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  1. #1

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    Read Before Buying a Savox Servo

    This is to help those who are interested in purchasing a Savox servo. Please add any information you may think is helpful.

    One of the most popular complaints with Savox servos is their tendency to draw too much current from the built in speed control's BEC. What this means in layman's talk is basically that the servo puts too much strain on the stock power supply. This thread will explain the symptoms of a Savox servo overdrawing current, why Savox servos do this, and the various solutions to this problem.

    -WILL THIS BE A PROBLEM FOR ME? IS THIS WHAT'S WRONG WITH MY CAR? If you haven't bought the servo yet, consider how likely you are that this may be a problem. If the vehicle is relatively light weight (5 pounds or under) and not a rock crawler, most of the time this won't be an issue. In more particularly demanding scenarios, such as rock crawlers or 1/8 scale RCs, a fix to the issue may be in need. If you already own a Savox servo and your car/plane/boat has started acting a little funny, more than likely it's your new, orange Savox servo. Acting "funny" can mean anything from glitches during normal driving, shortened radio range (although do be sure to check your antennae in this case), and/or poor servo performance. Continue reading for the appropriate "fix."

    -ARE THESE THINGS JUNK?! WHY DO THEY DO THIS? As someone who deals a lot with customers, it's understandable when a person who's just spent a good $50-70 on a pretty little servo can get angry when the Savox servo only seems to cause more problems, often glitching to the point of being undriveable, especially in heavier vehicles. The simple answer is no, Savox servos are not junk. Everyone has their own opinion, but they are one of the more well-known and well-thought-of brands out there, generally speaking. So why do they do this then? Well, the best answer I've found is not that they're inefficient, but the way in which they draw current. Unlike some of the other brands like Hitec, Savox servos tend to draw current from the BEC in a more jumpy, irratic fashion, for whatever reason. However, please understand that there is nothing "wrong" with the servo. It simply functions a little differently.

    -TELL ME HOW TO FIX IT!!!! The most important thing here is getting the issue fixed, or preparing for it to ensure everything runs smoothly. In RCs less than 5 pounds and excluding rock crawlers, most of the time a simple gltich buster will do the job. Glitch busters are manufactured by Savox, Novak, Castle, and Venom and generally range between $5-25.These pieces of equipment are simply capacitors prewired to plug right into any extra slot of your vehicle's receiver. The glitch buster counteracts the Savox's tendency to draw large amounts of current at once by providing "help" to the built in BEC. The advantage to using a glitch buster is that it's a breeze to install (literally plug it in and you're done). The only downfall is that since the glitch buster is simply a capacitor, it can only hold and charge and then release it when the servo needs it most, it cannot actually put extra electrical current into the circuit, which brings us to our other option. The second option is an external BEC. A couple major manufacturers of external BEC are HobbyKing and Castle, usually ranging between $5-30. An external BEC simply adds extra juice to the system to help power the hungry little servo. The advantage of this over a glitch buster is that this can actually substantially increase the servo's performance because it is adding extra power to the system. Most external BECs are also tunable (the user can change the voltage at which they operate which can increase a servo's reaction speed and torque). The downfall of choosing a BEC is that they are more work to install and are bulkier. Generally on rock crawlers and any RC weighing over 5 pounds, a BEC is the way to go with a Savox servo. Depending on the specific model, check to make sure you wire it properly, and note that soldering is generally required to be installed.

    A few links to the products mentioned above.
    -Glitch busters:
    http://www3.towerhobbies.com/cgi-bin...&I=LXNRE0&P=ML
    http://www3.towerhobbies.com/cgi-bin...&I=LXEBGH&P=ML
    http://www.horizonhobby.com/products...buster-VNR1654
    http://www.horizonhobby.com/products...k-CSE011000202 (requires soldering)

    -External BECs:
    http://www.horizonhobby.com/products...c-CSE010000400 (requires soldering)
    http://www.hobbyking.com/hobbyking/s...cessories.html (requires soldering)
    http://www.hobbyking.com/hobbyking/s..._for_Accs.html (requires soldering)
    Last edited by thehuntingterminator; 03-12-2014 at 08:33 PM.
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  2. #2
    SyCo_VeNoM's Avatar
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    Why no mention of HobbyWing UBEC's they are usually readily available in a variety of current ranges, and IMO pretty high quality

    Its seriously a crying shame what those companies are charging for a 25-50 cent capacitor... (specially CC... but hey their stuff must be made by magical elves who get paid a lot of money to need to sell that junk at that price)
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  3. #3
    Maj_Overdrive's Avatar
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    From what I have read Spektrum receivers seem to be the most likely to suffer from glitching with Savox servos. Spektrum receivers seem to be the most voltage sensitive and can actually shut down and turn back on if the voltage goes low enough. At least that's the case with the older ones, pre-sr3300 vintage.

    The reason glitchbuster caps and External Bec's work better comes down to amp capacity and voltage drop under load. All power sources have limits as far as how much voltage and how many amps they can put out. Draw too many amps and voltage drops. When voltage drops too much glitching occurs and servo performance suffers. Glitchbuster caps momentarily provide additional amps when needed so voltage won't drop as much if at all. External Bec's generally have a greater amp output so voltage won't drop under load. If you have a High Voltage servo and your esc internal Bec isn't capable of 7.4 volts an external Bec is your only choice to get that voltage.

    A great example is my nephews brushless LST. It has the stock JR590 servos and some LEDs with a Castle MMM esc with an internal bec rated at 5.1 volts and 5 amps. Servo performance was sluggish and the LEDs would dim whenever the wheels were turned even with the wheels off the ground indicating the Bec voltage was dropping under load. I then added a Castle 10amp external Bec and when set to the same 5.1 volts the LEDs would still dim but not nearly as much and servo performance improved. Since the JR590's are rated to 6 volts I set the Cadtle Bec to 6.1 volts and was really impressed. The LEDs don't dim at all and servo performance is a night and day difference. The servos can now turn the wheels when they're on the ground and have a proper response instead of that underpowered RTR feel.


    I don't want to get into whether Savox are actually amp hungry and why as I don't own any. But I am curious how you came up with the statement about Savox drawing their power in a jumpy fashion instead of spread out more evenly. To determine that is in fact the case you'd have to hook up an oscilloscope and operate the servo to plot the amp draw over time. A multimeter will only tell you the peak amp draw during spikes and you can get an idea of average draw but not of it draws it's power in lumps or more evenly.

  4. #4
    SyCo_VeNoM's Avatar
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    Quote Originally Posted by Maj_Overdrive View Post
    From what I have read Spektrum receivers seem to be the most likely to suffer from glitching with Savox servos. Spektrum receivers seem to be the most voltage sensitive and can actually shut down and turn back on if the voltage goes low enough. At least that's the case with the older ones, pre-sr3300 vintage.

    The reason glitchbuster caps and External Bec's work better comes down to amp capacity and voltage drop under load. All power sources have limits as far as how much voltage and how many amps they can put out. Draw too many amps and voltage drops. When voltage drops too much glitching occurs and servo performance suffers. Glitchbuster caps momentarily provide additional amps when needed so voltage won't drop as much if at all. External Bec's generally have a greater amp output so voltage won't drop under load. If you have a High Voltage servo and your esc internal Bec isn't capable of 7.4 volts an external Bec is your only choice to get that voltage.

    A great example is my nephews brushless LST. It has the stock JR590 servos and some LEDs with a Castle MMM esc with an internal bec rated at 5.1 volts and 5 amps. Servo performance was sluggish and the LEDs would dim whenever the wheels were turned even with the wheels off the ground indicating the Bec voltage was dropping under load. I then added a Castle 10amp external Bec and when set to the same 5.1 volts the LEDs would still dim but not nearly as much and servo performance improved. Since the JR590's are rated to 6 volts I set the Cadtle Bec to 6.1 volts and was really impressed. The LEDs don't dim at all and servo performance is a night and day difference. The servos can now turn the wheels when they're on the ground and have a proper response instead of that underpowered RTR feel.


    I don't want to get into whether Savox are actually amp hungry and why as I don't own any. But I am curious how you came up with the statement about Savox drawing their power in a jumpy fashion instead of spread out more evenly. To determine that is in fact the case you'd have to hook up an oscilloscope and operate the servo to plot the amp draw over time. A multimeter will only tell you the peak amp draw during spikes and you can get an idea of average draw but not of it draws it's power in lumps or more evenly.
    Oscilloscopes plot voltage over time not current draw you would have to know the internal resistance of the servo to figure out its current draw from that using Ohms law.
    Last edited by SyCo_VeNoM; 03-12-2014 at 11:11 PM.
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  5. #5
    Maj_Overdrive's Avatar
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    Quote Originally Posted by SyCo_VeNoM View Post
    Oscilloscopes plot voltage over time not current draw you would have to know the internal resistance of the servo to figure out its current draw from that using Ohms law.
    Really? You'd think with all the different functions they have it could plot amps over time. The last time I looked at an oscilloscope was over 15 years ago in some HS electrical engineering classes I took. Either way you'd need more than a multimeter and some way to plot over time to determine how the servo draws it's amps.

  6. #6

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    Thanks for the input. Anything that could be helpful to a newcomer is always appreciated. Someone on another forum did a test which seemed relatively accurate and that's where I got my statement about how Savox's draw current in a jumpy fashion, but I could be wrong. However, that does seem to make sense, and would explain why a simple capacitor makes so much of a difference. If they were just extremely power hungry, I would think that a capacitor would do very little to nothing at all because they would not be aiding in providing extra current for the BEC, which in my experience hasn't been the case.
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  7. #7
    Maj_Overdrive's Avatar
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    Quote Originally Posted by thehuntingterminator View Post
    This is to help those who are interested in purchasing a Savox servo. Please add any information you may think is helpful.
    Btw. Nice informative writeup.

    I've done some servo testing as well, just using a multimeter to measure amps and an adjustable voltage power supply. When measuring amps with a multimeter you can get an idea of average amp draw and also peak spikes but the amp draw changes too much and too fast to know anything more. To determine if amp draw is lumpy or smooth it really needs to be plotted out on a graph against multiple other servos. That was my point, not trying to discredit anyone's results especially when I don't know the procedure used to get them.
    Last edited by Maj_Overdrive; 03-13-2014 at 09:21 AM.

  8. #8

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    Quote Originally Posted by Maj_Overdrive View Post
    Btw. Nice informative writeup.

    I've done some servo testing as well, just using a multimeter to measure amps and an adjustable voltage power supply. When measuring amps with a multimeter you can get an idea of average amp draw and also peak spikes but the amp draw changes too much and too fast to know anything more. To determine if amp draw is lumpy or smooth it really needs to be plotted out on a graph against multiple other servos. That was my point, not trying to discredit anyone's results especially when I don't know the procedure used to get them.
    Thanks man I appreciate it. If anyone thinks it's good enough this could be made into a sticky so it could be more easily found. I could also edit it and add any information that y'all think should be added.
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  9. #9
    SyCo_VeNoM's Avatar
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    Quote Originally Posted by Maj_Overdrive View Post
    Really? You'd think with all the different functions they have it could plot amps over time. The last time I looked at an oscilloscope was over 15 years ago in some HS electrical engineering classes I took. Either way you'd need more than a multimeter and some way to plot over time to determine how the servo draws it's amps.
    Well to read current you would have to have a device mounted in series.
    I will be honest when I read what you wrote I was like what the.. did they make a new oscilloscope that can read current now? So I had to go double check as I know my 30ish year old one couldn't(got it for $5 ), and I knew last time I used an up to date one (roughly 10 years ago when I got a B.S. EET) they added a ton of new heavily needed features like the ability to play Asteroids, or Tetris so I figured they might have had some other advancement that I wasn't up to date on since.
    With great speed comes greater repair bills.
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  10. #10
    Maj_Overdrive's Avatar
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    No offense but I doubt this will make it into a sticky and I wouldn't make it one either. It's currently centered around Savox, a specific brand. If it was about internal and external Bec's, servo draw and performance with maybe a reference to Savox then it would be knowledge for everyone instead of a Savox help guide. In the interest of a Bec guide I'm including some more information in this post.

    Like I said, I've never owned a Savox but they do seem to be more power hungry from what I've read. You gotta remember servos have 2 parts that consume power. The control/positioning circuit has a constant draw that doesn't change. The other is the motor which actually moves the servo and the power it consumes is variable based on load. If you've ever seen an Eageltree graph or Castle data log you know electric motors don't consume a constant amount of power and the power consumed is highest when the load is highest. This is generally when moving from a stop. The same is generally true of a servo, except that the load is highest when the servo is stalled.

    The servo testing I did was with a simple multimeter set to measure amperage with the radio system powered by a variable voltage power supply set to 6 volts. I tested a total of 4 servos, all JR and Hitec, all installed for steering in a TMaxx with the stock tires both on and off the ground but all testing was done while stationary. Average amp draw was between .5-.75 amps when moving the wheel smoothly and not changing the direction of travel rapidly. When moving the wheel in one direction and then rapidly changing the direction midtravel, I'd see spikes from 1-1.25 amps. When the servos were stalled (full lock with endpoints set too high) amps would spike to between 1.25-1.5 amps. Readings were consistent between all the servos, the biggest difference between the most efficient and inefficient servo I was able to observe was .2-.3 amps.

    Bearing this testing in mind there are 2 possible explanations for Savox servos drawing more power. First is that they are not as efficient as others on the market. The second possible explanation is that they draw their power less often per second but in bigger gulps. I'm not sure how or why they'd do this as decreasing the frequency at which they draw power reduces response time because the servo can't move without power. It also would put a bigger strain on the Bec. It just doesn't make much sense. But the only way to prove they draw power less frequently per second is with equipment more advanced than a multimeter.
    Last edited by Maj_Overdrive; 03-13-2014 at 12:07 PM.

  11. #11
    Maj_Overdrive's Avatar
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    Quote Originally Posted by SyCo_VeNoM View Post
    Well to read current you would have to have a device mounted in series.
    I will be honest when I read what you wrote I was like what the.. did they make a new oscilloscope that can read current now? So I had to go double check as I know my 30ish year old one couldn't(got it for $5 ), and I knew last time I used an up to date one (roughly 10 years ago when I got a B.S. EET) they added a ton of new heavily needed features like the ability to play Asteroids, or Tetris so I figured they might have had some other advancement that I wasn't up to date on since.
    Do you mean you have to add a device to the scope? Or the more obvious answer, which is to put the device you're reading (servo in this case) in series with the scope?

    Edit: Nevermind, I stopped rushing and actually read your post again. Can't believe they haven't built amp reading into a scope yet.
    Last edited by Maj_Overdrive; 03-13-2014 at 12:13 PM.


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