UK Heli Log

The ultimate main gear upgrade to strength the Trex 700 drive train.

http://www.rcheliresource.com/review-helidirect-trex-700-mod-10-gear-conversion/

rcheliresource.com

When I first built the Trex 700 one of the many issues I found was the main gear moves several mm up and down (in addition to all the meshing issues).
I simply put it down to poor manufacturing tolerance and accepted it, but as it turns out this movement up and down is due to poor assembly of the “main oneway bearing assembly”.

After seeing several gears strip at the field in the weekend, this up and down main gear play was debated and someone (Peter – EMHC) explained how they removed it.

This is just another weak link in the chain that is the Trex700 drive train, which can be completely corrected, this is how.

Bearing Alignment Before Adjustment (NOT flush with the top of bearing housing)

Bearing Alignment After Adjustment (now flush with top of the bearing housing)

Steps to correct bearing alignment:

1. Take the main gear out and remove the auto-rotation gear
2. Remove the one-way sleeve, unscrew the oneway bearing housing, now remove the one-way sprag bearing
3. Get a 15mm or similar socket (from a socket set) and a hammer, use the socket and hammer to reposition the bearing flush with the top of the oneway bearing housing.
4. Re-shim the main shaft at the collar if required.
5. Done

Gear mesh on the 700 is very important as the main gear has a 0.7 mod (fine gear mesh normally found on 50 size heli’s). In order to mesh the gears correctly you need to adjust the main gear to pinon gear gap and also auto rotation gear to tail gear gap. This can be achieved by grinding down the nubs on the clutch block and plastic tail case (see photos). In addition you will need to replace the screws with standard non-specialty button head screws and use the specialty washers from the Trex 600. This will need to be done for clutch block, plastic tail case and engine blocks. This will give you enough play to adjust the mesh.

Upgraded Metal Clutch Block with Grounded Metal Nubs

Tail Case with Ground Plastic Nubs

Sunday turned out to be a good day for flying down at EMHC, I ended up getting some good piro work in. Towards the end of the day after about 5 liters of fuel I lost the heli on a high speed inverted backwards circuit. I over corrected and shaved off too much headspeed to re-correct and ended up in the long grass/hedge at the edge of the field. Fortunately the headspeed was low and grass long (thanks to the groundsman) so damage was minimised. At this point I remind myself why I invested in a Trex700, smile and order some more parts. The moral of the story is crashes happen at the end of a long day, so quite while your ahead

For me the moral of the story is crashes happen at the end of the day so quite while you’re ahead.

Well I did end up fliying for a brief moment today in between showers, all be it very windy. Turns out my tank is leaking quite badly due to the stupid second stopper in the middle of the tank.

Time for a mod…

I drilled a hole in the stopper and placed a 3mm button head screw and washer. On the inside another washer and nylock nut. I also used an old o-ring from a old 91 carb base and placed it on the outter side of the the stopper. I guess I’ll find out if it works next flight.