In what way is the Futaba S3151 better than the S3003?
 

Hi

Just bought a Futaba CAF 9 channel radio that comes with S3151 DIGITAL servos.

When I looked at the servo specs I found that there is very little difference between the S3151 and the S3003

I looked up the specs at Tower's site and the same are reproduced below


S3151
SPECS: Speed: 0.21 sec/60 degrees at 4.8V
0.17 sec/60 degress at 6.0V
Torque: 43 oz-in @ 4.8V
54 oz-in @ 6.0V
Dimensions: 1.59 x 0.79 x 1.42 in (40.6 x 20 x 36mm)
Weight: 1.5oz (42g)

S3003
SPECS: Speed: 0.23sec/60 deg @ 4.8V or 0.16 sec/60 deg @ 6V.
Torque: 44 oz-in @ 4.8V or 56.8 oz-in @ 6V
(3.2 kg-cm @ 4.8V or 4.1 kg-cm @ 6V)
Size: 1.6"L x .8"W x 1.4"H (41x20x36mm) w/o output shaft
Weight: 1.3 oz (37.2g)
Connector: "J" type with approx. 5" lead


While I have a general understanding on the advantages of digital servos I really do not understand as to why one should bother with the S3151 when there is so little to choose between it and the S3003 - of course the S3151 is about $25 more expensive

If I am missing something can someone please educate me

Thanks

RE: In what way is the Futaba S3151 better than the S3003?
 

with anything in rc, buy what YOU want. If you don't realize the benfits then you probably don't need it. but in a nut shell. The 3151 is going to develop it's full torque in about 1 degree, the the 3003 is take about about 10 degrees. the 3151 has about 3-4 times the holding power over the 3003. this is why the digital servo draws do much more current than an analog servo so get high capacity batteries or make sure you check them.
In a 40 sized model unless you really know your model you'll never notice the differance, If you do use them just use them on the rudder and elevator over two models, these extera cost is a waste on a throttle servo and most higher performance models use dual aileron servos which is more than enough power on standard servos. IN a 60 sized heavy bird you would notice.

RE: In what way is the Futaba S3151 better than the S3003?
 

Thanks for the info Redfox. I can appreciate the part about the 3151 servo developing full torque in about 1 deg compared to the 10 deg required by the 3003. But I do not understand how is the holding power (or torque required to overcome a held position) better on the 3151. Isn't the holding torque the same as specified for both servos i.e. approx 43-44 oz/in (at 4.8 volts).

RE: In what way is the Futaba S3151 better than the S3003?
 

I'm going to botch the explaination, so I'll refer you to these;)

http://www.futaba-rc.com/servos/digitalservos.pdf
http://www.hitecrcd.com/Support/Faqs...gitalservo.htm

RE: In what way is the Futaba S3151 better than the S3003?
 

All of the digital servos I have tested take at least 10 degrees to develop full torque. Non digital servos take about 20 degrees.
The holding torque is about the same for both types.
I sure would like to have a servo that develops its full torque at 1 degree. Please tell me which one that might be.

RE: In what way is the Futaba S3151 better than the S3003?
 

I'm not that impressed with the S3151 servos -- they suffer from the same cheap mechanics as the 300? because they're just the same servo with a digital amp. A far better servo (IMHO) for the money ($39.95) is the hitec HS5475. These are *mich* tighter and plenty strong -- they'll also take 6V without any problems.

As for the torque/degrees situation -- we need to define what percentage of torque is produced for a given angle of movement.

"full torque" means very little. I'm more than happy with a servo that develops 99% of its torque with a 1 degree angle of movment, even though that's not "full torque".

I've never had a problem with mid-range analog servos exhibiting an excessive lack of torque for small deflections -- they all seem to work just fine for me. I use both digital and regular servos on my planes -- it's very difficult most of the time to tell the difference in the air (or maybe I'm just getting old) -- I can hover my GeeBee profile with HS425BB servos as easily as my Mojo 60 with its HS5925 coreless digitals -- and both will knife edge without rudder blow-back.