There are a number of issues:
1) Main shaft straightness. Very hard to tell if the shaft has a slight bend with just the naked eye. You either need to roll it on glass or use a dial indicator.
2) Head shakes. Mechanical issues include notching main blocks bearings, bent main shaft, unbalanced blades. Electronic issues include exposure of FBL unit to high vibrations (high bona fide helicopter vibrations and/or not enough padding) or too high gains.
3) Blade balance. Generally speaking, most CF blades from reputable companies come pretty well balanced. However, if there is a concern about blade balance, you would need to measure the (1) respective weights, (2) the chordwise COG, and (3) the spanwise COG. With the
Maglev balancer, you are only balancing the spanwise COG. The
Maglev balancer does not tell you about weight or chordwise COG. I believe the best blade balancer for chordwise COG is the
Koll Rotor Balancer (which also balances spanwise COG just as well). Still, you would need a decent digital gram scale, ideally one with 2 decimal places like the
AWS 200g/0.01g scale. The SAB 570mm blades weight about 113.99g each (5.09g for stock 95mm SAB tail blades), so a 200g max scale should work fine for this purpose.
4) Top main block bearing. Make sure to not overshim this bearing in an effort to remove all the up/down play. My bearing fell apart mid flight.
On postmortem, the top main bearing (bottom left) fell apart, the main shaft got notched, and the shims (bottom right) were all deformed.
On the rebuild, I used a Synergy shaft collar (10mm ID) to remove the up/down play.
I used a few shims on top of the main bearing so that the Synergy collar would not interfere with block assembly.
Top of main bearing without shims.
Same area with shims added to the top of the main bearing.
I then added the Synergy collar on top.
With similar electronics, my Synergy E5 with 556/96 blades weighs 2,930g (without LiPo's) which is 188g more than my Goblin 570 with 570/95 blades at 2,742g. After flying the Synergy E5 and the Goblin 570 back to back, I decided to just sell the Goblin 570 and keep the Synergy E5.
The following pictures demonstrate the size difference between the Synergy E5 and Goblin 570.
Goblin 570 (bottom) and Synergy E5 next to G570.
Goblin 570 (left), Align T-Rex 550 v1 (middle), Synergy E5 (right)