I have heard chatter over the years of 'issues' with 2721 servos. is this founded? if so , has horizon fixed the issue? possibly running them on high voltage (6v+) was an issue? i am getting ready to install a whole slew of them in a jet project as recommended by the kit mfg. , they are already purchased so if i dont have to replace them with another type that would be a good thing.

thanks for the info.

Kirk

Kirk I have some of these in my L1011. I was running a 5.1volt duralite regulator and later learned that the 2.4 system would be better off at 6 volt. So I removed the regulator and the 2721's went crazy after a fresh charge on the batts. The fix was a inline regulator a friend had. I just put it in line between the rx and the servo. The regulator is a simple looking 6"extension and I haven't found a source for these yet. I think JR use to sell them. I will check with Andy @electric dynamics also. These are very good servos at 4.8v. Scott

I have them on my Kingcats flaps running through a powerbox system and haven't had any problems. There are a couple in my Super Bandit as well which will also have a powerbox system. I've never personally had a problem with a 2721 in any models I've had.

OK guys... i have never used them personally, and i have one on my Super Bandit speedbrake.....I will be running a SmartFly EQ-10 Powerexpander.. I am not totally sure but i think it regulates the voltage as well like a powerbox? I am also running A123 batts, so 6.6 of the charger? Anybody see a need for a regulator?

I use them all the time, but found out recently that a regulator is needed for 6.0v with this servo. I fried one and JR repair said it was over voltage that caused it. I added the Duralite 5.1 regulator(s) to my 6.0 v packs and all is well again.
PS-it took a while for the servo to fry, so it would probably be OK for a while, but might quit at the wrong moment. -Mike Oberst

I had several of them fail on flap applications. I sent them back to Horizon, and their instructions upon repair and return were to check to make sure there was no binding of the control surface. My hinges were surface hinges, painted, so they were a bit stiff, particularly at full throw. I concluded that the 2721's did not handle high resistance applications well. Switched to 8611's and never had another issue.

The good news was the lockup failures were preceded by twitching, so I found the problem on the ground, not in the air.

Nick,

The SmartFly Powerexpanders DO regulate the power to the receiver, but they DO NOT regulate the power to the servos. I'm not sure what the A123 batteries put out right after charge, but on the Powerexpander, UNLESS you are using a regulator, that full voltage will go to the servos. I use SmartFly's Super Regulator or Turbo Regulator, depending on the size of the model because I don't like sending over 6 volts to *any* servo...

Bob

Bob, they put out 6.6 off a charge. Thanks Bb

For what it's worth BV changed the Kingcat specs on flaps from 2721's to 8411's last month. Didn't specify why.

I went through several 2721's on Kingcat flaps. I would not use them on a primary flight control surface. They are also not a digital servos so won't center quite as well, and won't have the torque around center that a digital servo will. JR and spektrum also make an inline 2 channel regulator http://www.horizonhobby.com/Products...odID=JRPVR5203 that works very well. I have one on the gear servos for my Electra.

DR

I have been using the 2721's for years on my flaps, in both the KingCat, Composite and Balsa Bandits, etc. and have never had any issues with them.
They have never failed, in flight or on the ground in any of my applications.

I usually use a redundant battery system with Fomeco regulators, switches and 5 cell packs.
As the 2721 is an analog servo, when using them on your flaps, how can they draw as much current at any flap extension settings as a digital servo?

On a flap, you do not need loads of torque just off neutral, you just need holding torque, which the 2721 seems to have on the KingCat or Bandit flap areas.

Harley....Buddy.... re read Kirk's question. He is not talking about using the 2721's just on flaps. Personally I would not use them on a primary flight surface, because they are not digital, and because I had problems with them. BTW I have about 5 of them NIB want to buy them???

DR

In my experience in using them on a Kingcat, I had 2721's on the Rudders and flaps. I would getting jittering on the Rudders. When I switched to 2.4 most of the jittering left the Rudders and went to the flaps. I am using Lithium Ion Duralites with the Powerbox. I talked with Dustin at BVM about a month and half ago and he said that they were switching using 8411's in those areas that I had the problems with. I asked him about the Spec sheet that comes out with the Kingcat at that time and he said that was done a lot years ago. Since I changed out the flaps to 8411's there has been no more jittering. I even tried at one time an amlified lead. I am wondering if the Power box is not regulated to the same voltage as a normal volatage regulator. Anyways I think some time in the future I will probably change out the rudders to 8411's as well. Just my experience.

Alan

My Super Bandit specs were also all 2721's but I swapped them all for 8411's. Dustin told me the same thing. Old manual!

David,
I don't need to re-read the question, I know, he stated "a slew of them".......Flaps don't usually take a slew of them.
Same as you, I am merely stating my experiences with and usage of the 2721's. I still have them on a KingCat's flaps.
I have a new KingCat that is full of 8411A's. No 2721's in it at all.

I am not using them on primary flight controls either....8411's, 8611's do the job much better than the 2721 would.
I still have a Super Bandit with them on just the flaps. No problems so far.

Back in the day, I did use them on primary flight controls on two different Bandits, (back in about 1999 or 2000 I think) and I didn't have any problems with them in that application. Both of the Bandits are gone...one sold, the other was dumb thumbed, turning it into confetti). The 2721 was popular back then.
Since that time, many people have complained about their failure rate, but so far I guess I have been lucky.

Isn't the 2721 is a 4721 with a metal gear train replacing the 4721 plastic gears?.........did the 4721's exhibit as many failures as the 2721 reportedly has? Interesting.......

I have a drawer full of new servos, but thanks for the offer.

Harley,

I also used a lot of 4721's back in the day, good servos at the time but there are better choices now. Cpme to think of it I don;t recall ever having problems with the 4721's but I have had issues (qute a few) with the 2721's may be something to do with the metal gear train.

Yep.. same servo just metal vs plastic gears.