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HelicopterCentury Radikal G20-30 N640 Hawk Predator › Predator Main Gear Wobble
11-24-2006 12:33 AM  11 years agoPost 1
asong26

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VA

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Anyone had this issue with their setup?

It seems, my main gear may be warped. It does not create an issue with gear meshing, but when I get down to the ground (to get a closer look) and very low spin, I can see the that there is a high spot (wobbling up and down).

Would this create a problem with vibes, or is this common?

Andrew

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11-24-2006 01:25 AM  11 years agoPost 2
SteveH

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Texas

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Andrew,

I would double check the mounting screws...the ones that hold the main gear to the autorotation clutch, to make sure they are equally tight, and not too tight. If they are too tight the delrin gear can be warped.

The government cannot give you anything without first taking it from someone else.

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11-24-2006 01:45 AM  11 years agoPost 3
asong26

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Too late...

I was warming up the engine today, and noticed this wobble. So I stopped the engine, and brought it back home. Upon closer inspection, the gear is definitely warped. I've used digital calipers to measure the our rings thickness on all sides, the high side is definitely warped.

I've also just noticed that one of my inner gear's tooth is broke off, and another on it's way... I don't think it's the meshing issue. When the heli was put together, all gears have passed the paper ribbon test...

This is frustrating to say the least...

Andrew

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11-24-2006 02:06 AM  11 years agoPost 4
asong26

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Another $50, another week.... I guess that's just the way it goes...

Andrew

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11-24-2006 02:36 AM  11 years agoPost 5
Disciple4123

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USA

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Sorry to hear that. Since the main gears on the Predators have a separate tail crown gear arrangement, I believe that perhaps 0.5mm up and down wobble on the main is OK. Not enough mass, outward position for centrifugal loading, or speed to be inbalanced due to a main gear that wobbles, and it will float with plenty of room. My predator allowed a mm or 2 of free vertical slide on the main gear within the autohub assembly. (Referring to driven tail models only). Of course the wobble is a reflection of manufacturing quality, an area that sometimes has room for improvement

The crown gear having a chipping tooth may be post crash problem, any tooth that is missing on crown or main gears I consider to be an immediate problem, it will try to mount the next tooth with every revolution just behind or beyond it's expected postion and tear things up.

The good news is both gears come out pretty easy for replacement.

Got your call by the way, got in from work and going to bed.

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11-24-2006 02:51 AM  11 years agoPost 6
asong26

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You're right Eric,

The replacement should be very easy. Just need to take out the tail-boom, then the main shaft after that.

I want to continue the engine break-in, so that I can have it fully broken in (while I wait for the parts this weekend). With a tooth missing on the inner tail gear. how dangerous is this in terms of just letting it sit on the ground w/ negative 2 or 3 pitch 2/3 stick?

I've got about 2 more gallons that I want to go through this thing, before doing any flying at all.

Thoughts?

Andrew

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11-24-2006 02:55 AM  11 years agoPost 7
asong26

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Just to be safe, I am also replacing the tail transmission output shaft and the metal gear (to ensure true spin, and make sure that it's the the transmission that may be causing the wobble, and or the breakage of the tooth. This is again going under the microscope. $20 bucks more, I want to make sure that this does not happen again.

I've ordered most of the parts from Rick's instead of Century this time. Since century did not have all the parts that I needed. Hopefully, the heli will be completely ready by no later than Tuesday...

Andrew

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11-24-2006 06:28 PM  11 years agoPost 8
beavis1

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New York state

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missing tooth
Wow one tooth missing is real odd.
Did the tail blades ever come in contact with the ground or grass. That will pop a tooth.

Gear mesh problems will usually effect more than one tooth and most of the teeth will look worn or chewed.

The output shaft and gear could run a bit off from tolerances of the shaft to gear fit. I usually shim with .01 brass stock if needed to get a perfectly running pinion gear. The shafts have a tolerance when made.

Yes I have had some run out on the main gear as well. It is very odd as they are CNC machined derlin not molded parts. the main gear floating a little has never been a problem. I have however run into one crown gear that did not run true. I had perfect lash all around but one high spot. I sent it back for a replacement.

Now using the pinion as a way of setting the mesh is not really a good way of doing it. I set the pinion so it has 100% surface contact. With this the mesh is ususlly to tight. so to fix it you need to drop the crown. How you ask. Easy

I take out the lower bearing in the block and put in a crown gear spacer .01 or two if needed.

This gives me a perfect contact area gear mesh and no drag whatsoever. The head will spin like a windmill if there is any wind at the field.

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11-24-2006 06:35 PM  11 years agoPost 9
rcadd1ct

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Richardson, Texas

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Make sure the screws holding the gears on are not too long.

I had to trim mine down so they would clear the other gear mojnt on the auto hub.

My heli was an early SE kit, so I think they have fixed the issue since mine came out.

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-24-2006 08:17 PM  11 years agoPost 10
asong26

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beavis1:

The tail gears never came in contact with the ground. The gears are very new...

I am not clear on your explanation around the crown. What is the crown?

Also, are you referring the raising up the position of the gear by using a spacer?

Andrew

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11-24-2006 09:13 PM  11 years agoPost 11
rcadd1ct

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Crown gear is the bever gear in the middle.

There is a spacer under the auto hub that sits on the bottom radial bearing. You can shim here to tighten the gap between the two gears. You want play (air gap) between the two gears, but not too much, hence shimming.

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-24-2006 10:11 PM  11 years agoPost 12
asong26

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Now I understand.

Right below where the gear assembly sits (on the bearing), there is yellow thick copper space which is self centering. Are you saying that you put additional shim either on top, or below that to give the gear more life in position?

Andrew

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11-24-2006 10:22 PM  11 years agoPost 13
beavis1

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New York state

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No
If it was loose yes. But it will not be. You drop the lower bearing in the lower bearing block. put in the shim and put the bearing back in. That drops the whole gear unit to give more lash if needed.
Again it depends what you need.

It is advanced building so unless you are confident pressing bearings forget I got into it. :-)

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11-24-2006 11:20 PM  11 years agoPost 14
asong26

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My gear has no slack what so ever. It's new gear. I hear that the older ones used to have some slack where after installed, it would move up and down about 1.5mm.

Mine doesn't have any slack.

So, based on this, I am ok right? I don't need to add any more shims....

Andrew

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11-24-2006 11:25 PM  11 years agoPost 15
rcadd1ct

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Since you said the gear is almost touching the frame, I would be carefull not to shim too much and get the gear into the frame.

-RCA .......... Making Cuisinarts Fly!!!!!!!

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11-25-2006 01:03 AM  11 years agoPost 16
asong26

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Just to clarify, the gear is almost touching the frame at the bottom. If the new gears on order fit the same way, it can use some more spacing to life it up...

Andrew

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11-25-2006 02:14 PM  11 years agoPost 17
D.Magee

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kansas city mo.

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Beavis 1 I have also had this problem of gear to tight I have just let it wear in and now it is ok but if i replace it

( What do you think about fileing off the m10x14x3.5 spacer and the if needed shim there instead of pulling the lower bearing and adding shims there?)

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11-25-2006 02:51 PM  11 years agoPost 18
asong26

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Why would you file the spacer, if you needed more space than what the spacer provides?

The issue that I ran into is that first of all, the gears were warped. Second, the gear sat too low almost touching the bottom part of the carbon frame. So in this case, the shim would be proving a lift. If you file the spacer, wouldn't that make the problem worse?

Andrew

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11-25-2006 03:27 PM  11 years agoPost 19
D.Magee

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kansas city mo.

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I may not be understanding what Beavis was refiring to when he was shiming the lower bearing. I thought he was lowering the gear to get more clearance between the inter gear part hi6058m and the bevel gear part # hw3057 that is where mine is tight.

this is what i was refiring to

( I take out the lower bearing in the block and put in a crown gear spacer .01 or two if needed.

This gives me a perfect contact area gear mesh and no drag whatsoever. The head will spin like a windmill if there is any wind at the field. )

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11-25-2006 03:42 PM  11 years agoPost 20
asong26

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I think Beavis1 was referring to my gear meshing issue (or breaking). One of my tooth of crown gear is broken. I believe this may be due to the warped gear. The gear has a high point. If I looked at my gear spinning from the side, I can see 1 part going up, and then back down. It's the same spot every time. I later found that that gears were warped. When the high point of the warped gear reach the transmission gear, I guess that's where the strain happened. I've ended up loosing a tooth and a half.

Andrew

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HelicopterCentury Radikal G20-30 N640 Hawk Predator › Predator Main Gear Wobble
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