Thread: Discussion JR 398's?
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Old Jan 30, 2013, 02:44 PM
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United States, CA, Midway City
Joined Dec 2003
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Originally Posted by satinet View Post
I don't really understand the desire to know the dead band is. It's narrow.
The dead band was really narrow on the 378 and they have all accuracy of a drunken sailor wearing a blindfold.

The futaba s3150s doesn't have a particularly narrow dead band but it is a pretty accurate servo and has a good quality reputation.

Whether a servo can rotate to 60 degrees in 0.10 or 0.11 seconds isn't too important. I admire those people who can tell the difference though.

It's well known that manufacturer figures are not very accurate anyway. Especially torque figures.

Maybe it's the servo of the future?

The gear slop on the 378 wasn't anything to write home about. In that sense MKS are far ahead of the pack. Also is accuracy.
The Futaba S3150 is 1 microsecond deadband, which would be considered excellent. I won't buy a servo with more than 2us deadband anymore. At 3us you can tell the difference in the flaps at various flight modes if your linkages were correctly tight to begin with.

One of the reasons why the 378 buzzed so much more at neutral was because at 4us deadband and your tx/rx was giving it a command in between the 2 spots, it does not know where to go.
Most of today's subtrims are in increments of 1us and less, with trims also at 1us or less (user adjustable on most tx's), with pots on the sticks +- 1-2 all the time.

Speed is only really critcal on ele servo... ele resolution not as much due to "gearing" of the arms.

A 1mm error in today's te could mean you are not going up in a light thermal when others would or not make it home from downwind. It used to be we see slop of 2mm before, but most builders have gotten much better.

Anyway, for the wing, it pays to be able to fine tune the te to the smallest increments = smallest deadband possible.

Originally Posted by Francesco View Post
I have bought a few of the "servos of the future", and I won't be buying any 398 until I read some unbiased technical tests. I know that's more than I would ask from other servos, but I think that JR has to do some extra work to regain my trust.

Therefore, go Tuan! I am willing to share the cost, if you have the will and equipment to run some tests. I also volunteer for torque/current measurements.
Thanks for the offer Francesco. I'll be able to do some basic current, speed, deadband test on Joe's servo in AZ! If it passes intial tests, I'll order some standard ones to use on LiFe voltage. I don't like the HV ones on 6.6v as it looks like you are giving up 20% for speed and torque and I don't like to run Lipo in a sailplane. If you saw my servo bin you will understand why I am so relunctanct to buy servos just to test anymore ... maybe I go take a picture and post it
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Last edited by fnnwizard; Jan 30, 2013 at 03:01 PM. Reason: Added response to Francesco
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