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HelicopterMain Discussion › goblin or other belt heli
10-23-2012 09:40 PM  5 years agoPost 21
BladeStrikes

rrElite Veteran

Shelby TWP,Mi

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Just switched my Trex 600N from TT to belt and theres no difference what so ever..The ones having issues are ones not setting them up right....

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10-23-2012 09:43 PM  5 years agoPost 22
rstacy

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Rochester, NY

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Dood is right Scott.
I was thinking Goblin when I typed that reply as that is what the OP had mentioned in his initial question. There is no aluminum boom to expand or contract.

I completely disagree with RappyT.
The tail TT driven tail is not much snappier due to the more rigid power transfer than a belt can give.
Use the right size belt with the right size pulleys and they are equal in performance.
Disclaimer: I am only referring to well designed systems.

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10-23-2012 09:59 PM  5 years agoPost 23
RM3

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Killeen, Texas - USA

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The belts are not the issue. It's the expansion of the aluminum tail tubes.
If the tube expands with the heat
You have that backwards...Aluminum tube is not going to expand or contract to the point that the belt becomes loose...

The thermal expansion rate for the best alloy 7075 is 0.000013 inches per degree F.

The belt itself is what is shrinking and expanding...and the less internal belting (weaved fiber) it has the more its going to change.

remember the issue with the first tail belts on the Radikal G20 comming loose? they finnaly fixed that by going to a different belt material.

showing a preference will only get you into trouble, 90% of everything is crap...

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10-23-2012 10:01 PM  5 years agoPost 24
Scott1115

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Greenwich, CT

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Ray - you (and Dood) are right. I was explaining in more detail what Ed and I have noticed since we both keep are heli's inside (temp controlled) during the winter where the temperature changes are drastic. If I kept them in the garage, it would be less of an issue.

Also true, the tail on the Goblin , not being Aluminum, will not have this issue.

Compass 7HV, Trex 550E
RCRCC

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10-23-2012 10:08 PM  5 years agoPost 25
Steff Giguere

rrProfessor

St-Eustache, Quebec, Canada

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Also don't forget to change out the belt every 100 flights of so.
Had to do it on my old T-Rex, Logos and my belt Synergy. Also some belts, not all, could cause static.
I think that these are the only down side to belt, other they work great when properly maintained.

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10-23-2012 10:40 PM  5 years agoPost 26
rstacy

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Rochester, NY

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Also don't forget to change out the belt every 100 flights of so.
Had to do it on my old T-Rex, Logos and my belt Synergy. Also some belts, not all, could cause static.
I think that these are the only down side to belt, other they work great when properly maintained.
Excellent point. I have been leaving the belts in on our Goblins.
I want to know what the lifespan will be.

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10-23-2012 10:55 PM  5 years agoPost 27
JKos

rrProfessor

Redondo Beach, CA

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The belt itself is what is shrinking and expanding...and the less internal belting (weaved fiber) it has the more its going to change.
Does rubber have a negative expansion rate? It would have to in order to match what happens in real life. That is, the belt gets looser when the heli gets colder and tighter when the heli gets hotter.

My personal evidence against that statement is the difference between my belt driven helis when using an aluminum boom versus a carbon fiber boom. With the aluminum boom, exactly what has been said would happen. The belt would get looser as the heli got hotter and tighter as the heli got colder. With the carbon fiber boom... No chanage.

- John

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10-23-2012 11:13 PM  5 years agoPost 28
Justin Stuart (RIP)

rrMaster

Plano, Texas

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The new designs have a belt tensioner.

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

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10-24-2012 12:02 AM  5 years agoPost 29
RM3

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Killeen, Texas - USA

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JKos,
Think about it...we check our belt when its cold and adjust it on the ground (not at operating temp)...then we go fly and it warms up during flight because its flexing around the pullies at high speed...now the belt expands a little and gets loose....

And the expansion rate for rubber is around 30 - 45 (vs 13 for 7075 Alu) depending on compound....So still rubber expands at a faster rate than metal per given temp change.

As for the lack of change with the carbon tail boom, think...the boom is not just made with carbon fiber, its carbon fiber with tough epoxy all over it (basically a plastic)...and it expands/contracts more so than aluminum.

I belive the reason your not having an issue with the carbon boom is that its expanding/contracting at a closer rate to that of the belt, so the tension is changing much less.

showing a preference will only get you into trouble, 90% of everything is crap...

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10-24-2012 12:08 AM  5 years agoPost 30
Dood

rrProfessor

Wescanson

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I checked RM3s numbers. He seems to have a point here.

I did the math, and found that an 815mm, or 32 inch boom (90 size) if brought to an outside temperature of 20°F from room temp of 70°, the boom will shrink a total of .02 inches, roughly half of 1mm.

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10-24-2012 12:11 AM  5 years agoPost 31
RM3

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Killeen, Texas - USA

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Yup....

now do the math for the total belt length of 60 inches or so for the expansion rate of hard rubber (say 0.000040 inches per degree F) and you will see what I mean....

showing a preference will only get you into trouble, 90% of everything is crap...

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10-24-2012 12:13 AM  5 years agoPost 32
Dood

rrProfessor

Wescanson

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we check our belt when its cold and adjust it on the ground (not at operating temp)...then we go fly and it warms up during flight because its flexing around the pullies at high speed...now the belt expands a little and gets loose....
I disagree with this because your logic seems backwards.

From my own experience, bringing a warm helicopter outside to the cold made my belts VERY loose. By very loose, I mean falling-off-the-pulley loose. Just sitting there.

It took about 5 minutes for this to happen.

Flying (heat) would make the belt TIGHTER, not looser, the same as bringing a cold helicopter inside made the belt tighter.

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10-24-2012 12:23 AM  5 years agoPost 33
RM3

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Killeen, Texas - USA

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From my own experience, bringing a warm helicopter outside to the cold made my belts VERY loose
Well thats weird...my Radikals always have tight belts when cold sitting in the garage (less than 50 deg)...then they loosen after flying around a bit.

Maybe your belt is a different design internally with the fiber weave...this would make a difference.

Like just strait strands of string vs a weaved tube covered and also filled with rubber...the rubber would then expand on the inside of the woven tube, stretch the fibers outward and thus pull the belt shorter?

showing a preference will only get you into trouble, 90% of everything is crap...

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10-24-2012 12:23 AM  5 years agoPost 34
BobOD

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New York- USA

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-The thermal expansion of aluminum is about 12.5 uin/in/F
-The thermal expansion of Kevlar (common tension member in belts
) is about -3.6 uin/in/F (yes...negating coeff.)
-Since the belt is looped the length is double so the expansion is double.

Just estimating figures, a 30" aluminum boom going through a 40 degree F change will result in 0.024 in difference. That's more than enough for a belt to go from very tight to loose.

Inline with Dood's experience...and many others.

Team POP Secret

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10-24-2012 12:32 AM  5 years agoPost 35
RM3

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Killeen, Texas - USA

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I guess my cheapo Radikals are using plain ol Kite string for the belt fibers...vs the Kevlar stuff....in that case my plain string belts will loosen, the Kevlar stuff actually shrinks and tightens the belt....then yes thats makes sense...My radikal belts just suck

showing a preference will only get you into trouble, 90% of everything is crap...

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10-24-2012 12:43 AM  5 years agoPost 36
Dood

rrProfessor

Wescanson

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Come up to Wisconsin and fly with me this winter. Come see how loose your belt gets. 50° is NOT cold. I'm still wearing shorts and sandals when it's 50°.

I fly over the Wisconsin River once it's froze. One of these years, I'm going to host an Ice fishing/ fun fly. I think it would be fun. People can bring their ice fishing shacks to keep warm in, and maybe do some ice fishing between flights.

At the end of the day, we'll build a fire on the ice and fry up some blue gills and crappie. Then the night fly!

This is what typical ice fishing looks like for you Texans who may or may not know what it is-
Note the green 5 gallon bucket. The same bucket used to carry your rods and tip-ups doubles as a handy stool!

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10-24-2012 12:53 AM  5 years agoPost 37
RM3

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Killeen, Texas - USA

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Sure...after you come to Texas and fly in August when its 118 degrees...but considering you wear shorts in 50 degree weather, at 118+ you may get arrested

showing a preference will only get you into trouble, 90% of everything is crap...

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10-24-2012 01:20 AM  5 years agoPost 38
Rogman88

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West Monroe, LA

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The ones having issues are ones not setting them up right....

High Voltage just works better

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10-24-2012 01:40 AM  5 years agoPost 39
BobOD

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New York- USA

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Belts with polyester chords (kite string) probably stretch enough to avoid the issues with thermal expansion. Of course, that comes with a drawback...they'll stretch under load thus eff. loss. Or worse, it could skip under load. Nothing is ever free.

Now, how about going with belt AND TT and have the best of both.

Team POP Secret

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10-24-2012 01:49 AM  5 years agoPost 40
kw_rc

rrApprentice

Texas...south of Austin and north of Corpus Christ

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I believe the 7HV has a belt tensioner. Does the Goblin? If so, doesn't this negate the need to adjust the belt?

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HelicopterMain Discussion › goblin or other belt heli
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