What are the possible causes for this? I just got a set of retracts and the copter flew fine before them but once adding them would shake, but then once the retracts are retracted up it stops...
I’d check your props and motors’ balance. The retracts are a giant pendulum, and can amplify any mistakes in balancing elsewhere. You could have a resonance loop. There are physics at work on these copters that are pretty complex, and most of us (myself included) often overlook some of the causes.
Steve's right -- the retracts sounds like they're acting like a tuning fork with the copter acting as an excitation mechanism. I suspect that you'll have to live with the issue, though -- you probably don't want to add mass dampeners because of the additional weight. Andy.
I have been away a bit but this issue with the hex i built with retracts got me thinking. It flew perfectly fine before retracts then simply adding them caused the pulsing action by the motors. This got me thinking. My cinestar 8 started doing this one day and I don't remember what I had changed but I am assuming it has to do with COG and where i had mounted my batteries. I since have rebuilt my x8 and lowered my battery tray and will test again this weekend and see if lowering my battery tray helps. Ill report back.