RunRyder RC
 9  Topic Subscribe
WATCH
 2 pages [ <<    <    ( 1 )     2     NEXT    >> ] 1312 views
Scorpion Power Scorpion Power
HelicopterMain Discussion › Runout on mainshaft and head
12-19-2013 02:32 AM  3 years agoPost 1
Sam2b

rrElite Veteran

Seattle, WA

My Posts: All  Forum  Topic

What is an acceptable runout for the main shaft on a 700 size heli? To me, ~0.00125 is too much because it is multiplied about 29 times on the blade tip. Its no wonder to me why the heli wobbles on the skids during the first 2 seconds of spool up (on the grass), even after already spooling up allowing the blades to pull 180 degrees apart.

These images are taken with the heli clamped to the table, and the dial indicator secured to the table. I've gently and slowly turned the main shaft by turning the tail shaft several times to confirm consistent positions. You can see the head affected too.

The low side.

The opposite of low side.

I don't have any issues with my heli in flight (that I'm aware of), I was only checking for curiosity. I'm aware the only way to attempt to fix is to bend it in place with a plastic malad in a vice, but I don't want to if I don't have to.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-19-2013 03:19 AM  3 years agoPost 2
cdrking

rrElite Veteran

Seattle

My Posts: All  Forum  Topic

Sam,

Unfortunately this type of measurement has many inaccuracies including:

-Radial bearings
-Bearing blocks
-Frame assembly
-Frame flex
-Indicator base
-Main shaft trueness

I'm sure there are others that I've missed, but I would say your readings are darn good. If your main shaft is not bent while being measured in a set of V-blocks, then I would say it's not worth fretting over. But since it's winter here in the NW then have at it.

Jeff

To hover is divine, the alternative is rather PLANE.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 05:50 AM  3 years agoPost 3
Flyin for Jesus

rrVeteran

Dana Point, Ca.​92629

My Posts: All  Forum  Topic

If you think you're gonna get it straighter than .00125 without any specialized equipment... then you're GOOD. ( If you first overbend it then bend it back... you"ll have some "Z" shaped bend in there and it will never be right )

You can try a replacement first, however...
Your first pic... You're measuring the feathering shaft through the dampers in the head. Not too accurate sounding to me.

Second pic... If you're getting .00125 TIR ( total indicator runout ), then the C/L of the shaft is only .000625 from perfect.

With all the inaccuracy factors listed above... I don't think the main shaft will ever be any better than what you have now.

On the 29X multiplication at the blade tips, If you track the blades by adjusting the linkages so that the tips are equal, Now, the blade grips will only be out--- .00125"

PM  EMAIL  Attn:RR  Quote
12-19-2013 06:21 AM  3 years agoPost 4
Sam2b

rrElite Veteran

Seattle, WA

My Posts: All  Forum  Topic

Hmm, ok. It sounds to me this is all nothing to be worried about. Just to note, I was measuring the top of the head block, not feathering shaft.

What's interesting is I turned the head 180 degrees and bolted the head on, and now the top half of the head block had 0.003 runout. Considering the inaccuracies, I now know this is only a good try at best, but since the runout tripled, I'm leaning towards at least the head block being bent (no pun intended). The main shaft is fairly new with ~20 flights on it. But the head is ~2 years old and has had several large crashes.

Show's over. Thanks for the replies.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-19-2013 06:39 AM  3 years agoPost 5
Flyin for Jesus

rrVeteran

Dana Point, Ca.​92629

My Posts: All  Forum  Topic

My bad on the first pic... Thought the tip was thin and pointed getting down to the feathering shaft.
But an added note... The top of the head is irrelevant to its function. The profile is likely machined at full depth leaving room for inaccuracies due to taper and tool wear.
The important features in the head is the bore for the main shaft and the damper bores being 90 degrees to it. Everything else just needs to be shiny.

PM  EMAIL  Attn:RR  Quote
12-19-2013 10:41 AM  3 years agoPost 6
Richardmid1

rrProfessor

Leeds, England

My Posts: All  Forum  Topic

I seriously doubt even the 3 thou head run-out is causing the wobble on spool up.

Have you tried balancing the blades?

Have you tried another set of blades?

Are the blades both tightened equally and not overly tight?

Are the thrust bearings in the grips ok?

Is the feathering shaft bent?

Are the dampeners greased?

Is the tail fin in contact with the grass giving a more solid tripod affect?

60% of the time, it works every time!

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-19-2013 05:11 PM  3 years agoPost 7
rcnut

rrElite Veteran

Rockford, Illinois

My Posts: All  Forum  Topic

To properly check the run-out on your mainshaft, you need to remove the mainshaft from your heli. Place the mainshaft in 2 "V-Blocks" (one V-Block on each end of the shaft) and use the dail indicator to see what the run-out is across the length of the shaft.

Otherwise, and like everyone else is saying...you're adding the run-out of the two or three mainshaft bearing blocks, plus the ever so slight give of the carbon fiber...then there's the gap between the mainshaft and bearings.

Team Miniature Aircraft
"I love the smell of Nitro in the morning!"
...Citizen 654!

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 05:34 PM  3 years agoPost 8
Four Stroker

rrElite Veteran

Atlanta

My Posts: All  Forum  Topic

A completely intelligent and accurate thread. Surprising.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 05:48 PM  3 years agoPost 9
BobOD

rrElite Veteran

New York- USA

My Posts: All  Forum  Topic

Try those measurements on some other models and you'll be pleasantly surprised just how accurate that model is.

Team POP Secret

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 06:11 PM  3 years agoPost 10
S Crutchfield

rrNovice

Arkadelphia,Ar. usa

My Posts: All  Forum  Topic

Sam2b

Don't know where your coming up with these numbers.
The dial indicator in your pics is only accurate to 1/1000 of an inch (.001). Even if you guessed where the needle hit between the lines, you could only assume an accuracy of .0005. The play in your bearings and the limitations of your equipment makes it impossible to reach the accuracy you posted, which is 1/100,000 of an inch.
Plus or minus .001 is close enough IMO.
To properly check the run-out on your mainshaft, you need to remove the mainshaft from your heli. Place the mainshaft in 2 "V-Blocks" (one V-Block on each end of the shaft) and use the dail indicator to see what the run-out is across the length of the shaft.
+1 RCnut , and I will add that this needs to be done on a flat surface, such as a granite surface plate.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 08:44 PM  3 years agoPost 11
Sam2b

rrElite Veteran

Seattle, WA

My Posts: All  Forum  Topic

Very cool info here, thanks. I'm learning a lot. I admit I don't know advanced dial indicating, and thought I had a descent idea with how to approach. So this is a nice learning experience.

S Crutchfield,
Regarding the 0.00125, it's ok to estimate the 0.00025 just by looking at the needle if it is between the lines. Each line is 0.001. Well, obviously if the needle is between the lines, the runout must be 0.001<n<0.002. My eye can see it is between the half way point between a line, so I estimated the 0.00025. In my opinion, we shouldn't just round up or down. After several repeat turns, that is the high/low point that results. But, if I'm wrong, I'm wrong.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-19-2013 09:37 PM  3 years agoPost 12
P Johnston

rrVeteran

Ann Arbor MI

My Posts: All  Forum  Topic

My experience of heli wobble on spool up is a direct result of the main blades being too tight. Loosen them a little bit and try again.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 09:59 PM  3 years agoPost 13
BobOD

rrElite Veteran

New York- USA

My Posts: All  Forum  Topic

Also, make sure the drag on each blade is equal. Even if they are perfectly straight to start, as soon as the motor starts, one blade may lag a little bit more than the other.

Team POP Secret

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 10:26 PM  3 years agoPost 14
S CrutchfieldrrNovice - Arkadelphia,Ar. usa - My Posts: All  Forum  Topic

Sam2b
Sorry, didn't mean to split hairs. It's just a terminology thing. The amount of digits behind a decimal point implies accuracy levels. Didn't realize you were rounding.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-19-2013 11:12 PM  3 years agoPost 15
TMoore

rrMaster

Cookeville, TN

My Posts: All  Forum  Topic

Just as a point of reference a 1" travel indicator isn't very accurate under .001". That's why those of us in the biz use different indicators for precision under .001".

For what Sam2b is using it for it is fine. The runout readings posted in the first post aren't that bad. Jeff pointed out all of the obvious reasons that the setup could produce errors but one thing to keep in mind is that static tracking is a very important component to this process and if the blade roots aren't molded accurately it really doesn't matter how close the machined components build up, static tracking won't be close. If that's within an 1/8" the machine should be smooth if the blades are reasonably close in weight and CG's.

TM

Delayed Response Operator Not Engaged

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-20-2013 12:52 AM  3 years agoPost 16
icanfly

rrElite Veteran

ontario

My Posts: All  Forum  Topic

A completely intelligent and accurate thread
did you revolve the shaft in the hub 180 degrees to cancel out the approximately 1.5thou/in out of each piece? Centrifugal tug of both blades as they spool up should tug the cog/axis straight after that.

Got a similar but wild problem like this in my wee 300, it's much more violent and buzzes like crazy almost for a minute before equalizing and smoothing out. Vibes rob the motor of torque and horse power as I've seen with this thing.

You say you crashed a few times with that head, it may have bent slightly, try bending it back (very hard to get spot on).

regarding a dial indicator it is possible to accurately define 10thou/in with a magnifying glass. The machinist don't demand markings less than .0001 so why bother. The only time that small matters is when all those divisions in something add up to something of more significance. Same in weights and measures.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-20-2013 02:28 AM  3 years agoPost 17
Sam2b

rrElite Veteran

Seattle, WA

My Posts: All  Forum  Topic

Sweet, this thread is awesome (if I do say so myself) . I admit my blades do not smoothly rotate in the grip currently, and do stick a little when moving. I don't believe I have the blades too tight, though; they are tight enough to where they don't fall if I tilt the heli sideways, but will fall if I gently shook the heli while sideways. Maybe that's a bad method? I could try more loosely, but I prefer not to have the blade roots have any wiggle in the grip with all the positive/negative S&M 3D we do.

_Other blades do the same, likely for the same reason.
_I haven't greased the dampeners, but only slight oil to get the feathering shaft through (it's very tight).
_The blades each read 184g on a digital food scale when I weigh them each 3 times. I know I need a more precise scale, but my jewler's scale can't handle >100.
_My thrust bearings seems to be ok upon inspection, and installed the correct way (smaller diameter on the outside).
_The tail fin almost always is in contact with the ground because I have a custom fin about 2" longer. In the past I seemed to have hit the toughest patched of grass and busted so many carbon tail blades and gears.

Thanks some more.

_Sam B_
Team MSH USA * Protos Max * Xpert servos * Cyclone Blades * ProgressiveRC * VoltMagic * Ecalc

PM  EMAIL  HOMEPAGE  GALLERY  Attn:RR  Quote
12-20-2013 02:45 AM  3 years agoPost 18
steve9534

rrKey Veteran

yakima, wa.

My Posts: All  Forum  Topic

Sam

.00125 or .003", either way isn't enough to cause a noticeable vibration on spool up or any other time. I doubt the blades are equal within .003" anyway. The main reason the heli vibrates on spool up is because the blades lag different amounts when your accelerating the head up to speed, and it's only as you get close to the target head speed that the centripetal force pulls them out to the correct position. You can try and set the lead/lag position of the blades before you spool up, but even .010" differential between the two will cause more of an imbalance than the amount you've got in the head. Furthermore, unless you're spooling up very slowly and/or have the blades set very tight in the blade holders, they're going to lag some anyway as you spool up, probably unequally. If it's smooth when you get up to speed, I wouldn't lose too much sleep over this. steve.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-20-2013 04:25 AM  3 years agoPost 19
icanfly

rrElite Veteran

ontario

My Posts: All  Forum  Topic

and sam, if you want to raise the tail fins off the ground you can always add some spacers between the rear skid legs and chassis and it'll give the heli a cool rake. This helps when the heli lifts of as it flys forward ever so slightly before you are ready to go at it. At least the heli wont come back at you then.

PM  EMAIL  GALLERY  Attn:RR  Quote
12-20-2013 11:02 PM  3 years agoPost 20
cdrking

rrElite Veteran

Seattle

My Posts: All  Forum  Topic

Maybe we need this setup.

To hover is divine, the alternative is rather PLANE.

PM  EMAIL  GALLERY  Attn:RR  Quote
WATCH
 2 pages [ <<    <    ( 1 )     2     NEXT    >> ] 1312 views
Scorpion Power Scorpion Power
HelicopterMain Discussion › Runout on mainshaft and head
 Print TOPIC  Make Suggestion 

 9  Topic Subscribe

Friday, November 17 - 5:10 pm - Copyright © 2000-2017 RunRyder   EMAILEnable Cookies

Login Here
 New Subscriptions 
 Buddies Online