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Answer To A Long Time Question

Hey All,

I wanted to demonstrate the current handle capabilities of the EZ-B and at the same time doing a small test. Here's a quick video I made of Six with 18 servos, I know a few of you asked a long time ago if Six could run with 18 servos, the answer is Yes!:D

Six with 18 Servos Video


I also wanted to demonstrate the large in rush current demand that Heavy Duty servos can have and how it might effect your power supply or battery pack so I made another quick video :

In-rush current example Video

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#4  
Lookout Jeremie, you have Soundwave on your power supply. :)
#5  
Anthony, why don't you just use a mulitmeter and determine exactly just how much power your servos are drawing?... Guessing what the problem is seems to be getting you nowhere.... That's what I would do, anyway...
#6  
Hey thanks for doing this! It's a great way to show the mussel of the V4! I loved watching them!:)

I have another answer to an ultimate question of life, the universe, and everything else;....................... 42.:P (points on the origin of that one)
#7  
Please excuse the long explanation or if you already know this but this info important to know in this hobby:

@Ant. Amps are what your going to need to know because that's current. Current is made up of electrons and they are what do the work. Current is kinda like water in a pipe. The force pushing the water in the pipe would be the voltage and the current (amps) would be the water in the pipe. The third part of this is resistance and that would come into play with the type and size of wire your using. Simply put; the smaller and less conductive the wire the more resistance you have or the harder it is for the electrons to rush through the wire. Think about what happens when you try to force way to much water though to small of a pipe. In wire that's too small the electrons will keep squeezing through the wire, starving the load and causing heat and maybe melting the wire. This is also the principle of how a burner on an electric stove works.

Anyway, you need to really need to first know how many amps your load (servos in this case) will pull so you can match your power supply and wire size to it. Not every multimeter can measure amps. I had to buy one that does at Menards. You simply place the meter on the proper Amp reading setting and put the two leads in line somewhere between the positive battery post and the positive load (servo) connection. There are lots of Youtube vids out there showing how to do this.
#8  
Make sure that you use a (DC) Multimeter that is fuse protected at a higher rating than your anticipated amperage load. I use a Radio Shack meter with a 20 amp fuse. The meter is connected in series with the power supply (battery).

The meter itself must have a selection for measuring Amps not milliamps
#9  
this is great info, save to pocket...

j
#10  
Good point Doc... Most of the cheap ones are not fused on the 10amp setting, by the way so be careful...

I just bought a Uni-T UT61E and it's awesome....
United Kingdom
#11  
Thanks for the videos Jeremie.

It really does concern me that very few will do things the right way. What use is a robot that's had thousands of man hours spent on building it if it doesn't work or if the wiring melts inside?

I have expressed concerns about the power (is the battery capable? is the wiring big enough? etc.) in the past on some projects but it's generally been brushed aside. I don't like to say I told you so or be Mr. Know-It-All but, well I did tell a few of you.

@Ant, you need to set the meter to DC amps (DCA) and connect it inline between the battery and the connector that currently attaches to the positive on the battery.


User-inserted image



I've said it before, I'll say it again, design and calculations for everything is more important than anything else. If you want your robot to work you need to carefully think about what will power it, what will be powered but most important (and something that's not been touched on) what size the wiring needs to be.

No offence is meant to anyone by this and I'd much rather be saying "Wow, that turned out awesome and works well" than saying "you need to change your power supply and replace the cable that was smoking".
#12  
Couple of things.

1) Dave Schulpius. Wow, awesome analogy using the water pipe to describe volts, amps, and resistance. I am going to use that in the future...

2) A clamp on ammeter can measure the amperage without the power going through the multi-meter so it is possible to get a less expensive one that wouldn't be able to handle the current itself to measure very high amp circuits. See http://en.wikipedia.org/wiki/Current_clamp

I have a pretty cheap radio-shack meter, but it has a clamp on attachment and can measure hundreds of amps (not that we should need to measure that high on a robot, but still....).

Alan
#13  
Isn't the clamp on amp reader only used for AC amps ?
United Kingdom
#14  
You can get ammeters which can measure ac or dc. Powerstream make some, the PST-CM01 for example.
#15  
My cheapo radio shack one does AC or DC, although to be honest, I have only measured very high amp DC circuits (my Toyota Prius drive motor - 300 amps max under load).

Alan
PRO
Canada
#16  
@Anthony, sorry it took me a little bit to get back to you

For the 18 servo test I was using our 7.4VDC 1300mAh LiPo battery and was powering all the servos through the v4. Something to note: the servos cannot effect the regulated supply of the EZ-Bv4 and cause the EZ-B to reset unless the entire power supply browns out.

Something that I forgot to mention was that inside the robot we have a wiring harness that has low gauge wire and a deans connector that are designed for high current delivery from the battery to the EZ-Bv4 and then to the Servos. It looks like this:

User-inserted image


The micro deans adapter board is the same one as in the Power base (minus the 2.1mm barrel jack) and can be modified to use for your robot's wiring harness if needed.
#17  
Thanks for the clarification guys. I understand that there are Amp meters designed specifically to measure amps both ac and dc. The confusion entered when I was thinking and answering the question based on a Digital multimeter from my favorite Radio Shack store that has the ability to directly measure dc amps by being connected in series with the device under test.
United Kingdom
#18  
What battery are you using? Can it provide the required current to power all 13 servos?

From what I can find on those servos, they can pull 2500mA on startup and on stall. 13 x 2.5A = 32.5A (probably more if running above 6v)
United Kingdom
#19  
What voltage are you providing the servos? The datasheet only gives info for 4.8v and 6.0v, if you are pushing them at battery voltage this will increase the current draw (however it will vary depending on battery voltage).

Max continuous discharge may be more than 20x1.3A (26A) if all servos are under a full load. Inrush/Burst should be OK at 30x1.3A (39A) though.
#20  
Anthony no one replied regarding the posting of your meter pic and it may be obvious.... that meter will not measure above 10 amps. Not knowing all the particulars about your project is hard to say that the 10Amp scale would suffice.

Chris
#21  
Again, it comes down to what is the amperage consumption of your setup.
#22  
As Doc mentioned..... Everything seems to point to a power supply problem... Have you tried disconnecting all servos and then adding back one at a time until your get the ezb to reset? Do you have a picture of your setup (wiring, battery.... etc)? Is it possible to post your code here as well?
United Kingdom
#23  
@Ant you are comparing two completely different set ups. It's like asking why my work van will only do 60mph and takes a week to get there but my car does 155mph and takes 4 seconds to get there. Two totally different things.