Servo specs explained.

[biggman100]

I have been looking at cheap servos just as backups, but, unlike what im used to, there are so many different specs and options, im lost, as usual. The ones im looking at, these are the listed specs:
Stall Torque (5V): 19 kg/cm (263.8oz/in)
Stall Torque (6.8V): 21.5 kg/cm (298.5 oz/in)
Dead band: 3μs
Speed : 0.16 sec/60°(5V) / 0.14 sec/60°(6.8V)
Operating Voltage: 4.8 ~ 6.8 DC Volts
Weight: 60 g (2.12 oz)
Motor Type: DC Motor
Gear Type: Copper & Aluminum
Working frequence: 1520μs / 333hz
CE Certification: Yes
Size: 40 x 20 x 40.5 mm ( 1.58 x 0.79 x 1.60 in)

Would they be too fast for the 4WD trucks i have (Senton, Associated SC10, Granite, Torment, Terromoto, for example)? I compared them to some of the better brands (Arrma, Savox, Bluebird), and, noticed that most of those are in the 15KG or less range, (although i did find a Savox 20KG) and these say they are 20KG.

 

[Sledgehog]

There's really no such thing as 'too fast' when it comes to servos as long as they have enough torque for the size of the truck/tires you're trying to move. Those seem like good specs but what's the gear type inside as well. Speed and torque mean nothing if the gears are just going to strip on you, specially with a higher torque servo.

Get a good servo from the get-go and you most likely won't need a "backup." I say it a million times on these forums... "buy cheap, buy twice." $60-$80 isn't expensive for a servo when it can last as long as you have the truck.

Also as much as I love Arrma, their servos shouldn't be considered one of the "better" brands. Replacing the stock servo is generally the first upgrade anyone round here does on their vehicles.

 

[biggman100]

There's really no such thing as 'too fast' when it comes to servos as long as they have enough torque for the size of the truck/tires you're trying to move. Those seem like good specs but what's the gear type inside as well. Speed and torque mean nothing if the gears are just going to strip on you, specially with a higher torque servo.

Get a good servo from the get-go and you most likely won't need a "backup." I say it a million times on these forums... "buy cheap, buy twice." $60-$80 isn't expensive for a servo when it can last as long as you have the truck.

Also as much as I love Arrma, their servos shouldn't be considered one of the "better" brands. Replacing the stock servo is generally the first upgrade anyone round here does on their vehicles.

They are supposedly metal geared digital waterproof servos. I can get 4 for $55. I don't like to spend a lot of money on something that will more than likely sit for weeks and even months at a time, which is why i was looking at them.

 

[Sledgehog]

I would not trust the metal gears in a servo that costs $13 each. Just sayin.

 

[biggman100]

I would not trust the metal gears in a servo that costs $13 each. Just sayin.

We use cheap servos like those in boats up to 40 inches, and they work fine, but, i don't do a lot of car stuff, which is why i asked about them. If it was a TFL Zonda, like this one: https://rcboatbitz.com/product/41-zonda-r-12s-artr-75mph-in-stock-ready-to-ship/?v=7516fd43adaa then i wouldnt hesitate to spend that kind of money for the more expensive servos, usually Savox, but, for a truck that doesn't see much use, im lost on why they wouldnt work.

 

[Sledgehog]

It's super easy to strip cheap metal servo gears if your wheel hits something at speed, even with a servo saver. I doubt your bots are going 35-60mph and mostly stationary or going pretty slow in comparison.

 

[biggman100]

It's super easy to strip cheap metal servo gears if your wheel hits something at speed, even with a servo saver. I doubt your bots are going 35-60mph and mostly stationary or going pretty slow in comparison.

My boats actually average 40MPH. My Proboat Zelos (https://www.horizonhobby.com/boats/electric-boats/zelos-36-twin-catamaran-bl-rtr-prb08021) has been clocked at 54, and even my UL 19 (https://www.horizonhobby.com/produc...c-boats/ul-19-30-inch-hydroplane-rtr-prb08028), on 4S averages 45 (i have never run it on 6S, which they say it will do 60+). I run power boats mainly. I have one sail boat, one tug, 3 fast catamarans, and two deep v hulls that average 35 to 40, so, yeah they do tend to get that fast. The TFL Zonda-R 41 does 70-75 out of the box on 12S (one 6S pack per motor/ESC). I don't have one yet, but that is my next mission, to have one by next year. I do know a guy that does have one though, and my Zelos cant even come close. I think the big issue here is a bit of a misunderstanding though. I don't run my trucks at anything above stock, so, for example, the Senton im getting, it will be run on no bigger than a 5000MAH 2S 50c gensacearespammers battery. My fury, even though it has a Castle Sidewinder SCT, has never been run on anything bigger than the gensacearespammers i use in all my trucks, so, i doubt any of my trucks will see much above 25-30, ever, since i have no interest in 3S power in a land vehicle.

 

[Sledgehog]

I literally thought you meant small robots... your post said bots LOL. And again, it's a big difference between a boat going through water and a land vehicle grazing a large rock or tree at 25-30+mph turning the wheel against its will. Your cars at stock speeds will reach that easily. I've stripped servo gears just grazing the pipes on the side of a track going no more than 10-15mph with it.
You asked, I answered. If you want to disagree fine but these are the reasons.

 

[biggman100]

I literally thought you meant small robots... your post said bots LOL. And again, it's a big difference between a boat going through water and a land vehicle grazing a large rock or tree at 25-30+mph turning the wheel against its will. Your cars at stock speeds will reach that easily. I've stripped servo gears just grazing the pipes on the side of a track going no more than 10-15mph with it.
You asked, I answered. If you want to disagree fine but these are the reasons.

I wasnt disagreeing, i was just trying to clarify. I will be the first to admit, i don't know a lot about RC vehicles, except how to break them, so, the more i learn, the better. I typically buy a vehicle, bash on it for awhile, and, if it breaks, i might fix it, or it might just sit in a closet for the next few years. I fixed the message so it said boats. With boats, i think i have only replaced one servo in ten years, and that one, if i remember right, cost around $12 at most. I tend to break rudders more than anything else. These are the ones im looking at. I have a deal through a boat site where i can get 4 of them for $55: https://www.amazon.com/ZOSKAY-DS321...QQ4D95GP1KT&psc=1&refRID=156YYEAX7QQ4D95GP1KT

 

[Jerry-rigged]

Cheap metal gears are still better than cheap plastic gears.

On servo speed - I have found that servos slower than .15s make it harder to counter steer. I try to not buy anything slower than that. Also watch the voltage. If it is .12s at 7.4v, but you run 6v or 5v , it may not be fast enough. Too fast? My fastest serving was 0.8, and it was not too fast. I hear that around 0.6s, the servo can make the car start to feel jittery, though.

 

[biggman100]

Cheap metal gears are still better than cheap plastic gears.

On servo speed - I have found that servos slower than .15s make it harder to counter steer. I try to not buy anything slower than that. Also watch the voltage. If it is .12s at 7.4v, but you run 6v or 5v , it may not be fast enough. Too fast? My fastest serving was 0.8, and it was not too fast. I hear that around 0.6s, the servo can make the car start to feel jittery, though.

All the specs for them are listed in here, up above. It says 0.14s at 6.8V. I always run 7.4V 2S lipo's in my cars, but, it doesn't seem to list the speed for those. For comparison, and to get an idea, i used the specs from my Warhawk as a starting point, which are: 0.17 sec/60 deg @ 4.8V; 0.14 sec/60 deg @ 6.0V, 70 oz-in (5.0 kg-cm) @ 4.8V; 80 oz-in (5.8 kg-cm) @ 6.0V. The other servo says it is: Stall Torque (5V): 19 kg/cm (263.8oz/in), Stall Torque (6.8V): 21.5 kg/cm (298.5 oz/in), Speed : 0.16 sec/60°(5V) / 0.14 sec/60°(6.8V), which is where i got lost. The speed is the same, but, the amount of force is larger on one vs the other, and i honestly have no clue what it means. For boats, when and if i ever need a servo, i just go by the recommended one listed in the manual. I have allso found some 25KG ones that show specs for 7.4V, and the speed is the same as the other two.

 

[Sledgehog]

The voltage listed on servo stats is from your ESC/BEC output, not the battery. It should list its voltage somewhere in the manual or online. Usually they come stock at 6v and anything higher such as 7.4v requires additional hardware like a BEC.
For example, the Arrma BLX185 and BLX100 ESC has an output of 6v.

 

[biggman100]

The voltage listed on servo stats is from your ESC/BEC output, not the battery. It should list its voltage somewhere in the manual or online. Usually they come stock at 6v and anything higher such as 7.4v requires additional hardware like a BEC.
For example, the Arrma BLX185 and BLX100 ESC has an output of 6v.

Im using this ESC: https://www.amazon.com/dp/B00P8CQYZ...olid=1BOM3IFZAG0S0&psc=0&ref_=lv_ov_lig_dp_it
Which according to HobbyWing, has a 6V/2A linear mode BEC. So, then i should be looking at the speed at 6V? Some of the servos, like the Savox i looked at, just to compare, showed speed and torque at 6V and 7.4V.

 

[Jerry-rigged]

Yes, if the BEC voltage is 6v, then only look at the 6v specs.

Some esc can adjust the bec, for those you can up the voltage to get more power and speed out of the servo.

 

[biggman100]

Yes, if the BEC voltage is 6v, then only look at the 6v specs.

Some esc can adjust the bec, for those you can up the voltage to get more power and speed out of the servo.

For a 2WD or 4WD basher (for example, my Fury, Senton, or Warhawk), what exactly would having a faster servo really do? Would it shorten the turn radius, or would it just cause the wheels to turn and then the truck slide? I know, on boats, if you turn the rudder too fast, it can snap the rudder, depending on the boat. On some, a fast rudder can cause violent turns which then become violent crashes.

 

[Sledgehog]

It would be more apparent in a racing situation when cornering at speed and correction needs to be done more quickly or needing to "throw" your back end out over a jump to take an immediate turn on the track. For general bashing you won't notice much of a difference at all. You should be more concerned with the torque kg and just making sure it's strong enough to move the tires you want to move easily

Again, a land vehicle is a totally different animal than a boat. Turning too quickly is going to put a whole hell of a lot of force instantly on the rudder due to the water hitting it while a car's wheels will just 'skip" over land if turned too quickly (i.e. oversteer)

 

[Jerry-rigged]

IMHO, for a 2wd, having a speedy servo is more important vs 4wd. With a 2wd, you counter steer a lot - the quicker the servo can go lock to lock, the better you can catch the back end before it comes all the way around. I have a 2wd Torment, and for a while had a .20s servo in it - the back of the truck could come around faster than the servo could swing. Makes it mostly impossible to control in loose dirt.

 

[Sledgehog]

Yeah a .20 is pretty darn slow. usually the average range of "good enough" is round .14-.16. I have a savox 1210sg in my talion with .15 @ 6v and it's great on the track. Same with my Rustler which is 2wd and has the stock traxxas piece of crap with a savox metal gear set in it. That's .16 i believe and it's 'fast enough" for sure.

 

[slick2500]

I can assure you that once you get to 0.16 and slower for the speed, you can see and feel the difference when driving. I have a servo that is rated at 0.18 @5v that I run in my Summit and Omg they are soooooooo slow compared to the same servo running at 0.14 at 7.4v in my 4Pede.
And as far as the gears go in those cheap servos, I haven't had any fail yet but I have broken a few of the cases.

 

[Niz55]

Fan model fs-25 .

Extremely fast and torque.

$35 on Amazon .