Not sure what happened to one of my motors but it won't spin like it should, just sort of does spastic, little jerks instead of spinning. It's possible I did some damage to it in the process of removing my prop guards... I had one removed and started to replace the screws (they were not tightened back in all the way though) before someone on the forum warned me to be sure to use the old, shorter screws. In my opinion, crappy design if this can so easily happen, but anyway. I see motors for these for sale on ebay for about $30 or so, and I might sell this bird at a huge loss or may consider having someone else (who does electronic repairs) install a new motor for me. But I have questions about these motors.... I don't want to buy one and find it isn't somehow compatible, so any one who knows about this let me have the warnings now before I do more damage. Thanks.