Nah,,,,,

I think the 821's might be okay for the models they were intended for and if you pay attention to the length of the arm screws when you start putting different arms on them, there have been problems with the output shaft snapping off when the wrong screw length is used.

But basically the BIGGEST issue with using them for your application is that they aren't recommended for gassers nor anything that large. Here's the tech notes from Horizon;

Tech Notes
The DS821 servo is a powerful, accurate sport digital servo recommended for RC airplane applications up to 1.20-size. For helicopters, the DS821 operates best with 30-size glow models, and up to 50-size electric. Loads and vibration in larger models may cause premature failure of the servo resulting in damage or injury to property and persons.

Important: Do not use liquid thread lock with the DS821 servo!

Do not use any form of liquid thread lock to secure the servo arm screw to the output shaft of the DS821 servo. Chemicals in these liquids react with the polycarbonate gear set causing the plastic to become brittle, fracturing the final output gear.


Get yourself some good MG servos in an appropriate torque rating. My personal experience indicates that you ought to get something that is capable of providing at least 50% more torque than is specified by the manufacturers. There are a few exceptions to that, but it's generally a good practice.

OH, batteries.....

Yeah might as well go to six volt right now as you will later on anyway. Be aware that some servos, mostly coming from Futaba, don't play at six volts but there aren't many of them. If you're going to use a Spektrum radio system, you'll need to pay special attention to getting GOOD power setup for your model. That's also true of a 72MHz system, but the 2.4GHz Spektrums will bite you faster than the 72's if the power system is inadequate.