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Feb 14, 2015, 09:43 PM
Folding Spacetime
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Building a belted tail boom mount for a 450 Pro

For a long time, I have wanted to build a belted tail for my Trex 450 Pro, but I didn't want to rely on purchasing clone parts from companies located overseas. The quality is always poor, and the wait is too long. I thought there had to be a way to use Align 450 parts, available in my area, to build a belted boom mount for the 450 Pro. The more I looked into this subject, the more it seemed that the drive gear assembly for a 450 Sport should have everything I need. All I should have to do, I thought, is remove the pulley and bearings from the 450 Sport drive gear assembly and then install them onto the front torque tube (TT) gear assembly for the 450 Pro.

I didn't want to tear into my 450 Pro just yet because its TT tail working pretty well. So, I went ahead and purchased new parts for this little experiment. I bought a new Boom Mount for the 450 Pro, shown in Fig. 1, and a Drive Gear Assembly for a 450 Sport, as shown in Fig. 2. I already had a front TT gear set for the 450 Pro laying around the garage.

I began by pulling the top umbrella gear off the front TT drive shaft, as shown in Figure 3. I found that the top umbrella gear pops off easily by using ball link pliers. Next, I disassembled the 450 Sport drive gear assembly. As shown in Fig. 4, the 450 Sport drive gear assembly provides the drive pulley and bearings that are needed for the belted boom mount. It was quite a chore to remove the pulley from the Sport drive shaft, and the white drive gear broke during the process. No worries, though, the front TT drive gear already has a drive gear.

Upon comparing the drive pulley with the front TT drive shaft, as shown in Fig. 5, it is clear that the splines on the TT drive shaft will be a bit offset from the center of the drive pulley. Considering that I like to run my belts a bit on the loose side, I think the drive pulley will be suitably held onto the shaft by the splines. So, the next step is to press the pulley onto the TT drive shaft so that the pulley lines up with the hole through the boom mount.

Figure 6 shows the drive pulley and the bearings installed onto the TT drive shaft and positioned in the boom mount. I had to carefully drill the drive pulley with a 1/8" (1.17mm) drill before it would press onto the TT drive shaft. I chucked the pulley in my drill and mounted the drill bit in a vise in hopes that I would get a precisely centered hole in the pulley--as far as I can detect, this worked out well. Even after drilling the drive pulley, however, it took considerable force to press the pulley into the position shown in Fig. 6. This gives me further confidence that the pulley will stay put on the drive shaft despite the offset of the splines I mentioned above.

Figure 7 shows the pulley installed onto the 450 Pro boom mount. Working just by eye, I think I got the pulley reasonably well centered with the hole through the boom mount. Figure 8 shows the pulley with a Drive Belt for a 450 Sport installed. Although I think I should clearance some material from the hole through the boom mount, the belt passes through the hole without touching the walls of the hole, but it's close. To install the belt, I used a Tail Belt Unit for a 450 Sport and a Tarot boom I had laying around, but they aren't photographed just yet. While the belt is not all that tight, I think that I might want to shave about 1.0mm off the front of the boom to loosen up the belt just a bit, or to at least have the option of selecting a belt tension that I like.

Although I have not yet tested this belted tail on my 450 Pro, I have no doubts that it will work just fine. At any rate, I now know that it is definitely possible to build a belted tail boom mount for the 450 Pro without having to wait for cloned parts from overseas. Rather, I can just buy quality parts from nearby vendors.

Update: After some thought, I decided that the belt does need clearance in the portion of the boom mount where the TT bearings were. I posted a write-up on this, titled "Customizing a 450 Pro boom mount for a belted tail." Thank you for reading.
Last edited by navigator2011; Mar 07, 2015 at 01:46 PM.
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