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T-REX 450 › Belt coming off rear pulley
11-26-2007 08:59 PM  10 years agoPost 21
SSN Pru

rrElite Veteran

Taxachusetts

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As in a convex type of pulley? Like a "V timing belt pulley?

I don't think anything above what is already there is necessary. If Align would get their QC under control, things wouldnt be quite as bad heli to heli.

If the pilot takes the time to properly setup/track/tension the belt, the outcome should be satisfactory.

Stupidity can be cured. Ignorance is for life!

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11-26-2007 09:55 PM  10 years agoPost 22
Dave_E

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Stanwood, WA

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Don't dissagree with anything in this post. But as stated, one heli to another, things are different. I had the tail as perpendicular to the drive pulley as my old eyes would have it, tried the tracking thing, all looked good and 5 out of 9 flights, off it came. This was after replacing the tail shaft with the metal gear (100+ flights). So after the big crash yesterday, going to replace the entire tail.

CHECK 6

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11-27-2007 01:28 AM  10 years agoPost 23
Boidman (RIP)

rrKey Veteran

The Home Stretch

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I had the tail as perpendicular to the drive pulley as my old eyes would have it
If everything else is correct, the rotation of the tail on its fit around the boom will make no difference to belt tracking.

Imaginary front and rear pulleys that start out parallel to each other and at 90 degrees to the imaginary red line, and then in end view can be rotated around that red axis. Rotating your tail case on the boom will not change the belt tracking if the front and rear pulley shafts are perpendicular to the boom.

I have played with a few S's and SA's, and the tail cases have always seemed true, to me. The aluminum cases are where the small percentage of machining errors usually turn up.

Even with all the screws and 2 ears locating the tail drive assembly in the frames, with those screws just shy of snug, the assembly can often be rocked front to rear in between the frame sides. Every once in a blue moon, that rocking by hand can show considerable slop. More than just once or twice, I have found some where the shaft can't be made perpendicular to the boom without some gentle filing to move the holes in the frame one way or another. Keep in mind that further issues arise if the mesh with the auto-rotation gear becomes too tight or loose.

Often, when a belt is too tight, the boom will eventually slide in its clamp under higher belt-pulling maneuvers. Sometimes though, that belt load will tilt the tail drive assembly back. Belt crashes at the rear have done the same thing. People have different ideas about what are properly tightened screws, and that can allow parts to slip in the squeeze, until screws and/or ears bind against their clearance holes.

With the plastic tail-cased helis, I always look up front at the drive assembly first when there is a belt tracking problem. Almost always, if the belt is riding against the bottom flange of the front pulley, then the drive assembly needs to be leaned forwards, or backwards if the contact is against the upper flange.

That is all a somewhat simplistic view of what can become rather complex on a problem heli. Do remember that the greatest percentage of these little bastards work just fine without any diddling beyond a good original assembly. Also consider that most likely the majority of problems are solved by changing out parts, but sometimes disassembly and a lucky reassembly to new positions gets the job done.

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11-27-2007 01:48 AM  10 years agoPost 24
Funky Trex

rrElite Veteran

Westerville, OH - USA

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Just another happy "no-pulley" flyer. Do yourself a favor and just remove the pulley. Its not needed on the metal or plastic tail cases. It can run with the pulley if properly lubed/adjusted/etc, or you can run without the pulley for a much more forgiving setup. Why add drag to a system that doesn't need it. I have ran my belt anywhere from very tight to falling off loose and I have never had a tail belt fail or hang up on anything since I removed the pulley.

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11-30-2007 01:36 AM  10 years agoPost 25
Dave_E

rrApprentice

Stanwood, WA

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Hi All,

First off, thanks for all the good disscussion regarding the tail pulley and the belt. I thought the flanged pulley would be the cats rear, so I ordered a couple (glad they're inexpensive) but won't be putting them on. The inner hole for the shaft has a larger diameter than the lag screw we have on the 450 and the pulley will actually be capable of "worbling" all over the place, metal riding plastic, added resistance, possible belt wear etc. So I may try the "no pulley" thing. Based on the "fit" of this thing...it's not Align and it certainly doesn't fit correctly, wouldn't recommend it. Just my .02. Dave

CHECK 6

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11-30-2007 01:55 AM  10 years agoPost 26
The_Widowmaker

rrElite Veteran

Bear Valley Springs, CA

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What pulley did you get? I ordered the one for the MX400 and it fit perfect but then I have an SE V2.

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11-30-2007 09:04 AM  10 years agoPost 27
Heli-on

rrVeteran

Southern Cali, CA - USA

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I ordered the ones from Tower that someone posted in this thread (haven't rcv'd them yet).

Dave_E, are these the ones that seem to be the wrong fit?

I came across this place, too. The part is located just a little bit down the page. I wonder if this is more the ticket.

http://grandrc.com/align_upgrade_parts

-Gregg B.

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11-30-2007 04:00 PM  10 years agoPost 28
dlflyer

rrApprentice

Flushing, Michigan

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MY belt creeped off three times. Whipes out the edge of the belt and stops all rotation of moving parts. Never a good thing. Everytime it happened I had a tail rotor strike before it happened. My fix and it has worked for me 100% is try not to hit the tail in the grass and if I do stop flying and check the tension. I think when the T/R hits the belt must stretch or the tailboom slides in. Solved my problem with it.

We have a Great country Because we have Great People

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Helicopter
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T-REX 450 › Belt coming off rear pulley
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