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wonko

Servo Help

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First off, thanks again to all who responded to my other post about my first build.

I do have a question about servos.

I've been shopping different brands and models and I understand some servos are high torque whilst others are high speed.  My assumption is this is the same terminology as applies to motors.

However, I see Futaba has high torque servos and "high power" servos.  Is that the same as high-speed?

Also, what brands do you recommend for quality?

 

Thanks!

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3 hours ago, wonko said:

First off, thanks again to all who responded to my other post about my first build.

I do have a question about servos.

I've been shopping different brands and models and I understand some servos are high torque whilst others are high speed.  My assumption is this is the same terminology as applies to motors.

However, I see Futaba has high torque servos and "high power" servos.  Is that the same as high-speed?

Also, what brands do you recommend for quality?

 

Thanks!

I think manufacturers use them synonymously, but I prefer to look at what the actual specs say. My preference is speed over torque- anything less than .10 is good. Most servos give at least 4 or 5 kg torque, which is plenty for my bashing purposes. Depending on application/size of wheels etc anything around that mark should be fine I would think. Also, without end point adjustment, using very high torque servos could potentially damage chassis, servo housing and other parts of the car due to the servo trying to travelling further than it needs to to achieve full lock, and having the force/power to actually start damaging stuff.

Savox are very good servos - can be pricey, but worth it (also a good buy secondhand). Ultimately, depends how much you wanna spend. You can get servos at the cheaper end (sub 10 quid) that may suit your build/driving and be perfectly fine. Then there is the 15 - 30 quid bracket which are generally faster, stronger and more powerful (metal gears, ball bearings etc) and then there are the 40 quid plus - more aimed at your serious racer/crawler. I have 3 savox that I've had without issue for a number of years from the 40 quid plus bracket. I have a number from the 15-30 quid bracket that have also performed without issue. Some of my cheaper ones have had to be replaced, but they tend to get the most abuse (my kids' cars), so...personally, I would go for the 15 - 30 quid bracket, which should afford decent specs and build quality, without paying silly money (some servos are 100 quid plus...) because unless you're racing in the a final every week, I don't think you'd notice much difference in performance between mid price range servos and high end servos.

Edit- just to add; I bought one of these last month for cougar 2000 restore. It is very good for the money and appears to be on a par with the more expensive savox. Whether the specs are 100% i couldn't tell you - but it is certainly fast with plenty of torque. Build quality seems good. Now it is just a question of how long it will last. No reason to think it will go boom anytime soon, so I'll see how it goes 👍

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As stated, depends on your budget and how often you intend to use it. Sub £40 I'd go for the Core RC 9008, 9kgs torque (so plenty of turning  power), 0.8 sec (so plenty quick enough), digital, and metal geared. Slightly above that, Savox make good servos for about £50 (I have a 1258), also look at Alturn, stock levels can be hit and miss (in UK) but pretty good servos.

The way I justify spending a bit more on parts is, the more times you use it, the cheaper it gets. So if you see yourself using it a lot, invest that little bit more.

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"Quality" in brands is more like "consistency."  Not necessarily faster or stronger.  As other members said already, I would look at torque and speed, rather than brand.  

I've used more than a dozen Futaba servos in the 80s and 2000s, but now?  There are better things out there.  For example, I think cheap $4 servo (yes, that's Four dollars) from Hobbyking is just as good as Futaba S3003 that I paid $30 decades ago.  But cheaply made Hobbyking servos are not consistent. If I buy 3 servos, they might not have the equal speed.  Which is fine for bashers because they are still faster and stronger than Futaba S3003.  On the other hand, $60 Savox servo was glitchy, so I end up going with something 10 time cheaper.  

The very old "standard" servo was Futaba S3003.  4kg torque, 0.19 second to turn 60 degrees. $4 Hobbyking servo has 4.3kg torque and 0.17 second speed at 6v.  It's slightly better.  I use that as the new (minimum) standard. 

If you want more torque, $10 Hobbyking High Torque servo has 12kg torque, but slower at 0.22 second.  Instead of spending $60 for my Savox, I should have spent $20 for JX 4409MG servo which is about the same (9kg torque 0.11 sec speed).  Those two JX servos I got, don't glitch.  A lot of 20kg servos you see on Amazon have 0.14 sec speed.  For about $20 you can get a servo that's 5 times stronger and still faster than "standard" servos.  I like the 20kg servo too.  

Most of my bashers have either old Futaba, Hobbyking, JX, Turnigy, Tactic and other no-name servos.  I probably won't buy another Savox, but that's just me (I built a small glitch buster which didn't kill the glitch. So I bought a bigger one. I haven't tried it because I've got other servos).  But if you want a shiny servo that's stronger and faster, JX 4409 MG might be a good starting point.  

 

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Okay, so from what I understand:

  • 'Speed' is response time measured in seconds and the lower the number, the better.
  • 'Torque' is the amount of force which can be applied for steering.

@Silver-Can, you mention 4-5kg is plenty.  However, the servo you purchased is 25kg for the aircraft.  I assume you need that much torque for flight controls?

For a 1/10 rally and 1/10 on-road, what should I really look for?

Also, the batteries are 7.2V.  Looking at the Savox servos, they come in 6V and 7.4V.

Does this matter?

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@wonko you are correct  - it is a 25kg torque servo, although it is fitted in my schumacher cougar 2000 car rather than my rc aircraft. To be honest, it is massively overpowered for what I need it for - the cougar 2000 is a light, 2wd drive race spec car from the mid 90s - and it is only because I can adjust/limit the 'throw' of the servo to stop it from travelling further than it needs to that I have it installed. When first installed and prior to adjusting, the throw was such that going to full lock led to massive buckling of the steering support posts and potential damage. 

My personal view is that something around 5 kg would be enough for something like the grasshopper as this is a light 2wd vehicle with small and relatively skinny front wheels. Obviously, the bigger and heavier those wheels and tyres get (think monster beetle, madbull, clodbuster etc) the more oomph needed to shift them

The stated voltage for servos indicate how they will perform at those differing voltage. Typically, higher voltage, better performance. It refers to the BEC output voltage from your receiver, rather than your battery. Basically, your electronics get their power from the receiver, rather than the 4 AA batts like back in the day. As long as the BEC on your receiver can output 6v you will be ok. That said, some of the high spec high power servos can be power hungry, requiring more v than your receiver can give, resulting in electrical brown outs. This is why it is important to look fully at specs of servos/ESCs/receivers etc to ensure they can all work together without creating bottlenecks. 

So the savox you mentioned will operate between 6v and 7.4v. This is supplied by the BEC from your receiver. The battery plugs into the ESC, the ESC plugs into the receiver and then the receiver takes some of the battery v as BEC. The savox will operate more quickly with 7.4v than 6v (it may still operate with lower v too, only more slowly).

I know this all sounds like a bit of a mine field, and it does take a bit of getting your head around but once you get that, it's relatively straightforward. 

I guess the best thing to do would be post up what ESC, servo, rx/tx, motor and battery you're planning to use/buy and in what vehicle so that we can advise accordingly 👍🙂

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What are you using your cars for? I run savox 1258TG in my race buggies and they are worth every cent. They have lasted years and they're fast and strong.

You can't have too much torque (unless the end points are wrong and it can break stuff), but I look for around 10kg give or take for mine. That is plenty and allows for overstated specs in cheap servos. I had a Futaba S3003 in a monster beetle and it ran fine, despite low specs.

Speed, I aim for around .10sec, faster the better. I can slow it down with my transmitter but I havent done that.

Its a shame shipping is so bad now, as Banggood sell JX and SPT servos. JX are the OEM for a lot of other brands too but half the price. The JX 4409MG is cheap and works well, I have 4 of them. About USD13 from Banggood. It's become my go to for my bashers.

Oh yeah, as far as voltage goes. 4.8v used to be standard (4x AAbatteries). 6v was normal and now you'll see HV servos, which are rated at 7.4v. Thats the nominal voltage for 2S lipos so they should handle a 2s lipo fine. My nitro buggy runs a 2S receiver pack giving the full 8.4v to the receiver (rated at 7.4v but works fine) and the servos then take the full voltage too (pretty sure the rx doesnt have a BEC builtin but someone may be able to correct me?).

All my electric cars I run a 6V BEC as I don't need more, and all my servos are rated to 6V

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