Homebrew Balance Rod for Self Tightening Props
The key tool required to balance DJI's self tightening props is a rod (or rods) with LH and RH M6x1 threads. Various forum's members have made (or had made) such rods, and have sold some to others - they've come and gone, and the process has struck me as a bit iffy. The only "commercial" source I'm aware of is Atlanta Hobby. They want $9.95 for their rod which seems reasonable, but then you have to add shipping ... and many have commented that it's so short as to make the balancing process overly cumbersome. Besides, as an inveterate tinker, I often find myself scheming on how I can do something myself ... so I decided to take a shot.
Finding metric dies locally (especially LH) is a bit dicey (no pun intended), so I ordered a LH die from an eBay seller in China, hoping it would at least "work once" - $4.40 (free shpg). Then ordered a RH die via Amazon ($6.63 - free shpg per Prime). Finally a trip to a local hobby shop for a 1/4" x 12" aluminum rod ($1.80 - 1/4" is ~1/64" bigger than 6mm - as we used to say, "close enough for government work"). Though I've used handheld taps & dies before, I was concerned about cutting reasonably accurate threads - I don't have a lathe. But I do have a drill press. So I clamped the die to the drill press table, chamfered the rod with a file, chucked the rod in the drill press, lined the rod up over the die and, with gentle down pressure on the press handle, began turning the drill press chuck by hand. No doubt true machinists are having heart attacks at this point. But, frankly, I was surprised at how well it worked - the dies cut the aluminum like it was butter. Net investment, $12.83 and about 10 minutes. As you can see in the photo, I didn't have a handle that fit the RH die, but it turns out I didn't need one - it was big enough to be clamped on its own.
Ahh, but does it work? I had a DuBro balancer from my RC games years ago. As I worked through my DJI props, every one seemed well balanced. Ocassionally I'd get a repeatable stop but never with a blade pointed down ... so I'd move the rod in or out a bit relative to the DuBro, and it would no longer repeat. So I attribute that to imperfections in the rod where it happened to be resting on the DuBro wheels.
But with all the props apparently balanced, I wondered if my rod and Dubro combo were really working ... maybe it just wasn't sensitive enough. So I took a prop, put a 1/4" square of electrical tape on one blade, and put it to the test. Bam! The taped blade immediately spun to rest at the bottom.
I don't really know how accurate this combo is, but now I am feeling more comfortable that my props are reasonably well balanced.
