Damn belt jumped off tail pulley!

[Taipan]

Today I did a piroflip take-off and lost the tail immediately. Logo climbed up & pushed foward about 50ft, I was so stunned that only thought to hit hold just before it went in. Broke the frames, damnit. Lipo is ok thank goodness.

First thing I checked was that the rudder was working, it was, no damage to pushrod etc. Then saw the belt jumped off the tail pulley! In my preflight the tension was fine but wondering if it should've been tighter - it was always like that for quite a few flights anyway (push belt inbetween drive pulley and idler about 1/8" or 3mm.) The boom didn't slip as far as I could tell. Belt lost a few teeth and noticed it rubbed some black plastic off the side of the pulley.

I did replace the idler pulley at the back with two 3x8x4 bearings like many have done. Wonder if should put on 1 more bearing as 2 might've been too narrow. Or use a flanged pulley??

Scratching my head why it jumped?? How the F am I gonna trust it NOT to do it again??

[Klinger]

Originally Posted by Taipan

Today I did piroflip take-off and lost the tail immediately. Logo climbed up & pushed foward about 15m, I was so stunned that only thought to hit hold just before it went in. Broke the frames, dammnit. Lipo is ok thank goodness.

First thing I checked was that the rudder was working, it was, no damage to pushrod etc. Then saw the belt jumped off the tail pulley! In my preflight the tension was fine but wondering if it should've been tighter - it was always like that for quite a few flights anyway (push inbetween drive pulley and idler about 1/8" or 3mm.) The boom didn't slip as far as I could tell. Belt lost a few teeth and noticed it rubbed some black plastic off the side of the pulley. Scratching my head why it jumped?? How the F am I gonna trust it NOT to do it again??

Bloody hell Kev, you step on a black cat or something. I've heard of this happening to others and they've upgraded the idler width to help. I also did this to mine, did you see at coffs the bearings i've got in place of the idler so there's rolling surface about 10mm wide for the belt to run on, simple mod but as i said it never tracked off on me. the bearings i used were 8 x 3 x 4. If you do this you'll never have to worry bout that again. Hope you get it sorted mate
cheers

[Mercuriell]

Been there done that too - uncontrolled auto into a swamp with minimal damage - one thing I noted was that one edge of the belt was more worn than the other and I wonder whether that contributes to it - think the safest is a wide row of idler bearings as Russ suggests above

[Griffo]

For those interested Lithiumstatic posted the pulley mod over here:

https://www.helifreak.com/showthread.php?t=72198

[Flybar-less]

3 3x3x8 solved it for me. But I have replaced these when the opportunity arises, with 2 3x4x8F with one 3x3x8 in the center for better digestion.

https://www.helifreak.com/attachment...3&d=1207094993

[Taipan]

Thanks guys. I think a flanged idler pulley is a must, still haven't seen the new Mikado one??

What about increasing the diameter of the bearings from 8mm to 9mm or more? This will close up the gap with the tail pulley flanges and therefore no way the belt can slip through!

Btw I looked down the tail case and the pulley isn't centred! It's slightly off centre to the left,dunno why they designed it that way. The belt slipped off the right where the gap to the idler bearings is the largest - go figure!

[Mercuriell]

Originally Posted by Taipan

Btw I looked down the tail case and the pulley isn't centred! It's slightly off centre to the left,dunno why they designed it that way. The belt slipped off the right where the gap to the idler bearings is the largest - go figure!

Mine precisely the same and had worn down the flange on the tail pulley which mus have helped the belt jump over the edge

[treaves]

What's a good place to purchase the 3x4x8F ?

[OICU812]

Originally Posted by treaves

What's a good place to purchase the 3x4x8F ?

VXB Bearings, Boca Bearings,,,, just some examples.

[ShuNut]

Originally Posted by Taipan

.Thanks guys. I think a flanged idler pulley is a must, still haven't seen the new Mikado one?........

What !..... have Mikado got new one out or in the works ?

Originally Posted by Taipan

.....What about increasing the diameter of the bearings from 8mm to 9mm or more? This will close up the gap with the tail pulley flanges and therefore no way the belt can slip through!............

Sounds logical to me, would be interesting to hear what other think about this.

[MrMel]

Here is my mod, design is actually same as Mikados own, I just used some G10, a 4mm bolt, some nuts and a bearing with 4mm inner diameter..

tension against belt is adjustable, a paper between and then tighten and its perfekt

[ozace]

clever

[helicraze]

So is this bearing mod something that should be done on all the 600?

[Klinger]

Originally Posted by helicraze

So is this bearing mod something that should be done on all the 600?

It hasnt happened to me and now wont becasue of the mod but i've read half dozen cases where it has happened without the mod. Just do it for peace of mind!