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Sorting out servo specs

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I was hoping someone could help me sort out some of the different specs that are on servos and what I should be paying attention to.

Pretty much I have always used Futaba S3003 "standard" servos. They're cheap and have always worked for me. I'm building a TRF 201X to race and thought such a nice buggy deserved something better than standard so I got a Futaba S3151 servo. I chose it because it had bearings rather than bushings and it's digital rather than analog.

Here is a comparison of the two servos:

05.22.2015-11.37.png

I'm sure the 3151 is better than the 2003 but is it better enough for club racing a 2WD buggy? Assuming this is all for 1/10th scale, other than waterproofing and bearings vs bushings, what specifications should I pay the most attention to and why? Would the specifications I should be concerned with be different if I were running a 4WD buggy or a SCT? Maybe they're basically the same as for the 2WD buggy?

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Metal gears and a high torque figure are essential too, you'll want to dump the servo saver pretty soon for a direct metal horn and anything with plastic gears will just stripstrip on the first impact. To keep steering you'll need a minimum of 9kg and I have been told a lot of guys where I race have about 12kg (I used to use 12kg in eighth rallycross!).

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I'm sure the 3151 is better than the 2003 but is it better enough for club racing a 2WD buggy? Assuming this is all for 1/10th scale, other than waterproofing and bearings vs bushings, what specifications should I pay the most attention to and why? Would the specifications I should be concerned with be different if I were running a 4WD buggy or a SCT? Maybe they're basically the same as for the 2WD buggy?

that 3151 is just a standard servo driven by digital signal board... which is only useful if your radio can take advantage, otherwise analog works just fine too

For an Offroader 1/10 I'd be looking at more torque 80oz+, for racing I'd want more speed 0.10-0.12s, ball bearings and metal gears are nice to have. Then there's the coreless or brushless motors, faster vs conventional armature motor. Some run higher voltage too.

Torquey fast race servos from big name brands can go over $100+.

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I'm using a Futaba 3PL transmitter now. Would I have to go up to something like the Futaba 4PX to gain advantage of a digital servo?

After looking at both of your suggestions and wading through the very many servos Futaba lists, I've landed on this one:

05.22.2015-13.41.png

I keep reading about high current draw. What precautions should I take when using such a servo vs servos like the 3003 or 3151?

The Futaba S9452 sells for $85 @ Tower which seems to be the going price at all the vendors I checked. I might be able to return the 3151 and exchange it out for the 9452... It's unopened, in the box. Is the 9452 a solid choice for my TRF 201X? Remember, I'll be racing it at two local tracks. The nicest of the two is called Thornhill Jr.

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Why not run a standard one until talent gets the better of it and then upgrade

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Why not run a standard one until talent gets the better of it and then upgrade

I'm all for that provided the 3151 I have doesn't put me at a serious disadvantage nor is it at risk for a hyper-early grave. I've taken the "use what you have and upgrade as you get better" approach to the ESC/motor so I'm certainly not above starting out in the shallower end of the performance spectrum. ;)

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If it doesn't have to be Futaba, you could give Savöx a try. I had only good experiences with the SC-0254MG, although you should check first if it's in your desired speed range.

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I found this very informative sheet about digital servos. I also called Futaba customer support. In order to use digital servos the receiver must be capable of "sport" mode. As it so happens, my transmitter will not bind to a receiver which has that capability. I would definitely need to go with a 4PLS or 4PX transmitter. If I try to use the S3151 servo I bought, they said I'd burn it out pretty quickly. So first order of business is to return the S3151! So my next question to him was if I can't use a digital servo, what servo would he recommend I use for club racing a 1/10th buggy. His recommendation was the S9405.

05.22.2015-14.40.png

So I can use a S3003 if I want or I can install the S9405 and avoid the inevitable upgrade.

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If it doesn't have to be Futaba, you could give Savöx a try. I had only good experiences with the SC-0254MG, although you should check first if it's in your desired speed range.

While that's true, I could use another brand servo but would I see considerable enough savings or performance improvement to counter balance my OCD of not having the receiver and servo brand match? :huh:

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Being a Spektrum user, I am not familiar with this Futaba Sport Mode that you mention, but as far as I know, you can reap at least some of the benefits of digital servos even with old analogue radio gear.

I have always considered the primary benefit of digital servos to be the increased drive frequency. Whereas an analogue servo controller only sends a signal to the servo motor when it receives a signal pulse from the receiver (usually between 30 and 50 times per second), a digital servo controller drives the motor far more rapidly, up to 400 times per second.

If the marketing blurb is to be believed, this means that small servo movements are performed with more torque, the deadband is tighter and the holding power is greater when stationary. And since these are advantages inherent to the servo's internal controller, they apply no matter what radio gear you use the servo with.

To my knowledge, from the receiver's standpoint, analogue and digital servos don't "look" any different. What is Sport Mode supposed to do, and why is it supposedly required for digital servos? Sounds a bit fishy to me, like someone is trying to sell you a radio upgrade you may not need...

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Being a Spektrum user, I am not familiar with this Futaba Sport Mode that you mention, but as far as I know, you can reap at least some of the benefits of digital servos even with old analogue radio gear.

I have always considered the primary benefit of digital servos to be the increased drive frequency. Whereas an analogue servo controller only sends a signal to the servo motor when it receives a signal pulse from the receiver (usually between 30 and 50 times per second), a digital servo controller drives the motor far more rapidly, up to 400 times per second.

If the marketing blurb is to be believed, this means that small servo movements are performed with more torque, the deadband is tighter and the holding power is greater when stationary. And since these are advantages inherent to the servo's internal controller, they apply no matter what radio gear you use the servo with.

To my knowledge, from the receiver's standpoint, analogue and digital servos don't "look" any different. What is Sport Mode supposed to do, and why is it supposedly required for digital servos? Sounds a bit fishy to me, like someone is trying to sell you a radio upgrade you may not need...

XV, that is exactly how I understood the information as it was presented. The CSR at Futaba was very clear, and I repeated back to him to ensure I fully understood. If I use a digital servo with a non-"sport" rated receiver I will eventually burn out the servo. He explained that this happens because the servo will poll the receiver for information faster than it can deliver. (Those are my words on how I understood what he was telling me.) Since the receiver can't feed the servo the information it needs fast enough, the servo spazzes out a bit. Over time, the spazzing burns up the servo. I'm sure that's not very accurate on the technical bits on the hows and whys of this but I think that's the jist of it.

I called Spektrum today after I got off the phone with Futaba. I bought a Spektrum DX4C for my daughter's birthday gift Pink Neo Scorcher. They said that their transmitter/receiver would have no problems at all using a digital servo. So here is what I'll do:

This Futaba S3151 will go in her Neo Scorcher. I figure while she will run it on the track, she's really just going to be bashing around a track so having a servo with normal speed and torque will be perfectly fine for her. The more precise nature of the digital servo will serve her well because her Spektrum controller has AVC. The Spektrum should be able to take advantage of that precision control making the AVC more effective. Right? That's my theory anyway and I'm sticking with it. ;)

I've ordered up a Futaba S9405 to use in my TRF 201X. Yeah, I have an S3003 I could use but it seems a waste to use a standard servo in such a sweet buggy. Especially one that I plan to race and hope to eventually become competitive at the club. I know myself and not optimizing the servo from the get go will just eat away at my insides. Installing it from the outset alleviates the inevitable upgrade. :)

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FYI, I use the SC-0254MG, which is a digital servo, with a Carson Reflex Wheel Pro LCD 2.4GHz, which is a pretty humble radio and not being advertised as having a sport mode.

To check if the servo draws excessive current, have a look at its specs, and compare this to the max. current draw your receiver allows. If the servo draws more, you can retrofit an external BEC with higher amps capability.

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If it doesn't have to be Futaba, you could give Savöx a try. I had only good experiences with the SC-0254MG, although you should check first if it's in your desired speed range.

Oh and Greg, I didn't want you to think that I ignored your suggestion, because I didn't and I very much appreciated your input. After looking at that Savox its still not quite fast enough to meet race speeds bases on these other fine gentleman's suggestion. Incidentally, the Spektrum CSR also suggested a servo with a speed rating of .12 or faster for racing 1/10th scale buggies so you guys are spot on with that target.

05.22.2015-20.06.png

This Savox is a .14 so it's quite close and given that it's 1/2 the cost of the Futaba it probably would have been a fine choice TBH. Am I going to be able to tell a speed difference of .03 between the Futaba I bought and this? Unlikely. For me though, it was worth the extra cost to get the most optimized servo for this buggy since it's going to be my only car.

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I use that Savöx in my Mad Bull, where it has to shift big wheels (and does it way better than metal geared Carson servos in the 20 Euro price range). But yeah, there might be room for improvement regarding speed in a lightweight 1/10 scale buggy, so I would put trust into what WillyChang said.

EDIT: That S9405 looks to be a nice servo, and just like you, I use Futaba S3003 servos in any vehicles where I need reliability for a reasonable price.

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My requirements for a servo for one of my race cars is pretty similar to what Willy said..

0.10-0.12S/60* ... 9-10kg, ball bearings and metal gears...

My servo of choice for my TC was a Futaba S9551 low profile.. IMO, this servo would be suitable for a 2wd buggy as well..

The servo I used in my stadium truck was also a Futaba, with similar specs to the S9551, so possibly the S9452 that you posted..

The biggest thing that I noticed when going to a faster, stronger servo, was that I didn't have to start turning in 3 metres before the corner, waiting for the servo to "catch up".. LOL.. The extra torque is also handy in being able to hold the wheels at full lock, where a lesser servo may not cope.. The metal gears and ball bearings just add to the life of the servo...

You need to look at one of these servos as being an investment, much like a top end radio, as a good quality servo will last you many years, generally well beyond the lifespan of any racing buggy, so it should see use in quite a few different cars throughout its life..



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Had a peek at the fleet... last time I bothered looking at fancy fast+torquey+metalgear servos, Futaba 9550/9551 was it. Shortly afterwards Savox 1251 came out. Yeah that era coincided with shorty/aileron size cases but they're kinda handy for layout tbh especially in a 2WD buggy with central servo - battery can sit further forward.

Only thing "new" these days is waterproofing IMHO... but afaik the Operator & Transmitter ain't too waterproof if you ask me. :P

Be a bit wary that some Savox can be power hungry, if your ESC's BEC cannot keep up with the juice the brown outs can cause glitching. You may need a stutter stopper or worst case an external addon BEC.

Good thing with fancy servos is you can buy spareparts... Spare cases, spare gears! (In the old days Futaba even supplied spare motor & spare circuitboard, but these days probably uneconomic repair.)

ok ok Futaba will sell spare cases and spare gears for S3003/S3001/etc too to be fair... sometimes can buy the casing for S3010 or whatever the ballbearing version is and retrofit onto basic servo model of same family.

Hitec made some good gear at great prices too before Savox, OMG etc appeared. But Hitec was PITA as T didn't have horns that fit them; them newcomers mostly copy Futaba spline so that's much easier.

For a good midrange servo I kinda like Traxxas' 2075 like what's used in the Slash.

Anything lesser, Hobbyking housebrand works swell for pennies.

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Being a Spektrum user, I am not familiar with this Futaba Sport Mode that you mention,....

To my knowledge, from the receiver's standpoint, analogue and digital servos don't "look" any different. What is Sport Mode supposed to do, and why is it supposedly required for digital servos? Sounds a bit fishy to me, like someone is trying to sell you a radio upgrade you may not need...

yeah Futaba loves their special largely-interuncompatible protocols like HRS, PCM1024 etc etc then again Spektrums can have DSM/DSM2/DSMX plus switchable framerate modes of 16.5ms, 11ms, 5.5ms... but all this is just the talking between TX & RX

What the RX feeds out is still standardised modulated pulse code signal, centred around 1.50-1.55us I think... different companies differ, so when you intermix brands sometimes the neutral point differs slightly.

Servo is just a motor & a position sensor, linked in close feedback loop.

Where analog vs digital differs is how it processes that incoming PCM signal. Analog is just an amplified comparator, it compares the position sensed vs what signal says it should be. Digital might have some fancier position sensor than a resistive trimpot, I dunno, maybe something optical. It'll have finer steps, higher frequency/resolution gives faster response, more accurate hold on position and less overshoot.

What digitals don't tolerate as much is bashing against end travel, this burns them out fast. So set your EPAs accurately! But even with analog servos with high torque, they don't live long when you let them hit stall every move.

Hitec used to have a fancy program box for their digital servos, where you can program the exact throw into the servo itself. This leaves your radio EPA at full throw, allowing the best/widest possible travel range for the control pots instead of a cutdown fraction.

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