Copster the 525 is a bad choice. It is a fine servo but you really do not need a 5pole motor for the throttle. A standard 311 or so would do fine. I am not sure of the other ones. They seem pretty large for the purpose. Try a 635 or a 5475 digital with a 6 volt (5 cell battery pack). i think they would work. You might try the 3-D section here. a post there may bring more answers. Also metal gears wear faster and end up with more slop in them. I would not use them if I could find something else. BTW the 2 I reccomended have the new 'Karbonite" fiber gearsets. They are supposed to be almost as strong as metal gears but last a considerable time longer. Good luck with your UCD.

Mark Shuman