|Dec 03, 2012, 03:14 PM|
Ruggedizing the grip arms of the Align Trex 450 DFC rotor head
After having put the Hybrid 450 Pro into the air without any problems, and having sold all of my V400D02-related equipment, it is time to return my attention to my other 450 Pro. In the course of building the Hybrid 450 Pro, I found that the clone rotor head was irreparably warped, and so I substituted the Align rotor head from my regular 450 Pro. The Hybrid 450 Pro is flying very smoothly with the Align rotor head, but this left my regular 450 Pro without a decent rotor head. This seemed like a good time to spring for an Align Trex 450 DFC Main Rotor Head Upgrade Set, Part Number AGNH45162.
I suppose I didn't research this purchase quite well enough because only after receiving the DFC rotor head did I start encountering postings about the DFC grip links snapping. It appears that the tiny threaded grip links do not extend deep enough into the plastic ball links to provide adequate support, possibly during flight and certainly not during a crash. While there are many people flying just fine with the DFC links, there seems to be a growing number of people who've crashed and cannot determine whether the links simply snapped on impact or actually broke first and caused the crash. In either case, the threaded links that come with the 450 DFC kit look very small and fragile by any standard. There is no way I will put a heli into the air when I have foreknowledge of a weak link that I fear could cause a crash, so my 450 Pro has been grounded for a while as I work to figure this out.
Upon browsing around for solutions, I found that the weak grip links in the 450 DFC rotor head are a well-known problem, and it seems that the prevailing wisdom is to just purchase a Tarot DFC rotor head, and to skip the Align DFC altogether. While the Tarot DFC rotor heads are undoubtedly more rugged than the Align parts, I didn't want to start down the Tarot road after having already purchased the Align parts. One particularly interesting solution, discussed at HeliFreak in a thread entitled "DFC Links are too fragile?", is to install linkage rods for the Trex 600, Part Number HN6065TA. While the thread does go into the details of modding the 450 DFC links, there are not a lot of pictures. The lack of pictures is one reason I decided to post here. As shown in the pictures below, the Trex 600 linkage rod is quite a bit thicker and longer than the threaded portion of the 450 DFC link. The idea is to remove the tiny threaded links from the aluminum arms of the 450 DFC rotor head and then drill a larger holes in the arms so that they will accept the 600 linkage rods.
The threaded portion of the 600 linkage rod has an outer diameter of about 2.12mm and the smooth portion of the rod has a diameter of 2.00mm. Thus, a standard 5/64" drill bit, equivalent to 1.98mm, is just about right for enlarging the holes in the aluminum arms. I decided to start with a 1/16" (1.59mm) drill bit, however, to make sure that I get a very well centered hole--there's not a lot of room for drilling errors on the parts. I don't have very sophisticated equipment, so I resorted to resting my drill on its side on my bench while holding each aluminum arm in my hand. With the drill at a slow-to-medium RPM, it was easy to feel when the drill bit reached the deepest portion of each hole. I didn't want to drill the holes any deeper for fear of throwing the aluminum arms out of balance with one another--that still may be a problem, and I'll find out shortly. The 1/16" drill bit didn't seem to remove all that much material from the aluminum arms, but the 5/64" bit certainly did remove a fair amount of metal from each arm, making it somewhat more difficult to detect when the drill had reached the bottom of each hole. I feel that it is important that the holes in the two arms are drilled to the same depth, and I hope I got this step correct.
Once the holes were drilled out correctly and debured, it was time to assemble the 600 linkage rods. I do not have a Tap Drill kit capable of threading such a small hole, but I read that the steel linkage rod was quite capable of threading the hole in the aluminum arm. While holding one end of the linkage rod with pliers and a paper towel to protect the threads, I carefully screwed the other end into the aluminum arm. Every once and a while I backed the linkage rod out a just a bit before continuing--this reduced the torque needed to screw in the linkage rod. Unfortunately, I must not have gripped the pliers tight enough because I found the threads on the exposed portion of the rod got carved up a bit. That's OK, Part Number HN6065TA supplies four rods in the package, so I had a second chance with each aluminum arm. On the second attempt, I put a bit of blue thread lock on each linkage rod, and found that the rods easily screwed into the desired position.
After cleaning up the excess thread lock, I measured the total length of each aluminum arm all the way to the tip of the 600 linkage rods. The lengths of the aluminum arms turned out to be within 0.10mm of each other. Next, I screwed a 600 ball link onto the end of each linkage rod all the way as far as possible. Measuring the total length again gave a length of 31.97mm for one arm, and 32.00 for the other arm--only 0.03mm difference in length! This is closer than I have been able to achieve on the regular long grip links of the standard 450 Pro rotor head, and I hope it will make for perfect blade tracking. The assembled 450 DFC rotor head is now much stronger and ruggedized as compared to the stock 450 DFC rotor head.
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|Feb 11, 2013, 11:29 PM|
Hay Nav, Don't know how many hits you've had on this but I picked up a 45162 as a crash backup to my ALZRC dfc head. Nicely done and I'm performing the upgrade to mine. I'm also picking up a 2 x 0.4 mm tap for this. Thanks for your hard work, Bob
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