Mulberry
USA
Asked
— Edited
Resolved by Rich!
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?
Thanks,
Daniel
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
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
With all due respect I think you all are doing Daniel a disservice by talking him out of using power supplies.
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.
Alan
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
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.
Daniel
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.
Cheers,
Steve.
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.
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.
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.
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.
I thought that's what I said?
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).
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 ;).
Thanks for all the help,
Daniel
Daniel
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
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