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Home✈️Aircraft🚁Helicoptere-JR-HeliForza 700 › Forza 700 tail gear mystery
11-27-2016 09:13 PM  3 years ago
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tgreen

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Western Pennsylvania

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Forza 700 tail gear mystery
Just finished a Forza 700 with Scorpion/Castle 120HV ESC. Spun it up for the first flight. The head speed seemed pretty high, but I set the RPM for 1800 on the ESC (flight mode 1). Right before it was ready to lift off, the blade noise changed as if the head speed dropped. I noticed the tail was no longer turning. I found the tail trans. pinion gears were both stripped, nearly melted. I was 100% confident that the tail blades did not touch the ground, but there were grass stains on the blades so I thought it must have touched and taken out the gears. I replaced the gears and spun it up again and the same thing happened. Both tail pinion gears were totaly stripped. The tail never touched and the heli never lifted off. I've been in this hobby for a long time but have never experienced this. It almost seems as the head speed was too high and then for some strange reason, the tail gears stripped. This has to be a mechanical or program issue, but I cant seem to figure it out. Any ideas??? I uploaded a pic onto my clipboard. First time I've done that. Hopefully it will be accessible.
Thanks

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11-28-2016 01:26 AM  3 years ago
Heli Fanatix

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Fountain Valley, CA

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I have built a Forza 700 and the quality is top notch. Without seeing what you did, let's go back to basic. I would break it down the tail drive system from front torque down to the tail blade grips. Possible issue might be
- bolts holding the tips of torque tube
- torque tube bearings
- bearings in tail case

Lastly, sudden acceleration might case the gears to melt. I've taken my Forza swinging 710mm up to 2458 HS and used the Kosmic Auto Rotation Bail-out feature without an issue.
- you can set up the ESC to fix point
- V Curve just to trouble shoot

Prior to flight
- remove main blades
- spin with finger
- should have no resistant

Hope this helps
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11-28-2016 01:38 AM  3 years ago
tgreen

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Western Pennsylvania

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The quality is top notch. That's for sure. I'm excited to get this bird dialed in once I get past this problem. The drive system did move smoothly when spinning the head on the bench. I checked that after I replaced the gears from the first incident. I think it may have something to do with the sudden acceleration. The head speed seemed way too high but the ESC governor was programmed. The gears seem like they are more melted. If it were a problem with something stopping the tail abruptly, I would expect to see a few teeth missing and then subsequent damage. But the gears don't show that. I'm going to double check what you suggested and then maybe eliminate the governor mode of the ESC and use a throttle curve to manage the RPM. Then I'll make sure I have someone else with me when I try it and have them watch the head speed with a tachometer while it spools up. I'll also try to take a video in case the problem still occurs. I had a difficult time finding the replacement gears. I know JR is in the process of internal changes. Once I get another spare set of gears I'll be ready to try again. Thanks for the help. I'll be back soon hopefully with a "problem solved" post or more help.
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11-28-2016 01:05 PM  3 years ago
LaDon

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Fort Dodge .Ia

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Chances are when you put the tailboom on if the torque tube didn't line up and slide in the front gear squarely you pushed the bevel gear forward just a little and it tightened the gear lash. Easy to do. Make sure that it turns real smooth after putting it in. If not you can take a flat end screwdriver and push it back just a little. Also make sure the torque tube and tail turn smooth with.no binding when it is off

If you need a set of gears and you can't find any I might have some
Team Jr
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11-28-2016 04:04 PM  3 years ago
Skeezix

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Katy, TX - US of A

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From the picture I'd say the mesh was way too tight which caused the issue. The issue isn't stripping as there aren't any teeth left at all. I would take the box apart and rebuild from the ground up and carefully check the mesh and shim if needed. Nick Maxwell has a very good instructional video for this regarding the E700 Raptor, but the principles apply to all helis.
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11-30-2016 01:24 PM  3 years ago
tgreen

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Western Pennsylvania

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Thanks for the additional advice. I was able to find a set of gears in England from Ebay. They are on the way. As soon as they arrive, I'll rebuild the box again. Thanks for the link on the shims. I'll definitely check that out before I rebuild the box. Hope to have some positive results within a week.
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11-30-2016 01:27 PM  3 years ago
LaDon

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Fort Dodge .Ia

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There are no shims in the front box. Just make sure you don't push the bevel gear out when you install the torque tube. In the rear box there are shims. We run ours without anyTeam Jr
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12-18-2016 11:57 AM  3 years ago
CoachE

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Cincinnati, ohio -usa

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Results???BD Team Pilot / Get !T - Got !T - Perfect !T
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