Belt Problem / Any Ideas ?

[ROGER G]

I have had my Protos 500 for a while now, but now I have a problem with the belt coming off. I can't tell if it is coming off the pinion or the main gear, but this has happened 3 times now. The belt is in perfect condition and I know how to properly tension the the belt front and rear. The only thing changed is I got a set of metal pulley's from Amain and when I compare the plastic pulley's to the metal one's is that the top and bottom of the plastic pulley's is MUCH wider than the metal one's. So my thought is that maybe they sent pulley's for the Mini Protos instead of for the 500. I put back the plastic pulley's by the tail boom, but I only have the metal pulley for the one in front, by the motor. So, I am kind of afraid to fly it again till I can order some more plastic pulley's, and I am not sure if that is we're the problem is. Just guessing about the pulley's. Has any one had this problem ?? Or does anyone have an idea why my belt keeps coming off ??

Roger

[rossk]

The only reason I can see for the belt coming off is not enough tension.
I have noticed that sometimes during setup, I get it tight, but then realise that it is actually running on top of the main gear instead of meshing, turning it and retensioning after meshing means moving the mount about 5mm.
On the 500's I run the belt pretty tight, nearly as tight as I can get it with out trying hard.

[Ah Clem]

Look for a post by E3DFlyer.

He added a second idler pulley to correct the same issue.

His belt has not come off since.

[ROGER G]

Thanks, Rossk
Since this has happened more than once, I check the tension before every flight. Also, have checked where the belt is on the main gear and it is perfectly centered. I seem to get in 5 or so flights before the belt comes off, but again, every thing was checked before each flight. I wonder if I have the tension on the pinion side to tight, and it is distorting the main gear in flight ? Do you think I should not worry about pulley's ? It just seems to be such a small lip on the top and bottom of the pulley's and I thought maybe the belt was somehow riding up and over the small lip.

Roger

[ROGER G]

Ok, Thanks also, Ah Clem
I will try to find the post by E3DFlyer. If I can't find it by user name, do you know the title of the post ? I'll look by user name first ! From what you say, this sounds like the exact problem I am having !

Thanks
Roger

[ROGER G]

Say, Ah Clem
I searched for posts by E3dFlyer and only came up with posts about the one way bearing but nothing about adding a second idler pulley. Can you or anyone help ?
Thanks,
Roger

[Dr. M]

This is the first time I've read about this issue. Something must be wrong with one of the pulleys, they should not allow the belt to run off track. Perhaps one of them is installed at a slight angle (not seated all the way in the holder)? Or the bearings are jammed up and it's not spinning freely?

[Trini92]

I had a similar problem. My belt would slip off every other flight or so. Part of the problem was i didn't have enough tension on the belt. But then i also realized that with the tail boom bracket/case you have some up and down play which helps to keep the belt straight on the main gear. I did a couple of tests and noticed the belt kept riding up on the main gear to the point where part of it was off the gear. When I secure the boom case i play with how it sits in the frame to either slightly angle the belt up or down. Once i figured this out no more slipping belt. Hope this helps.

[asasan]

I have the same issue and given up flying Protos for months now.

Equal tension on both sides and if I make it any tighter, it won't rotate freely. Still the belt pops off every time I fly... gave up this "magnificent heli" that's every one's favorite.

[Dr. M]

Originally Posted by asasan

I have the same issue and given up flying Protos for months now.

Equal tension on both sides and if I make it any tighter, it won't rotate freely. Still the belt pops off every time I fly... gave up this "magnificent heli" that's every one's favorite.

Sounds like your belt is too loose. I'm not sure what you mean by "rotates freely", but there's definitely quite a bit of drag in my heli from the belt tension when I spin it by hand. I basically have the belt as tight as I can stretch it with one hand.

That's how cogged belts work. Pull them tight on the bench, because in flight, centrifugal forces on the belt pull it away from the drive pulleys, greately reducing drag, while at the same time making the belt push against the idler pulleys on the smooth outside, securing it in place. It's a very simple and elegant concept.

[alexf1852]

For me, having the belt nice and tight to prevent belt slipping under hard cyclic moves is more important than having the rotor head being easy to turn.

[desertstalker]

Originally Posted by asasan

I have the same issue and given up flying Protos for months now.

Equal tension on both sides and if I make it any tighter, it won't rotate freely. Still the belt pops off every time I fly... gave up this "magnificent heli" that's every one's favorite.

You did check all the guide pulleys right? one of them misaligned or damaged (the flange has been known to crack) could allow the belt to ride off the main pulley.

As stated before, it is possible to move the tail boom a little vertically, check to make sure yours is straight and lined up with the main pulley. If the tail has a downward angle (even very slight) it would cause the guide pulleys to lift the belt off the main pulley.

[ROGER G]

I am ready to try the Protos again after reading the excellent possible solutions and trying each one of them together. However, could this be the problem, I did notice the main gear seems to have some FLEX to it. In other words, not very stiff, at least compared to a Trex 500 main gear. I checked it and it is not cracked or broken, but just not stiff. It's as though the lightning holes are to large. Anyway, if the belt comes off again, we'll that's my last option, but if a new one isn't ' stiff ' but has a lot of flex like the one I have now, I'll have to put the Protos aside for awhile. Shame, because the Protos is my favorite ! By the way, even though the Trex 500 has lighting holes in the main gear, it also has ' stiffening ribs ' which makes for no flex at all. Very solid, unlike ( my ) Protos main gear. Maybe my gear is somehow defective in this regard.

Roger

[flint723]

I just flexed my main gear, it seems pretty flexible too. I think it's probably normal, as this gear does not have the same stresses on it that a gear driven setup has. The belt wrapping around it kind of naturally (in theory) keeps the main gear on a level axis.

[Dr. M]

The Protos main pulley is nothing like the Trex main spur . A pinion puts a lot of load on a spur, that's why it needs to be beefy, whereas the belt drive wraps around the main pulley on the Protos, equalizing the side loads.

[crickr1]

Same problem here with belt, Haven't flown in a while for other reasons but started to diagnose.

1 Confirm collar on top is tight and shaft has no up down play, this will cause walk of

2 Chk boom to be 90deg to main shaft, easily shifted up/down will cause improper alignment

3 idler brkt, boom support at idler pulleys, could have shifted or cracked

4 pulley bearings, replace, metal pulleys good (imho) but tight bearing will cause uneven tension

First had this problem w/plastic frame,holes for boom mount were worn and boom shifted, changed to cf frame, recently started same prob after a crash, after items 1+2 improvement but still occasional belt pop. Noticed if tail blades hit tall grass after landing ,auto w/ T/H, belt will pop. Have new bearings, did not yet replace, going to soon. Think that will resolve problem.
Belt tension can do some funky stuff, as simple a design, everything needs to be in proper condition and alignment. A belt drive is more forgiving then a tt set up but to diagnose can be tricky, for it allows for some play, as long as its all tracking well.

[ROGER G]

Well, flew 4 packs on the Protos today and no belt pop off. But, all is no quite right. First of all, the comments made about some up or down play for the tail boom are correct, and playing around with that, I found I could cause the belt to ride a little higher or lower on the main gear. Normally that would be great except for the fact that if the belt is perfectly centered on the main gear ( looking at the left side ) the belt is also centered on the left rear pulley, BUT when looking at the right side, the belt is riding a little higher on the main gear and also riding higher on the right side rear pulley. Now like I said, I can adjust a slight amount of up or down play on the boom and of course back an forth ( for belt tension ) but I can't rotate it, which of course would probly solve my problem. So right now I'm at a stalemate on this problem. Probly have to think about this for a few weeks, to come up with a solution. Any more ideas ??? Oh, the pulleys rotate freely and when I check the belt, after each flight, the belt keeps it's position, centered on the left, riding high on the right.
Very, very puzzling !

Roger

[rossk]

You wouldn't read about it, I just popped the belt off on my stock p500!
No damage, another emergency auto.
I have tightened the belt back up, see how it goes, I checked it right before the flight, it did seem a little loose...

[rossk]

I tightened it a lot, it lasted about 10 flights, before popping off again!
This time the auto was not so great, dented the boom and snapped the tail fin.
I'm goin to replace the belt, pinion and main gear, see how that goes...

[branmuffin]

i am also having the belt riding alittle lower on one side of the main pulley than the other. The right side it is perfectly center on the pulley, left side it is at the bottom 1/3 of the pulley. I have flown it without issue but makes me wonder how to get it centered on both sides.