EXPLOSION!!!

[Team-MAYHEM]

So...after recently flying my 600 through a tree, I put everything back together and got ready to fly it again. Keep in mind that both frames were destroyed in that crash, so it was basically a complete rebuild.

During my preflight inspection, I noticed that the drive belt was riding high on the main tail gear. I checked to make sure that the belt was positioned in the idler pullies correctly, and it was. I checked to make sure that the tail gear pin was seated all the way in the bottom of the tail gear, and it was. Last check to make sure that the belt tension was correct and it was...hmmmm..."must just be how it went together this time", I thought to myself.

Went outside and spooled the heli up to full head speed and two seconds later, while still sitting on the ground...BOOM...the top half of the frames and the head went one way, flinging electronics everywhere and the lower half stayed put.

When I picked up the upper half to inspect it, I noticed the the belt was lodged in between the main tail gear and the frames and broken slightly after where it was lodged. The belt had jump up and off of the gear and tried to stop the blades and literally twisted the heli apart....grrrrrr!

Has anyone else ever had this happen??? I do not understand how I could have adjusted how the belt was riding on the gear...any suggestions as I DO NOT want this to happen again.

Maybe bigger flanges on this gear would significantly help to avoid this being possible, they are rather short.

Before you ask, I only had one small spacer above the gear like the manual says...I'm just lost, this isn't the first time I put this heli together, and I've never had this problem before. I'm just scared to put this thing back together and have it happen again (not to mention my wallet can't handle it)!

[wlfk]

Is there any possibility the belt might have been twisted round an extra time within the shaft?

Just a thought,

K

[LITHIUMSTATIC]

So...after recently flying my 600 through a tree, I put everything back together and got ready to fly it again. Keep in mind that both frames were destroyed in that crash, so it was basically a complete rebuild.

During my preflight inspection, I noticed that the drive belt was riding high on the main tail gear. I checked to make sure that the belt was positioned in the idler pullies correctly, and it was. I checked to make sure that the tail gear pin was seated all the way in the bottom of the tail gear, and it was. Last check to make sure that the belt tension was correct and it was...hmmmm..."must just be how it went together this time", I thought to myself.

Went outside and spooled the heli up to full head speed and two seconds later, while still sitting on the ground...BOOM...the top half of the frames and the head went one way, flinging electronics everywhere and the lower half stayed put.

When I picked up the upper half to inspect it, I noticed the the belt was lodged in between the main tail gear and the frames and broken slightly after where it was lodged. The belt had jump up and off of the gear and tried to stop the blades and literally twisted the heli apart....grrrrrr!

Has anyone else ever had this happen??? I do not understand how I could have adjusted how the belt was riding on the gear...any suggestions as I DO NOT want this to happen again.

Maybe bigger flanges on this gear would significantly help to avoid this being possible, they are rather short.

Before you ask, I only had one small spacer above the gear like the manual says...I'm just lost, this isn't the first time I put this heli together, and I've never had this problem before. I'm just scared to put this thing back together and have it happen again (not to mention my wallet can't handle it)!

Man, that's a rough one.

The kit should have come with a few extra thin washers like the one used above the gear. You can use these extra washers to shim the gear up or down. Also make sure the lower mainshaft bearing is seated all the way in the frame.

[Team-MAYHEM]

Is there any possibility the belt might have been twisted round an extra time within the shaft?

I'm SURE this was not the case...I know I double checked that


The kit should have come with a few extra thin washers like the one used above the gear. You can use these extra washers to shim the gear up or down.
In order to get the gear to go up, I would have to remove the spacer above it. Do you suppose its okay to run it with no spacer between the bearing and the gear? I guess, it shouldn't matter, the inside race and the tail gear should be spinning at the same rate.


Also make sure the lower mainshaft bearing is seated all the way in the frame.
This makes some sense...I mean, I'm pretty sure it was seated properly, but that would explain it. Also, I never really double checked that, cause I pushed it in and was done with it.

***I still think that gear should have more of a flange on it. My raptor tail gear has 3x the flange that the Mikado on does. That belt would NEVER jump off the gear...even if the alignment was wrong. I'm just saying, it really wouldn't be hard for Mikado to make that change to prevent this from happening in the future. After all, they changed the thickness of the mainshaft almost immediately after a couple of folks broke shafts in flight.

[Mercuriell]

I'm running the drive belt pulley without a shim above it as I thought the belt was running to close to the lips of the idler pulleys. Good luck with the rebuild :thumbup:

[OICU812]

The only way this could have happened is if the top and bottom bearings were not fully seated in the frames allowing for the vertical movement, that is the only way this can happen. The belt would have to be so lose to jump off it would have been constantly slapping and you would have surely noticed the tension being to lose prior to startup.

If the flange had been wider as you say then you would have been able to take off, even then with vertical movement then it would have surely bound the same and or chopped the belt from idler pullies, I had this happen on my Raptor where the top shaft collar broke and allowed vertical play and cut went the belt, piro did the heli, and lastly eat dirt did the heli as well. No matter how you roll those dice something is going to give or fail if a component is not fully seated, installed etc... Sorry to hear of your loss.