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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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@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.
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).

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.

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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.

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