I have been running a very old scat cat in the 140mph range till this sunday when the aileron servo HORN broke. So i have purchased a GP viper 500. What servo to use? My scat cat I used futaba S3004.

must have a 350 chev motor to get a Scat Cat to go 140.

On a Viper any servo that fits will work fine, wanna spend more than 10 bucks a servo? you will get better centering and maybe the model will hold trim a little better. that's what spending the big bucks will do. Any sport servo will do fine. I notice a differance when I use the 20 some dollar servo over the 10 dollar ones.

No 350 just a TT.46 with a venturi a jett tuned muffler a 250mah pack, castle creation micro stamp, no rudder, 4oz bladder tank, and no landing gear. Yes I know it is not Q-500 but at our club it's run what ya brung. Which surface do you think needs a HT/MG servo I was thinking the 2 ruddervator servos. I think a standard BB S3004 for the aileron with a heavy duty arm would be okay. What do you think? Thank for your help. Any trouble areas that need to be modified on the viper.

The poop on metal gear is that they developed slop more quickly than nylon geared servo's. I race and hang with 20 some different flyers on the weekends with these contraptions and I'll see a whole range of stuff. I see guys use Hitec 225's and everything in between.

I think the biggest quailty that you need is centering , meaning when you bank and yank and you let go of the stick, it has the same trim each time so your not fussing and stiring the sticks making you slow down. hitec 225's lack good centering, I use JR 3121, or the digital 3421

The jr stuff is a little pricey. Would the hitec 225 be the wat to go? What servo would you buy for under $39.00? Would the nylon gears of a servo strip? Thank you for your help. I think Iam being a little to crittical I just don't want a servo to fail and hurt someone.

I understand safety, I have lot's of 225's in service, for 28 bucks there good , they save on weight have lots of torque, they give up a little bit on terms of centering.

There's a generic brand called expert , they heve a knock off 2131 for like 25 bucks.

225's are tried and true , but as our readers see this they may be tempted to add there 2 cents worth,,,hmmm , boys?

Never seen a nylon servo strip under normal conditions , they will fine

On the Viper , run extra CA along all the joints and glue on the fuel door once the tank is in. with a TT engine you'll be OK. I've flown a couple with Nelsons and they held together fine.

For a viper, you can use the Hitec 225MG's for the rudder/elevator and even the aileron, and a 81MG for the trottle, that is what I have in my viper that I run in the 424 class. They seem to hold up well. I do agree with the cheaper JR servos, called Expert, I have had good luck with them as well. In 428 class, I fly all Futaba, 3102 on the throttle, 9650 on the rudder/elevator and aileron.... which is in the 170mph range.... had great luck with all. Digital is the way to go for the centering aspect of it. For what is worth...

Scott

Thank you for all the input! I found in my shop some towerhobbies TS-35 55oz/torque same torque as the Hitec 225 (I think they are the same?) They just don't have the metal gears I have heavy duty arms for them. What are your thoughts on using them. Also do I need a rudder. Can I just run one standard HT servo for an elevator? I flew my scat cat with no rudder?

I've always been more comfortable having some rudder control. For AMA 424 racing, I believe you have to have yaw control, not just pitch and roll, so you'd need the rudder for that.

Also, I've never felt the need for metal geared servos, have run nylon gears for a lot of years, all the way from 424 (thunder tiger) quickees to old .15 quarter midgets, formula ones, and 428 (nelson) Q500's. Only gear trouble I've ever had was destroyed gears because of the crash, not the crash because of bad gears!

Thank you for that. So the tower TS-35 with their 55 oz torque for rudder/elevator and one on the aileron would be Okay?

I would think they'd have plenty of torque. I am currently using some Hitec 225's in a 424 plane, and don't seem to have any trouble with centering, etc, in that plane.

JR also makes a "JR Sport" servo line that includes a MN48 mini-servo with 48oz-in torque, I've been meaning to try them sometime.

http://www.horizonhobby.com/Products...rodID=JSP20040

The hitec 225 don't really seem to have centering problem. As far as i can see they seem to be a good sevo for 424. I run the nylon gear version on the ruddervators in my viper, keep the the arms short and give yourself the greatest mechical advantage possible and they hit the mark every time.

Small
lightweight
Plenty of torque
no backlash

...GOOD SERVO

This got me thinking about the servos I've used for racing. So I dug though the old UHAUL box that holds pretty much just baggies of retired servos that were used in pylon racing since I started. One other thing, the box is the one cubic foot size, and is filled to the top. Must be at least 100 servos in the box, though I am afraid to count ($$).

Kraft KPS-12 and KPS-14
Ace Bantom Midget
Novac NES-1A
Airtronics 94554
Futaba FP-S130 plus a long list of other Futabas and their ever changing numbers.
Hitec HS-80 HS-205 HS-81 HS-225

I entered my first race in 1974, but really didn't get serious until 1982. Then the next 18 years, pylon was all I flew and I must have entered 150+ contests over the years. Yet in all that time, I can't remember ever having a servo arm fail, and can only think of maybe two or three servo failures. Not one of them was due to gear failure, but rather feedback pots or motor failure. Wish I could say that the history of receivers were as good, or batteries and switches.

From observation over the years, if you have stripped the gears in flight, you have flutter if the servo is connected to control surfaces. Connected to the throttle, a vibrating from the engine is getting through. I use a mechanical filter to isolate the throttle servo from the engine.

keep the the arms short and give yourself the greatest mechical advantage possible and they hit the mark every time
This is the best advise that anyone will ever post on servos used in racing. I go so far as to drill new holes in the servo arms closer to the center and use pretty long moments on control surfaces. Also, use the wheels if at all possible, they are much stronger than the arms.

To put the entire concept to test, I put 5 of the weakest servos in existance into a Nelson powered quickie. Five Hitec HS-80 servos were used with two on ailerons. It finished 40 or 50 flights before a mid-air knocked it from the sky. No servo problems. The wing survived, so I built another fuselage and flew the setup with more of a sport setup - ST40 with Nelson long quickie muffler (his original design). Another 10 hours, with no failures. This test did uncover the main weakness of the HS-80/81 servo - no output bearing. If you choose to use this type of servo (and I really don't recommend it) use at least the HS-85 with output bearing. Finally, I put a nelson back on it to go to a race in Denver, and all was fine until a mid-air.

So I can pretty much say that if you are having servo problems, most likely it's not the servo. Mounting the servo, it is important that it is isolated from the model framework. Getting the control geometry correct is important. Free moving controls help too, and avoiding flutter. Avoid using loc-tite on servo screws (it makes some plastics brittle) and be careful where that drop or two of CA goes in field repairs. Don't backdrive any servo.

Unbelievable!

I find myself agreeing with High Plains.

Ed S

I've written this before but maybe it bears repeating. Many times the centering problems with 225 servos can be traced to a tight iron/ oilite bushing at the base of the output gear. These servos have a ball bearing on top of the gear / the bushing on the bottom. Replace that bushing with another ball bearing from an old servo or a new one from some place like Boca and you will be amazed how much better they center. These are good rugged servos that offer quite acceptable centering if these bushings are not too tight. The ball bearing is less than $5.00 new if you go that route.