat sink the motors & cut the canopy for better cooling

http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXVVM4

these would work but you would have to cut one end that is closest the heli & cut the canopy on each side to allow these to stick out and use thermal adhesive to stick it to the motor

http://www.ebay.ca/itm/270717024919?...84.m1438.l2649
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Old Feb 21, 2012, 04:49 PM
Different fly 4 different guy
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Canada, BC, Salmon Arm
Joined Jan 2011
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I have a F28 that I got from an aquaintance. The servos are sloppy (flys with a major wobble), motors are on last leg, and batteries are done. But many of the other parts are still good and some were recently replaced.

I will be listing all the useable parts shortly as a package for cheap (shafts, gears, blade grips swashplate, buckles, bearings, PCB, etc.). Will make a good crash kit.

You can see it in this photo back when I owned it, and before he got a hold of it.
.
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Old Feb 24, 2012, 10:25 PM
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I have had my F28 since the first of January and it had this wobble straight out of the box. I have changed main shaft, both gears and even the lower bearing hoping to fix this issue. It's been apart more than it has flown. Does changing the servo fix this issue? My battery that came with the unit is trashed already, swelled up like a balloon. I am very unhappy with this heli. I thought Mjx had good quality rigs. Thanks for listening to me cry.
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Old Feb 25, 2012, 01:43 AM
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Canada, BC, Salmon Arm
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Originally Posted by Mblev2 View Post
I have had my F28 since the first of January and it had this wobble straight out of the box. I have changed main shaft, both gears and even the lower bearing hoping to fix this issue. It's been apart more than it has flown. Does changing the servo fix this issue? My battery that came with the unit is trashed already, swelled up like a balloon. I am very unhappy with this heli. I thought Mjx had good quality rigs. Thanks for listening to me cry.
In general MJX has very good quality helis but the F28 is certainly not their best effort. The 3.7V system is very underpowered. Also, their servos cannot withstand crashes very well, and and their blade holders are poorly designed, both of which IME can contribute to wobbly flight.

You might beable to reduce the wobble by tightening your blades. You will probably need to sand down the holders (where the screws go in) until the blades have no slop but can still swivel.

A puffed battery usually indicates either improper li-po battery management or simply a faulty battery. You can try one of these cheap replacement batteries here which might even improve performance.

Stop flying as soon as full throttle is required to maintain hover. Draining a li-po too far will kill it. Also cool 10 min before and after charging.

Fly-->Cool-->Charge-->Cool

You might be at the point where you have to decide if you want to throw more money at the F28 or move on to something else. I decided not to spend any more on mine, but it did have a very rough life (not from me). The helis I currently fly in this size range are HQ852 and NE Solo Pro 328a, but they are not perfect either.
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Old Feb 25, 2012, 08:47 AM
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Thanks for the info gordonzo. I bought a couple of those e-fly batteries of eBay a month ago and they seem to be good. I did not know that lipos should not be fully discharged. I will take better care of these two. I will also try the blade mount mod.

I have just purchased a Blade 120sr. I like that I can pickup local parts. I am going to fly this for a while and see how it goes.
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Last edited by Mblev2; Feb 27, 2012 at 12:02 AM. Reason: Grammar
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Old Feb 27, 2012, 12:01 AM
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I tried the blade mount mod that Gordonzo informed me of and the problem got worse. I thought I might have gotten them to tight, but I can push the blade and it moves very easy. Any more ideas would be appreciated.
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Old Feb 27, 2012, 10:11 AM
Different fly 4 different guy
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Canada, BC, Salmon Arm
Joined Jan 2011
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Quote:
Originally Posted by Mblev2 View Post
I tried the blade mount mod that Gordonzo informed me of and the problem got worse. I thought I might have gotten them to tight, but I can push the blade and it moves very easy. Any more ideas would be appreciated.
The blades need to flop down on their own when you tilt the heli or they are too tight. I did a little at a time until the wobble was reduced but I was unable to totally eliminate it.
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Old Feb 27, 2012, 10:20 AM
S107G MSR MSRX 120SR Nano QX
United Kingdom, Coventry
Joined Jan 2012
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Quote:
Originally Posted by gordonzo View Post
In general MJX has very good quality helis but the F28 is certainly not their best effort. The 3.7V system is very underpowered. Also, their servos cannot withstand crashes very well, and and their blade holders are poorly designed, both of which IME can contribute to wobbly flight.

You might beable to reduce the wobble by tightening your blades. You will probably need to sand down the holders (where the screws go in) until the blades have no slop but can still swivel.

A puffed battery usually indicates either improper li-po battery management or simply a faulty battery. You can try one of these cheap replacement batteries here which might even improve performance.

Stop flying as soon as full throttle is required to maintain hover. Draining a li-po too far will kill it. Also cool 10 min before and after charging.

Fly-->Cool-->Charge-->Cool

You might be at the point where you have to decide if you want to throw more money at the F28 or move on to something else. I decided not to spend any more on mine, but it did have a very rough life (not from me). The helis I currently fly in this size range are HQ852 and NE Solo Pro 328a, but they are not perfect either.
Hmmm! Having ordered a F28, as well as a 2012 S107, tested them, and now have to wait until 11/3 for my birthday to get to play, I'm slightly unnerved by the comment highlighted above. Hope i won't be too disspaointed for my first helis.
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Old Feb 27, 2012, 10:20 AM
S107G MSR MSRX 120SR Nano QX
United Kingdom, Coventry
Joined Jan 2012
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Old Feb 27, 2012, 01:03 PM
Different fly 4 different guy
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Canada, BC, Salmon Arm
Joined Jan 2011
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Quote:
Originally Posted by micro2000 View Post
Hmmm! Having ordered a F28, as well as a 2012 S107, tested them, and now have to wait until 11/3 for my birthday to get to play, I'm slightly unnerved by the comment highlighted above. Hope i won't be too disspaointed for my first helis.
The F28 may very well be a good heli for you if you treat it well, so don't be discouraged. And if you can find a better battery it could make a big difference.

I flew my F28 about 30 uneventfull flights before I sold it, and it flew quite well. What I did not like was that it runs low on power after about 3 minutes of agressive flying. But I did not have any mechanical issues with it.

The new owner was pretty hard on it but it still kind of flys. After a number of hard knocks, it seems the servos and blade holders get sloppy resulting in wobbly flight.
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Old Feb 27, 2012, 01:07 PM
S107G MSR MSRX 120SR Nano QX
United Kingdom, Coventry
Joined Jan 2012
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Thanks G, any suggestions for a "better" battery ?
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Old Feb 27, 2012, 01:32 PM
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Joined Jan 2011
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I was considering this one.

I don't know if it is bettery quality, but it has a higher C rating which should get more even power discharge, even it doesn't run longer.

So if you are planning to get a second battery, maybe try one. I would avoid buying another stock one.
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Old Feb 27, 2012, 01:35 PM
S107G MSR MSRX 120SR Nano QX
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Joined Jan 2012
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Free shipping to UK, with a recommendation - cant beat that - many thanks
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Old Feb 27, 2012, 04:00 PM
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Joined Jan 2011
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Originally Posted by micro2000 View Post
Free shipping to UK, with a recommendation - cant beat that - many thanks
Let me know what you think of that battery as I have not tried one. But Force Power makes inexpensive batteries for some of my other helis so I am curious about their quality.
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