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Old Jan 11, 2013, 03:16 PM
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My 9118 heli won't hover.. is it a duff gyro

Hi guys, I'm kinda new to this so please bear with me.

I've done all the mods most often mentioned but I cannot get my 9118 to lift off and hover, I should add this is inside the house so there's no cross winds etc.
I've read much about the toilet pan effect and have done all the that I can but still it just wants to swirl around and around in a big loop.
I have all the usual control, backward forwards left and right which I have to use to stop it crashing.
Is it possible the gyro isn't working?

Any help would be much appreciated.

Thanks.
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Old Jan 11, 2013, 06:16 PM
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Jim Lee's Avatar
United States, WA, Port Orchard
Joined Apr 2007
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My 9118 heli won't hover.. is it a duff gyro

Check to see if either one, or both of the big spur gears Is loose on the shaft. That's what I've found to be the cause on mine when it just wants to sit on the ground and spin around.

If thats not the problem, Then I don't know what to tell you to look for.

J
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Old Jan 12, 2013, 01:20 AM
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My 9118 heli won't hover.. is it a duff gyro

Thanks Jim for your reply.
I think I've miss led you in as much as it does lift off okay but simply will not hover in one spot, all it wants to do is drift away in any direction, though typically in a big circle, with me keep twitching the controls to stop in smashing into the walls...it's a pretty big room so there's plenty of room to fly.

Mike.
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Old Jan 12, 2013, 02:56 AM
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Jim Lee's Avatar
United States, WA, Port Orchard
Joined Apr 2007
990 Posts
My 9118 heli won't hover.. is it a duff gyro

Do you know anyone else that has a DH9118?, If so try using their Tx to fly your DH9118 Heli, If it still does the same thing, Bind your Tx to their Heli and If the problem goes away, Then You probably have a bad PCB.

If it is the Printed Curcuit Board, Or Tx, You can get replacement(s) here.

http://www.xheli.com/9118parts.html

J
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Old Jan 12, 2013, 07:09 AM
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Sadly not I'm afraid, I live out amongst the farmlands around Boston UK, nothing here accept potatoes and cabbages :-)

Anyway I've decided to bite the bullet and order a new control board, if that doesn't do it then I think I'll have to pull the plug so to speak. Maybe buy a fixed single blade jobby.

Regards,
Mike.
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Old Jan 12, 2013, 11:29 AM
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Canada, BC, Salmon Arm
Joined Jan 2011
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Originally Posted by jazzman22 View Post
Sadly not I'm afraid, I live out amongst the farmlands around Boston UK, nothing here accept potatoes and cabbages :-)

Anyway I've decided to bite the bullet and order a new control board, if that doesn't do it then I think I'll have to pull the plug so to speak. Maybe buy a fixed single blade jobby.

Regards,
Mike.
I don't have the 9118 but I have had a number of similar coax's, and from what you're describing, I really don't think you need a new board.

It is time to learn heli repair 101 - diagnose before throwing parts at it. If you have Toilet Bowl Effect (TBE), in which the heli makes ever larger circles with the nose pointing always forward, there is an issue in the upper head.

Crashing a single rotor will still require repairs.

The gyro only controls motor speeds to keep the heli pointed in the same direction.

Did it fly ok before modding?

Is there more to the story? Did you crash or hit something when it started doing this?

When you flick the flybar does it bounce a couple of times?
Is there some slop in the blade mounts?

Look at the photo below. Your 9118 might have a metal shaft rather than those plastic nubs.

regards . . . g
.
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Old Jan 12, 2013, 12:39 PM
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Hi G, thanks for your interest.
Mine has a steel shaft in the head and I've been through all the usual adjustments and lubrication things for TBE, but still it's all over the place. Blades are free but not sloppy, buckle's are not binding, balance bar is completely free. I even tesedt the balance bar for equal weight in hope that might be it but it was dead on. By the way this is with the mod bar though I got the same effect with the original steel one.

There is one historical event that bias's me towards a new board, that is I hooked up a new lipo that I'd just bought believing it was a 2s 7.4v, switched the heli on but never ran it when I suddenly realised I had a 11.1v battery. So you can see this sort of haunts my thoughts that it might be the cause... BUT I cannot remember the heli ever hovering on the spot.
Last point to add is this is my first large heli and I've been fighting to control it from day one.
Is that for my lack of ability or knowledge or was there something wrong from day one hmmm??

Mike.
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Old Jan 12, 2013, 02:01 PM
Different fly 4 different guy
gordonzo's Avatar
Canada, BC, Salmon Arm
Joined Jan 2011
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Quote:
Originally Posted by jazzman22 View Post
Hi G, thanks for your interest.
Mine has a steel shaft in the head and I've been through all the usual adjustments and lubrication things for TBE, but still it's all over the place. Blades are free but not sloppy, buckle's are not binding, balance bar is completely free. I even tesedt the balance bar for equal weight in hope that might be it but it was dead on. By the way this is with the mod bar though I got the same effect with the original steel one.

There is one historical event that bias's me towards a new board, that is I hooked up a new lipo that I'd just bought believing it was a 2s 7.4v, switched the heli on but never ran it when I suddenly realised I had a 11.1v battery. So you can see this sort of haunts my thoughts that it might be the cause... BUT I cannot remember the heli ever hovering on the spot.
Last point to add is this is my first large heli and I've been fighting to control it from day one.
Is that for my lack of ability or knowledge or was there something wrong from day one hmmm??

Mike.
They all have a steel shaft and all have a plastic top piece attached which can wear or break. Regarding blade slop, I meant right at the shaft not the blade holders. But if you have already investigated all of that then it can ruled out.

Feeding it 11.1v could definitely be an issue.

==> Is it lifting ok and then the nose stays forward when it 'circles' or is it just spinning?

==> If you give it some fwd elev does it move in a straight line until putting it back to hover?

Coaxials should stay on hover while you to go to the bathroom and back. If it lifts off but has severe tbe, I am still not convinced it is the board. Any chance of a video?

regards . . . g
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Old Jan 12, 2013, 04:01 PM
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The only aspect I'm not sure about is where the top blade mount has a steel pin that penetrates the main vertical drive shaft to give power to the blades. There is a good amount of slack or slop right here.
To clarify, if the top blades are pulled out straight one can rotate the blades raising and lower the leading edge just as they are supposed to ...but there is also a good amount of play along the line of the blades so that you can lift one blade end up its causes its opposite partner to fall by as much as 3/4" ...should it do this or should it be a lot firmer?

When it lifts the heli wants to drift off to one side sort of diagonally, looking from overhead it would be heading towards maybe the 10 o'clock position though it could equally drift to the 2 o'clock position. If I don't attempt to bring the nose round it will crash sideways in the direction described.
Given that one has to make sure the heli is balanced from front to back typically pushing the battery in or pulling it out, is it be possible that it needs balancing sideways as well?
I've read so much about balance but never from left to right always end to end.

When I give it a little forward stick it does go forward in a straight line but return it to neutral and it drifts again.

Mike.
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Old Jan 12, 2013, 04:14 PM
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I should just add that if I weight the heli so it goes slightly backwards on lift off it will drift towards the 4 o'clock or 8 o'clock position. Main thing is however I weight it it drifts.

Mike.
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Old Jan 12, 2013, 04:22 PM
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Reading through your last mail I see I misunderstood what you meant by the top shaft.
Which suggest that this indeed maybe where the issue is. I'll wait on your reply to this detail before making any mods.

Off to my bed right now so its good night from chilly England.
Mike.
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Old Jan 12, 2013, 05:00 PM
Different fly 4 different guy
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Canada, BC, Salmon Arm
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Quote:
Originally Posted by jazzman22 View Post
Reading through your last mail I see I misunderstood what you meant by the top shaft.
Which suggest that this indeed maybe where the issue is. I'll wait on your reply to this detail before making any mods.

Off to my bed right now so its good night from chilly England.
Mike.
There should be 1 or 2 screws holding that plastic upper head assy on there and then it can come right off with the blades and flybar attached.

It is possible that blade shaft is bent (or missing). Sometimes they have o-rings to remove the play.

Dissassemble and inspect. Report back.

regards . . . g
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Old Jan 13, 2013, 06:13 AM
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Hi Gordonzo, I took the top blades to pieces and found the steel pin rattles about in the steel bush that goes though the mount. the pin measures just about 2mm dead and being a watchmaker I have a stock of pivot steel and found a piece 2.13mm which was a much better fit, not perfect but better. Anyway I flew the heli and it does perform a whole heap better.

Now when I lift one blade tip I get a travel of about 3/8th" to maybe 1/2" at the other end.
The heli still wanders but nowhere near as much as before, so I'm wondering if I should turn a dedicated steel pin that's a good close sliding fit in the bush?
Is it possible that such a poor fitting pin and bush could have been fitted at the factory?
By the way it's about a month old so I can't see how it could have worn to such a degree.

Mike.
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Old Jan 13, 2013, 07:03 AM
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Further to my last mail. I took the head apart again and had a look at the steel bush the goes right through the head and found a lot of play there, I've now eradicated that and now there is 1/4" play between one blade tip to the other. There's still plenty of freedom on the bearing points but no slop or slack at all.
While I had the main shaft out I put it in my watch lathe to check for it being out of line, fortunately it was dead on and true in its length.
I also weighed the blades individually and they came out at 15.04 g and 15.05 which is pretty remarkable.
I just can't get my head around the blade weight being so precise yet the pin to bush fit was like a knitting needle in a bucket!!

I've got to go out shortly so won't be able to do another test flight till tomorrow :-(

I think it safe to say at this point that you were dead right Gordonzo and I thank you for that.
It a learning curve for me in a new subject which I'm finding really interesting and challenging, and it's thanks to guys like you who share your experience and ideas that stops folks like me giving up.

I'll update flight results as soon as I can.

Thanks again,
Mike.
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Old Jan 14, 2013, 12:55 PM
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I'm afraid there's no update on the heli as we have snow and wind and I aint going out there not for no one not no how !
While I wait on the weather I'll have a look round at what my next heli's going to be heehee :-D

Mike.
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