Servo 101-Servos for Dummies

[Greengaunja]

With my motor landing on the 16th and foams in Wednesday/Thursday, my speed build is finally coming to an end. The last 3 days have been spent looking into servos. I know I don't need high speeds or high torque(40kg is plently) I have been wondering which servo to use. It makes sense where others here say its stupid to rely on Amazon cheapies in an RC heavily invested into. I know mine will clear $2k easily so I want to offer it an added layer of protection/security. Having a cheapie fail mid run would suck. The one quality needed that fellow speed runners state is "centers and holds center well" has been my objective. Locally, the 40kg OMG has been suggested.

I just came back from my LHS where again the above servo was suggested.
It's $130 so just slightly above what I budgeted for a servo. I have no idea if this is generic or if generics are based on this but Amazon and AliExpress has a bunch of very similar looking ones $50-70 cheaper.

The main nerd/tech guy at my LHS won't be back in until Monday and no one there today could really answer these next questions, so I'm hitting you guys up for some.

When it comes to specs, I get and understand the voltages, speeds, and torque. But this next group is Chinese to me. I assume neutral position is the centering aspect, but the next value and Russian looking word has me lost. And which one would show its "holding center" capability? Can anyone give a Cliff Notes on this and what kind of values I should be looking for? Thanks in advance and it might be a good idea to pin something to our electronics section. If already there, it's not coming up in searches.

 

[Dan B.]

Subbed. @Diem Turner ?

 

[Greengaunja]

Subbed. @Diem Turner ?

Why didn't I think to message him? He seems to have a great understanding of specs like that. And I've already gotten some pretty good advice/re-assurances from him regarding this build too.

 

[Dan B.]

Why didn't I think to message him? He seems to have a great understanding of specs like that. And I've already gotten some pretty good advice/re-assurances from him regarding this build too.

Yes, he’s very smart and has a great understanding of many things that typically turn my brain into tapioca. I’ve asked him to mansplain several things, and he always gives me a better perspective than I could have developed on my own.

 

[Senton_Prime]

How come you don't just get a name brand you know will be reputable, why worry yourself or complicate the process!?

 

[Greengaunja]

How come you don't just get a name brand you know will be reputable, why worry yourself or complicate the process!?

Savox? They don't deliver. PowerHD? Same thing. (Im still sore about their "waterproof" claims). Some would say you are paying for brand name with them instead of function.There are others I could use but price point on them (PM, Protek, MKS) is astronomical for something that will likely be destroyed with one smack into a curb. My last speed runner had the servo being the most replaced component.(mostly DS3235's/Ecoboost/GX etc) So I'm looking for mid-range and reliable. Plus, I admit I don't have the familiarity with servos as some here do. To be able to properly compare among the brands, that section of specs needs to mean something to me. And for all I know, this is a brand name. They sell alot of other servo related products too(horns, arms, GB's, mounting hardware etc..).

 

[Senton_Prime]

Savox? They don't deliver. PowerHD? Same thing. (Im still sore about their "waterproof" claims). Some would say you are paying for brand name with them instead of function.There are others I could use but price point on them (PM, Protek, MKS) is astronomical for something that will likely be destroyed with one smack into a curb. My last speed runner had the servo being the most replaced component.(mostly DS3235's/Ecoboost/GX etc) So I'm looking for mid-range and reliable. Plus, I admit I don't have the familiarity with servos as some here do. To be able to properly compare among the brands, that section of specs needs to mean something to me. And for all I know, this is a brand name. They sell alot of other servo related products too(horns, arms, GB's, mounting hardware etc..).

So what rig is this for?

 

[Greengaunja]

Custom build, Senton specs
Dedicated speed runner/'lot ripper

 

[Senton_Prime]

Which power HD failed you.. 3 or 6s

 

[Greengaunja]

The all aluminum 45kg(blue)
My bad.. 40kg. This one, twice

First one did its own thing(responding without input), and was warrantied. Second one lasted 2/3 outings in my SCX10.iii before shorting out due to water getting inside.

 

[SrC]

A DS3235. And other similar ones. Buy 2, keep one as a spare. Servos are consumable items. I never felt that simply because I invested much $$ into a build that I also need an Expensive Servo. Unless it is a RACE track build, an AMZ special will work fine. Even a Less expensive BLX servo is in order. A coreless one at the very least. Which most but Not all are though. One has to consider the precision and slop across the whole Steering geometry. Then choose a servo that equates on that level. An expensive precison servo, is just icing and bling at some point. With no real gain in performance, if the model in hand doesn't match up. Doesn't matter how much bling or upgrade parts and $$ you have invested. It becomes a vicious cycle of spending more $$. Just because you spent $200.00 in alloy hubs all around, and another $200.00 for Fr and Rr Bulkheads, for example, doesn't always justify a $150.00 +servo.
Not for a Basher use model.
Whatever you choose, Absolutely try and source an alloy case servo within you wallets budget. Understnd that just because a servo states 40kg's or whatever, doesn't always mean you are getting that. Servos have been tested and they rarely give the advertised specs with speed and torque. Sometimes as low as 30% lower in reality.
Just some food for thought.

 

[Senton_Prime]

Dang man that sucks, got the same one in my 3s senton.. it's like 2.5 years old!! Luck of the draw eh!!

 

[Greengaunja]

A DS3235. And other similar ones. Buy 2, keep one as a spare. Servos are consumable items. I never felt that simply because I invested much $$ into a build that I also need an Expensive Servo. Unless it is a RACE track build, an AMZ special will work fine. Even a Less expensive BLX servo is in order. A coreless one at the very least. Which most but Not all are though. One has to consider the precision and slop across the whole Steering geometry. Then choose a servo that equates on that level. An expensive precison servo, is just icing and bling at some point. With no real gain in performance, if the model in hand doesn't match up. Doesn't matter how much bling or upgrade parts and $$ you have invested. It becomes a vicious cycle of spending more $$. Just because you spent $200.00 in alloy hubs all around, and another $200.00 for Fr and Rr Bulkheads, for example, doesn't always justify a $150.00 +servo.
Not for a Basher use model.
Whatever you choose, Absolutely try and source an alloy case servo within you wallets budget. Understnd that just because a servo states 40kg's or whatever, doesn't always mean you are getting that. Servos have been tested and they rarely give the advertised specs with speed and torque. Sometimes as low as 30% lower in reality.
Just some food for thought.

I loved the DS3235 or DS3225s in my 3s Senton, both blue and red versions. Held up well. Did what I needed it to do. And when I screwed up and smacked into things and destroyed them, it was cheap, easy, and fast to replace. For some reason they didn't like the SCX10.iii and I'm guessing because the crawler needed more torque and even though my Senton runs fine in the rain, completely submerging the servo is another story. And yep, my LHS said the exact same thing you just did regarding overstated torque or even speeds.

Dang man that sucks, got the same one in my 3s senton.. it's like 2.5 years old!! Luck of the draw eh!!

I MIGHT have been able to warranty the second one too. PowerHD provides a responsive and attentive CS department. But I opened it up to see what went wrong and that voided the warranty right off the bat(I didn't know and told them that). By contrast, when I bought my PM DS630BLHV, the first thing John told me was to "open her up and see where the money went. And no worries, that won't void the warranty".

 

[SrC]

I will say that my Axial and TRX4 Crawlers, They truly Need strong servos. And the ST endpoint adjustment is quite critical. Most of all, Crawlers never run any Servo Saver. This will wear out most any servo faster IMHO. And with Crawling, Servos get very hot, because they are always "Stalling". Just the nature of Crawler Platforms. Unlike most any Basher rigs, "servo stalling" is much more intermittent and always run a Servo Saver. I eat servos faster in my Crawlers.
But still run the DS3235. Have a Savox 1210 in my TRX-4, Can't say it is much better. Yes a bit stronger and faster. But not by much to write home about. Since it is 4 times the price of a DS3235. When it fails a 3235 will replace it. I have replaced the 1210 Case twice over. At least it is replaceable... at $15.00. The "ears" crack off easily. Never broke a 3235 ear. And the 1210 does get glitchy and noisey when it warms up. Any rig, with any ESC at any BEC setting. Not a fan of Savox 1210's. Have 2 of them. One sits in my bin. Both are the same way. And amp hogs for sure.

 

[Diem Turner]

With my motor landing on the 16th and foams in Wednesday/Thursday, my speed build is finally coming to an end. The last 3 days have been spent looking into servos. I know I don't need high speeds or high torque(40kg is plently) I have been wondering which servo to use. It makes sense where others here say its stupid to rely on Amazon cheapies in an RC heavily invested into. I know mine will clear $2k easily so I want to offer it an added layer of protection/security. Having a cheapie fail mid run would suck. The one quality needed that fellow speed runners state is "centers and holds center well" has been my objective. Locally, the 40kg OMG has been suggested.View attachment 299409I just came back from my LHS where again the above servo was suggested.
It's $130 so just slightly above what I budgeted for a servo. I have no idea if this is generic or if generics are based on this but Amazon and AliExpress has a bunch of very similar looking ones $50-70 cheaper.View attachment 299411 The main nerd/tech guy at my LHS won't be back in until Monday and no one there today could really answer these next questions, so I'm hitting you guys up for some.View attachment 299410When it comes to specs, I get and understand the voltages, speeds, and torque. But this next group is Chinese to me. I assume neutral position is the centering aspect, but the next value and Russian looking word has me lost. And which one would show its "holding center" capability? Can anyone give a Cliff Notes on this and what kind of values I should be looking for? Thanks in advance and it might be a good idea to pin something to our electronics section. If already there, it's not coming up in searches.

I don't think there are any sort of "optimal" values regarding these specs (if you want to call them that). The numbers are denoting the width of the pulse in the signal transmitted between Tx/Rx in µsec. As far as I'm aware, they all have a neutral position of 1520µsec. How far the servo will turn (90°, 180°, 270°, etc.) will have some bearing on the pulse width range (presumably a greater movement range will bring with it a broader pulse width range). This illustration should help visualize what these numbers mean (1520µsec = 1.5ms):

Hope this helps

 

[Greengaunja]

I don't think there are any sort of "optimal" values regarding these specs (if you want to call them that). The numbers are denoting the width of the pulse in the signal transmitted between Tx/Rx in µsec. As far as I'm aware, they all have a neutral position of 1520µsec. How far the servo will turn (90°, 180°, 270°, etc.) will have some bearing on the pulse width range (presumably a greater movement range will bring with it a broader pulse width range). This illustration should help visualize what these numbers mean (1520µsec = 1.5ms):
View attachment 299657

Hope this helps

Thanks for that. Not sure it helped but no fault of yours. So basically there really isn't any listed specs to denote a centering and holding center ability of servos? It's more trial and error among brands to see what works and what doesn't. @SrC made a good point too onnhow those 2 abilities are dependant on factors that have nothing directly to do with the1 servo's operation. That's obvious and I've eliminated maybe 75% of all slop and I'm hopping getting most of the remaining slop when I get the foams and make my final adjustment.

So for servo I just want know reliability?

BTW...I brought this topic up on today's crawl with a bunch of guys. One friend commented that for "holding center", the higher the torque the better it does that. Half the group is all "makes sense" whereas the other half, myself included, are not too sure that's how a servo works. I mean outputting a torque when turning and using the same torque to hold center. What's your take on this?

 

[Dan B.]

BTW...I brought this topic up on today's crawl with a bunch of guys. One friend commented that for "holding center", the higher the torque the better it does that. Half the group is all "makes sense" whereas the other half, myself included, are not too sure that's how a servo works. I mean outputting a torque when turning and using the same torque to hold center. What's your take on this?

It makes sense that a higher torque servo may center more easily and not get knocked off center as easily.

I don't think there are any sort of "optimal" values regarding these specs (if you want to call them that). The numbers are denoting the width of the pulse in the signal transmitted between Tx/Rx in µsec. As far as I'm aware, they all have a neutral position of 1520µsec. How far the servo will turn (90°, 180°, 270°, etc.) will have some bearing on the pulse width range (presumably a greater movement range will bring with it a broader pulse width range). This illustration should help visualize what these numbers mean (1520µsec = 1.5ms):
View attachment 299657

Hope this helps

Wait, so there’s no standard or data to ascertain the centering ability of a servo? I’m just being a bit flip. But where is the SAE for RC‘s?
Your explanation makes perfect sense, which made it even more apparent that it’s essentially meaningless information in terms of performance and just represents whatever metric is returned on an oscilloscope at various rates of articulation at a certain voltage.

 

[Diem Turner]

Thanks for that. Not sure it helped but no fault of yours. So basically there really isn't any listed specs to denote a centering and holding center ability of servos? It's more trial and error among brands to see what works and what doesn't. @SrC made a good point too onnhow those 2 abilities are dependant on factors that have nothing directly to do with the1 servo's operation. That's obvious and I've eliminated maybe 75% of all slop and I'm hopping getting most of the remaining slop when I get the foams and make my final adjustment.

So for servo I just want know reliability?

BTW...I brought this topic up on today's crawl with a bunch of guys. One friend commented that for "holding center", the higher the torque the better it does that. Half the group is all "makes sense" whereas the other half, myself included, are not too sure that's how a servo works. I mean outputting a torque when turning and using the same torque to hold center. What's your take on this?

That is correct.

I think it stands to reason that higher torque value should give a servo better center holding capabilities, although I would agree that the servo's ability to evaluate its own off-centeredness is the second part of the equation. I'm not aware of any metrics or specs that would indicate a servo's ability to do so and I'm not sure that's even possible because...how would you account for both electronic sensitivity and mechanical imperfections such as gear lash and the like? I'm not saying it's impossible but first we'd even need to find some sort of metrics that would give us any meaningful information regarding the two.

It makes sense that a higher torque servo may center more easily and not get knocked off center as easily.

Wait, so there’s no standard or data to ascertain the centering ability of a servo? I’m just being a bit flip. But where is the SAE for RC‘s?
Your explanation makes perfect sense, which made it even more apparent that it’s essentially meaningless information in terms of performance and just represents whatever metric is returned on an oscilloscope at various rates of articulation at a certain voltage.

Not that I'm aware of. And yeah, the whole µsec specs aren't indicative of any sort of performance...not that I've been able to ascertain anyways. If anyone has different information...I'm all eyes.

 

[SrC]

I loved the DS3235 or DS3225s in my 3s Senton, both blue and red versions. Held up well. Did what I needed it to do. And when I screwed up and smacked into things and destroyed them, it was cheap, easy, and fast to replace. For some reason they didn't like the SCX10.iii and I'm guessing because the crawler needed more torque and even though my Senton runs fine in the rain, completely submerging the servo is another story. And yep, my LHS said the exact same thing you just did regarding overstated torque or even speeds.

I MIGHT have been able to warranty the second one too. PowerHD provides a responsive and attentive CS department. But I opened it up to see what went wrong and that voided the warranty right off the bat(I didn't know and told them that). By contrast, when I bought my PM DS630BLHV, the first thing John told me was to "open her up and see where the money went. And no worries, that won't void the warranty".

That's kind of odd that you can't open up your PHD servo or risk Voiding the warranty. That does not = Any great CS support in my book.
Many name brand servo's, offer replacement Gear trains and Cases to repair them, by the user. Like Savox, Futaba and others. Opening up a servo is no big deal. I even opened up my DS3235 Servo, took pix and sent them to the Company, and they had no issue with replacing one free, it was DOA.
PHD company is just finding a way to deny a warranty claim. That sucks of them. I will remember that next time I consider buying one.... Not..

That is correct.

I think it stands to reason that higher torque value should give a servo better center holding capabilities, although I would agree that the servo's ability to evaluate its own off-centeredness is the second part of the equation. I'm not aware of any metrics or specs that would indicate a servo's ability to do so and I'm not sure that's even possible because...how would you account for both electronic sensitivity and mechanical imperfections such as gear lash and the like? I'm not saying it's impossible but first we'd even need to find some sort of metrics that would give us any meaningful information regarding the two.

Not that I'm aware of. And yeah, the whole µsec specs aren't indicative of any sort of performance...not that I've been able to ascertain anyways. If anyone has different information...I'm all eyes.

A servo is only as good as its Potentiometer. This is what separates the men from the little boys, when buying Mid to High end ones.
Japanese Pots. are the most precise.
PM brags that they only use Japanese Pots and Motors FWIW.
I believe Futaba, a Japanese brand, also obviously does.

 

[Dan B.]

That's kind of odd that you can't open up your PHD servo or risk Voiding the warranty. That does not = Any great CS support in my book.
Many name brand servo's, offer replacement Gear trains and Cases to repair them, by the user. Like Savox, Futaba and others. Opening up a servo is no big deal. I even opened up my DS3235 Servo, took pix and sent them to the Company, and they had no issue with replacing one free, it was DOA.
PHD company is just finding a way to deny a warranty claim. That sucks of them. I will remember that next time I consider buying one.... Not..

John at ProModeler will actually scold you for not opening his servos. After a few packs, he recommends opening them up, cleaning them thoroughly after run-in, and re-greasing them. He maintains that it significantly extends the service life of his servos.