LMH Helicopter Discussion of all LMH helicopters both electric and glow.

Corona tail rotor gear box help !!!

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Old 04-02-2005, 12:49 PM
  #1  
clint cox
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Default Corona tail rotor gear box help !!!

I have had two gear boxes crack, I believe that it is happening do to the incapability of the plastic and lube. I used a silicone grease on the first one which caused it to crack overnight not just little cracks but actually spidering cracks. On the second one I use the lite machines heavy grease and the same thing happened in about three days, I didn't use thread-lock on any fasteners nor did I use CA accelerator like the instructions told me not too. Need less to say I am very frustrated and I turning to your wisdom for help. Any help or comments even on after market upgrade part to get rid of the fragile stock piece would be greatly appreciate.
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Old 04-02-2005, 01:23 PM
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ChopperMike
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Default RE: Corona tail rotor gear box help !!!

I doube very much that the silicone grease or the Lite Machines grease is causing the problem. I had both a LMH 117 with the Norvel .061 engine and the Corona. I never had any issues with the tail gear box. Don't know what to tell you. Something is wrong, out of alignment, I don't know.
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Old 04-02-2005, 09:31 PM
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Default RE: Corona tail rotor gear box help !!!

I used silicone grease on mine. Hope it dosn't happen to mine. I havn't flown it yet. My ESC started getting hot when I was setting it up and I had to send it back. www.chopper-1.org had aftermarket parts and guarentee their tail gearbox won't break. I ordered their complete system with titanium boom. Haven't got it yet. $90.00
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Old 04-04-2005, 12:46 AM
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Default RE: Corona tail rotor gear box help !!!

Don't overtighten the bolt on the TR gear box... I've never had a problem using LM grease.

There's an upgraded indestructable box, never tried it myself though.
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Old 04-04-2005, 08:48 PM
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Default RE: Corona tail rotor gear box help !!!

There has been stated that some gearboxes have processed at to high of a temperature which cause the plastic to become brittle. Also if you are using CA glue to glue on your tailfins, that will also weaken the plastic. And also, Ive heard that over tightening the bolt will crack the gearbox. Also Ive heard the more tail strikes wil weaken the gearbox. The only other route Ive seen was an aluminum gearbox. Someone out there also makes another gearbox out of another plastic based material that is suppose to be much stronger than the stock gearbox.
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Old 04-05-2005, 11:20 PM
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clint cox
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Default RE: Corona tail rotor gear box help !!!

I just wanted to say thanks for your help. I just ordered a gearbox from chopper 1 hope it helps. Also wanted to say I know that over tightening the bolts will crack the gearbox but I seem to have the most problem with the cracks around the bearing closest to the rotor. Also the instructions said that you should not use petrol grease or the plastic would "craze". as far as I know both of the greases I have used are not petrol based. I have yet to try flying due to the gearbox problems. Both have been scrap in as little as 36 hours.
But thanks again.
Hope next time I can tell you what I broke!
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Old 04-10-2005, 06:56 AM
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Default RE: Corona tail rotor gear box help !!!

Some stock gear boxes seem to crack easy. Best I can tell is that some batches are great and last. Some of them crack on your first crash. I have many people that have cracked up to 5 stock gear boxes before installing one of my upgraded boxes. Happy to say not one of my gear boxes has cracked.

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Old 08-18-2005, 05:30 PM
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Default RE: Corona tail rotor gear box help !!!

I used carbon fiber wrap and have not broken any more,I have 9 new tail housings if you need one
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Old 09-22-2005, 03:54 PM
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Default RE: Corona tail rotor gear box help !!!

The lubricant being used (silicone or the LMH stuff) isnt the problem the problem lies in the manufacture of the part actually. When the gearbox is being injection molded there are issues with how the plastic fills the mold and joins together, also the retaining bolt causes serious stress concentrations in that area further leading to failure. Im in the process of creating a solid model of the stock gearbox using solidworks and once done Ill take the file into school and use injection molding simulation software to get a better idea of where problems are coming from. Also I hope to get a redesigned gearbox designed and made also at school, hopefully Ill be able to make a decent number of them from a different plastic and offer em for sale
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Old 09-22-2005, 04:23 PM
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Default RE: Corona tail rotor gear box help !!!

My tailrotor box is cracked too. I just think it's a sloppy cheapo design and if you are a conspiracy theorist, an agreement between Lite Machines and the upgraded parts peddlers- which are probably the same people! lol
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Old 09-22-2005, 04:52 PM
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Default RE: Corona tail rotor gear box help !!!

Im hoping to make my part available for much less than the ones currently available on various websites. I cant justify $40 for a gearbox .
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Old 09-22-2005, 07:51 PM
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Default RE: Corona tail rotor gear box help !!!

Brets gearbox is an end all to the cracked gearbox syndrome. I went through more than 40$ worth of stock gearboxes.
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Old 09-23-2005, 10:40 AM
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Default RE: Corona tail rotor gear box help !!!

There were times that I would go through a gearbox a day. Like Darth I easily went through 40 bucks of gearboxes and probably more, I use to have 2 as spares because they broke so easily. I got lucky and picked up one of Bret's when he first started making them off of E-bay, and he guaranteed that if I could crack it, he would replace it. Never had to take him up on that offer. Good luck.
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Old 09-23-2005, 10:58 AM
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Default RE: Corona tail rotor gear box help !!!

I had lots of gear box cracks also, and lots of plastic gear box replacements. But I found that my gear boxes were cracking because the Tail fin was glued to the gear box and every time the tail fin hits the ground during a sloppy take-off or landing, the impact was transmitted into the gear box, So I solved the problem by attaching the tail fin to the gear box with VELCRO!
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Old 09-23-2005, 12:30 PM
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Default RE: Corona tail rotor gear box help !!!

Im aiming for my gearbox to weigh about 10 grams and cost about $10 each
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Old 09-24-2005, 12:19 AM
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Default RE: Corona tail rotor gear box help !!!

Im aiming for my gearbox to weigh about 10 grams and cost about $10 each
That will be short lived. When you start figuring in your time and material, you will find you will be selling yourself short. By the way what material you plan on using ?
Bret If you read this I need another gearbox (not a replacement for the one I have) but for another Corona. Do you have anymore closed gearboxes ? PM me as to what you have and cost. I have several Coronas Im working on.
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Old 09-25-2005, 12:56 PM
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Default RE: Corona tail rotor gear box help !!!

For a price of $10.00, are you going to mass produce with injection molding~? Seems like that would be the only way to keep the price down that low. Like Darth says, don't sell yourself short. Good luck.
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