The arms are made to allow up to 7″ props. To get more nose/tail spacing between the motors, the designer put a small angle in the arms. Since I only plan on using 6″ props, I oriented the arms such that the arms all “bend” backwards. It looks like this will let me put a 4S 1800mAh battery on the quad and still balance very close to the center of lift. You can see the arm bend in the top view photo below — the rear arms look more swept back and the front arms look more straight out. This does make the front arms slightly wider than the back arms, but I don’t expect that to matter.
In this configuration, the motor to motor distance is about 285mm. Overall weight without a battery is 610g, so that should be about 840 with a 4S 1800mAh 65C on it. Motor thrust should be 3 times what it was with my previous setup, but the previous weight was only 570g with a 1300/3S battery. Thrust to weight ratio before was about 2.7:1. It should now be about 5.5:1. With a 1300/4S, it should be right at 6:1.
Alright, picture time. Here’s my ZMR250 with the old motors and arms along with the new upgrade parts.
During the disassembly, I figured out why one of my old arms was a litle out of place. This must have been a pretty good crash.
You can see the difference in the new and old arms in the next two photos.
Cobra 2208 2000kV motors come with very long leads. I wanted my ESCs on the arms, so I did some serious trimming.
With the addition of a 4S battery, I also had to add a voltage regulator for my Sony Super HAD II 600TVL FPV camera. Here’s the completed rebuild.
Sadly, it’s blowing 35mph outside right now. First flight will have to wait. Can’t wait!