Broken servos, repair or replace.

[matt01]

Morning everybody. Have been roaming around the forum as I try to get my heli off the group and do my first hover. I have a Trex 450 with a DFC head, Castle ESC, Robird G31, and a DX6i/AR6200. The servos are DS415M for the swash and Spektrum 5020G for the tail.

I got the robird up and running but obviously had/have something wrong with it or my radio. After getting the blades balance it spools up really smooth but about midway-75% throttle it dips to the left when the tail is facing me. About the third time of spooling up and messing with settings the blades touched the carpet in my living room. Checked the head and found the swash servos were trashed. Funny thing is I had just replaced the gears in one of the swash servos. $15 lasted about three minutes, the joys of being new I suppose.

In an honest opinion, am I better off buying new gears to refurbish the two servos I broke, and possibly the 3rd in the near future, or should I buy new servos? I haven't read to many good things about the 415s so far but I'm not going for 3D flying anywhere in the near future. Being able to get the dang thing off the ground and land it with out breaking something would be a victory for me.

[jml79]

I don't know the DS415 but please stop spooling a 450 up in your living room. FBL's like to be flying and the vibration of slowly spooling up and sitting on the ground can mess them up. If you aren't comfortable enough to hover that bird yet take a step back and play with the sim and a micro until you are confident enough to get it outside and airborne.

DFC heads are known to be hard on servos. They transfer the forces of a crash or blade touch directly to the servos without any give or flex and offer very little advantage to a new or sport pilot. My advice would be to spend the money and get a FBL head and the slightly longer shaft. My personal favourite is the Tarot. Well made and well priced and it locks on to the mainshaft. It may save you a lot of servo repairs.

As for servo sizing. Everyone is raging about the mks/kst/tgy fast and heavy servos. I have a set of the KST's but haven't run them yet. The problem with these servos is power. They like a lot of it and some people have experienced brown outs. On a 325mm (non stretched 450) bird I have had no problems running more moderate swash servos. I have a set of 9025 digital servos and a set of MG90S servos and they have worked well for my level of flying (sport, loops, rolls, flips and inverted hovering). The DS415M should work well for you.

[Felix the cat]

JML 79 is right on the money in all aspects. Follow his advice, specially NEVER spool up indoors. 450's can and will inflict serious damage.

What you seem to be experiencing is the "tip over on spool up" typical to FBL's, their gyros are constantly sending corrections to the servos and expect feedback in the form of pitch (nose up/down-cyclic) and roll changes. When on the ground this feedback doesn't happen because the bird is not airborne so the gyro sends more input, (feedback loop) leading to the tip over.

The best way to avoid it is to develop proper headspeed with a tad of neg. pitch to stick it and then pitch-pump it out of wash. This however is a bit complicated and very dangerous practice for a novice flyer.

Get a LOT of sim time. DO NOT go flying out of control on the sim as it will only worsen your skills. Try controlled bunny hops, slides and small hovers.

Most of us learned on bar helis, much more forgiving on takeoff, (harder to fly once airborme) but you need to develop your cyclic management skills and they fill that need.

On FB or FBL: get some training gears, dial in some neg expo, about 50%, on FBL see if you can lower the ail and elev. gains and start by SLIDING/DRIVING your heli like a car in all directions. My instructor always asked me; once in the air............. what are you going to do when it starts drifting ? Granted, trainers make for unstable flights but are a necessary evil until you can take off, hover and land tail-in.

As far as servos, Aligns 410 or 415 have been crap to me. Others find em just fine, guess I got the worst couple of batches. I use Turniggy 306HV, for about the same price as Align and are much sturdier IMHO. The problem is power, on a(n) FBL heli you'll most likely require at least 5amp Ext BEC. or higher.

Hope this helps