Spin Me Around Like A Record ... Or the Other Way

As one of the motors of my Phantom quadcopter developed a bearing damage I had to service the hardware anyway. And then I had this glorious idea to upgrade my first generation Phantom a little bit...

CW and CCW Motors and Threads

Some few months ago DJI's Phantom design underwent a small modification (called version 1.2): two out of the four motors are now equipped with a left-turning thread for fixing the propeller nuts. No big deal, but a nice improvement of operating safety. It may save the day in one or the other case where propeller nuts would have gone loose otherwise. I never had any such issue so far, but taking care of safety is surely a good idea to do anyway.

CCW motors for the Phantom.
DJI ships these new motors with left-handed threads as spare part #22 under the name Phantom Left-hand Thread Motor. So I orderd two of them for my intended hardware upgrade. The #22 motors already come with corresponding propeller nuts, so you don't need to order them separately as I did. So I now have some spares, just in case...

The interesting question now is: which two motors do I need to upgrade this way? Unfortunately, DJI's documents don't seem to have gotten any upgrade on this topic so far. In consequence,  I had to thoroughly think about it myself. You have to replace the right motors, as otherwise you are actually lowering the safety of your quadcopter if done wrong. Thus, this is not the easiest question if you are confronted with it for the first time ... maybe a good question for all those self-proclamatory significant Assessment Centers.

Update: I've found a new DJI upgrade video tutorial that is proof that my upgrade idea is correct. Lucky, me. Or the result of successful thinking. Oh, no chance to enter Politics or get a job as an investment banker...

This simple rule of thumb comes to our rescue: thread-orientation and propeller (or motor) turn orientation need to be in opposing directions.

To make things difficult, we are left with multi-rotor terminology that may not really be obvious. For instance, the intented turning direction of a motor is usually described as seen from the motor base towards the propeller. Yet, DJI specifies motor turning directions as seen when looking from above onto the multi-rotor model.

As you please, you may now regard the DJI motor specifications CW and CCW either as (1) refering to the thread's direction or alternatively (2) as the motor turning direction when seen from above. My impression is that, according to what has been printed on the DJI bag, it's the first one: CW and CCW refers to the threading direction. Anyway, remember it the way you want, but remember it correctly and consistently.

CW and CCW motor positions of the Phantom.
Instead of even more messed-up explanations, I drew up a little figure. It shows which motor positions need CW motors and which ones need CCW motors. Numbering and position of the motors is seen from above and the same as in DJI's documentation for the Phantom and Naza-M. I go with DJI's nomenclature in order to keep things consistent.

The figure is correct in that for a case of a circle arrow going clockwise(!) you'll find that this position requires a CCW motor. Of course, the same crazy situation also holds for the symmetrical motors. You will need a CW motor on a position where the propeller turns counter-clockwise.

The Joy of Soldering With Lead-Free Lead

When doing the hardware upgrade, soldering unexpectedly turned out to be a major hurdle. The lead wouldn't melt at all. It turned out that since I'm an old school soldering guy (from those times where 1/10" wireboards were all the rage) that DJI uses those fancy new lead-free leads. And these needs much higher soldering temperatures. After asking some experienced guys working with the new lead-free leads for some time I was convinced to turn up the head up to approximately 370°C. Now, soldering off the damaged motor and the CW motors turned out to be not of any major concern anymore and soldering in the replacement and CCW motors also worked. A 50W soldering station and a new, wide soldering tip also helped completing the job successfully.

Just to be on the safe side I replaced only one motor at a time and then run a functional check immediately after each upgrade or replacement. That included powering up the Phantom without propellers and pushing the throttle stick up to full power to see if the ESC still worked as expected. In the end, the upgrade went through properly and I could do some successful test flights at the flying field.

Of course, there are maintenance works that are more convenient to carry out. However, this way I've gained some experience I will surely need when I want to upgrade my Phantom with a Zenmuse H3-2D camera gimbal. This requires the Phantom's main board to be replaced by a new one with integrated PMU and GMU. So this is about soldering off and resoldering big wires again. Sigh.