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Fun with T-Rexes Simon Lockington
However it's coming into summer now, and nothing screams summer more than some after-work T-Rexing in a local park, so it was time to bring Tiny back into the light. Some quick repairs were called for such as soldering up the reciever antenna Tiny so graciously tore in half during a prior unplanned liason with the ground. With the reciever fixed and the usual components replaced (spindle shaft, main shaft bearing, main shaft, main gear, servo gears etc), Tiny came out to the field with his (much) bigger brothers. I had forgotten just how challenging flying a T-Rex can be and how squirrelly they can get if you don't take charge of the situation. The difference between hairy situations with a T-Rex and a large nitro is you're generally laughing about the situation as it occurs rather than sweating like a Meerkat amongst Tigers. Flying a T-Rex agressively can't help but sharpen your skills, the unpredictible nature of their actions means you have to be on your toes else you'll be replacing main gears (and servo gears) momentarily. Another advantage to flying them is collective management, you can't afford to just stick bang a T-Rex, you've got to let it breathe and recover. I thought I might document some of the adventures that Tiny and I have on our quest for a T-Rex that flies well and is easy to maintain. Tiny is a stock out of the box T-Rex SE with the standard 430 motor, Hitec HS56 servos on cyclic and an 877 on the tail with a GY 401. I'm also running the Align 325 Carbon blades. IMPROVING THE TAIL One of the problems I've always had with Tiny is the tail. It has been difficult to get it to hold properly and stop wagging. With the 877 on the tail, I had the gyro set to digital mode and a LOT of gain on to get any kind of reasonable holding power. Naturally, this yielded wagging which was annoying. Ofcourse you can go and purchase the Futaba 9650 which is supposed to make the tail great, but I wanted to keep the capital expenditure on Tiny to a minimum. Align have an 'upgraded' tail drive system (the blue gears) that basically raise the ratio of head rotations to tail rotations (ie slowing down the tail). The feedback from many of the reputable guys I asked was that this modification improved the tail. Given that Tiny was in bits on the bench after an 'upgrade opportunity' I ordered the blue tail upgrade to see if that could improve things. In the package was included one of the new Hitec HS-65 servo to have a play with. I decided that since I had no better application for it, I may as well try it on the tail. I figured I had nothing to lose as I wasn't very impressed with how the 877 worked. It always seemed to be behind the eight ball, even on the bench it looked like it was behind the action rather than quickly counteracting it. Installing the blue slow down gears for the tail is a bit of effort. You see it's not just the large gear that sits under the main gear, included in the kit is two more gears, one for the take off shaft that drives the belt and another for the tail output shaft, so there's a fair bit of work involved to implement the upgrade. Another change I implemented was one I found on www.holmesrc.com where you pull the tail hub to the end of the tail output shaft and then screw it down again. This in effect increases the total tail travel available. Down at the park for testing, it was immediately noticeable how quiet Tiny had suddenly become, instead of the usual high pitched noisy howl, there was a much quieter whine. We were flying in pretty high winds, and yet the tail was MUCH better than normal. Tornadoes even going into wind were fine as long as you didn't load the machine up. While it's hard to attribute which change (tail gears, tail servo, or moving the the tail hub) might have had the most impact, Andrew noticed significant improvements on his 450 XL just by moving the tail hub. It's worth doing, just make sure you do that set screw up tight! DAMAGE CONTROL While I was ordering the tail upgrade, one of the other parts I ordered was the plastic components for a T-Rex XL. Why would you order that Si? I hear you ask? After all, Tiny is an SE with all the bling bits on it, why are you ordering plastic? After undertaking extensive analysis of numerous crashes by 450 XL's and my own 450 SE crashes, I've come to the following conclusions: 450XL's commonly break the following (amongst other things):
However most of the time the mainshaft bearings and servo gear sets survive. 450SE's commonly break:
However I've never broken any of the metal bits on the head block. My theory with XL's doing less gear sets than SE's is because something just about always snaps off on the head first thereby reducing the shock forces transmited to the servo gear sets, whereas on the SE's nothing normally snaps off on the head so all the force of the crash is directed into the servos. I plan on kitting out Tiny with the new Hitec HS65s which are metal geared to try and help this, however I've heard that since the gears don't strip, the pushrods start to bend. Something has to give! However pushrods are a whole lot more convenient to replace. My theory is that SE's do main shaft bearings more than XL's because of the metal bearing blocks which don't allow any flex. So I ordered the plastic components for the XL to see if changing the top bearing block on an SE to the plastic one would help with bearing life. In the couple of crashes since this modification, I haven't had to replace the main shaft bearings. Normally I would have by now, but I'm not sure if I have enough data yet to validate this little exercise.
E-WATTS 2200MAH BATTERIES I always stop flying after five minutes on each pack, however the flight was much more enjoyable with the E-Watts batteries as the T-Rex felt more alive. After a flight with the E-Watts batteries, I ran one of my old Align packs and noticed that the headspeed was down and in general the machine felt sluggish. Now I'm not saying the Align packs are not as good, it could very well be that after year of usage that they're just no in peak form. I don't know enough about electrical theory to know if that's a valid point or not, but certainly could be. I had Andrew try one of my E-Watts batteries straight after flying one of his PolyQuest packs. Immediately we noticed the headspeed to be higher and his T-Rex was a lot snappier. So far, the E-Watts batteries seem to be a very worth while investment! |
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