Hi, if you read the review of the HBK2 (RCU user reviews/find & review prodects) the editor acctually replaced the stock Esky servos with Hitec HS-55's adding that he said it flew great with them. My HBK2 still has the stock Esky servos, however my uncle flys his Belt CP with Hitec HS-55's. Just remember the Hitec like Spectrum servos operate backwards from the stock Esky's so you'll have to reverse them in order for the cyclic and collective to operate right. Good luck.