THXkid No and Yes, you can modify the E129 battery by removing the 2 small pointed tips on the top of the battery, then the battery will slide further down and make connection, they are smaller batteries so I would say you will loose about 20% of your flight time. Not ideal solution but if you can find any K127 batteries, better than loosing the use of the K127.

THXkid Or buy the batts for the E129, modify them by sanding off the click tips on them so they slide all the way down, you will loose some flight time, they are smaller batteries.

THXkid vibration can be bent shaft, bad head, loose or too tight of main blade, out of balance blade or bad gyro on flight board.

THXkid Yes all parts can be bought at the RC ERA web site, I have checked them out, all parts are available.

THXkid all controllers by RC ERA can be changed to mode 1 or mode 2, hold landing button then switch on power choose which mode to band then its set, turn off, turn back on and you have it set to that mode, can be switched back and forth any time.

THXkid No either can be set on the controller to mode 1 or Mode 2 only.

THXkid You can switch any of the controller to either mode 1 or mode 2, hold landing button then switch on and choose mode 1 or mode 2, turn off, now its set for that mode.

THXkid RC ERA web site sells very part for all their helos there.

THXkid You can switch any of these remotes from mode 1 or mode 2 by holding the landing key while turning it on, I have done this many times.

THXkid well rushed motors have brushes and over time they can wear out of all the 100+ helos I have owned I have never had a brushed or coreless motors quit or burn up on me, as long I used the proper battery. Over voltage higher c rated batteries will burn these up much faster, but not the stock batteries.

THXkid go into debug mode, trim button just left of on off switch push down hold turns optical flow off and is no in debug mode so you can trim and save your settings. Even inside can not be any fans or or air blowing from any air ducts to get hands free hover, can on mine.

THXkid Yes, after arming helo, pull and hold left stick to bottom left corner at same time pull right stick down to bottom right corner, the helo motors will start up. to manually shut down motors on landing land helo and hold left center down for about 3 seconds and motors will stop.

THXkid kinda hard to explain, but here goes, on a mode 2 the trim button just left of the on off switch, press down and hold the debug hover kicks on, that disengages the optical flow you can also trim to set and save in this mode also once you press and hold the trim button down again optical flow is back on and trim settings saved. There is NO way to permanently turn off optical flow unless you get inside to the board and manually unplug it off the board has a plug in connector to board

THXkid brushed and coreless for the tail motor, NO heat sink on main motor.

THXkid Yes I can use 1 controller for my C138, C123, C186, C187 so one controller for all these helos.

THXkid No, banggood says it does but mine came without and so far banggood doing nothing about this issue.

THXkid NO it does not come with a sensor and I had to file against banggood as it clearly says here it has a optical flow sensor, dont let them get away with this if yours does not come with one, dont buy this helo any way, its very squirely, the C138 is a much better flyer

THXkid Notsure what your asking about the right or left controls, mode 1 or Mode 2?, Mode 2 throttle on the left, mode 1 throttle on the right, they are easily can be switched by holding a certain button on the remote then powering it on and choose right or left to arm to make it mode 1 or mode 2

THXkid This also more pronounced on 4 channel helos, I dont notice it at all on the 3 servo 6 channel helo, I am sure its there but being collective pitch its not as bad than on a fixed pitch helo.