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Peak or Stalled Current Draw On Common Servos
  • Question #1.

    Does anyone know a source for finding out current draw of servos under load?  I do not see this data being posted on the manufactures websites.  I downloaded a database from a French website but I do not know how current it is.  I don't think it is because it doesn't list many of the current poplular servos on the market today.

    Any help with that would be appreciated.

    My next question has to wait on the results of the answer above.


  • Hi. That is a question that I tried to answer when I was working on my RC calculator. My conclusion at the time was that 2 amps was the typical maximum that they can handle. Of course, that is going to vary a lot between different servos. It should not be too hard to create a harness and measure the currents using a multimeter.

  • Thanks Carlos and I'm sure it wouldn't be hard to make a harness, but I would have to purchase a ton of servos, some I'd never use and I simply could not afford to do that.

    As with many brushless motors and their prop data, I have to believe someone, somewhere has done just that and posted it on the WWW.  The hard part is locating that data.

    Does anyone have any leads or tips?


  • Carlos,

    I was thinking, if I did decide to creating a database on servo draw with all the servos I purchase from here on out, what amp and voltage meter do you recommend? I don't mind spending money on decent equipment since I subscribe to the theory of "buy quality once" when it comes to buying tools.

    Thanks and I'll do some digging on how this can be accomplished without too much trouble.

  • I own two multimeters. One is a pretty old JDR Instruments. A couple of years ago I got a high end UEi. Truth is, I am happy with both. I paid about $250 for the UEi, but I'm sure you can get a decent multimeter for less. This blog publishes good reviews:


    On the servos, I have found that smaller and/or less expensive ones are less efficient. But you probably already knew that. You are out on the west coast, right? There are some big RC clubs out there - borrow servos for testing. But come up with a good testing procedure first.

  • To really test servos, you would also have to measure travel range, speed, torque, idle current, and centering accuracy. Now things get a lot more complicated!

  • Thanks Carlos!  Appreciate the info.  The info that I need is the in use amp draw and the stalled amp draw, but I'm sure as I get deeper into this, I may want more data.

    That is a great idea.  I am and/or have access to a number of clubs in my area.  I'm sure I can get a lot of different servos to borrow.

    Thanks again and I'll keep you posted on progress.  It may take me some time to get this going.

  • Quick update for those following in my footsteps.  I got this all figured out and had all the stuff I needed to do this already with my my RC goodies.  I didn't have to order anything.  To do it right though, I do need to go by Home Depot and get some wood to build a test stand but that's it.

    I'll post pics when I get it all set up.

    No more guessing on whether to use an external BEC and no more brownouts or potential crashes.  Just think of all the crashes that could have been avoided if data like this was already on the WWW.

  • That sounds great!

  • I'm bummed out.  I need to amend my last comment.  The wattmeter I was using to record amp draw is not sensitive enough.  One time it will give an amp draw number, power down and back up and it will give a different number.  Back to research.  I need to find a good meter.  Looking to see what I can find based on your link above.

  • UEi makes very sensitive meters and they are an excellent value. The Fluke instruments are very popular, but in my opinion they make more sense when they are in a commercial lab where they get used every day. For the accuracy they give you, Flukes are expensive. This is the UEi I have:


  • Thanks for the link and info Carlos.  I was pricing the Flukes but they were too expensive for me.  The meter you have seems like a very nice.  I watched the meter shootout from EEV and bought the one Dave recommended which was the BK 2709B.  

    It should be here Tuesday and now I just need to make some adapters and I'm ready to test servos.  Going to Home Depot today to get some wood to build my test stand.

  • That BK is a nice meter. Good choice.

  • Thanks Carlos.  It came in the mail already!  haven't had a chance to make the adapters yet.  Perhaps this week sometime.

    I did build the servo tester box.  I used pine and popular wood and then "stained" it with Old English.  It looks like a piece of furniture now.  It really came out that well.  :)  Now I just have to install the dowels that will hold the rubber bands on it for servo resistance.  

    I'll post a photo when I am finished just in case someone else wants to experiment with servo current draw.  This really has been an excellent learning opportunity for me.  I'm glad I have decided to take on this challenge.

    When I get up and running I'll even make a short video of my test parameters.

  • All of that sounds fantastic. When I needed a work table a few years ago, I went and bought a solid wood door at Lowe's for something like $50. Then I got a quart of a boat deck stain and put about ten coats on it. It still looks incredible.

  • @ Murcoflyer, (or Carlos)

     Was the BK fast/sensitive enough? I did have access to one of the (better?) Fluke Clamp-On meters (a neighbors) that was capable of reading such fast voltage spikes but the screen would not show all the numbers and before he could repair it, he moved. The new neighbor has an older Oscilloscope that I could possibly gain access to. I don't know if that technology can be used in this case, I ASSofU&ME it can. The learning curve can't be that difficult since I can add 4 + 2 and get 4.2 like everyone else. I'd sure like to check my Hitec's and Solar's at least to see how close I am to my UBEC limits. Hope Murcoflyer hasn't overdosed on test results.

    michael clyde

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