Asked — Edited
Resolved Resolved by Rich!

No Response To Gws Servo

Afternoon All

I'm stumped.

I'm trying to make a connection with a non-EZ GWS servo but am having no luck. I've tested the EZ with standard servos that came with the kit and they function fine. This GWS is rated at 4.5 volts to 6 volts and I've tested it at these and even lower. The port is correct, the board is properly selected, I restarted the EZ, insured I have the latest version but still get no movement or indication a signal is reaching the servo. It doesn't appear locked because I can turn the gears by hand. I'm hesitant to take it apart just yet.

Any suggestions?




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  1. Are you sure the servo is plugged in correctly?
  2. Have you made sure the min and max settings in your servo are 1 - 180 respectively? Assuming you are using an EZB4.... 1 - 100 if using an ezb3
  3. Do you have another one to test in case this one is defective...
  4. Are you sure your connected to ARC
  5. What battery are you using?
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It's an obvious question but it's best ask, have you connected the servo to the EZ-B the correct way round? Also trying a servo under its rated voltage won't help at all. If anything you could try a slightly higher voltage. A 4 to 6 volt servo will work ok with a 7.4 LiPo battery for example. Also have you checked the min and max values?

  1. Are you sure the servo is plugged in correctly? White servo wire to white port

  2. Have you made sure the min and max settings in your servo are 1 - 180 respectively? Yep

Assuming you are using an EZB4 1 - 100 if using an ezb3 EZB4

  1. Do you have another one to test in case this one is defective... Nope but the standard servos that came with EZ work from that port

  2. Are you sure your connected to ARC Yep 5)What battery are you using? Adjustable Work Bench tester. I've been hesitant to increase the power beyond 7.5.


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I wouldn't go beyond 7.4 volts. You say you are using a bench power supply. I would ask if it's suppling enough amps, but I take it that's what you used to successfully control the EZ Robot servos?

Have you got a multimeter laying around to check if the servo/servo wire is ok?


You may need to use a battery... If your work bench power supply can't provided enough amps then the servo won't move.... Can you confirm that the ez robot servos do indeed work with your current setup... Also double check you haven't plugged in the GWS servo backward... White to white may not match up as the signal wire...


I had another look at the servo in question... White to white looks correct... Check again that an ez robot servo works then plug the GWS in again....


Your servo may be defective... Your setup should work unless as mentioned the servo is duff.... However, try a battery in case the servo needs more juice than the EZ Robot servos do.... 7.4v battery briefly should be ok.... As DJ said, he has never had a servo that couldn't take 7.4V....


Thanks for all the advice guys. Here is where it stands:

Switched to a battery and got no response. So I changed all wires but still nothing. Then I connected the servo directly to the EZ board including power and ground (all 3 wires) and got momentary control but then the board broke the connection with my laptop. Repeated testing had the same problem including when I tried a second board.

All EZ servos work fine so I'm assuming the board is operating.

Perhaps I should be making additional ground connections between the EZ port, my battery, and the servo?


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I don't think a "common ground" will help you unless using a separate supply. The ground ports on the EZ-B are in series, so the battery and servo will be using the same ground connection. No additional ground should be needed as its already making a commen ground connection.

What battery did you use with your testing earlier, and was you using the battery when you finally got a response, or did you switch back to the bench supply?

If the dev kit servos are still working, then you are correct and the EZ-B is fine.

You also say that you have now connected the servo directly to the EZ-B. How did you have it connected before?


I am confused... You should be plugging the GWS servo directly into one of the 3 pin digital ports of the ezb... Have you not been doing this? What have you been plugging it into if it wasn't the ezb4? If the ezb disconnects it usually means a brown out... This means something is sucking the power away from the ezb so it disconnects from ARC...

  1. Plug the GWS servo directly into one of the ezb4 ports...
  2. Power the ezb with a good Lipo or niMh battery... you need amps here
  3. Use a generic vertical or horizontal servo control set at 1 min and 180 max
  4. Slide the servo control back and forth to try and make the servo move

just a thought some servos are wired differently check the wires in the servo plug Hope this helps

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If you had the servos ground and positive connected directly to the battery and white signal wire to the EZ-B, connect the ground and possitive servo wires the the EZ-B instead, and either use the bench supply and 6 to 7.5 volts using at least 5amps or more (the EZ-B can take 20amps), or depending on your battery type and voltage, insure the battery is fully charged before testing the servo again.


@Steve... I am still seriously confused why isnt the op just plugging the servo directly into the ezb4 and then use a rechargeable battery like a lipo or nimh with the ezb... Why all the wire bypass stuff?

@geoffhitch we have already been over that, doesnèt seem to be the problem

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That's what I'm wondering. It wasn't until he mentioned "plugged directly to the EZ-B" I remembered he also said "connected White to white" with no mention of anything else, which got me thinking that he may have been powering it straight from the power pack, in which case a common ground may be needed. Is that correct @mulberry ? What ever power you give the EZ-B is what comes out of the red VCC digital pins.


@Steve... Cool, I thought it was just me having a little too much of that Canadian beer tonight... LOL. It has to be either a power problem or a defective servo....

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Lol, My thoughts exactly. My money's on power as he said the did get the servo to move, briefly.


Just stepped out to buy gin so now I'm set.

See I created some dust-up. Sorry for the confusion

This heavy duty servo is to lift the bubble head of my B9 robot (several pounds). I wanted to reduce the power draw through the EZ (I have lots of components running through it) but now after working with the board I suppose that's unnecessary (fingers crossed). Let's step back and take this approach:

I have a GWS 6 volt servo I need to control. I've used a vertical servo control set at 1 to 180 degrees (to be modified later because of my mountings). Ports look good, proper board is selected, and power is from a bench power supply is set at 6V.

When I hit the center button the servo the board disconnects but I do get a wee bit of movement from the servo before that happens.


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If the board is disconnecting it's usually a sign of a power failure, often caused by drawing too much current.

However, if power is supplied by a separate source this shouldn't affect the EZ-B, it will only affect it should the same power supply be powering the servo and the EZ-B.

The EZ-B needs a common ground. double check the ground of the EZ-B power supply and the ground of the servo power supply are connected. Failure to have them connected will cause some faults.


@Mulberry .... Power problem... The servo needs more amps... You bench supply is probably not able to supply enough... Plug your ezb4 directly into a Lipo or niMh battery and try again....

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No worries mulberry. We're all friends here :P. When you hit "centre" the board disconnects. What happens when you try to move it when changing the min/max values. Does the servo try to move or does the board disconnect?

Putting the bench supply aside for a moment, what type/voltage battery do you have for testing the servo? I think the bench supply is what's causing the problems.


No worries mulberry. We're all friends here. When you hit "centre" the board disconnects. What happens when you try to move it when changing the min/max values. Does the servo try to move or does the board disconnect?

I tried Rich's advice with a battery source and connected the servo ground to the EZ ground. This gave me some control but movement was very jerky and the system disconnected often.

Putting the bench supply aside for a moment, what type/voltage battery do you have for testing the servo? I think the bench supply is what's causing the problems.

This latest test was with a 6 volt battery pack (4 Ds at 1.5 each).

Its got to be a power issue. I wonder if its the fact this is a heavy duty servo but at 6 volts EZ should be able to manage it. Maybe not.

Daniel confused

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The EZ-B can handle it. The HD's will need extra power (amps) for the extra torque. Also the batteries your using won't really be sufficient to power a servo, especially for the power in-rush servos use to start moving. When I suggestted using a battery earlier I was hoping you had a LiPo. A LiPo or similar really is your best options and really should solve the issue.


@Mulberry .... Plug the servo directly into the ezb.... no other wires nothing else attached to the ezb... Alkaline batteries (even D) cannot provide enough current either.... LOL... One more time... Use a Lipo or niMh battery plugged into the ezb...

So to recap...

  1. Plug your GWS servo directly* did I mention directly LOL...into any port on the ezb...
  2. Plug a ****Lipo or nimh **** battery into the ezb use 6v or 7.4v doesnèt matter

So just 3 things here... servo, ezb and powerful battery 3) Open ARC and connect... 4) use a horizontal or vertical servo control 5) Make sure the servo control reflects the port the servo is on 6) set min to 0 and max to 180 7) Save 8) slide the servo from position to position and watch the servo move...



This servo obviously needs a lot of juice...

  • alkaline battery.... No
  • bench power supply.... No
  • 7.4 Lipo.... ding, ding.... Hells yes!
  • 6v or 7.2V nimh.... ding, ding.... Hells yes!

Problem solved.... :)

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Let's look at it this way at whats been tried so far with actual servo movement...

We've gone from bench power, no movement at all. Then on to the D cell batteries, a bit of movement. So the next step in using a LiPo or nimh will yeald excellent results with a fully moving servo. like I said, I'd put money on it. ;)


Bazinga. I think we resolved it (at least it worked :D)

I separated power supplies for the EZ and the servo with 6 volts going to the servo, 6 volts to the EZ and a common ground between the two I seem to have full control with no drop in connection, and no jerky motion.

Huzzah! Second martini for everyone cool


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Nice job. At least you got it working now and you now know it was a power issue as I thought, and not the servo being faulty. :)


@Daniel, I'm glad you got this worked out. I knew it was a power issue. Hope out private discussions helped a little.



@Richard, There's nothing wrong with using a bench power supply if it can supply enough amps to provide the servo's power hunger. In fact it if it's large enough I would argue that it's a better and more stable source then any battery.

Also when supplying power to a large servo or motor I will always advise bypassing the EZB and run a separate power circuit to the motor. Why use the EZB as a power conduit and risk power starving it when the large motor starts sucking the juice?;) @Daniel, Remember that Amps and Volts are two different things. :)

The trick when either using a bench power supply or a battery is to make sure it will supply enough amps for your needs. Make sure you give your self enough overhead for any amperage inrush as the motor powers up.


@Dave ... I didn't say there was anything wrong with a bench power supply in general. All I was saying is the one that Mulberry was using didn't look like it was putting out enough juice... Minimum bench supply for revolution bots I would say is 20Amp... For my inMoov I would use a minimum of 50amp supply....

What I was trying to do was reduce or minimize all the variables that could have been causing his issues... In a sense get the everything down to the lowest common denominator (an ezb, the servo in question and a good battery).... Then work up from there.... If you have a million other things, wires, other servos, sensors and different power sources, etc hanging off the project it would be that much more difficult to trace the problem.....

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Just to note, the only reason why I suggested "putting the bench supply aside for a moment" was to do some back to basics troubleshooting using a tried and tested method which a lot of us have used, of testing servos using a battery. Mulberry mentioned that he has an adjustable bench power supply which I why I suggested using a higher amperage, but it looks like this supply didn't have an option to change this. Even though I didn't know at first what batteries Mulberry had, D cell batteries were used which although not sufficient to power a servo, it did yeald some results which is what we were looking for.

Bench supply produced no servo movement... D cell batteries produced, although erratic, some servo movement = power supply issue which I suspected and mentioned early on.

As myself and Richard mentioned, LiPo or nimh batteries are excellent, especially when powering servos, and advised that these little bad boys should be used. In the confusion I said earlier that a common ground wouldn't be needed as this was on the assumption that the servo was connected directly to the EZ-B (signal, Vcc, Ground), but did mention, along with Rich that a common ground would be needed if powering the servo from a separate source which has now been done with good results.

As Dave had correctly said, using a bench power supply is really a great option for testing which was never in dispute, and it really needs to be supplying 20 amps at least, especially for testing/using a servo or multiple servos. Remember the old adage regarding touching the third rail on a train track. "It's not the volts that will kill you, it's the amps", which gives an idea how important amps are when powering power hungry devices. I don't have bench supply myself, just LiPo batteries, but I'm seriously considering getting myself one as they are a good investment and great addition to a workshop and robot building. I just need to save up some beer tokens to get me one ;). A multimeter is always handy to have around as well.

As well as helping Mulberry, again I'm glad you finally got some good results, hopefully this info will help someone else who comes across this thread facing similar issues. :)


Yes guys, great troubleshooting advice you gave. It's like an art form and is sometimes hard to understand and actually do successfully. You really have to have a good understanding of how what your working on really works at the basic level and what effects it. Just like Richard says, it's best to remove everything except what your having trouble with if possible. Take it down to the lowest level. Sectionalize.

When I started working with motors and servos I was very amazed at how many amps the bigger ones pulled and how big of a power supply was needed to run several of them (even running several smaller motors). Up to then I had extensive experience with power distribution but not a lot with application. I knew how to build the circuit and supply the power but less about matching it to the devices needing it. That's where Application and Electrical Engineers come in handy. Robotics and building a big robot like B9 has helped close this loop for me. Also help from good people like the ones on this forum has made all the difference in my education and success(es). ;)

Electricity is very hard to understand and there's a lot of it that is still unknown about it. It's very unpredictable sometimes but can be tamed and channeled if handled properly. It has a lot of the same characteristics of water. It's very lazy and will follow the path of least resistance (sometimes that's through a human body). Like water you also have to give it a conduit big enough to flow through that is leak free. Then when you get to to what you want to turn, like water, you have to have enough of it to do the work. :)


Well that victory was short lived. Although the connections were not touched overnight now this morning when I powered up I got nothing, in fact the EZ board now shuts down completely (blue light goes ), and doesn't just break the signal like before. The gears on the servo turn freely by hand so it isn't locked. I suppose the motor is somehow shorted inside and that in turn shuts down the board (I've tried it with 2 boards). I'm totally stumped. This is the second servo that I've tried for this function. I'm thinking this may not be the best approach for what I need.

Thanks to everyone for their help.


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Sorry to hear that. Maybe the board in the servo go damaged through all the testing with various connections and insufficient power supply being pumped through it, or your still facing power issues. There not much else I can suggest other than what's already been mentioned, or look at using a different make of servos. If the EZ Robot ones don't meet your requirements, Hitec servos are pretty good and work well with the EZ -B, and they have lots of different voltage and torque choices available. May be something to think about.


What are you using to power the servo? If it was burned, it would smell really bad.... I still think it's still a power problem... The servo needs a Lipo or niMh battery.... Your bench supply or D cell battery won't work....

As Steve suggests... there is only 2 reason why the servo isn't working... Not enough power or it is defective...

Can you just use one of the ez robot servos in it's place? They are pretty much one of the strongest servos I have seen for their size?...


No smell and the unit doesn't get warm when it's powered. The shutdown of the EZ concerns me. Since it works freely with standard EZ servos I'll assume the HD servo was damaged with the testing (lesson learned) .

Next step will be a new servo (It's got to be along the configuration of this one to fit my bracket) and try a stand alone battery recommendation (like a LiPo). I do have a couple of 12 volt rechargable HiTec batteries but that would require a voltage converter to bring it down. I wanted to avoid batteries if possible since my robot is stationary and most of my build is 12 volts (from a wall outlet) distributed with a block to converters for a few components that require less power but I'm letting that approach go.

Oddly enough I though the electronics of this build would be far simpler than the physical construction which took 3 years. Its looking like animation will take as long.

Daniel :P

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Testing with a new servo and LiPo really is your best bet. Going back to the "amps" issue, that's something you would also have to consider IF you decide to use a voltage regulator to reduce and match the servos voltage requirements. Good luck and keeps informed on your progress. :)


I just don't understand how you guys can feel that testing with a battery is the best way to go. Could you please explain this to me? I'm not being a smart a** here but just trying to understand your advice. Maybe I've been missing something but don't you have to match the battery to your devices amp draw plus some overhead room just like you would do for a power supply? If he has a properly sized ps why mess with a battery that will be draining down while you trouble shoot and configure? Seems simple, find the max amps the motor will pull when stalled and get a quality power supply that will supply more amps than you need. We're not talking about the common wall wart here. Again, what am I missing?


@Dave Schulpius,

Search the forum for "inrush current" and specifically read anything posted by @jeramie.

In short, the issue is that when first starting to move, servos draw way more amperage than they are otherwise rated for. Most power supplies limit to 5 amps, and you need more like 15 or 20 when the servos first start.

There are power supplies that will work, and in fact jeramie recommends one in one of the posts that talk about this, but they aren't cheap.

Alkaline batteries also can't deliver the amps, but NiMH and LiPo can.


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Just to echo what Alan said about LiPo's and nimh's being able to supply the amps needed to deal with the start up power inrush, and the fact that standard batteries (alkaline) and many transformers cannot. Also to refer back to what I mentioned earlier about using a tried and tested method many people use successfully in the aim to narrow the issue down further. Not to say alkaline batteries can't be used, but you would need to put a multiple battery packs in parallel to get enough current , but that could end up being a lot of batteries. Thats how I understand it anyway. :)

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@Steve - In parallel increases current. Series increases voltage ;)

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Oops, that's what I meant. Honest. :)

(Corrected post above)


Steve just curious. How would this be different from a workbench power supply like the one below:



@Mulberry ... There is a huge difference... Your bench supply is rated at only 2 amps, Steve's is rated at 20 Amps. 10 times more power... 2 amps is not nearly enough to run a project with servos....

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@Mulberry, the image indicates it's only a 2A supply. This is enough to operate a single, heavy duty servo like the Tower Pro under about 75% load. Inrush current will be more than 2A.

I haven't read all posts but presume you are trying to run something which pulls a lot more than 2A.

To put it in perspective, the revolution robots (JD, Six & Roli) need a 20A bench supply. A B9, with larger motors and servos will need more than 2A for sure!


Ah. Slowly sinking in :D

I had planned on a bench supply to feed all systems but the one I have is only 2 amps so I need 20 amps even if the big guy is not mobile. I'll check what I have at home. I have two large 12 volt rechargeable hobby batteries but I don't know their amps as well as two power systems I purchased last year on recommendation from another B9 builder.

Everyone's advice is much appreciated. I'm a research psychologist with no electronics experience except what I've picked up. And clearly a little knowledge can be dangerous :P


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You may need more than 20A. It depends what you are trying to run.

Work out the inrush current for everything that you are trying to power. That is the minimum current you need to supply. To do this count up the number of servos, number of motors etc. Multiply the number of servos by their inrush current. Multiply the number of each type of motors by their inrush current. Add everything together and that's the amps to aim for.

For instance, if you are running 3 servos with an inrush current of 4A, 2 motors with an inrush current of 5A and one motor with an inrush current of 3A... 3 x 4A = 12A 2 x 5A = 10A 1 x 3A = 3A Total inrush current is 25A.

If the power supply cannot provide the amount of current required it will cut out.


@Mulberry That's why we keep pushing batteries like Lipos or niMh on you.... they can supply enormous amounts of current (amps) to power hungry devices like motors and servos.... Your 12V hobby batteries (I assume they are SLA) can give the current you need, however 12V is too high for servos.....


Sorry guys. You still are not selling me on this battery business. I've never used a single battery in my B9 and never have I had a power problem. I use a monster servo for my bubble lifter, the Tonegawa-Seiko PS050. It pulls 9 amps max and I can run 12 vdc right into it (5vdc fot the control side).

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The 12 amp power supply I use never skips a beat. it also supplies power to a few other smaller servos too. Is will handle a Cold-start current of 35A at 115V.

There is no reason why a person cant run several of these and split the load between them. Here's the one I use and it only costs $22 USD.

Genssi 150W 12V Regulated Power Supply LED Driver AC-DC Converter

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I'm not saying that your Lipos are not a good choice but just saying a good power supply will be just as good or even better depending on your setup.

I also am using a 30 amp Mean Well power supply for my arm DC motor and servos (one DC motor and 4 servos). It cost $55 USD:

Meanwell 12 Volt 350 Watt Ul Switching Power Supply 120 Volt Input Constant

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With all due respect I think you all are doing Daniel a disservice by talking him out of using power supplies.


Several of us have said that an appropriate power supply is fine, but the 2amp one he was using was not going to cut it.

I think the idea of using NiMH or LiPo batteries to start was to troubleshoot that the issue really was inrush current brownout, not necessarily a permanent solution.



I do appreciate all the input. A lot of my issues have to do with lack of experience but luckily you guys are bringing me along. None of my graduate work had to do with electronics:D I think what's most important is I sit down, calculate my power needs, and map out the wiring. Currently my connections look like a Rube Goldberg orgy.

BTW the Torquemaster LC batteries I have are rated at 7 amps so even with two they wouldn't cut it.

Hi Dave

I actually have two of those Genessi's based on your recommendation last year however they came with no information on connections/configuration so they scared me off :D I'll take another look.

In hindsight perhaps I should have gone with the servo you used. It looks like I'll be at 150.00 for servos just for my bubble lifter.

Ultimately my goal is to make the B9 a plug-in unit. I'm fine with a battery to run a servo until I have the confidence the house won't burn down......or I'm divorced.



@Mulberry to confuse you even more... Don't confuse battery capacity (as you mentioned your Torquemaster LC 12V SLAs are 7amp) with the ability to deliver current.... Think of the 7amps in those 12V batteries as a gas tank.... In SLAs, 7amps can be delivered very quickly (like for starting a car)... If that same battery was a 12V 7amp alkaline (yes I know they don't exist, this is just for demonstration purposes here)... It still has the same 7amps in the gas tank but it can only give you those 7amps very slowly... wouldn't even light up your dashboard in the car...

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I just woke up and saw you post so figured I would add my thoughts. No offence intended or anything like that ;), I just want go over why I have suggested what I have.

I was never "trying to do a dis-service" when suggesting LiPo batteries, as again, it's a tried and tested method and recommended by many people. As we all know, a lot of robots are mobile so these are a great option. Mulberry only mentioned recently that his robot is static which is why I went web surfing for him to find him a bench power supply that was reasonably priced and met his basic needs. Not knowing any details of his set up I started with the minimum requirements. (20 amp)

Again, I'm not against using bench supplies and never said not to use them, I only said for a temporary period not to use it while testing the servo out. As it turns out, that was the issue with it only suppling 2 amps. The power supplies you mention are indeed great, simply because they produce 12 amps with 30 amp cold start for a 9 amp MAX servo, and a second supply capable of 30 amps. But the fact that mulberry was using was a 2 amp supply which is far from adequate for a HD servo now points to a solution.

The suggestion of a pack battery (LiPo, nimh) was purely for testing purposes and suggestion to use with mobile platforms, and I never said that they should replace or are better that a properly rated mains supply. Indeed, I'm going to get a mains supply myself as I think they are a great option for bench testing.

Again no offence or any of that negative stuff intended if there was any. Far from it. You certainly know your stuff and have way more experience than I do, but I just wanted to explane my suggestions for a solution with the knowledge I have, as I have been there myself (as I'm sure most of us have) not to long ago. Hopefully we'll get mulberry back up and running in no time. :)



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Hey buddy. To put you mind at rest a little and to help yourself and others out have a look at what I wrote below. Some of this you may probably know, but there migh be some thing you may not been aware of.

So, let's take a simple 12 volt servo. voltage Giving it 24 volts will fry it. Giving it 4 volts could damage it. A 2 volts saftey margin is pretty safe (see LiPo's below).

Amperage Not suppling enough amps will cause problems, and the servo will not move. Suppling to many amps won't cause any damage. The servo will only take what it needs. Caution is needed though. Using "very" high amperage and enountering a short circuit, it can cause a lot of damage.

Servos use a lot of amps when they first start to move (in-rush) or when they stall (physicly being held while its trying to move) much like a DC motor. In fact a servo has a small DC motor inside, only difference is that a servo is designed to read and remember it's position, and are a lot of the time limited to how far they can turn. Putting an amp tester on a DC motor with a wheel attached and power supply, start running the motor you will see (for example) the amps spike to say 15 amps, then settle back to a steady 4 amps. Holding the wheel with your hand and you will see the amps rise again. Running weight on the same motor and wheel (robots body for example) on a carpeted floor, that 4 amps will go up a bit to compensate for the extra torque.

Using a 12v alkaline (or dry) battery for this test, generally you would start with 12 volts but not enough amps. You could then use several alkaline batteries in parallel to keep the same voltage, but increase the amps. But alkalines will decrease in power as they drain.

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LiPo's and NiMH batteries work differently because of how they are made. A 11.1 volt LiPo is the equivalent to a 12 volt alkaline. A fully charged LiPo will be more like 12.5 (going back to the 1.5v safety margin statement). This will hold the power better than an alkaline that drains. A LiPo will obviously drain too, but differently. Only thing to note using our 11.1v example is when the LiPo drains to about 5 volts it should stop being used and charged. Anything below that and it may not charge up again. These batteries can supply enormous amounts of amps for their size and act like portable mains power packs. Of course the more amps that are drawn from the LiPo, the quicker it will drain (mAh amp hours, a whole other topic)

Then of course we have the mains power supplies. Vary in price, vary in voltage output, vary in amp/current output, but Al do one thing and one thing well. They supply a continuous amount of power, volts and amps. Homework is needed here to work out your requirements and select the right mains supply for their needs. For an EZ-B running a few standard servos and a couple of sensors, an 20 amp supply is recommended. Running many Heavy Duty servos, you may want to look at using something like a 30 or 50 amp supply.

So to answer the original question of why the servo was not moving, it's the amps my friend, or rather lack of them. A 7.4v LiPo or NiMH battery will have the servo working. But as you have a robot that is static and has more servos, sensor ect, then a bench power supply of at a minimum of 20 amps is probably the solution for you, although I would suggest something around 40 to 50 amps depending on what your robot has.

Hope that helps you out buddy and to anyone else with similar problems. Power and power hungry devices can be a lot to get your head around (trust me, I went through all this too). Anyway, keep us informed of your progress and "holla" if you need more assistance.

Steve. :)

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Steve, you cant supply too many amps. Think of current as water in a tank and the accessories as taps. Too much just doesn't get used. Too little and it doesn't give everything enough.

That's in very basic terms.

Consider this image. The circles are your "amps", the rectangle is your battery capacity and the channels coming off are your discharge rate.

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Now imagine there are devices connected to the channels which will take the amps away as they need them. The thinner channel has less amps to supply. If you have devices that take a lot of amps (more than are in the channel) it wont work and everything will fail.

The more amps the better. And there can't be too many as if there are they just don't get taken away.

Sorry for the crude explanation, I'm at work right now but when I get home I'll explain a little better if I find time.

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I thought that's what I said?


Suppling to many amps (within reason) won't cause any damage. The servo will only take what it needs.

Unless your referring to the "within reason" comment. I said that because if using very very high amperage and someone enounterd a short circuit, it can cause a lot of damage. (Post has been edited to reflect this).

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Yes thats the part I was referring to And thought Id expans on the explanation of current capacity and discharge rates.

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Cool, no worries. I only said that because the more amps being used, the bigger the spark if there is a short circuit. :)


This is an excellent subject and conversation. I'm glad we can do it as adults without personality. This kind of information on a common understandable level is always needed. ;)

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It's like you said. It's like art, with many peoples interpretations that are interesting and differ, but ultimately point to an agreed understanding and resolution. The aim to help, inform and of course learn something on this community, and do it collectively without upsetting or belittling each other (like you say, do it like adults) is the reason I keep coming back and get involved in this forum. As well as looking at all the cool robots like yours of course ;).


I've acquired a 6 volt NIMH battery I'm currently charging. If I can activate the servo with that I'll switch to my regular power supply (most likely the Genissi if I can figure out the connections).

Thanks for all the help,



Tested the servo and it doesn't respond except to shut down the EZ board. Its toast as I suspected. So I'm two servos down.



Does your set up work with the ez robot servos? Before buying anymore servos confirm that your setup with the 6v Nimh works... Can you post a picture of your project... I for one would like to see how you are wiring things....

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I see that you marked this thread as resolved before testing which it clearly looks like it is not. If you're still having trouble with this make of servo with a NiMH battery and the wiring is correct, then you should really consider change to another make of servo as I suggested before.


Morning All

I closed the thread because I think the question was resolved. I tested the servo with a 6 v NIMH battery (fully charged) and its pretty clear the servo itself is dead. When I connect it to the EZ the board shuts down (blue light goes out and the connection is broken) and it happens with each of my 3 EZs. All other servos work fine, unfortunately I need a heavy duty one to lift this head. I'll look around at other brands. Again most likely the damage happened with me testing it and I fried something inside. I've tossed into my bin of "damaged but possibly salvagable goods"

Lesson learned.

Daniel :)


That servo may work if he adds a servo helper to it like springs. It's certainly a decent price at $40 USD. The bubble section he's trying to lift can weigh more then 5 lbs sometimes. The HS-805BB is a plastic gear servo. This servo also comes in a metal gear model (HS-805MG & is $60 USD). That one may stand up to the pressure better.

Another option would be a standard servo using a ServoCity gearbox. You can get them that will handle up and over 200 Oz-lbs with different mounting options. A bit pricey at $240 USD but it will lift a horse and is very smooth. To lower the price you could order it without the high priced HS-7950TH servo and install a less expensive standard size servo.

SPG7950A-BM bottom mount servo Power Gearbox