From my understanding, the only real preventative maintenance that can be performed on our Inspires that would be considered critical to a continued flight, are the 4 motors and props. Prop replacement is a no brainer. The landing gear transformation drive-train isn’t critical. The electronics are obviously critical, but the only preventative maintenance you can do on these is to replace each and every circuit board. After all, how can you predict which electronic circuit will go bad. You are basically at the whim of good/bad luck if any one of them fails. So, motors should be the focus of a good preventative maintenance program in which there are two options. First option would be to replace the entire motor after some pre-determined number of flight hours. The second option would be to replace just the bearings in the motors. Since the Inspire motors are brushless, the only thing that could experience wear, under normal circumstances, are the bearings. Since replacing bearings is significantly cheaper than replacing the entire motor, it was my choice for my Inspire.
As it turns out, replacing the bearings is pretty straight forward as long as you have a reasonable amount of mechanical skill. In fact, I think it is less involved than replacing the entire motor. Since I could not find a decent video that focused on the Inspire motors, I decided to create one and share it with the members of this forum. I hope some of you find it helpful. The video is about 17 minutes long and covers the tools, disassembly and re-assembly.
There are 2 bearings on each motor. Start to finish, each motor took between 18 and 30 minutes. I chose to replace the steel bearings with the ceramic hybrid that I purchased from Boca Bearing (part # BMK-013C-OS). Less expensive bearings are available from Boca. The proper size is: 5mm Bore, 11mm Diameter, 5mm High.
All the tools required are pretty standard and covered in the video. One of the 2 bearings needs to be driven out with a drift (punch), but the remaining bearing removal, and the installation of both bearings is handled by a tool I built which is nothing more than a 2 inch #10 Allen head bolt fitted with a nut and a couple of washers. When removing the bearing, just the head of the bolt will work in most cases. However, something that is not covered in the video, but could happen in some cases, is the situation where in the process of removing the first bearing with the drift, only the inner race is punched out. Not the entire bearing. In this case, you need to remove the opposite bearing using the bolt/washer combination. You will find that with the inner race missing, the Allen head bolt can now be used on that second bearing. After that bearing is removed the tool fitted with a washer slightly under 11mm, can be used to extract the partially removed (broken) bearing.
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